Lithium Production from Spodumene
by
Ernest Mast
A Thesis submitted to the Faculty of Graduate Studies in partial fulfillment
of the requirements of the degree o f Master of Engineering.
I
Department of Mining and Metallurgical Engineering
McGill University, Montreal, Canada
© Ernest Mast
May 1989
rtf
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To the incomprehensible forces which started it all.
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ABSTRACT
A new metallo-thermic reduction process designated "Melt - Leach Evaporation " is under development for the extraction o f lithium and other
Group IA and IIA metals.
The metal to be recovered is leached out of the ore
or concentrate by an excess o f liquid metal reductant which is then vacuum
refined to recover the metal as a solid or liquid condensate.
The experiments performed contacted approximately one mole of Beta
spodumene, LiAlSi^O^, with molten aluminum-magnesium.
The molar ratio of
the aluminum to spodumene was approximately 86 to 1 and the molar ratio of
magnesium to spodumene was increased from zero to ten.
The experiments were
performed in alumina crucibles, under an argon atmosphere, at 900°C for
ninety minutes.
Mixing was provided by mechanical stirring.
Assays of lithium and silicon in the cast ingot confirmed that lithia
and silica contained in the spodumene were reduced and dissolved into the
excess molten aluminum reductant.
As much as 60 % o f the lithium in the
spodumene was recovered to the aluminum ingot cast after the experiment.
Increasing the magnesium to spodumene ratio improved the recovery of lithium
to the ingot.
This was as predicted by a thermodynamic model.
X-Ray diffraction results detected spinel, MgAl20 4 and silicon in
the powder residue for all experiments.
These compounds were formed
by the following two-step reaction process,
Li20 Al20 34 S i0 2 + 11 A1
Li20 A l 20 3 + Mg
=
=
L i20 A120 3 + 4Si + i A l ^
2Li + M g O -A l^
[i]
[2]
which produced the lithium and silicon dissolved m the cast ingot.
A one-step reaction may have occurred simultaneously at magnesium to
spodumene ratios greater than or equal to eight to one,
Li20 A l 20 3-4Si02 + 9Mg
=
2Li + M g O A l ^ + 4Si + 8Mg0.
I
i
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m
RESUME
Un nouveau procedd de reduction thermo-m^taJlique commundment appeie
"Fusion - Lixiviation - Evaporation" est sous ddveloppement pour 1'extraction
du lithium et d ’autres metaux du groupe IA et IIA.
Le metal k extraire est
lixivie a partir du mineral ou du concentre par un exc&s de r^ducteur
metalhque liquide
Ce dernier est ensuite raffine sous vide pour recouvrer
le metal d ’interet sous la forme d ’un solide oud ’un liquide condense.
Les essais expenmentaux imphquaient une reaction avec pr6s d ’une mole
de spodumene Beta, LiAlSi.,0 , et un alliage d'aluminium -magnesium liquide.
Le rapport tnolaire aluminium/spodumene etait environ de 86 pour 1, tandis que
le rapport magnesium/spodumene variait suivant un accroissement de zero h
dix.
Les experiences furent condmtes en tenant compte de certains para-
metres ltnportants tels que- des creusets en alumine, une atmosphere d ’argon
et une temperature de 900°C duiant 90 minutes avec agitation mdcanique.
L’analvse chimique des lingots d ’alumimum a confirmee que 1’oxide de
lithium et la silice contenus dans la spodumene ont dtd rdduit et dissou,-.
dans l’exces d’aluminium liquide.
Jusqu’a 60% du lithium present dans la
spodumene a ete recouvre dans le lingot d ’alumminm aprbs l’expdnence.
L ’augmentation du rapport magnesium/spodumene a demontrde une meilleure
extraction du lithium dans le lingot.
De plus, ce resultat a et6 prddit ti
l ’aide d ’un modele thermodynamique.
Les resultats obtenus par diffraction-X ont ddmontrds que le rdsidu
poudreux obtenu lors des experiences etait forme de spinel, (MgAl20 4) et de
silicium.
Ces composes ont ete formes en deux etapes considerant les
reactions suivantes,
Li20-A l20 3 4S i02 +
Li20-A l20 3 + Mg
A1
=
=
L i 20-A120 3 + 4Si +
i A120 3
2Li + M gOA l2C>3
m
[2]
lesquelles ont produites le lithium et le silicium dissous dans le lingot.
Par contre, une reaction considerant une seule etape peut avoir eu lieu
pour un rapport magnesium/spodumene plus grand ou dgal k huit.
Li O A1 0 4SiO + 9Mg
2
2 3
2
=
2Lt + MgO A1 O + 4Si + 8MgO.
2 3
11
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pi
ACKNOWLEDGEMENTS
I would first like to express gratitude to my supervisor, Dr. Ralph
Harris, who was most responsible for my decision to undertake this endeavour.
His foresight, patience, encouragement and special talents were much
appreciated.
The author is indebted to members of Dr. H am s’ group: Robert Selby,
Zhou Wang, Liu Jin and especially Birendra Jena for their helpful
assistance in all aspects of the project.
I would like to acknowledge the helpful suggestions from Professors
James Toguri and Bert Wraith of the Universities of Toronto and Newcastle,
respectively.
Thanks to all of the students, technicians and professors in the
Department for making the author’s stay at McGill a most rewarding one.
The author wishes to acknowledge The Tantalum Mining Company of Canada
and especially Mr. John Fleming, for expressing an interest in this project,
H
providing matenals and performing chemical analyses.
Thanks to my office mates, Murray Brown, Weixing Wang and Sugundo for
their companionship and acceptance o f my territorial expansion within the
office.
I would like to thank my family for their support.
A special thank you to Cannen, my girlfriend, for being herself.
i
11 I
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TABLE OF CONTENTS
1
Page No.
A BSTRA CT
RESU M E
ii
ACKNOW LEDGEM ENTS
iii
T A B L E O F C O N TEN TS
iv
L IS T O F TA B LES
viii
L IS T O F FIG U R ES
x
C H A P T E R 1: IN T R O D U C T IO N
1. 1.
Melt-Leach-Evaporation
1
I 2.1.
Characteristics and Uses of Lithium Metal
1
1.2.2.
Lithium Occurrence
4
1.2.3.
Lithium Industry
5
1.2.4.
Lithium Extraction Technology
6
1.3.
Alpha to Beta Spodumene Transition
8
C H A P T E R 2: L IT E R A T U R E SU R V E Y
11.1.
Metallo-Thermic Reduction Processes
12
11.2.
Lithium Production by Metallo-Thermic Reduction
12
11.3.
Lime-Spodumene Reactions
13
11.4.
Interfacial Phenomena
14
I
IV
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CHAPTER 3 :THERMODYNAMIC ANALYSIS OF SPOD U M EN E
R ED U C TIO N
III. 1.
Reducing Agent
17
C H A P T E R 4: L IM E -SP O D U M E N E TESTS
IV. 1.
Introduction
22
IV.2.
Apparatus and Reagents
22
IV.2.
Procedure
23
IV.3.
Results of Lime-Spodumene Tests
24
IV.4.
Discussion
26
IV.5.
Conclusions, Lime-Spodumene Tests
28
C H A P T E R 5: E X P E R IM E N T A L
<
V .l.
Objective
29
V.2.
Experimental Variables
29
V.3.
Materials
29
V.4.
Apparatus
30
V.5.
Experimental Procedure for Spodumene Reduction
Tests
34
V.5.1.
Experimental Preparation
34
V.5.2.
Experimental Procedure
34
V.6.
Experimental Program
35
C H A P T E R 6: RESULTS
VI. 1.
Spodumene Transition
37
VI.2.
Visual Observations of Reduction Products
39
VI.3.
XRD Analysis of Reduction Products
47
VIA.
Atomic Absorption Analysis
49
VI.4.1.
Sampling For Atomic Absorption Analysis
50
VI.4.2.
Atomic Absorption Analytical Methods
50
VIA.3.
Atomic Absorption Results
54
VI.5.
Scanning Electron Microscope Analysis
58
C
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C H A PT E R 7: EXAMPLE CALCULATIONS
VII.I.
VII.2.
Determining Sample Concentrations From
Absorbance Readings
60
Sample Calculations o f Analytical Error
61
C H A P T E R 8: D ISC U SS IO N
VIII 1.
Introducr.on
VIII.2 1.
Discussion of Present Experimental Program
63
VIII.2 2.
Discussion of Experimental Procedure
63
VIII.2.3.1.
Relative Errors of Sample Assays
64
VIII.2.3.2.
Comparison of Assays with an Outside
Analysis
VIII.3.
Experimental Modeling
67
VIII.3.1.
Determination of Gas Purging Rate
67
VIII.3.2.
Formation of Solid Species
69
VIII.4.
Mass Balances
70
VIII.5.
The Effect of Magnesium Addition on the
Reaction Products Assays
73
VIII.6.
Kinetics of the Spodumene Reduction System
86
VIII.7.
Discussion of XRD Results
88
V III.8.
Wetting Effect of Magnesium
88
VIII.9.
Discussion of Reaction Mechanisms
89
VIII. 10.
Discussion of Reaction Pathways
90
VIII. 10.1.
Two-Step Reaction Pathway
90
VIII. 10.2.
One-Step Reaction Pathway
91
V III.11.
Vacuum Refining of Lithium from Aluminum
91
VIII. 12.
Comparison of Experimental Results with
F*A*C*T Calculations
93
VIII. 12.1.
Introduction
93
VIII. 12.2.
Comparison o f Thermodynamic Model
with Experimental Results
V
VI
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93
C H A P T E R 9: C ONCLUSIONS A N D FUTURE WORK
IX.
1. Conclusions
101
IX.2.
Future Work
102
C H A P T E R 10: C O N T R IB U T IO N S
104
REFEREN CES
105
A P P E N D IC E S
A:
B:
F*A*C*T Simulation o f Alumino-Thermic Reduction
of Spodumene
109
Phase Diagrams
116
i
VI I
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LIST OF TABLES
Table 1.1.
Physical Properties of Lithium
2
Table 1.2.
Lithium Bearing Minerals
4
Table 1.3
Uses of Lithium Metal in the U.S. (Short
Table 1 4
Operating Conditions for Li Electrolysis Cell
Table 1 5.
Crystal Structural Data for Alpha and Beta
Tons)
5
8
Spodumene
10
Table 2.1.
Surface Tensions for Selected Liquid Metals
15
Table 3.1.
Characteristics of Possible Reductants
18
Table 3.2.
Standard Free Energy of Solution o f Elements in
Liquid A1 and their Absolute Entropies
Table 3 3.
F*A*C*T Output o f Spodumene Reduction with Al-Ca
A l'oy at 1173 K and 1 Atm.
Table 3.4.
19
20
F*A*C*T Output of Spodumene Reduction with Al-Mg
Alloy at 1173 K and 1 Atm.
Table 4.1.
Spodumene Assays
Table 4.2.
XRD Results of Lime Spodumene Sinters and
20
22
Compounds Predicted by F*A*C*T
26
Table 5.1.
Specifications of Aluminum (Weight%)
29
Table 5.2
Spodumene Reduction Experiments Performed
36
Table 6.1.
Products o f Spodumene Reduction Expenments
40
Table 6.2.
Settings for Li A.A. Analysis
51
Table 6.3
Settings for Mg A.A. Analysis
52
Table 6.4.
Settings for Si A.A. Analysis
53
Table 6.5.
A.A. Raw Data for a Set of Li Standards and Ingot
Assays
55
Table 6.6.
Assays of Condensate (Weight%)
55
Table 6.7.
Assays of Flue Powder (Weight%)
56
Table 6.8.
Assays of Residue (Weight%)
56
Table 6.9.
Assays of Ingot (Weight%)
57
Table 6 10
Assays of Dross (Weight%)
57
Table 6.11.
Lithium Assays from Kinetic Samples
57
Table 6.12.
SEM Assays of Particle in Figuie 6.12, (Weight%)
59
Table 7.1.
Results of Linear Regression
60
VII)
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Table 8.1.
Average Relative Errors in Sample Concentrations
65
Table 8.2.
Comparison o f Analytical Results
66
Table 8.3.
Mass Balance for Lithium
71
Table 8.4.
Mass Balance for Magnesium
72
Table 8.5.
Mass Balance for Silicon
72
Table 8.6.
Volatility Coefficients of Various
Solutes in Molten Aluminum
€
<
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92
LIST OF FIGURES
Page No.
Figure 1.1.
The Acid Process for Lithium Carbonate
Production from Spodumene
7
Figure 1.2.
The Silica Tetrahedral
9
Figure 1.3.
Correlation Between Crystal Structure and the
Strength of Tetrahedral Frameworks
10
Figure 2.1.
The Contact Angle Between a Liquid and Solid
15
Figure 2.2.
Surface Tensions for Aluminum Alloys at 50°C
16
to 80° C Above Liquidus Temperature
16
Figure 3.1.
Free Energy o f Formation for Lithium and Potential
Reductants
Figure 3.2.
17
Thermodynamic Simulation of the Lithium
Extraction from Spodumene by Reduction with
21
Al-Mg and Al-Ca Alloys
Figure 4.1.
Apparatus used to Perform the Lime-Spodumene
Experiments
Figure 4.2.
23
Reaction Product from Lime-Spodumene Experiments
at Temperatures of 1050°C and Below
Figure 4.3.
Reaction Product from Lime-Spodumene Experiments
at 1100°C
Figure 4.4.
24
25
Reaction Product from Lime-Spodumene Experiments
at 1150°C
25
Figure 5.1.
Experimental C ap Assembly.
30
Figure 5.2.
Experimental Apparatus used to Perform the
Spodumene Reduction Experiments
Figure 6.1.
XRD Patterns o f the Raw Materials in this Study
and Various Lithium Aluminum Silicates
Figure 6.2.
37
Cumulative Size Distribution of Alpha Spodumene
38
and Transformed Material
Figure 6.3
31
Microphotograph of the Received and Transformed
Spodumene
39
Figure 6.4.
Condensate
41
Figure 6.5.
Fine Black Powder
42
Figure 6.6.
Fine Black Powder Lost During an Experiment
43
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£
Figure 6.6.
Fine Black Powder Lost During an ExpeHment
43
Figure 6.7.
Powder Residue
44
Figure 6.8.
Dross
45
Figure 6.9.
Metal Ingot
46
Figure 6.10
Material S'uck to Inside of the Crucible
After an Experiment
Figure 6.11.
47
SEM Microphotograph o f Particle in the Powder
Residue
Figure 8.1.
59
The Analysis o f Solid Formation in the
Reduction of Spodumene for Two Reaction
Paths
Figure 8.2.
70
Lithium Weight% in the Ingot and Dross vs. the
Magnesium to Spodumene Ratio
Figure 8.3.
74
Lithium Concentration in the Residue and
Very Fine Black Powder vs. Magnesium to
Spodumene Molar Ratio
Figure 8.4.
75
The Masses of the Powder Residue and [3
Spodumene Charge vs. the Magnesium to
to Spodumene Ratio
Figure 8.5.
75
Lithium Weight% in the Condensate vs. the
Magnesium to Spodumene Ratio
Figure 8.6.
Lithium Weight% in the Very Fine Black Powder vs.
the Magnesium to Spodumene Ratio
Figure 8.7.
79
Magnesium Concentrations in the Ingot and Dross
vs. the Magnesium to Spodumene Ratio
Figure 8.10.
78
The Silicon Weight% in the Powder Residuevs. the
Magnesium to Spodumene Ratio
Figure 8.9.
77
The Silicon Weight% in the Dross and Ingot
vs. the Magnesium to Spodumene Ratio
Figure 8.8.
76
80
Magnesium Weight% in the Powder Residueand Very
Fine Black Powder vs. the Magnesium to Spodumene
Ratio
Figure 8.11.
81
Lithium Extraction from the Powder Residue vs.
the Magnesium to Spodumene Ratio
Figure 8.12.
82
Lithium Recovery to the Metal Ingot vs. the
Magnesium to Spodumene Ratio
i
XI
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83
Figure 8.13.
Lithium Distribution in the Reaction Products
for each Experiment
Figure 8.14.
84
Silicon Distribution in the Reaction Products
for each Experiment
Figure 8.15.
85
Magnesium Distribution in the Reaction Products
for each Experiment
Figure 8.16.
86
Rate of Lithium Recovery to the Melt vs. Time
for Various Experiments Performed in the Study
Figure 8.17.
87
Lithium Extraction from Spodumene from
Experimental Results and F*A*C*T Calculations
vs. the Magnesium to Spodumene Molar Ratio
94
Figure 8.18.
Lithium Extraction from Spodumene vs. Temperature
96
Figure 8.19.
Lithium Extraction from Spodumene vs. the amount
of excess liquid aluminum
Figure 8.20.
Lithium Extraction from Spodumene vs. Pressure
at 900°C
Figure 8.21.
98
Pressure of 100% Lithium Extraction vs.
Temperature
Figure 8.22.
1
97
99
Magnesium’s Effect on the Lithium Extraction
from Spodumene as Temperature Changes
XI I
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100
I. INTRODUCTION
1.1.
MELT-LEACH-EVAPORATION
In the Melt-Leach-Evaporation (MLE)(1) process for extracting Group IA
a n d Group IIA metals, solid particulate ores or concentrates are contacted
w ith an excess o f molten metal.
The excess molten metal extracts volatile,
metal species into solution by reducing compounds o f the species present in
the ores or concentrates. The dissolved species are then vacuum refined from
the excess molten metal.
An advantage of MLE is that it improves the materials handling and
production kinetics as compared to a powder process, such as Pidgeon
type vacuum retorts.
By using an excess liquid metal reductant, the
activity o f the recovered species would be lowered by dilution in the
excess molten metal and thus more o f the species would enter the
solution.
The extraction of lithium from spodumene (Li2O-Al20 3-4Si02) b y
molten metallo-thermic reduction w as the subject of this thesis and is a
representative example of metal extraction by MLE.
The evaporation of the
lithium from the excess molten metal was not examined experimentally
in this thesis.
1.2.
1.2.1.
LITHIUM
CHARACTERISTICS AND USES O F LITHIUM METAL
Lithium is the third element in the Periodic Table and it is the first
of the alkali metals.
Lithium was first discovered in 1817 by Arfwedson in
Sweden(2) and the metal was first isolated in 1855.
The first commercial use
occurred when the German firm, Metallgesellschaft A.G., used lithium as a
hardener in a lead alloy(2).
Since then, scientists and engineers have
envisioned many new uses for the metal, due to litnium ’s unique physical
properties shown in Table 1.1.
1
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Table 1 .1 .
(3) (4)
PHYSICAL PROPERTIES OF LITHIUM
PROPERTY
DENSI TY,
MP,
°C
BP,
°C
VALUE
gem '3
REF.
0 . 534
3
1 8 0 .5
3
134 2
3
F I R S T I O NI Z A T I O N POTENTIAL k j / g m o l e
519
3
ELECTRON A F F I N I T Y k j / g m o l e
5 2 .3
3
CRYSTAL STRUCTURE
BCC
3
3 .5 5
3
4 .3 9
3
-3 .0 5
4
3 .8 6
4
S P E C I F I C HEAT AT 25 ° C ,
S P E C I F I C HEAT AT MP,
kj/k g
STANDARD POTENTIAL AT
ELECTRO.
CHEM.
kj/kg
°C
°C
0 °C,
V
EQUIVALENCE A - h o u r s / g
Lithium’s density makes it the lightest o f all metals.
Alone it can not
be used as an structural engineering component due to its reactivity with air
and water.
However, it is a very effective alloying element, especially with
aluminum.
One weight percent lithium added to aluminum decreases the density
by three percent and increases the elastic modulus by six percent.(5)
Aircraft manufacturers and users aie excited about using
lithium-aluminum alloys to increase the payload capacity, fuel economy,
flight distance, and overall performance of their aircraft.
These advantages
will also be available for other users of lithium-aluminum alloys.
Lithium’s density combined with its very high electrochemical standard
potential and electrochemical equivalent make lithium an exceptional anode
material for energy cells.
Many variations o f lithium cells exist depending
on the cathode material and electrolyte used.
Characteristics o f lithium
cells are:
1) Flat discharge. Constant current production with respect to voltage
and impedance.
2) Longer shelf life. The lithium-manganese oxide battery available
commercially can be stored
for ten years at room temperature and
retain 85% of its capacity.
A zinc alkaline battery can be stored
2
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for only 2-3 years(6).
Storage for one year at 170°C is also
possible for lithium cells.
3) Wider operating
temperatures.
Lithium batteries with organic
electrolytes can be operated at temperatures as low as -155°C.
4) Higher voltage. Higher cell output reduces the number of cells
in a
battery pack by a factor of two when compared with regular zinc anode
batteries
5) High energy density.
The energy density of lithium batteries is 2-4
times higher than zinc alkaline batteries.
6) Virtually no self-discharge. This is due to the hermetic seal o f the
battery case.
These characteristics translate to the specialized use of lithium cells
in cold climates as portable energy sources and in components which are
activated occasionally but perform vital functions, such as back-up power for
an important installation.
Lithium use in batteries for radios, toys,
calculators, etc, etc.. is increasing and a number of companies are
1
( )
developing this technology .
Lithium has a very large temperature range between its normal melting
^
and boiling points which, combined with its large heat capacity, make lithium
a potential high temperature heat transfer medium.
The use of lithium in fusion energy reactors as a blanket material is
also anticipated. Lithium reacts with the neutrons produced in the fusion
plasma in the following manner:
Li + Neutron = He + Tritium
[ii]
The large amounts of energy carried by the neutrons would be transferred
to the excess lithium and then removed by a heat exchanger.
Tritium is a
fuel for the fusion process, so the lithium blanket material has the benefit
of regenerating a fuel.
The future of lithium is very promising
All reports are optimistic on
the metal’s increased use and importance as the twenty first century
approaches.
<
3
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f
1.2.2.
LITHIUM OCCURRENCE
Lithium is widely distributed across the earth.
clays, rocks and water bodies.
It occurs in soils,
The average lithium content of the earth’s
(OS.
crust is 20 ppm
ppm(8).
The average concentration of lithium in seawater is 18
Presently two types of lithium deposits are economical as an ore;
brines and pegmatite rocks.
Eighty percent of the world’s lithium reserves are present as brines.
The major lithium-bearing bnne deposits are sub-surface and include Salar de
Atacama(Chile), Salar de Uyuni(Bolivia) and in Silver Peak(Nevada).
Pegmatites are coarse grained igneous rocks.
The lithium-bearing
minerals are shown in Table 1.2.
Table
NAME
SPODUMENE
EUCRYPTITE
PETALITE
L EPI DOLI TE
1.2.
L i t h iu m B e a r i n g M i n e r a l s
FORMULA
L i 0 • AL 0 • 4 S i O ,
2
2 3
2
L i O -A l 0 •2 S iO
2
2 3
2,
L i 0 • A1 0 • 8S i O
2
2 3
2,
COMPLEX L i MICA
LiALSi 0
2 6
LiAlSiO
4
L iA lSi O
4 10
O f these minerals spodumene is the most important.
It hasa theoretical
lithia and lithium content of 8.03% and 3.75% respectively.
Major spodumene deposits are King’s Mountain(North Carolina), The
Greenbush property(Australia) Bemic Lake(Mamtoba), The Bitka
Pegmatite(Zimbabwe) and The Kitotolo deposit(Zaire), which is the world’s
largest.
The mined ore contains usually 2.5-3.5% lithia and is upgraded by
froth flotation to a maximum of 7.5% lithium oxide.
Other possible sources which are not economically feasible at present,
/Q\
are geothermal bnnes and hectonte clays of the Western United States .
Information on lithium reserves of the U.S.S.R. and China is not
available.(9)
4
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1.2.3.
LITHIUM INDUSTRY
I
The largest producing and consuming nation of lithium is the United
States.
Most of the production is from North Carolina pegmatite ores by the
Lithium Company of America and the Foote Mineral Company.
These companies
have agreements with South American governments to co-develop the Chilean and
Bolivian brine resources.
Despite prior beliefs that a lithium shortage is
imminent(10)<11) the present established reserves are estimated to be 7.6
million tons for pegmatites and 14.0 million tons for brines(9? The probable
cumulative demand for the period of 1983-2000 is 179,000 tons(12) o f contained
lithium.
The applications of lithium are changing with time.
The uses of lithium
during the period between 1978 and 2000 are shown in Table 1.3.
percentage of the total lithium used is in metallic form.
A greater
This trend is
expected to continue as more lithium is used in energy cells and alloys.
T ab le
1.2.4.
1 .3 .
USES OF LITHIUM METAL IN THE U . S .
(SHORT TONS)
1 9 7 8 (12)
1 9 8 3 (13)
2 0 0 0 U3)
T o t a l U se
3400
22 0 0
5600
U se
in
B a tte rie s
0
50
150
U se
in A l-L i A llo y s
0
0
750
% of
M e ta l U se
0
2 .2 7
1 5 .1
(%)
LITH IU M EXTRACTION TECHNOLOGY
The only commercial method of producing lithium metal today is molten
salt electrolysis of lithium chloride.
This process is applied to all
lithium bearing raw materials and, therefore, lithium chloride is an
essential intermediate product in lithium metal production.
Three methods exist to treat spodumene ore for the purpose o f lithium
extraction.
They are 1) The Acid Process, 2) The Alkaline Process and 3) Ion
Exchange.
The Acid Process is the only method used commercially and a flow sheet
«
5
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is shown in Figure 1.1.
The spodumene concentrate is first converted from
its a phase to its more reactive p phase by heating to approximately 1050°C.
The ore is then leached with hot sulfuric acid at 250°C.
Hydrogen ions from
the H2S 0 4 replace the lithium ions in the spodumene, thereby forming a
soluble lithium sulfate and an insoluble gangue.
During purification, the
acid solution is neutralized with ground limestone and filtered to eliminate
iron and aluminum impurities.
After a preliminary purification step,
hydrated lime is used to precipitate magnesium and soda ash is used to
precipitate excess calcium.
The solution is then adjusted to a pH of 7 - 8
and concentrated by evaporation to 200 - 250 g/litre of lithium sulfate
prior, to formation of lithium carbonate via Na2C 0 3 addition.
The spent
solution contains about 15% of the original lithium and must be recycled.
Prior to it rejoining the process at the purification stage, it is cooled to
0°C where sodium sulfate, which precipitates on cooling, is separated and
sold as a by-product.
I
?
%
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
t
SPODUMENE
CONCENTRATE
1
a TO 0 CONVERSION
1
A CID ROASTING
1
LEACHING
-» S I L I C A AND TAILS
!
-»
P U R IF IC A T IO N
-» Mg (OH) 2 , C a C 0 3
I
CARBONATION <-
Na CO
2
3
1
GLAUBER RECOVERY <------ SEPARATION
i
N a SO
i
PRODUCT
2 4
L i CO
2
PRODUCT
3j
CONVERSION TO L i C l
I
1
MOLTEN SALT
ELECTROLYSIS
Figure 1.1.
—
L i METAL
The acid process for producing lithium carbonate which
is converted to lithium chloride for molten salt
electrolysis to produce lithium metal.
An interesting feature o f the flow sheet shown in Figure 1.1 is that
lithium carbonate is made pnor to the production of lithium chloride.
Lithium carbonate is the most widely used lithium chemical, used in aluminum
production, and it serves as the raw material for the production of all other
lithium cherricals.
If lithium metal were to approach lithium carbonate in
usage, the process could be easily modified so that the stream o f lithium
bearing liquor was transformed directly into LiCl.
Some o f the parameters o f the molten salt production of lithium are
listed in Table 1.4.
C
7
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t
T ab le
1.4.
OPERATING CONDITIONS FOR I d ELECTROLYSIS CELL
L iC l
M aterial
E le c tro ly te
Tem perature
(15) ( 1 6 )
L ic l %
48-50
KC1 %
6 5 .8 -5 0
°C
450-460
C e l l C u r r e n t (A)
3500
V o lta g e
4 .8 6 -8 .1 9
C urrent
(V)
G raphite
Anode
Pow er
A nalysis
I
T heoretical,
(kWh/kg L i )
3 1 .5 -3 9 .2
T o ta l Power,
(kWh/kg L i )
1 4 0 (16)
9 9 .0
Li%
The result of this process is a lithium product with a market price of
$CDN 65.45 / kg(16) for a standard lithium ingot of commercial purity.
tonne of spodumene concentrate costs $Cdn 450.
One
The concentrate has a
contained lithium value of,
1000 kg/tonne x 0.0325 Li x $ 65.45/kg Li =
$Cdn 2127/tonne
[1.2 ]
The cost analysis shows that an effective extraction method could be
profitable.
1.3. ALPHA TO BETA SPODUMENE TRANSITION
The reactivity of the lithia species in the spodumene can be improved by
its polymorphic transformation from the stable alpha phase to the more open
beta phase.
The alteration of the crystal structure is not unique to the
mineral spodumene and occurs for many silicates, the most well known are the
five polymorphs of quartz: high and low quartz, tridymite, and high and low
I
8
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cristabolite.
Polymorphism occurs when the ambient crystal structure is not
the most stable phase at other temperatures and pressures.
In practice, the transformation is found to occur at temperatures
greater than 900°C.
Above 930°C, the mechanism is by almost instantaneous
nucleation with umdimensional growth of the nuclei while below 930°C only
nucleation occurs
(17)
. The higher temperature is necessary to overcome the
activation energy of the transformation, equal to 289 kj/mole above 930°C and
753 kJ/mole below 930°C(18).
To better understand the effect of the a to p transformation
an examination of silicate chemistry is useful.
The building block
of silicate chemistry is the Si04 tetrahedral, displayed in Figure 1.2.
I
Figure 1.2.
The silica tetrahedral.
Open circles represent oxygen atoms
and full circle represents a silicon atom.
The silicon atom in the center is covalently bonded to four oxygen atoms
and is known as a tetrahedral site (T).
Large crystal networks are formed
when tetrahedra share a common oxygen atom.
Some of the ideal structural requirements of silica are
:
1) ideal bond length d(Si-O) = 1.605A
2) strain-free Si-O-Si bond angles of 140°
3) good space filling with as many bonds per unit volume (in order to
attain maximum free energy per unit volume): ideal V
= 15 A3.
The correlation between the stability of the tetrahedral frameworks and
crystal data is shown in Figure 1.3(19).
i
9
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1
t
K
10
.PARACELSIAN
8
0
i
.K EA TITE
HEXACLLSIAN h
.QUARTZ
U
2
PYROXENES
0
-15
-10
5
0
5
15
10
20
25
A T -0 -T I °l
Figure 1.3.
Correlation between the difference in oxygen density (AV^),
Si-O-Si bond angles (A T-O-T) and relative stability of the
tetrahedral frameworks and chains of silica and A1 containing
alkali and alkaline earth silicates. The frameworks and chains
are less stable, the larger the distance from the point AV = 0
and A T-O-T = 0.
Table 1.5(20) shows structural data for a and (3 spodumene.
T a b le
1 .5 .
CRYSTAL STRUCTURAL DATA FOR ALPHA AND BETA SPODUMENE
T -O -T
V
ox
a SPODUMENE
1 3 9 .0
1 6 .2
0 SPODUMENE
1 4 9 .4
2 1 .7
«
10
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A lpha spodumene’s crystal structure is much closer to the ideal than
that of (3 spodumene: 1° for bond angle difference for a versus 9.4° for (3 and
AV = 1.2A3 for a versus 6.7A3 for (3.
ox
The AT-G-T and AV
ox
for a spodumene
corresponds to the stable pyroxene structure which is a three dimensional
framework.
The data for (3 spodumene give it a keatite structure, a two
dimensional chain structure which may be easier to penetrate in the
metallo-thermic reduction process.
Another difference is that the aluminum cations in the (3 spodumene
occupy T sites while alpha spodumene does not have its aluminum cations in T
sites.
T h e importance of this difference in the location of the aluminum
atoms is that in the a phase, where less interstitial volume exists, more
non-tetrahedral cations must be accommodated.
In 3 spodumene, the lithium
atoms have larger interstitial volumes to fit into and no interstitial
aluminum cations are present.
The difference in the V
and the crystal structure leads to a density
difference between the polymorphs.
Alpha spodumene has a specific gravity of
3.150 g/cm 3 and (3 spodumene has a specific gravity of 2.400 g/cm3(3)
As a
result (3 spodumene is 23% less dense than a spodumene and a corresponding
volume expansion occurs during the transition.
The conversion of spodumene to the [3 phase from the a phase creates a
more reactive raw material by:
1) Increasing the volume o f the material and thus increasing its surface
area
2) Giving the lithia species more mobility in the material.
3) Weakening the crystal structure of the material.
Beta spodumene appears to be more amenable to metallo-thermic reduction
than a spodumene and the spodumene transition would be an effective
pretreatment of spodumene for metallo-thermic reduction.
<
11
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II. LITERATURE SURVEY
1
H .l.
M ETALLO-THERM IC REDUCTION PROCESSES
The m ost widely known metallo-thermic reduction process is the Pidgeon
Process for the production of magnesium(2l).
In this process, magnesium is
produced from calcined dolomite by reduction with ferrosilicon in a vacuum
retort.
The reaction is described by the equation:
2[CaO-MgO](s) + Si(s) = 2Mg(g) + 2 C a 0 S iO 2(s)
[2.1]
This process is one o f the methods used to produce magnesium commercially.
Alumino-thermic reduction processes are used for the production of
manganese, chromium(22)(23) and calcium(24).
II.2.
LITHIUM PRODUCTION BY M ETALLO-THERM IC REDUCTION
Kroll and Schlechten(25) were able to reduce lithium oxide, in the
presence of lime, with silicon, aluminum and magnesium as shown below:
2Li20(s) + 2CaO(s) + Si(s) = S i0 2-2CaO(s) + 4Li(g)
[2.2]
3Li20(s> + CaO(s) + 2A1(S) = Al2O3'Ca0(s) + 6Li(g)
[2 3]
Li 0(s) + CaO(s) + xMg(s) =
[2 .4]
CaO + MgO + Li + (x-l)M g
Their experiments had recoveries of the order of 90%.
They stated that
lime was essential in all the systems, except in the study using
magnesium where the lime "had no chemical function" and the condensate
contained magnesium impurities.
Stauffer
/nf.\
earned this process one step further by reducing spodumene
directly with ferrosilicon (FeSi ).
90% were attained.
Once again recoveries of the order of
It was noted that lime was an absolutely essential
reagent for the process because of the way it "tied up" the alumina and
silica species in spodumene and without lime, poor recoveries were obtained.
12
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In both sets o f experiments a combination of reducing agent, lime and
lithium raw material were combined in varying concentrations into a
^
briquette.
The briquettes were then placed in a vacuum retort and the
condensate product was analyzed for lithium.
Pidgeon and Morris(27:i measured the vapor pressure of lithium in the
lithium oxide-calcium oxide-silicon system
They found that the vapour
pressure increased with temperature between 972°C and 1025°C and was
sufficient to commence commercial production(28).
Fedorov and Sharmai
examined the kinetics o f the reduction o f lithium
aluminate by aluminum in vacuum;
3 L i 20 A l 2O 3(s) + 2 A l(s ) =
6 L i(g ) + 4 A 1 20 3(s>
by utilizing a method of continuous weighing.
[2.5]
They concluded that a period
of constant reaction rate existed and that the kinetics varied considerably
with temperature.
All the above studies and processes utilized powder reactants in a
vacuum retort.
The previous studies on lithium production were successful yet the
^
process was never successfully industrialized.
Reasons why the commercial
process did not succeed were;
- slow production rates due to the fact that only small briquettes could be
used for fear that the Li vapours would not be released.
- a small demand for lithium metal at the time.
- poor metal vapour condensation technology.
With a MLE process, large reactors could be constructed and the process
could be developed into a high yield, continuous one.
The lithium may be
able to be condensed as a liquid.
II.3.
LIME - SPODUM ENE REACTIONS
In the previous studies o f lithium production by metallo-thermic
reduction of lithium oxide and spodumene, calcium oxide played an important
role.
In view of lime’s importance to a proposed process, this section
examines the literature o f spodumene-lime reactions.
Various work has been done on the reaction of lime with lithium
I
13
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materials
(29 30 31)
' .
In the most comprehensive study of lime-spodumene sinters,
Lainer and Nazirov(32), stated that the first stage o f the reaction might
proceed according to the equation:
Li &O A1LOj -4SiOL + 8CaO = LiI O-Al 1O5 + 4(2CaO S iO J
[2 .6j
and in a second stage excess lime would break up the lithium aluminate to
form lithium oxide.
In Chapter IV it w as investigated whether a lime pretreatment would be
used in the MLE process.
II.4.
INTERFACIAL PHENOM ENA
Solid oxides and molten metals are not materials which readily mix and
are often described as non-wetting.
Wetting phenomena were important in this
study of the MLE process because the reactions involved were between solid
oxides and molten metal and if no wetting occurred, no reaction would occur.
A measure o f wetting between a liquid and solid can be described by the
contact angle, 0, shown in Figure 2.1.
The contact angle can be expressed theoretically by Young’s equation;
( Ysv ' YSI)
COS0 =
----------------
\v
where y
, y
o V
and y
o L
represent the surface tension between solid and
L .Y
vapour, solid and liquid and liquid and vapour respectively.
I
14
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[2.71
VAPOUR
VAPOUR
LIQUID
LIQUID
Figure 2.1.
The angle between the tangent of the liquid-gas interface
and the solid plane is the contact angle, 0.
In the above
Figure, 0, is greater than 02 and as a result greater wetting
will occur at surface 1.
Table 2.1 shows y
for selected molten metals and their solid phases
compared to ylv of the same metals with their vapours.
The table shows that
if yLV for metal A is much larger than yLV f° r metal B then yS L for metal A
will be larger that ysL for metal B.
Table
2.1.
SURFACE TENSIONS FOR SELECTED LIQUID METALS<34) <35>
Metal
Li
Na
A1
Ag
L v
*SL
398
191
914
903
30
20
122
126
Using Equation 2.7, the contact angle, 0 for a spodumene particle in
contact with either aluminum or an aluminum-magnesium alloy can be compared.
For both liquid metals, y
would be equal.
According to the relationship
15
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
between ylv and ysl established from Table 2.1, Equation 2.7 can be
rewritten,
n
CO S0
( ?sv '
=
— — --------------- —
128)
Ylv
thus the contact angle would increase as yiv decreases.
Figure 2.2 shows that the surface tension, yLv, of aluminum decreases
with magnesium addition.
As a result the contact angle between an oxide
particle and molten aluminum would decrease with magnesium addition,
improving the wetting.
800
i
6
0c)
>*
T3 700
Sn
c
o
(A
c
41
0> 600
o
O
3
CO
500
400.
Figure 2.2.
Surface tensions for aluminum alloys at 50°C to 80°C above
hquidus temperature.
(35)
I
16
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«
IH . THERMODYNAMIC ANALYSIS OF SPODUMENE REDUCTION
ff l . l .
REDUCING AGENT
The Ellingham Diagram in Figure 3.1 and the thermodynamic computer
program F*A*C*T [Facility * for the Analysis * of Chemical *
Thermodynamics](36) developed by Bale, Thompson and Pelton were used to choose
the molten metal reductant.
A list of the possible reductants and their
characteristics is shown in Table 3.1.
The characteristics of lithium are
also given.
-200
u
►
j
o
x:
►-Jin
MO
ru
>-W
03
KO
bW
» w
w
IX
-600
-800
-1 0 0 0
-12 0
00
1000
1500
2000
2500
TEHPERATURE ( K )
Figure 3.1. Free Energy of Formation for lithium and potential reductants.
17
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T a b le
3.1.
CHARACTERISTICS OF LITHIUM AND POSSIBLE REDUCTANTS
PROPERTY
MATERIAL
Li
A1
Ca
Mg
Si
MELTING P OI NT ° C
180
660
839
648
1410
BOI LI NG P OI NT° C
1342
2467
1484
1090
2355
C O S T ( $ C / k g ) <17)
65. 45
2 9
7.0
3.6
1.3
The Ellingham diagram shows that aluminum and silicon are not suitable
reducing agents at atmospheric pressure.
Only calcium and magnesium could
reduce lithium oxide to form lithium.
However, neither is suitable as a bulk
metal due to cost, reactivity or vapour pressure.
Aluminum is an ideal bulk metal because of its low cost, suitable
melting point and very high boiling point, 1 e , a low vapour pressure,
iO '10Atm, at the anticipated operating temperature of approximately 1000°C.
Since calcium and magnesium have the oxygen affinity necessary to reduce
lithium oxide the reducing agent chosen was a molten mixture of aluminum
with calcium or magnesium.
Magnesium is superior to calcium in terms of economics.
It has a lower
cost $CDN 3.55/kg vs. $CDN 7.00/kg.
Magnesium was also found to be thermodynamically superior.
The F*A*C*T
program, EQUILIB, was used to simulate the reduction o f spodumene by an
aluminum alloy containing magnesium or calcium.
EQUILIB predicts the most
thermodynamic stable compounds that should be produced from the given amounts
of reactants at a certain temperature and pressure.
Thermodynamic data was obtained for dissolved magnesium, silicon and
lithium in liquid aluminum and this data was added to the F*A*C*T data base
and included in the simulation.
Thermodynamic data was obtained for the
/ 07s
1) free energy of dissolution in liquid aluminum
entropies(38) of the dissolved species.
and 2) the absolute
The data used is shown m Table 3.2.
The data for calcium was from estimates by Richardson(39).
The procedure
outlined in the F*A*C*T DATAENTRY program was followed to create the
dissolved species.
Reproduced with permission o f the copyright owner. Further reproduction prohibited without permission.
Table
3.2.
STANDARD FREE ENRERGY OF SOLUTION OF ELEMENTS I N
AND T H EIR ABSOLUTE ENTROPIES
METAL
Si
Mg
Li
Ca
AG°
( k J / MOL E )
40,145.0
-14,551.9
-24,267.2
-43,513.6
LIQUID A1
S°
( J / MOLE)
- 47.241T
1 .255T
+ 13.440T
18.82
32.51
28.03
41.63
For the calculation, Inputs 3.1 and 3.2 below were used.
approxiamated the experimental trials described later.
These roughly
The <A> value was
varied from 0 to 10 in increments o f 1.
L i20 'A l2O 3-(Si02)4 + 85.5 A1 + <A> Mg
[3.1]
L i20 A l20 3 (Si02)4 + 85.5 A1 + <A> Ca
[3.2]
The complete F*A*C*T output for the magnesium simulation is given in
Appendix A.
The results of the simulation are summarized in Tables 3.3 and 3.4 and
Figure 3.2.
When the <A> value w as zero. F*A*C*T predicted that the molten
aluminum would fully reduce the silica species to form silicon.
six percent of the lithium oxide in the spodumene
Ten point
wasreduced tolithium and
the remainder was converted to lithium aluminate. Thus the task
of a
reducing agent would be to decrease the lithium aluminate predicted and form
m ore pure lithium.
Table 3.3 shows that the simulation predicted that the
total number of moles of free lithium decreases, with calcium addition.
Instead of reducing the lithium aluminate, the calcium was predicted to form
the compound CaAl4
to occur.
When magnesium is added, more free lithium is predicted
This is due to magnesium reduction of lithium aluminate to form
spinel and lithium dissolved m the molten metal.
70% recovery of the lithium was predicted.
A t ten moles of magnesium
If the amount o f magnesium was
increased above ten moles more lithium would be produced.
t
19
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Table
3.3.
F*A*C*T OUTPUT OF SPODUMENE REDUCTION WITH A l- C * ALLOT
AT 1 1 7 3 K AND 1 ATM.
1
_____________________________
MOLES PRODUCTS
<A>
A1
Li ( 1 )
L i A l O *3 I s)
CaAl
4
( 1)
-
A1 O ( s )
2 3
S i (a)
0
1
0.140
0.134
0.079
0.075
1 . 781
1 .790
1.0
2.81
2.81
3.99
3.99
2
3
0.128
0.122
0.072
0.071
1 .797
1 .809
2.0
3.0
2.81
2.79
3.99
3.99
4
5
0.117
0.111
0.066
0.062
1.818
1 . 827
4.0
5.0
2.79
2.78
3.99
3.99
6
7
0.105
0.099
0.059
0.056
1 . 836
1 . 845
6.0
7.0
2 .78
2 .77
3 . 99
3.99
8
9
10
0.093
0.087
0 .081
0.052
0.049
0.048
1 . 854
1.864
1 . 873
8.0
9.0
10 . 0
2.76
2.76
2 .75
3.99
3.99
3.99
Table
3.4.
F*A*C*T OUTPUT OF SPODUMENE REDUCTION WITH A l-M g ALLOT
AT 1 1 7 3 K AND 1 ATM.
MOLES PRODUCTS
<A>
[ L i ] Al
Lid)
L lA lO ^(s )
MqAl O ( s )
2 4
A1 O ( s )
2 3
Si (s )
0
1
0.140
0 .141
0.079
0.079
1 .781
1.780
0.79
2.81
1.75
3.99
3.99
2
3
0 .142
0.278
0.080
0.156
1.777
1.565
1.79
2.21
0.42
0.00
3.99
3.99
4
5
0 .410
0 .514
0.231
0.289
1.356
1.197
2.32
2.40
0.00
0.00
3.99
3.99
6
7
0.603
0 .682
0.339
0.383
1.058
0 . 934
2.47
2.53
0.00
0.00
3.99
3.99
8
9
10
0.755
0 .823
0.888
0.425
0.463
0.499
0.820
0 .713
0 . 612
2.59
2.64
2.69
0.00
0.00
0 .00
3.99
3.99
3.99
-
1
20
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Mg
Ca
z
o
ho<
er
x
U
j
MOLES REDUCTANT
Figure 3.2.
Thermodynamic simulation of the lithium extraction from
spodumene by reduction with Al-Mg and Al-Ca alloys at 1173 K and
1 atm.
i
The lithium extracted from the spodumene is plotted
against the respective magnesium and calcium to spodumene molar
ratios.,
Figure 3.2 shows that magnesium is the superior reductant in this study.
An aluminum-magnesium alloy was thus chosen as the reducing agent in the
experimental program in this study.
The drawback with magnesium as the alloying element is its vapour
pressure, which is similar to lithium ’s and which would pose a contamination
problem during lithium distillation and recovery.
The similarity in vapour
pressure may be resolved by fractional condensation o r distillation using
lithium ’s much lower melting point as compared with magnesium’s, 180°C
versus 648 °C.
C
21
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IV. LIME - SPODUMENE TESTS
IV .l.
INTRODUCTION
Kroll and Schlechten(26 ^stated that lime was chemically inactive in the
reduction of lithium oxide by magnesium.
However, Stauffer(28) found that
lime was essential in the reduction of spodumene by ferrosilicon.
From this
information a decision whether to use a lime pretreatment in this study can
not be made.
A senes of lime-spodumene tests were thus performed to determine if the
lithium oxide portion of the lime treated spodumene was significantly more
amenable for reduction than that in p spodumene.
The results o f the tests,
thermodynamic analysis and common sense were used to decide whether a lime
pretreatment of the spodumene was necessary in this study.
IV.2.
APPARATUS & REAGENTS
A muffle furnace was used to heat the fire clay crucibles used to
contain the reactant mixtures in the lime-spodumene tests.
Temperature
measurements were obtained via type K thermocouples, placed in alumina
sheaths and inserted into the center of the mixtures.
The apparatus is shown
in Figure 4.1.
The spodumene was a high grade concentrate obtained from The Tantalum
Mining Co. of Canada (Tanco), Bernic Lake, Manitoba with the Tanco assays
shown in Table 4.1.
Table
Li 0
Na 0
7.0-7.5
0 . 16
2
(t)
4.1.
SPODUMENE ASSAYS
2
K 0
2
0.06-0.15
( % ) (t>
Fe O
2
0 .05
3
P 0
2
5
0.15-0.2
Assay performed by Tanco.
The lime was commercial grade obtained from Jolichaud in Montreal,
and was calcined at 600°C for one hour, a recommended calcining treatment*40*.
9
22
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TEMPERATURE RECORDER
i
1
•
- •
1000
ALUM IN A SHEATH
THERM O CO UPLE
«
MUFFLE
FURNACE
CRUCIBLE
& MIXTURE
Figure 4.1.
Apparatus used to perform the lime-spodumene experiments.
IV.2. PR O C ED U R E
Two arbitrarily chosen mixtures o f lime and spodumene containing 38.4
wt% and 68.7 wt% spodumene, respectively, were heated at temperatures o f
900°C, 950°C, 1000°C, 1050°C, 1100°C and 1150°C for four hours in fire clay
crucibles in a muffle furnace.
cooled.
The crucibles and contents were slowly
The lime to spodumene molar ratios of the mixes were 4:1 and 10.5:1,
respectively.
The products of reaction were analyzed by X-Ray Diffraction (XRD).
raw data was obtained by a 37 minute scan between 10° and 100° and then
analyzed using the Phillips APD 1700(41) software analysis system.
23
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
The
IV.3.
RESULTS OF LIME-SPODUMENE TESTS
Three distinct reaction products were apparent after experiments at
different temperatures.
Photographs are shown in Figures 4 2 - 4.4.
At
1050()C and below, a grey powder, slightly affected by the a -> (3 expansion of
the spodumene, occurred for both lime-spodumene mixes.
a green, friable, sinter that had expanded was obtained.
For trials at 1100°C,
At 1I50°C, a white,
fused product was obtained.
Figure 4.2.
Reaction product from lime - spodumene experiments at
temperatures of 1050°C and below
I
24
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 4.3.
Figure 4.4.
Reaction product from lime - spodumene experiments at 1100°C
Reaction product from lime - spodumene experiments at
1150°C.
25
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Table
4.2.
XRD RESULTS OF LIME SPODUMENE SINTERS AND COMPOUNDS
PREDICTED BY F*A *C *T
T °C
RATIO
IDENTIFIED PHASES
950
10.5:1
SPODUMENE
10 5 0
1100
115 0
IV.4.
LiAlO , C a
2
II
4:1
100 0
F *A *C *T
LiAlO
2
2
Si O , CaO
4
, CaSiO
3
L i A l O , C a Si O , CaO
10 . 5 : 1
2
4 :1
If
10 . 5 : 1
II
LiAlO
LiAlO
2
2
4
, CaSiO
3
, C a S i O , CaO
2 '
2
4
4:1
LiAlSi
10 . 5 : 1
Ca A1 S i O
4:1
Ca A1 S i O
10 . 5 : 1
NO S P E C I E S DETECTED L i A l O , C a S i O , CaO
4:1
Ca S i O
2
2
3
O
L i A 1 0 2 , CaSi O^
8
2
2
7
C a Si O
2
4
LiAlO , C a
2'
2
Si O , CaO
LiAlO , CaSiO
7
2
?
2
3
2
LiAlO , CaSiO
3
4
4
3
DISCUSSION
The goal of the lime - spodumene tests was to examine the results from
the XRD and thermodynamic analysis and using those results, to determine the
necessity of a lime pretreatment of the spodumene.
At 1050°C or below, spodumene was detected for all products except
for the 4:1 molar ratio at 1050°C, where the lithium alumino silicate,
LiAlSi 3 0 o , was detected by XRD.
At temperatures at and greater than 1100°C, products containing
calcium silicates and calcium alumino silicates were identified, indicating
reaction between the lime and spodumene.
At 1100°C these products were
gehlenite (Ca2Si2A107) and lamite (Ca2Si04).
Both are greenish in colour
and were the cause of the green colour of the products.
For experiments run at 1150°C, the white mineral, wollastomte (C aSi03)
was detected by XRD.
The EQUILIB program from F*A*C*T was used to predict the most
thermodynamically stable products o f the lime-spodumene pretreatment.
26
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The
lamite (Ca2S i0 4) and lime for the 10.5:1 molar mix at all temperatures.
For
the 4:1 mix, lithium aluminate (LiA102) and wollastonite (CaSiOp were
f
predicted.
In addition F*A*C*T predicted that gehlenite (Ca A1 SiO ) would
Z
Z
/
have a high activity in the system, but not high enough for it to form.
The
XRD analysis verified the F*A*C*T calculations by detecting, gehlenite,
larnite and wollastonite.
with work by Nazirov
The F*A*C*T prediction of lithium aluminate agreed
nil
The reaction products predicted by F*A*C*T were the same for all
temperatures.
However, as mentioned above, three different experimental
products were observed.
This was due to the very slow kinetics at lower
temperatures and the activation energies necessary to commence reaction
( 1 ON
.
No simple method was available to separate the lithium containing
species from the calcium containing species in the products.
Thus it threw
into question the desirability o f the lime-spodumene sinter product over (5
spodumene as a feed material for molten metallo-thermic reduction.
The salient information is as follows:
1) The pretreatment did indeed break up the spodumene structure and free
lithium oxide species to either form the aluminate or remain as an
|
oxide.
Neither of these species were identified in the XRD study.
2) The lime pretreatment diluted the lithium content in the material.
3) As well, the addition of lime introduced calcium into the system which
was shown in Chapter III to have a negative effect on the thermodynamics
of the system.
4) The thermodynamic study in Chapter III shows that the reduction of the
spodumene with an aluminum-magnesium alloys is feasible without a lime
pretreatment.
It was concluded that a lime pretreatment was not nescessary and
furthermore that lime’s importance in the powder experiments performed
by Stauffer was due to the passive oxide layer on the surface o f the
powder reductants.
In those experiments, lime was necessary as a flux
to decompose the oxide layer and expose free metal for reaction.
Since the reactions were performed in vacuum, no further oxidation,
aside from the formation of reaction products, occurred.
With the MLE
process, molten metals, free of oxide surfaces, would be the reducing
I
27
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agent, so the fluxing properties of lime would not be necessary.
IV.5.
CONCLUSIONS; LIME - SPODUMENE TESTS.
The lime pretreatment of spodumene was not considered advantageous for
the MLE process for the following reasons;
1) Dilution of lithium in feed material for reduction.
2) Thermodynamic feasibility of system without lime.
3) No distinct disassociation of the lithia species from alumina and silica.
As a result, the reduction of spodumene was attempted without lime
pretreatment in this study.
T
i
28
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V. EXPERIMENTAL
V .l.
OBJECTIVE
The aim of the experimental program was to determine the effect of
changing the magnesium concentration of an aluminum-magnesium molten
reductant, on the recovery of lithium to the molten phase, via spodumene
reduction at 1 Atm. and 1173 K.
V.2.
EXPERIMENTAL VARIABLES
The process variables which were controlled during the experiments were:
a) melt temperature
b) A r gas flush rate
c) stirring mechanism and rate
d) reaction time
e) amount o f excess molten aluminum
The process variable which w as altered was the amount of magnesium added
to the system, calculated as the molar ratio of magnesium to spodumene.
V .3.
M ATERIALS
Three charge materials were used;
a) high grade spodumene concentrate supplied by Tanco and converted in
house to (3 spodumene.
b) aluminum, commercial grade supplied by ALCOA, Pittsburgh,
Pennsylvania with the specifications shown in Table 5.1.
Table
5.1.
S P E C I F I C A T I O N S OF ALUMINUM( + 1WEIGHT%
Si
Fe
C
Mn
Mg
Zn
Ti
V
0.033
0.029
0.004
0 .001
<0 .001
0.005
0.004
0.012
( t) Assay performed by emission spectrometry at McGill University.
29
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c) magnesium, commercial grade supplied by Timminco, Haley, Ontario.
V.4.
APPARATUS
The experimental apparatus used to perform the reduction experiments is
shown in Figures 5 .l.and 5.2.
I
Figure 5.1. Experimental cap assembly.
V
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
DRIVE CHAW
STIRRING DRIVE
MOTOR
SHAFT SUPPORT
IMPELLER SHAFT
ARGON INLET
EXHAUST GAS
CRUCBLE CAP
INDUCTION
FURNACE
IMPELLER
ALUMNA
CRUCBLE
IMPELLER DRIVE &
SUPPORT VEHICLE
Figure 5.2.
Schematic of experimental apparatus used to perform the
spodumene reduction experiments.
C
-------------------------------31
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Below is a description of the equipment used.
m
Induction Furnace:
100 kW, Bradley Controls:
tilting capabilities, removable crucibles,
gas ventilation.
Crucible:
Bonded alumina, 28.8 cm high , 12.8 cm in diameter, supplied by
Engineering Ceramics, Gilberts, Illinois.
Impeller:
For Experiments 1-3: stainless steel blades, 11.8 cm blade to blade
diameter, 1.0 cm blade thickness, 11 cm blade height, welded onto
1.90 cm diameter shaft.
For experiments 4-8: high temperature refractory cement bonded onto
stainless steel mesh reinforced blades, 11 8 cm blade to blade
diameter, 1 cm blade thickness, 11 cm blade height with a 2.54 cm
shaft diameter
]
Impeller
shaft:
Machined to 1.58 cm diameter at top to fit into brass connector.
Experiments 1-3: 1.90 cm diameter 36 cm height.
Experiments 4-8: 2.54 diameter, 36 cm height.
Brass Connector:
Hexagonal shaped, 2.54 cm from edge to edge, 1.58 cm hole drilled in
underside to accommodate impeller shaft, three 0.635 cm threaded holes
for screws to secure impeller shaft, threaded at top to accommodate
drive shaft.
Impeller Drive and Support Vehicle:
Movable in any direction, raising and lowering of steel angles
attached to shaft support, ball bearing attachment of drive shaft to
shaft support, two levels of storage.
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32
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Thermocouple:
Handheld Omega type K thermocouple probe with 30.48 cm long, with
0.3175 cm tip diameter coated in clay protection.
Motor:
Tigear two speed motor, sprocket and chain system used to drive shaft
at 36 or 60 rpm.
Gas:
Liquid Air prepurified 99.998% A r gas.
Less than 10 ppm water vapour,
less than 10 ppm oxygen.
Flowmeter:
Flowrate controlled by Gilmont flowmeter, size no. four, with a ball
diameter of 0.9525 cm, ball mass of 1.142 g and ball density of 2.53 g
cm"3
Sampler:
^
Steel crucible, 1.4 cm outer diameter, 1 cm inner diameter,
Steel wire, 0.1 cm diameter, spot welded onto crucible side for
lowering into the melt through viewport.
Crucible Cap:
Mild steel, 17.1 cm in diameter, 1.2 cm thick, a groove machined into
underside provided a fit between cap and crucible, two 1.59 cm holes
drilled through cap, one for gas exhaust and other for viewport /
temperature measurement / sampling, one 1.59 cm threaded hole for Ar
gas intake, 1.905 cm copper tubing leading from gas exhaust to
ventilation system, 0.635 cm copper tube laid over and soldered to
surface with connectors leading to PVC hoses for water intake and
outlet.
Experiments 1-3: 1.90 cm hole drilled in center,
Experiments 4-8: 2.54 cm hole drilled in center.
33
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V.5.
EXPERIM ENTAL PROCEDURE FOR
SPODUMENE REDUCTION TESTS
f
V.5.1.
PREPARATION O F EXPERIMENTS
Prior to the reduction experiments the a -> P treatment of the spodumene
was performed.
The as received a spodumene was heated at 1050°C for three
hours in the muffle furnace in fireclay crucibles similar to the ones used in
the lime-spodumene tests.
When a new crucible was used in the reduction experiments, the crucible
was installed so that its nm was parallel to the ground.
This was done to
ensure that the impeller entered the crucible at an angle of 90°.
The
crucible was surrounded by coarse silica particles which provided packing and
insulation.
The silica was covered with cement to contain it during the
casting of
the reduction experiment products
cement to
A spout wasmolded from the
provide a channel to improve pouring.
Prior to a reduction experiment, the impeller was coated with an alumina
cement and allowed to dry for 24 hours.
After which, it was heated to 900°C
for 5 hours to eliminate moisture in the alumina paint and to strengthen the
J
bonding o f the paint.
V.5.2.
EXPERIM ENTAL PROCEDURE
Charging consisted of placing pieces o f pure aluminum into the crucible.
The power was set at 35 kW. and melting, which varied with the shape of the
aluminum pieces, due to different efficiencies in energy utilization, took
about ninety minutes.
Once molten, the temperature of the aluminum rose very
quickly.
At a temperature of 900°C, magnesium was added in cut blocks by dunking
with tongs.
Black oxide believed to magnesium oxide was visible on the
surface of
the aluminum as dissolution was occumng. This oxide formation
decreased the efficiency of the experiments as it consumed magnesium.
Following magnesium addition, (3 spodumene was added to the top of the melt.
The impeller and cap weie then attached to the cart and moved into place and
the water cooling and argon gas flow w'ere
The impeller was lowered slowly into
prevent thermal shock
connected
the melt, by the manual winch, to
As the impeller was lowered,
it was turned slowly by
34
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hand to ensure that no contact of impeller and the crucible wall occurred
(i.e., that the impeller was centered properly).
The immersion of the cold
impeller extracted a great deal of heat from the liquid metal.
Once the
temperature again reached 900°C, stirring and argon gas flow began.
This
marked the starting point of the reduction experiments.
Temperature measurements sampling were taken every 20 minutes for one
hour.
The temperature was held at 900 ± 20°C.
During a temperature
measurement, the impeller was stopped, the temperature measurement hole
uncovered and the thermocouple probe inserted into the melt.
Sampling was
performed every twenty minutes or at every second temperature measurement.
The sampler was lowered into the melt through the temperature
measurement/sampling hole to obtain the samples.
Ninety minutes after the beginning of the experiments stirring was
stopped and the impeller and cart apparatus were removed.
The melt was
allowed to cool to approximately 750°C pnor to pouring the entire contents
of the crucible into a mold.
Some molten, viscous material remained inside
the crucible and was scraped out of the crucible into the mold.
A thin metal skin was removed from the impeller after each experiment
and added to the products.
The removal of this metal stripped the alumina
paint and some cement from the impeller.
As a result the impeller was
touched up with cement and repainted prior to an experiment.
i
35
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V.6.
EXPERIM ENTAL PROGRAM
The experimental program consisted of eight experiments listed in Table
5.2.
Table
5.2.
EXP.
1
2
3
4
5
6
7
8
SPODUMENE REDUCTION EXPERIMENTS PERFORMED
REACTANTS
<g)
MOLES REACTANTS
A1
Mg
SPOD
AL
Mg
SPOD
2340.5
2291.0
2355.8
2410.3
2439.8
2220.0
2280.5
2269.8
97.6
0.0
104.0
47.6
143.3
191.9
220.6
224.8
365.7
343.8
369.0
368.6
370.2
361.8
342.1
348.4
86.7
84.8
87.2
89.3
90.3
82.2
84.5
84.1
4.1
0.0
4.3
2.0
6.0
8.0
9.2
9.4
0 .98
0 .92
0 .99
0.99
1.00
0.97
0 .92
0.94
Mg/ SPOD
mole
ratio
4.2
0.0
4.3
2.0
6.0
8.2
10.0
10.0
1
1
36
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VI. RESULTS
i
VI.1.
SPODUMENE TRANSITION
The transformation of alpha to beta spodumene during the treatment
resulted in a volume expansion.
The crucible contents were loosely packed
prior to the treatment but afterwards they were densely packed together.
In
some cases the pressure from the expansion was so great that the crucible
cracked.
The XRD patterns of the a spodumene and of the transformed material
are compared with the patterns o f a and (3 spodumene in Figure 6.1.
- io 1
5 .0 0
4 .0 0
3 .0 0
A
£-00
1 .0 0
11
-i—4-J-
lL.i. J l . l J 1 1- . .J i
4 0 .0
6 0 .0
8 0 .0
100.0
J_L L
4^.0
jJ U .
6.0 .0
8 0 .0
100.0
2 0 .0
4 0 .0
00 .0
8 0 .0
100.0
2O.0
4 0 .0
tO . 0
8 0 .0
100.0
2 0 .0
B
uu_
1O0.0
3 0 .0
6 0 .0
4 0 .0
£0 . 0
II l i 1.1
?0 . 0
.10J
1 .00
0 .3 0
0 .6 0
0 .4 0
0 .2 0
-
D
144-
i l-i.
1 00.0
3 0 .0
6 0 .0
4 0 .0
20.0
Figure 6.1.
XRD patterns of the material received from Tanco(A), a
spodumene(B), the transformed material(C) and P spodumene(D).
<
37
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The difference in the patterns between the a spodumene and the
transformed material and the resemblance between the patterns of the
transformed material and P spodumene indicated a successful pretreatment.
The cumulative size distribution of the feed material was altered by the
treatment as shown in Figure 6.2 and microphotographs o f a and p spodumene
are shown in Figure 6.3.
100
ALPHA
BETA
CO
3CL
5s
IU
>
53
2
3
O
-38
+58-75 +106-150 +212-300
+38-58
+75-106 +150-212
+300
SIZE FRACTION (MICROMETERS)
Figure 6.2.
The cumulative size distribution of the received alpha
spodumene and of the transformed material.
Although the
spodumene expanded during the treatment, the fifty percent
passing size of the transformed material was finer due to
cracking and subsequent breaking of the particles during the a
to P conversion.
Sixteen point two percent of the p spodumene
compared to only 10.8% of the a spodumene was finer than the
smallest size fraction, -38 microns.
f
38
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 6.3.
Microphotographs of the as received (above left) and transformed
spodumene. The a to {J conversion altered the crystal structure
of the material and the forces involved were great enough to
cause cracks in the particles.
VI.2.
VISUAL OBSERVATIONS OF REDUCTION PRODUCTS
4
Five different materials were identified at the end of an experiment.
They were:
-a white condensate
-a very fine black dust
-a powder residue
-a dross
-a metal ingot.
The material scraped out of the crucible at the end of an experiment
and the metal skin on the impeller were included in the dross.
Photographs o f the products are shown in Figures 6.4 to 6.10.
The masses o f each of the products and the total mass recovered compared
to the initial mass o f reactants is presented in Table 6.1.
i
39
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T ab le 6 . 1 . PRODUCTS OF SPODUMENE REDUCTION EXPERIMENTS
1
EXP
1
2
3
4
5
6
7
8
REACTANT
MASS( g )
2803 . 8
2634 . 8
2828 . 8
2826 . 5
2953 .3
2782 .7
2843 .2
2843 .0
PRODUCT MASS( g)
METAL
INGOT
DROSS
881.0
2062.5
2099.1
2098.1
2110.1
2056.1
2299.7
2201 0
133 6.3
90.4
157.9
133.7
225.0
178.3
117.1
160.9
POWDER
RESI DUE
415 8
415 . 9
477 . 1
433 . 8
455 .7
389.3
361.6
467 .2
FINE
POWDER
COND.
1 .12
0 .00
1 .03
0 . 00
0.35
0 . 47
1 .35
0 .08
3.00
0.00
1.05
11.80
5.93
20.22
4.82
8.28
TOTAL
%DI FF
2264 .2
2568 .8
2735 .1
2665 . 9
2791.1
2624 .2
2779.8
2828 .2
-19.0
-2 . 5
-3.3
-5.7
-5.5
-5.4
-2.2
-0.5
The products were complex and the mass balance was complicated by
material losses such as particle emissions from the crucible and adherence to
the crucible walls.
The % difference of input versus output masses,
calculated as,
M
OUT
- M
16. 1]
IN
100%
M.
IN
had an average value o f -5.5% that was considered acceptable and indicates
that by and large most of the reaction products were collected.
During the experiments, a white plume was evident emerging from the
exhaust tube o f the reactor.
Numerous attempts were made to photograph this
vapour, but were unsuccessful.
Some vapour did condense on the underside of
the cap and in the exhaust tubes, as shown in Figure 6.4.
fineness, -75 microns, gave it a soft texture.
The condensate’s
Condensate was collected for
each experiment by scraping the underside of the cap and the inside of the
tubes. No condensate was observed for Experiment 2, in which no magnesium
was used.
40
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1
Figure 6.4. Condensate
41
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 6.5. Fine Black Powder
A fine black powder, -75 microns, was produced during the reaction and
portions were carried into the exhaust tubes by the argon flushing gas where
it settled in the horizontal portion of the tube.
During temperature
measurements and visual observations of the melt, gas escaped the reactor
from the temperature measurement port and carried some fine powder with it.
The fits between the cap and crucible and between the impeller shaft and cap
were not hermetic, thus permitting the escape of the flue powder.
illustrates flue powder losses around the reactor.
Figure 6.6
Varying amounts o f flue
powder were collected from each experiment but the quantities lost, prevented
accurate determination of the total amount produced.
42
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 6.6a, 6.6b. Fine black powder lost during an experiment
The amount of fine black powder lost varied among tests.
out o f the reactor and onto the cap or furnace.
around the crucible.
It was carried
Figure 6.6a shows the losses
Figure 6.6b shows the losses on the cap.
During
temperature measurements particles would spout out of the reactor and onto
the cap surface.
These particles consisted mostly of fine powders but
occasionally some small droplets of molten metal would emerge.
The above
examples represented experiments with extreme loses o f fine black powder.
i
43
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 6.7. Powder Residue
The powder residue contained unreacted spodumene, solid reaction
products of the reduction, bits o f impeller and minute pieces of aluminum
separated from the main body o f liquid metal
floating/resting on the melt surface.
After the experiments, it was
It was separated from the other
products after the entire contents of the reactor were poured out into a
mold.
In the above Figure of the powder residue from Experiment 3, one can
see white, unreacted spodumene particles, powder agglomerates, brown powder
assumed to be a reaction product, and pieces of metal.
The powder residue
was a melange of matenals of many different sizes.
!
44
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
1
Figure 6.8. Dross
T he dross recovered was present on the melt surface and possibly along
the crucible walls.
It was composed of irregularly shaped metal clumps with
highly oxidized surfaces.
Some dross had cavities containing powder residue.
All the dross had some powder attached to its rough surface.
Any powder
that was shaken off the dross was added to the powder residue but some
remained in cavities, as inclusions, or embedded in the surface.
As shown in
Table 6.1, the masses of the dross varied only slightly, except for
Experim ent 1, where 1338.3 g was formed as a result o f impeller problems in
that experiment.
<
45
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 6.9. Metal Ingot
The metal ingot was the largest contributor to the total mass of the
products, except in Experiment 1
A small amount of powder residue and
silica induction furnace packing, which spilled during pouring, was embedded
into the ingot’s surface.
The ingot from Experiment 2, in which no magnesium
was added, was shiny.
For experiments where more magnesium was added, the
surface of the ingot was dulled due to increased oxidation
The above ingots
were from Experiment 3 on the left and Experiment 2 on the right.
The ingots
were 28 cm long and 8 cm wide.
V
46
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 6 10. Material stuck to inside of the crucible after an experiment
At the end of each experiment, a layer of material was attached to the
•J
inner surface of the crucible as shown m Figure 6.10.
rem ove this layer
It was impossible to
Since a new crucible was not used for each experiment the
buildup present after an experiment varied.
Figure 6.10 shows the buildup
after Experiments 7 and 8
VI.3.
XRD ANALYSIS O F REDUCTION PRODUCTS
X Ray Diffraction (XRD) analysis of the non-metallic samples was
performed to determine the materials present in these samples.
The XRD
analysis system was the same as was used for the the lime - spodumene
experiments
All the species which were matched by the Phillips system are
listed by name, compound formula and identification number.
Those that
"scored high enough" to be positively identified by the analyzing software
*
are noted by an asterisk .
The powder residue was analyzed and the following species were identified:
C
47
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
E xperim ent 1: synthetic spinel , M gAl.,0 (21-1152), silicon
(27-1042), aluminum (4-787),
(5-565), silicon
low quartz (33-1161), and
synthetic iron (6-696).
Experim ent 2: spodumene , LiAlSi 2 O ti (35-797), aluminum (4-787), lithium
-------------------------------------
alumino silicate, LiAl(SiO )., (31-706), and synthetic iron
(6-696).
Experim ent 3 : silicon
*
(5-565), silicon (27-1042), aluminum (4-787), and
synthetic spinel , MgAl 2O4 (21-1152).
Experim ent 4 ; spodumene
*
(35-797), lithium alumino silicate (35-794),
LiAlSi3Og, FeAl20 4 (35-794), Mg„Al20 4 (33-853), aluminum
(4-787), synthetic spinel , MgAl.,0 (21-1152), lithium alumino
silicate, LiAl(SiCy2 (31-706), synthetic iron (6-696).
*
(4-787), synthetic penclase , MgO(4-829), silicon
*
(5-565), silicon (27-1032), synthetic iron (6-696), lithium
Experim ent 6: aluminum
*
alumino silicate, LiAl(SiO ),,
(31-706), synthetic spinel,
MgAl20 4 (21-1152), spodumene (35-797)
%
Experim ent 7 : spodumene (35-797), silicon (5-565), silicon (27-1042),
aluminum (4-787), synthetic penclase, MgO (4-829), synthedc
iron, (6-696), lithium alumino silicate, LiA l(Si02)3 (31-706).
Experim ent 8 : The powder residue greater than 20 Mesh; silicon (5-565),
silicon (27-1042), synthetic spinel , MgAl O (21-1152),
^
2 4
synthetic penclase , M gO (4-829) and aluminum (4-787).
Powder residue less than 65 Mesh;
silicon (5-565), silicon (27-1042),
The black powder was analyzed for cenain expenments and the following
species were identified.
Experim ent 4 ; aluminum
*
(4-787), silicon
★
(5-565), silicon (27-1042),
synthetic iron (6-696).
48
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
E xperim
5: aluminum (4-787),
silicon ( 5-565), silicon (27-1042),
—
——— ent
_____
^
synthetic spinel , MgAl20 4 (21-1152) and synthetic iron (6-696)
E xperim ent 6: synthetic periclase , MgO(4-829), hercynite ,FeAl2 0 4 (34-192).
---------------------------
The condensate was analyzed for Experiment 7 and the following species were
identified:
*
synthetic periclase , MgO(4-829), aluminum (4-787), synthetic
iron, (6-696),
The detection of the synthetic iron in many o f the samples was caused by
the iron backed sample holder which was utilized in the XRD apparatus.
The
detection of hercynite in the Expenment 6 black powder was due to it being
an iron spinel and having a similar pattern to other species present.
The XRD analysis showed that the powder residue was a complex material.
It was composed of aluminum, spinel, silicon, spodumene, lithium alumino
silicates and penclase
The flue powder was composed of aluminum, silicon and spinel.
All these
constituents were present in the powder residue and may have been a part of
the fine sized portion of the powder residue, which was physically
transported from the reactor by gases
The condensate was formed by the condensation and subsequent oxidation
of magnesium.
Some aluminum was detected but due to aluminum’s low vapour
pressure at 1173 K, 10‘10 Atm, it was unlikely that aluminum vapourized and
condensed.
VI.4.
A TO M IC ABSORPTION ANALYSIS
Atomic Absorption (A.A.) was the method o f analysis used to perform
numerous chemical assays tor silicon, magnesium, and lithium.
common and versatile of the analytical methods for metals.
It is the most
I* is a sensitive
analytical method and elements whichhave enhancement or depression effects
must be known
Other factors which may cause spunous results are
differences in the composition between
effects.
standards and samples, known as matrix
As well, the viscosity o f the solution will affect the reading as
it affects the aspiration rate of the flame.
With the knowledge of the A.A.
characteristics for each element, one can decide how to prepare standard and
49
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
sample solutions to obtain the best results.
A technique used to counter interferences from the elements in solution
is masking the sample solutions by the standard solutions.
masking is as follows
An example of
A solution being analyzed for element A contained b
amounts of element B known to affect the absorbance of element A.
To ensure
that accurate results were obtained, the standards were made so that they
contained b amounts of B as well.
This would "mask" the presence of element
B in the solution and minimize its effect on the calculated concentration
of A
All reaction products of the reduction experiments were analyzed for
lithium.
Analysis for magnesium and silicon was done whenever it was thought
necessary.
VI.4.1.
SAMPLING FOR ATOM IC A BSORPTION ANALYSIS
The following sampling method was used to obtain ingot samples:
Drillings were made at various locations on the ingot at various
depths.
The shavings were mixed together to accumulate a one gram sample.
This was done to avoid segregation.
For the dross samples, small bits were cut off various dross clumps to
form a one gram sample.
A representative sample of the powder residue was obtained by separating
the powder into observable groups by hand such as fused or sintered powders,
impeller bits and the rest, massing each part and then adding each component
according to its mass fraction.
The sampling method for the flue powder and condensate was collection
by scraping or brushing from their respective sources.
VI.4.2.
A TOM IC ABSORPTION ANALYTICAL METHODS
Dross and Ingot Assays:
One gram samples of ingot and dross samples were dissolved in a 40 ml
aqua regia solution containing 10 ml nitric acid and 30 ml hydrochloric acid.
Ten milliliters of water was added to the beaker prior to contacting
the samples with the acid in order lessen the violence of the reaction
between samples and acid
The reaction between magnesium and hydrochloric
50
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acid was extremely explosive.
precautionary procedure.
The acids were also added in stages as a
The liquor was diluted to 250 ml with distilled
water.
For lithium analysis, the solutions were further diluted four times so
that the solutions contained,
lg / 250 ml x 0.25 = O.lg / 100 ml
[62 ]
of sample, which can be converted to ppm by the following equation;
1 ppm = 0.001 g / 1000 ml
[6.3]
Therefore the solutions contained 1000 ppm of sample; the majority being
aluminum.
For lithium analysis, aluminum causes depression of the absorbance(42).
Standards were made to mask the solutions so that they contained 1000 ppm
aluminum as well.
Another element present in large quantities was magnesium,
which has no effect on lithium readings(43).
Silicon was another element
present in the ingot and it too has no effect on lithium readings(43).
S
%
A.A. machine settings for lithium are shown in Table 6.2.
The
These settings
were also used for the lithium analysis of the other experimental products.
Table
6.2.
SETTINGS FOR L i A . A .
PARAMETER
S ETTI NG
CURRENT
VOLTAGE
8 mA
460 V
BANDWIDTH
0.5
WAVELENGTH
BURNER
6 7 0 . 8 nm
air-acetylene
ANALYSIS
nm
For magnesium analysis, the liquors produced for the lithium analysis
were used as the stock solution and diluted 100 times, which resulted in a
background concentration of 10 ppm aluminum.
I
Magnesium readings are
sensitive to depression effects by lithium, silicon and aluminum.
As well,
51
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
the acids used for dissolution have a large effect on the A.A. readings.
The
concentrations of the other elements were estimated and masking of the
solution by standards was attempted.
The absorbance readings of the masked
magnesium standards were erratic and a proper calibration curve could not be
obtained.
Thus masking was unsuccessful.
A different technique was
utilized.
A chemical agent, strontium nitrate, was added at concentrations
o f 2000 ppm to the solutions and standards for the purpose o f canceling the
effects of other the dissolved elements(4J)
This was found to be successful.
The analytical parameters for the magnesium analysis are shown m Table 6.3
Table
6.3.
SETTINGS POR Mg A . A .
ANALYSIS
PARAMETER
VALUE
CURRENT
VOLTAGE
4 mA
530 V
BANDWIDTH
1 nm
WAVELENGTH
BURNER
2 8 5 . 2 nm
air-acetylene
I
Silicon does not dissolve in aqua regia, thus new ingot and dross
samples were dissolved in the following manner:
A one-tenth of a gram samples from drill shavings were added to
polyethylene beakers containing 10 ml of water and 15 ml of hydrochloric
acid.
Fifteen milliliters of hydrogen peroxide were then added in small
portions.
After cooling, two milliliters of hydrofluoric acid were added.
The liquor was filtered and diluted to 100 ml with distilled water.
The
background concentration was;
0 .lg / 100 ml = 1000 ppm
(64]
Aluminum depresses the silicon readings as it does lithium readings and the
same masking strategy used for the lithium analysis was employed for the
silicon analysis.
The A.A. settings for the silicon analysis are shown in
Table 6.4.
i
52
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
T able
i
SETTINGS FOR S i A . A .
6.4.
PARAMETER
VALUE
CURRENT
VOLTAGE
12 mA
5 30 V
BANDWIDTH
0 . 32 n m
WAVELENGTH
BURNER
2 5 1 , 6 nm
air-nitrous
ANALYSIS
oxide
Condensate Assays:
The condensate was analyzed quantitatively by atomic absorption.
An
amount of approximately one gram was dissolved in 15 ml o f slightly heated
nitric acid.
The condensate absorbance was compared to lithium standards.
The standards contained no magnesium, since it has a neglible effect on
lithium absorption as mentioned earlier.
B lack Pow der Assays:
I
About one gram of black powder was dissolved into an aqua regia
solution containing 5 ml HNC>3 and 15 ml HC1.
Afterwards it was analyzed for
lithium and compared with pure lithium standards.
A black residue remained.
Pow der Residue Assays:
The preferred method of analysis for oxide powders is X-Ray Fluorescence
(XRF)
This is a x-ray spectrographic method.
excitation of the atoms occur
The sample is heated so that
X-ray photons are emitted with an energy
proportional to the atomic number Z of the element, detected and counted to
determine the chemical composition of the sample.
However, lithium can not
be analyzed for because its x-rays are too low in energy to pass through the
beryllium window used between the chamber and the x-ray detector.
platinum crucible is used to contain the sample.
In XRF a
The powder residue
contained pure silicon and pure aluminum which would react with and destroy a
platinum crucible.
£
Therefore X RF was eliminated as an analytical method and
A.A. was used to assay the powders.
53
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The residue samples were sent to Tanco where they were analyzed for
lithium, sodium, potassium, and aluminum.
The liquors were sent back to
McGill to be analyzed for silicon and magnesium.
For magnesium analysis, the
liquors were diluted by 100 times and strontium nitrate was added to cancel
effects of other elements.
Analysis of the Tanco liquor for silicon was
impossible due to the method used to the prepare the liquor.
Thus, silicon
analysis of the powder residue was performed at McGill.
A one gram sample of powder residue was added to a polyethylene beaker.
One hundred and fifty millilitres of hydrochloric acid and 50 ml of nitric
acid were added to it.
After the reaction subsided, 30 ml of hydrofloric
acid was added to the solution.
The beaker was heated to 90°C by placing it
a water filled metal tray, heated by a hot plate.
After reaction ceased, the
solution was cooled to 1000 ml and the volume was made up with the addition
of distilled water
The samples were compared against standards containing
40 ppm aluminum.
VI.4.3.
T
*
ATOMIC ABSORPTION RESULTS
An example of data generated from a set of lithium standards with 1000
ppm aluminum is given in Table 6.5.
The error was calculated as the standard
deviation of the absorbance readings and is also shown in Table 6.5.
I (x -x ) 2
n
54
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Table
6.5.
A . A . RAW DATA FOR A SET OF L i STANDARDS AND INGOT
ASSAYS
STANDARD
ppm Li
0.5
1.0
2.0
3.0
4.0
ABSORBANCE
(x)
ERROR( s )
MEAN (x)
0.074
0.146
0.268
0.421
0.559
0.087
0.157
0 .291
0.428
0 .577
0.088
0.162
0.296
0.436
0.083
0 .155
0 . 285
0 . 428
0. 568
0.008
0.008
0 .015
0.008
0 .013
0.167
0.002
0.073
0.217
0.291
0.395
0.403
0.382
0.232
0.003
0.070
0.221
0.302
0.406
0.406
0 .407
0.240
0.003
0.072
0.217
0.311
0.404
0.409
0.418
0 .213
0 . 003
0 .218
0 .072
0 .301
0 .402
0 .406
0 .402
0.040
0.001
0.002
0.002
0.010
0.006
0 .003
0.018
I NGOT
SAMPLE
1
2
3
4
5
6
7
8
From the absorbance data the concentration and errors of the solutions
and samples were determined utilizing the method outlined in the
examplecalculations in Chapter VII.
The calculated weight perce ~ and the
corresponding relative errors of the products analyzed for are presented in
Tables 6.6 - 6.10.
The relative errors, AC, are discussed in
Section ViII.2 3.
Table
ASSAYS OF CONDENSATE
(WEIGHT%)
M g : SPOD
RATI O
MASS
1
2
4.2
0 .0
1.12
0.00
0.42
-
0 .033
-
3
4
4.3
2.0
1.03
0.00
0.57
0.55
0 .053
0.023
5
6
6.0
8.2
0.35
0 .47
0.94
0 . 68
0.045
0 .056
7
8
10.0
10.0
1.35
0 .08
0.26
0 .20
0 .006
0 .007
EXP
«
6.6.
(g)
C
Ll
AC
Ll
(Wt%)
55
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T a b le 6 . 7 . ASSAYS OF FLUE POWDER (WEIGHT %)
EXP
M g : SPOD
RATIO
C
AC
C
Ll
(Wt%)
u I
(g)
AC
Mq
<Wt%)
Mg
1
2
4.2
0.0
3.00
0.00
3
4
4.3
2.0
1.05
11.80
1.27
0.050
20.11
0.024
5
6
6.0
8.2
5 . 93
20.22
1.18
1.22
0.056
0 .042
24.40
33.10
0.031
0.026
7
8
10.0
10.0
4.82
8.28
1.22
1 . 12
0 .059
0.034
39.97
35.45
0.028
0.028
MASS
ASSAYS OF POWDER RESIDUE
C
1 "
Mg: SPOD
RATIO
6.8.
o
T able
EXP
MASS
(g)
C
A_
<20
C
Na 2 O
C
(WEIGHT %)
S l
AC
si
(Wt%)
C
Mg
AC
Mg
(Wt%)
1
2
4.2
0.0
415.8
4 15 . 9
1.56
2.53
33.2
31. 6
0.08
0.11
0.18
0.21
8.48
15.28
1.52
1.69
16.90
-
6.140
-
3
4
4.3
2.0
477 . 1
433.8
1.24
1.89
38.1
33. 6
0.07
0.09
0 .12
0.16
4.73
12.47
0.50
2 .25
13.26
9.08
1.260
6.140
5
6
6.0
8 2
455.7
389.3
1.07
1.06
45.7
37 2
0.10
0.09
0 .13
0.16
4.88
7.28
0.59
0.80
16.84
20.00
1.410
1.410
7
8
10.0
10.0
361. 6
467 . 2
1.08
0.83
32.7
41 2
0.11
0.08
0.30
0.12
9.36
6.41
0.76
0.57
122.20
19.48
-
I
56
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
1.260
T able
EXP
M g : SPOD
RATI O
6.9.
ASSAYS OF INGOT
C
MASS
(g)
Ll
c
Ll
(Wt%)
1
Mg
AC
C
Mg
(Wt%)
S1
AC ,
si
(Wt%)
1
2
4.2
0.0
881.0
2062.5
0.15
0.02
0.034
1 .39
-
0. 15 9
-
3.31
2 .72
0.59
0.34
3
4
4.3
2.0
2099.1
2098.1
0.15
0.05
0.008
0.008
1 .50
0 .51
0.220
0.178
3.82
1.54
0.60
0.43
5
6
6.0
8.2
2110.1
2056.1
0.21
0.28
0.013
0.011
1 .57
4 .71
0.164
0 . 2 62
2.32
3.74
0.16
0.75
7
8
10.0
10 . 0
2299.7
2201.0
0.29
0.28
0.008
0.019
4 .69
3 .84
0.187
0.201
3 .37
3.03
0 . 47
0.54
Table
EXP
?
AC
(WEIGHT %)
M g : SPOD
RATI O
6.10.
MASS
ASSAYS OF DROSS
C
(g)
Ll
AC
C
L1
(Wt%)
(WEIGHT %)
Mg
AC
Mg
(Wt%)
__
C
S1
AC
Sl
(Wt%)
1
2
4.2
0.0
1336.3
90.4
0.12
0.01
0.007
0.001
1.26
-
-
2.42
1.63
0.37
0.24
3
4
4.3
2.0
157.9
133.7
0.17
0.19
0.011
0.007
2 . 05
1.11
0.438
0.469
2.36
1.93
0.26
0.33
5
6
6.0
8.2
225.0
178.3
0.24
0.34
0.001
0.027
2.59
4 . 90
0.800
0.706
1.75
2.27
0.37
0.32
7
8
10 . 0
10 . 0
117 . 1
160.9
0.39
0.34
0.037
0.012
6 . 60
6.81
0.541
0.823
2.68
6.39
0.49
0.85
Table
6.11.
LITHIUM ASSAYS FROM KINETIC SAMPLES
Mg:SPOD
Li ASSAY IN SAMPLE
RATIO
20 MIN
40 MIN
60 MIN
4
2.0
0.05
0.09
0.04
5
6.0
0.14
-
0.22
6
8.2
0.21
0.29
0.31
8
10.0
0.25
0.26
0 .30
EXP
(Wt%)
I
57
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VI.5.
SCANNING ELECTRON MICROSCOPE ANALYSIS
A JEOL JSM-T300 scanning electron microscope (SEM) was used to analyze
the powder residue
The goal of the SEM examination of the powder residue
was to locate evidence of reaction and the manner by which reaction occurred
between the spodumene and molten reductant.
Samples for SEM analysis were
made by impregnating a resin with the powder residue and then allowing the
resin to set
The resin was polished on a 0.3 micron alumina wheel with the
aim o f exposing a cross-section of a reacted spodumene particle.
Prior to
the SEM analysis, the sample was carbon coated to avoid electrical charging
in the sample chamber
The SEM is capable of performing chemical analysis in a manner similar
to the XRF unit described in Section VI.4.2.
The SEM analysis system has two
major drawbacks concerning the analysis of the powder residue:
1) A beryllium window is used between the sample chamber and the x-ray
detector and as a result lithium and oxygen can not be analyzed for
because their characteristic x-rays do not possess the energy to pass
through the window.
2) Without oxygen detection, the analysis could not distinguish between pure
metals and their oxides, which would make the results speculative.
Therefore, analysis results from the SEM were used qualitatively and not
quantitatively.
The SEM analysis used was the SQ program of the Tracor
Northern(44) TN-5400 software analysis system.
Figure 6.11 shows a reduced spodumene particle observed in the residue
from Experiment 5 at an accelerating voltage of 10 kilovolts. The particle
was characterized by large and small cracks all over its surface and some
of these cracks were contained within the outer edges o f the particle.
chemical assay is shown in Table 6.12.
I
58
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Its
Figure 6.11.
SEM microphotograph o f particle in the powder residue.
Magnification equals 2000x.
«
---------------------------------------------------------------------------------------------------------Table
6.12.
SEM ASSAY 0 7 PARTICLE I N FIGURE 6 . 1 2 ,
Si
Mg
A1
28. 6
11.7
59.8
WEIGHT%
spodumene.
T he particle showed no evidence o f the existence o f a boundary layer
between spodumene and molten reductant or a deposited reaction product.
finding raises questions concerning the reaction mechanism which occurred
which are dealt with m the discussion.
»
59
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This
VII. EXAMPLE CALCULATIONS
VJI.1.
DETERMINING SAMPLE CONCENTRATIONS
FROM ABSORBANCE READINGS
Lotus 123(45) was used to perform a linear regression between the
concentration of the standard sections (X) and the corresponding absorbance
reading (Y).
The regression output from the data of the standard solutions
in Table 6.5 is shown in Table 7.1.
Table 7 .1 .
RESULTS OF LINEAR REGRESSI ON
SLOPE (m)
I NTERCEPT (b)
R SQUARED
STANDARD ERROR OF SLOPE (Am)
STANDARD ERROR OF Y ESTI MATE
1
(AY)
0
0
0
0
0
143
0
998
002
009
The regression line was forced through zero, the absorbance o f a distilled
water solution.
The value for r squared obtained, 0.998, revealed an
excellent fit of the data to the linear regression.
The standard error in
the Y estimate is the standard error of the regression and was used to
determine the analytical error.
A calibration curve, Equation 7.1, was constructed from the regression
results.
The purpose of the calibration curve is to define a relationship
between the absorbance readings of a species in solution and the
concentration of that species in solution.
Y = mX + b
1711
where,
Y is the absorbance, counts
m the slope of the regression line, counts-ppm’1
X the concentration, ppm
b the intercept = 0.
I
60
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The concentration of the sample solutions was determined by modifying
Equation 7.1, so that,
X = Y/m
[7.2]
To calculate the sample assays from the measured A.A. concentrations,
a series of calculations were required, as shown below for the lithium
concentration in the ingot from Experiment 3.
For the ingot in Experiment 3 the absorbance was 0.219, thus the lithium
concentration of the solution was equal to, using equation 7.2,
0.219 / 0.143 = 1.53 ppm or 1.53 mg Li / litre.
[7 3 ]
The solution was diluted by a factor of four, therefore theoriginal
concentration of the liquor was,
4 x 1.53 mg Li / 1 = 6.12 mg Li / 1
[74j
the original solution’svolume was 250 ml, therefore it contained,
i
0.25 1 x 6.12 mg Li / 1 = 1.53 mg Li
[7si
The solution was obtained by dissolving 1000 mg sample, therefore the lithium
concentration of the original sample was,
1.53 mg Li / 1000 mg sample x 100 % = 0.153 wt % Li
V n.2.
[76i
EXAMPLE CALCULATIONS OF ANALYTICAL ERROR
Two factors contributed to the error of the sample assays:the error in
the regression and the error from the absorbance readings.
In the Lotus output, the error in the regression curve is given as the
standard error of the Y estimate, which was, for the Lotus output from Table
6.5, 0.009 units of absorbance.
This can be converted to an error in
concentration by the following equation,
61
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
AC,
REG
=
S.
[7.7]
m
t
where,
ACreg is the error in concentration due to the error in the Regression
curve.
is the standard error of the Y estimate from the regression,
m is the slope of the calibration curve obtained from the regression.
For the present example, i.e., the Li assay of the ingot in Experiment
3, the error in the lithium concentration from the regression curve was
0.0063 ppm.
To determine the error due to the sample absorbance readings, the error
in the absorbance readings, calculatedusing Equation 6.6, replaces
the
error
in the Y estimate inEquation 7.7.
For Experiment 3, the standard deviation of the readings was 0.002.
This corresponded to a concentration error of 0.014 ppm.
The total error in concentration,
AC, for the ingot sample in Experiment
3 would then be,
AC = AC
KuG
+ AC
A A.
= 0.0063 + 0.0014 = 0.0077 ppm Li
[7.8]
where A C „ is the error in concentration form the regression and AC
REG
A A
is
the error in concentration of the absorbance readings.
Replacing the concentration of lithium in the onginal liquor, with the
concentration error, AC, calculated in Equation 7.4 and following Equations
7.5 and 7.6, the error in weight % was calculated and found to be 0.008 wt %.
This represents a relative error of,
0.008
[7.9]
x 100 % = 5.28 %
0.153
in the lithium reading in the ingot from Experiment 3.
The error incurred by
mass and volume measurements was considered to be too small to have an effect
on the weight % error.
62
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VIII. DISCUSSION
V in .l.
INTRODUCTION
The goals of the discussion are:
1) to critique the experimental program, experimental error and analytical
errors encountered.
2) to examine the quantitative and qualitative results from the experiments
and explain their significance in terms of the physical phenomena
occurring in the system.
3) to compare the quantitative results with those predicted
thermody n amic ally.
VIIL2.1.
DISCUSSION O F PRESENT EXPERIM ENTAL PR O G R A M
The goal of the experimental program was to determine the effect of
magnesium addition on the lithium extraction from spodumene.
This goal was
achieved satisfactorily but the largest amount o f magnesium added,
corresponding to a magnesium to spodumene molar ratio of 10.1, was chosen
arbitrarily
Thermodynamic analysis showed that increased magnesium addition
past a molar ratio of ten further increased lithium extraction.
Therefore
tests at greater magnesium concentrations could be useful.
V in.2.2.
DISCUSSION OF EX PER IM EN TA L PRO CED U RE
Various expenmental errors were incurred during the study.
They are
brought to light and their impact on the findings are discussed in this
section.
The order and method in which the reactants were charged was determined
by the experimental apparatus.
The impeller could only be inserted into
the reactor when the metal reductant was molten and the crucible cap could
only be placed after the impeller was inserted.
Therefore, the
melting of the reductant alloy was performed in air and some oxidation o f
magnesium and aluminum occurred.
A better method o f commencing the
expenment would have been to heat all three charge matenals simultaneously.
This could only be done in a reactor with the proper design.
Temperature control was an important experimental parameter in this
63
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study.
Later in this chapter, Figure 8.12 predicts the theoretical effect o f
temperature on lithium extraction.
The precision of ± 20°C would have
affected the recovery but the temperature fluctuation above and below 900°C
would decrease the net effect on recovery
White vapours were observed leaving the apparatus which must have
contained some lithium since lithium was detected in the condensate.
This
lost lithium would not have been accounted for in a mass balance.
A
condensing apparatus that collected all of the vapours would have improved
the investigation on the condensate and retrieved more lithium.
The separation of the powder residue from the ingot, would have been
improved upon if the powders were skimmed or scraped from the metal surface
prior to pouring the ingot
This would have resulted in more homogeneous
dross, ingot and residue samples.
The atmosphere in the reactor was argon.
Using a noble gas was
essential to the success of the experiments due to the highly oxidizing
nature of aluminum, magnesium and lithium
The seal of the reactor with the
outside atmosphere was not perfect and during temperature measurements, plugs
were removed from the crucible cap.
The argon flushing
gas created a positive pressure inside the reactor preventing atmospheric
gases form entering the system and oxidizing the melt during sampling
and temperature measurements.
In the present study, there is ample evidence that reduction of the
spodumene by the molten reductant occurred.
A question which then arises is
why were the impeller, whose surface was an alumina paint, and the crucible,
a ceramic made from a silica - alumina combination, not reduced.
An
explanation is that oxide formation occ< .red at the interface between the
excess metal reductant and these objects.
This oxide would achieve a
thickness which would prevent attack of the crucible or impeller.
VIII.2.3.
DISCUSSION OF ANALYTICAL ERROR
VIII.2.3.1.
RELATIVE ERRORS OF SAM PLE ASSAYS
As mentioned earlier, the error in the atomic absorption analysis arose
from the errors in the regression curve and absorption readings.
In this
section, the error from each source is analyzed separately to see if any
trends exist.
64
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The average relative errors o f the sample concentrations from the
regression and from the absorption readings are listed in Table 8.1.
Table
8.1.
SAMPLE
AVERAGE RELATIVE ERRORS I N
SAMPLE CONCENTRATIONS
REGRESSI ON ERROR(%)
Li
ABSORBANCE ERROR(%)
Mg
Si
Li
Mg
Si
DROSS
3.4
7.6
4.5
3.8
5.3
8.2
RESI DUE
-
8.0
7.8
-
1.9
4.2
INGOT
4.3
7.2
7.2
4.6
1.7
13.5
BLACK POWDER
2.6
7.4
-
1.2
1.0
-
CONDENSATE
3.3
-
-
1.5
-
-
AVERAGE(%)
3.4
7.5
6.5
2.8
2 .5
8.7
Table 8.1 shows that not all elements are similar in their A.A.
characteristics in terms of regression and absorbance variance.
the best element for regression analysis.
3.4%.
Lithium was
Its average relative error was
Next best was silicon with an average relative error o f 6.5%.
Magnesium analysis produced the worst regression having a relative error of
7 5%.
The error arising from the variance o f the absorbance readings was
affected by the d n ft in the absorbance readings over a period of time for a
series of readings.
For example, an absorbance reading for a sample solution
and was identical to the absorbance for a standard solution containing 1 ppm.
After other solutions were analyzed the absorbance was retaken for these two
solutions.
The readings were identical again, but were 10% less than
obtained before.
The precision of the machine has not changed but the
variance of the solution readings has increased.
Thus the errors calculated
due to the variance of the absorbance are artificially high, as they do not
compensate for the machine drift
The amount o f dnfting which occurred for each element varied.
had severe drifting, causing an average relative error of 8.7%.
Silicon
As a result
of the large absorbance dnft when analyzing for silicon, it is recommended
that the amount samples analyzed for silicon in one sitting be restricted.
The relative error from the absorbance drift for lithium and magnesium were
65
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2.8% and 2.5% respectively.
For magnesium, the absorbance error from the
dross of Experiment 5 was 15.7%.
If it was excluded the average relative
absorbance error for the dross would have been 2.7% and the average relative
magnesium absorbance error would have been 1.8%.
VIII.2.3.2.
COMPARISON OF ASSAYS W ITH AN OUTSIDE ANALYSIS
The results from an outside analysis performed at Centre Recherches des
Minerales (CRM) are shown with the corresponding assays used in this work in
Table 8.2.
Table
COMPARISON OF ANALYTICAL RESULTS
ANALYTICAL
LAB
Wt
EXP 5
POWDER RESIDUE
CRM
0.84
_
16.8
EXP 5
POWDER RESIDUE
TANCO
1.07
-
45.7
EXP 6
METAL INGOT
CRM
0.10
1.54
EXP 6
METAL INGOT
MCGILL
0.28
3.74
SAMPLE
I
8.2.
% Li
Large differences exist between the results.
Wt % S i
Wt % A l
w
However, the outside data
are inconsistent with the mass balance for lithium performed in Section
VII.4. The total lithium accounted for at the end of the experiments was less
than that contained in the spodumene.
The CRM values were less than those
used for the mass balance, therefore, if they were to be substituted into the
mass balance the lithium deficiency would increase.
However, the fact that the difference in some values is so large is
disturbing and unaccounted for.
For future researchers the following recommendations should be
considered:
-The size of the sample should be as large as possible but balanced
against practicality in terms of manageable solutions and safety, for
increasing the amount of sample also increases the violence o f the reaction
66
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with acid.
-Segregation exists within the ingot and therefore the samples must be
m ade by collected drillings and pieces from as many different locations as
possible.
V III.3.
EX PER IM EN TA L MODELING
This study, although it did not concentrate on the process phenomena
occurring in the m :tallo-thermic reduction o f spodumene, did rely on, and
was affected by, various process phenomena.
In this section, two process
phenomena are examined.
VIII.3.1.
D ETERM IN A TIO N OF GAS PU RGING RATE
The inert argon atmosphere above the melt surface was essential in
preventing oxidation of the molten metal.
The rate of argon purging was
determined from the volume above the melt surface and the rate of argon
input.
The volume o f above the melt surface was
calculated by subtracting the
volume of the molten aluminum, spodumene and
impeller from the crucible
volume.
The volume of the magnesium added was not included and thus to
compensate, the mass of aluminum used in the calculation was increased to
2400 g.
The intenor dimensions of the crucibles were 28.8 cm high and 12.8 cm
diameter.
T he cap overlapped the crucible by one centimeter.
Thus the
effective volume of the reactor was:
(28.8 -1) cm x it 12.82 cm 2
= 3 577.4 cm3
is.i]
The volume of the impeller was calculated by adding the volume of a) its
blades coated in cement, b) the upper portion o f the shaft and c) the lower
part of the shaft, coated in cement.
The total impeller volume, assuming it
operated two centimeters from the bottom of the crucible was,
67
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a) blades
4 (4.95 x 11.0 x 1.0) cm3
b) m e ta l shaft
(2 7 .8 -2 -1 1 ) x re L90» cm3
4
c) s h a f t coated in cement
11 x k 6 . 352 c m 3
d) t o ta l
610.95 cm 3
[8 .2 ]
[8.4]
An amount equal to one mole of spodumene was added to the reactor which had a
volume of,
v = 372 g + 2.6 ggem'3 = 143 cm3
[85]
however, in its loose form and resting on top of the melt it was estimated to
have a porosity of 50% making the effective volume of the powder 286 cm3.
The volume of 2400 g of molten aluminum can be calculated from its
density, given by the equation for molten aluminum(46),
p = 2385 - (0.28 (T-933)) kg m'3
[8.6]
at the operating temperature of 1173 K the specific gravity of the aluminum
would be,
p = 2385 - (0.28(1173-933) = 2318 kg m3 = 2.32 g cm'3
[8.7]
this would make the volume of molten aluminum equal to,
2300 g + 2.32 g cm'3 = 1034.5 cm3
Thus the total volume o f the materials in the reactor was 1 931.4 cm3,
leaving 1 646 cm of free space.
The average residence time, x, of the argon was,
!
68
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[8 8]
where,
v is the volume
Q is the flow rate o f gas.
The equation for the gas purging of a system is,
f(t) dt = -exp
[8 10]
where,
f(t) is the fraction of gas purged form the system
t is the time in seconds
x is the gas flow rate entering the system in m s '1
Solving Equation 8.10 by integration with respect to time determines
that 83.8% of the gas would be purged every minute.
1
VIII.3.2.
FORMATION OF SOLID SPECIES
A possible, practical difficulty with this process is the formation of
solids during reaction.
Figure 8.4, presented in Section VIII.5 shows
that more solids were present as residue at the end o f an experiment than the
amount of spodumene added.
In this section, two reaction paths having one
mole of spodumene react with an excess (XS) of aluminum are examined: one
where two moles of magnesium react with the spodumene and the other without
any magnesium, to determine the theoretical amount o f solids produced.
each reaction path the spodumene is reduced 100%
i
69
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In
REACTION PATH 1:
Li20 Al20 3-4Si02 + XSA1 +2Mg=2Li+2MgO-Al O + (XS-6)A1 + 4Si + 3A120 3
MASS POWDER IN : SPO DU M EN E
=
MASS POWDER OUT: M g O - A l 2 0
372 g
284 g
S IL C O N
*(112) g
306 gz
D IFFER EN C E
R E A C T IO N
L i O A l
2
2
+218 + jc( 112) g
PATH 2:
0
3
M ASS POWDER
4S i 0
2
+
XS A 1 = 2Li + (XS-3)A1 + 4Si + 4A1 O.
2
I N : SPODUMENE
M ASS POWDER OUT: A 1 0
2
= 372 g
408 g
3
S i
* (1 1 2 ) g
D I FF E R E N C E
Figure 8.1.
3
+36 + jc( 112) g
The analysis o f solid formation in the reduction of spodumene
for two reaction paths.
X is the percentage of silicon that
would enter the powder phase.
Figure 8.1 shows that as the reaction progresses more solids are formed.
This would result in a build up of solids in the reactor which would have
adverse effects on the process.
For a continuous process, to counter the
buildup of solids, occasional mechanical removal of the solids would be
necessary.
The formation of solids is greater when magnesium is added due to
the formation of spinel.
VIII.4.
MASS BALANCES
In this study, three elements were very well suited to mass balance
analysis: silicon and lithium in the spodumene and magnesium from
70
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the additions.
The total mass of an element existing from an experiment was
calculated by multiplying the assays o f the products from Tables 6.6 - 6.10
by their respective masses from Table 6.1
The mass balances for lithium,
magnesium and silicon are shown in Tables 8 3 - 8 5 respectively.
The
silicon and magnesium impurities in the aluminum reactant metal were
negligible, as shown in Table 5.1, and were not incorporated into the mass
balance.
Table
1
8 3.
MASS BALANCE FOR LITHIUM
EXP
MASS
I N ( g)
MASS
OUT( g)
%
DIFF
1
12 . 3 6
9.40
-24.0
2
1 1 . 62
10 . 5 9
-8.9
3
12 . 4 7
9 . 41
-24.6
4
12 . 4 6
9 . 51
-23.7
5
12 . 5 1
9 . 93
-20.6
6
12 . 2 3
10.76
- 1 2 .0
7
11.56
11.16
-3.6
8
11.78
10 . 68
-9.4
The average difference in the lithium mass balance is minus 15.8%.
The
sources of the lithium discrepancy could have been, analytical error and loss
of lithium vapour
It is possible that lithium diffusion due to a lithium
concentration gradient between the molten alloy and the crucible and impeller
occurred.
Lithium has long been known as a destructive material and it
/n\
destioys a solid by imbedding itself into the lattice
which could have
occurred with the impeller and the crucible.
During the experimental program the crucibles were changed occasionally
due to cracks and material build-up.
However, it was not recorded whether an
experiment used a new crucible or not.
The lithium mass balances appear to
divided into two groups: those with a lithium deficiency between 20.6% and
24.6% and those with a lower lithium deficiency between 3.6% and 12.0%.
would be very interesting to determine if a relationship existed between the
lithium deficiency and the crucible used.
C
71
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It
8.4.
T a b le
MASS BALANCE FOR MAGNESIUM
i
EXP
MASS
IN (g)
MASS
OUT( g )
%
DIFF
1
97 . 60
100.85
3.3
2
0.0
0.0
3
104.00
99.01
-4.8
4
46.71
53.91
13.2
5
143.20
117.46
-18.0
6
191.90
190.57
-0.7
7
220.60
560.74
154.2
8
224.80
189.48
-15.7
The mean, absolute, difference in the magnesium mass balance excluding
Experiment 7, where a spurious reading was obtained for the powder residue,
was 9.3%.
Magnesium losses occurred through volatilisation and the losses of
fine magnesium oxide and spinel in the fine black powder.
T a b le
8.5.
MASS BALANCE FOR SILICON
EXP
MASS
I N (g)
MASS
OUT( g )
%
DI F F
1
110.44
97.41
-11.8
2
103.83
121.16
16.7
3
111.44
106.48
-4
4
111.33
89.04
-20.0
5
111.80
75.03
-17.5
6
109.90
109.26
-0.0
7
103.31
114 .50
10.8
8
105.22
1 0 6 . 98
1.7
4
The mean, absolute, difference in the silicon mass balance was 8.90%.
Sources of the silicon could have been losses to the fine black powder and
analytical error.
72
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VIII.5.
THE EFFECT OF MAGNESIUM ADDITION ON THE
REACTION PRODUCTS ASSAYS
The experimental program varied the magnesium addition to the system and
in this section its effect on the lithium, silicon and magnesium assays in
the products is analyzed.
The data used to plot the graphs in this section
was obtained from the assays presented in Section VI 4.
Figure 8 2 shows that the lithium concentration in the ingot increased
as the MgiSpod molar ratio was increased up to a ratio of 8* 1. where it
leveled off.
Thus, as more magnesium was added as a reductant, more lithium
was released and dissolved into the excess molten metal.
When no magnesium
was used, very little lithium was determined to be in the ingot, thus no
reduction of lithia in P spodumene occurred.
The weight % Li in the dross
also increased steadily.
The lithium concentration was higher in the dross than in the ingot for
six ol the eight experiments.
This was due to the formation of dross in
areas of the reactor where the powder was in good contact with the molten
metal, i e., on the surface of the melt and along the walls.
«
\
i
73
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N a tio n a l L ibrary
o f C an a d a
C anadian T h e s e s
S ervice
B iblioth& que n a t i o n a l e
du Canada
S erv ice
des
th& ses
can ad ien n es
NOTICE
AVIS
THE QUALITY OF THIS MICROFICHE
I S HEAVILY DEPENDENT UPON THE
QUALITY OF THE THESIS SUBMITTED
FOR MICROFILMING.
LA Q U A L I T E
DE C E TT E M I C R O F I C H E
DEPEND GRANDEMENT DE LA QUALITE DE LA
THESE SOUMISE AU MICROFILMAGE.
UNFORTUNATELY
THE
COLOURED
ILLUSTRATIONS
OF THIS
THESIS
CAN ONLY YIELD DIFFERENT TONES
OF GREY.
MALHEUREUSEMENT,
LES
DI F F E R E N T E S
ILLUSTRATIONS EN COULEURS DE CETTE
THESE
NE PEUVENT DONNER QUE DES
TEINTES DE G R I S.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
0.45
INGOT
0.40
— X- _
0.35
DROSS
Li
0.30
WEIGHT%
0 25
0.20
0.15
0.10
0.05
0 00,
Mg SPODUMENE MOUVR RATIO
Figure 8.2.
Lithium weight % in the ingot and dross vs. the magnesium to
spodumene ratio.
The lithium concentration in the powder residue, Figure 8.3. decreased
curvilinearly at a decreasing rate with the Mg:Spod ratio.
The range was
from 2.53% Li at a Mg:Spod ratio o f 0:1 to 1.06% Li at a ratio of 10:1.
The
decrease in the amount of lithium in the residue could have been due to
lithium extraction from the fi spodumene or dilution due to the formation of
other oxides in the residue.
case.
Figure 8.4 shows that the latter was not the
The powder residue did have a greater mass than the charge mass of P
spodumene as a result of inclusion o f metal pamcles, alloy oxidation and
the production of reaction products such as, silicon and spinel.
However,
the difference was roughly constant and not enough to account for the
decrease of the lithium in the powder residue.
74
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3.0
2.5
2.0
z
2
ai
5
0 0,
MgSPODUMENE MOLAR RATIO
<
400
----
............ K - -----------
------- -
500
X
Lithium concentration in the residue vs. Mg:Spod ratio.
......................
Figure 8.3.
>
-
i
4 -+
x
-
RESIDUE
X
+
►
MASS (g)
CHARGE
4
300
200
100
10
Mg SPODUMENE MOLAR RATIO
Figure 8.4.
The masses of the powder residue and (3 spodumene charge vs.
the magnesium to spodumene ratio.
75
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The lithium concentration in the condensate, Figure 8.5, increased to a
peak o f 0.94% at a Mg:Spod ratio of six and then decreased as more magnesium
was added to the system.
The increase of lithium in the condensate was
believed to be due to increased liberation of lithium from the spodumene as
more magnesium was added to the system.
The decrease iuier a ratio o f six
was due to the increased vapourization and subsequent condensation of
magnesium, thereby diluting the lithium in the condensate.
This data
indicates that the vapours richest in lithium were produced in Expenment 5
which had a Mg:Spod ratio of six to one.
0.8
0.6
i
o
ui
5
0.2
Mg
Figure 8.5.
SPODUMENE MOLAR RATIO
Lithium weight % in the condensate vs. the magnesium to
spodumene ratio.
I
76
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The lithium concentration in the fine black powder, Figure 8.6, remained
constant at appoxiamately 1.2% Li, as the Mg:Spod ratio was increased from
two to one to ten to one.
This suggests that the lithium present in the
very fine black powder is unaffected by the amount of magnesium addition.
0.8
0.6
0.4
0.0.
Mg SPODUMENE MOLAR RATIO
Figure 8.6.
Lithium weight % in the very fine black powder vs. the magnesium
to spodumene ratio.
V
77
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The silicon concentration in the ingot and dross, Figure 8.7, increased
slightly with the increase in the Mg:Spod ratio.
The presence of silicon in
the ingot when no magnesium was used, confirms that aluminum reduces the
silica in the (3 spodumene to form silicon.
The silicon concentration of the
dross sample from Experiment 8 (Mg:Spod ratio of 10:1) was extremely high and
attests to the non-homogeneity of the dross.
INGOT
6.0
—x—
DROSS
5.0
W EIGHT%
V)
4.0
3.0
x
2.0
«
JT
.0
" '0
2
4
6
8
10
MgtSPODUMFNE MOLAR RATIO
Figure 8.7.
The silicon weight % in the dross and ingot vs. the magnesium
to spodumene ratio.
C
78
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The silicon concentration in the powder residue, Figure 8.8, decreased
with the increase in the Mg:Spod ratio and then leveled off.
The range of
the silicon concentrations v/as from 15.3% at a Mg:Spod ratio of zero to
4.7% at a Mg:Spod ratio of 4.3.
The leveling of silicon concentration can be
explained by either 1) no further reduction o f die silica species in the
spodumene occurred or 2) further reduction o f the silica with the silicon
product remaining undissolved in the molten reductant.
The phase diagram of
the aluminum-magnesium system shown in Appendix B shows that at 900°C a
liquid solution exists until liquid metal is 37 wt% silicon so
therefore a
saturated silicon solution did not occur in the present study.
However, it
is possible that the silicon remained undissolved for unknown reasons.
16.0
14.0
WEIGHT%
Si
12.0
10.0
8.0
6.0
4.0
2.0
0 . 0,
Mg:SPODUMENE MOLAR RATIO
Figure 8.8.
Silicon weight % in the powder residue vs. the magnesium to
spodumene ratio.
1
79
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The magnesium concentration in the ingot and dross increased as more
magnesium was added to the system as shown in Figure 8.9.
The concentrations
are less than the weight % magnesium expected according to the stoichiometric
amounts of the reactants.
This is due to loss of magnesium from the alloy
via oxidation, volatilisation, and reaction.
INGOT
WEIGHT%
Mg
DROSS
Mg:SPODUMENE MOLAR RATIO
Figure 8.9.
Magnesium concentrations in the ingot and dross vs. the
magnesium to spodumene ratio.
f
V
80
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The magnesium concentration in the powder residue increased as the
Mg:Spod ratio increased as shown in Figure 8.10.
The magnesium concentration in the flue powder, also shown in Figure
8.10, increased with Mg:Spod ratios.
The flue powders were thought to be
composed of the finer sizes o f the residue.
At the higher Mg:Spod ratios,
m ore fine magnesium particles were produced, such as magnesium oxide, and
w ere carried away by the flushing gas.
RESIDUE
40
-
-x —
FLUE POW.
20
M gS PO D U M E N E MOLAR RATIO
Figure 8.10.
The magnesium weight % in the powder residue and very fine
black powder versus the magnesium to spodumene ratio.
81
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The lithium extraction from spodumene shown in Figure 8.11 was
calculated as the difference in the mass of lithium between the charge, P
spodumene, and the powder residue divided by the charge mass of lithium in
the p spodumene times one-hundred percent,
^EXTRACT =
<Mi,SS L ’SPO0 ' M i >SS ‘' ‘r I S . d J
+ M ^ SS L W
100%
[8.U1
It increased curvilinearly as the Mg.Spod ratio increased at decreasing
rates.
The largest lithium extraction was 67.2% and occurred at a MgtSpod
ratio of ten to one.
LU
Z
LU
2
3
Q
O
Q.
W
I
8l
Z
O
H
O
X
LU
Mg:SPODUMENE MOLAR RATIO
Figure 8.11.
Lithium extraction from the powder residue vs. the magnesium
to spodumene ratio.
1
82
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The lithium recovery to the ingot, Figure 8.12, was calculated as the
mass o f lithium in the metal ingot divided by the mass of lithium in the
spodumene charge times one-hundred percent,
U RIZCOVERY =
(
W ‘%
L i INO OT ' M “ W
+
M i * SS “ s P O lP
'
100%
l!'121
The lithium recovery to the ingot increased as the Mg:Spod ratio increased.
The maximum recovery attained was 58.1%
The lithium recoveries were less than the lithium extraction from
spodumene due to lithium occurrence in dross, flue powder and condensate as
well as lithium losses to the vapour phase.
T he low recovery value at a
Mg:Spod ratio of four to one was for Experiment 1 and was due to the small
ingot obtained in that trial.
«
s
z
cc
UJ
>
LU
cc
Mg SPODUMENE MOLAR RATIO
Figure 8.12.
Lithium recovery to the metal ingot vs. the magnesium to
spodumene ratio.
i
83
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
A summary of the mass balances and the lithium, silicon and magnesium
distribution to the reaction products for each Experiment is shown in Figures
8.13 to 8 16
These Figures show much information that has already been
presented earlier, but in a slightly different manner, which may aid the
reader in grasping the relationships put forwaid in the previous section.
New evidence presented is discussed for each Figure
The lithium distribution in the reaction products shows that the
percentage of lithium present in the ingot increased as the magnesium to
spodumene ratio was increased.
Conversely, the distribution shows that the
lithium percentage of the powder residue decreased as the magnesium to
spodumene ratio increased.
The lithium distribution for the experiment with
a magnesium to spodumene ratio of zero shows that about ninety percent of the
lithium remained in the powder residue, attesting to die small amount of
lithium reduction which occurred in this experiment.
The amount of lithium unaccounted for decreased as the magnesium to
spodumene ratio increased for undetermined reasons.
NGOT
RES.
BP
EZlZ Z I
LOST
41
20
6.0
44
100
62
M gS P O D tM M MOLAR RATIO OF TEST
Figure 8.13.
Lithium distribution in the reaction products for each
experiment.
!
-------------------------------------------------------------------------------------------
84
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
The silicon percentage of the powder residue decreased as the magnesium
t
to spodumene ratio increased.
The silicon distribution in the other
reaction products is inconsistent among the experiments.
\\\V
aQ
RES.
Q
J,
l/l
sssss
Iff
BP
u zm
S ll
o
B
Q_
1
in
II i
1
41
20
44
ao
LOST
i
io o
&2
100
MgSPOOLMEFE MOLAR RATO OF TEST
Figure 8.14.
Silicon distribution in the reaction products for each
experiment.
85
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
The distribution for magnesium shows that the percentage o f magnesium in
the powder residue decreased as the magnesium to spodumene ratio was
increased
This meant that at the lower Mg:Spod ratios a greater percentage
of the magnesium was utilized in the reduction reactions and magnesium oxide
products contained in the powder residue weie formed
The second bar from
the right was excluded from the analysis due to the spurious reading of the
magnesium concentration in the powder residue from Experiment 7.
NGOT
Q
uQ
5
2
□
(/)
U
i
z
o
DROSS
u
5
Q.
I
0
41
20
60
44
100
S2
100
MgrSPOOLMM MOLAR RATIO Of TEST
Figure 8.15.
Magnesium distribution in the reaction products for each
experiment.
VIII.6.
KINETICS OF TH E SPODUMENE REDUCTION SYSTEM
The rates of spodumene reduction were qualitatively determined
from the plot of lithium recovery to the kinetic samples versus the sample
time, Figure 8.16
The lithium recovery was calculated as the lithium assays
of the kinetic sample divided by the nominal lithium concentration, according
to the amount of reactants, of the excess molten reductant, i.e.,
86
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
REC
Li
Li-KIN =
^M U
18.13)
K IN
SPO D ^ ^ M E L T
^
High rates of lithium recovery occurred for the first twenty minutes of
the experiments and then decreased considerably thereafter.
Also, the rate
of lithium recovery and amount of lithium recovered increased with increased
magnesium to spodumene ratios.
The latter finding is consistent with the
results of the lithium recovery to the ingot samples, shown in Figure 8.12.
$
6
&
§l
U
10
cc
3
0
10
20
30
40
50
60
TIM E (MINUTES)
Figure 8.16.
Rate of lithium recovery to the melt versus time for various
experiments performed in this study.
The decrease in the rate may have been a result of the following,
1) Equilibrium was attained by the system.
2) A rate limiting step has been reached.
3) Depletion of (3 spodumene ore.
4) Depletion of magnesium reductant.
However, a discussion of these is beyond the scope of this thesis.
87
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
VIII.7.
DISCUSSION OF XRD RESULTS
The XRD results gave insight into the reactions which occurred and
aided in the determination of the physical mechanisms which took place.
The XRD analysis showed that the powder residue was a very complex
material.
It was composed of aluminum, spinel, silicon, spodumene, lithium
aiumino silicates and penda.se
The aluminum in the residue was caused by the entrainment of aluminum in
the powder phase.
The spinel was a reaction product from the reduction of alumina by
magnesium
The pure silicon detected in the lesidue was the product of the
reduction of silica in the spodumene by aluminum or magnesium.
The spodumene present in the residue indicated that not all of the
spodumene reacted.
This may have been because some o f a spodumene feed may
not have undergone the a -> (3 transformation and was thus added as relatively
inert a spodumene.
In fact, the lithium aiumino silicate species, 35-797 and
31-706, detected in the powder residue have XRD patterns similar to a
spodumene.
In the spodumene conversion performed, the concentrate expanded
and packed itself into a very dense material.
It is possible that some
particles were "crushed" by others and the resulting compressive forces
deterred the transformation of certain crystals
It is recommended that
future researchers perform spodumene conversions in vessels that allow the
spodumene to expand freely.
The magnesium oxide present in the residue was fro-
ihe oxidation of
magnesium; during dissolution and by reduction of the spoc ; nene.
The flue powder was composed of aluminum, silicon ,tnd spinel.
All these
constituents were present in the powder residue and were believed to have
been a fine sized portion of the powder residue, which was physically
transported from the reactor by the argon flushing gas.
The condensate was composed of magnesium oxide.
It formed via the
vapourization of molten magnesium in the liquid alloy and its subsequent
condensation and oxidation on the underside of the crucible cap.
VIII.8.
WETTING EFFECT OF MAGNESIUM
It was thought that magnesium dissolved in aluminum would improve the
wetting between the molten alloy and the spodumene as explained in Section
88
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II.4.
In Experiment 2, where no magnesium was used, silicon recoveries to
the ingot, shown in Figure 8.7, were similar to those encountered in the
other tests.
This meant that sufficient wetting occurred, without magnesium,
to permit the reaction between molten aluminum and spodumene. Thus
magnestum’s importance in the other experiments was thermodynamic.
The kinetic study o f the lithium recovery to the molten alloy showed
that increased magnesium addition increased the rate of lithium extraction.
This effect could be due to improved wetting caused by the magnesium but a
more plausible explanation is that the lithium extraction was faster due to
a higher magnesium activity, though the exact relationship is not known.
VIII.9.
DISCUSSION O F REACTION M ECHANISM S
The reaction mechanism describes the physical nature o f the reaction
between the spodumene particles and the molten reductant
The reaction
mechanism which occurred in the present work is in fact is beyond the scope
o f this thesis.
However in this section, observations pertinent to the
reaction mechanism are mentioned and the questions which they raise are
discussed:
1) There was an absence o f a layer of reaction products on the reacted
particles’ surface by SEM analysis:
This meant that the reaction products dissolved or were released into the
molten reductant.
Another possibility is that the reaction products
formed within the spodumene and not just at the surface.
2) There was positive identification o f spinel and silicon in the powder
residue:
This result more than any other indicated that reduction o f the spodumene
occurred as these are products o f spodumene reduction.
However, the
presence of silicon in the powder also meant that the silicon did not
dissolve in the excess reductant.
This is an entirely unexplained
observation
3) The kinetic study found that reaction occurred very rapidly in the first
twenty minutes and then slowed considerably:
A very fast reaction mechanism occurred.
This was invariably due to the
89
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
small size o f the spodumene charge
»
However, for a system dealing with
solid crystals and molten metal, the rate was higher than anticipated.
4) There were cracks and holes evident in the powder residue reaction
particles:
These phenomena may have resulted from in situ reaction by diffusion of
reductant atoms and the subsequent diffusion ot the reaction products out of
the crystal into the excess molten reductant leaving the holes.
would have facilitated the transport of atoms.
The cracks
A mobile small atom such as
lithium would have a very high diffusion rate and thus the greater amount o f
it produced would enter the molten reductant.
Silicon, which would have a
slower diffusion rate would only partly enter the molten phase.
An oxide
product, such as spinel, would station itself in the crystal lattice and not
enter the melt
This would explain the: detection o f spinel and silicon in
the powder residue and the silicon assay o f the metal ingot.
VIII.10.
It
DISCUSSION O F REACTION PATHW AYS
Pinpointing the reactions which occur in a system is an important task
which raises the level of understanding of a system.
Information obtained
from the different modes of analysis were utilized to develop two proposed
different reaction pathways in this Section.
VIII. 10.1.
TW O-STEP R EA C TIO N PATHWAY
From the XRD results o f the powder residue and the silicon assay of
the ingot from Experiment 2, where no magnesium was used, the reduction
of the silica in the spodumene by aluminum must have occurred, i.e.,
Li^O-Al 0 -4SiO + m
2 3
2
3
A1
= J A1 0
3 2 3
+ 4Si + Li O AI O
2
2> 3
i*.i4]
This first step is in agreement with the F*A*C*T simulation o f the
system and would have to have occurred by a liquid-solid reaction mechanism.
In the second step, the magnesium in the molten aluminum reduced the
lithium aluminate to form spinel and lithium, l e.,
f
90
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Mg
+
Li 0 A1 O
2
2
3
=
2Li
+
MgO-Al O
°
2
1815]
3
It is not known which of the two reactions was rate limiting, but as
shown in the kinetic study in Section VIII.6, the rate at which the majority
of the lithium entered the alloy was very fast.
VIII. 10.2.
ONE-STEP REA CTIO N PATHWAY
In the one-step reaction pathway the aluminum does not participate
in the reduction process, only the magnesium reacts,
L i20-A120 3'4S i 0 2 + 9Mg = 2Li + 4Si + MgO-AI^O + 8MgO
[8t6]
due to a much higher rate of reaction with the spodumene by a gas-solid
mechanism than that for aluminum by a liquid solid mechanism.
The one-step
reaction pathway requires a magnesium to spodumene ratio of nine to one.
Magnesium oxide or penclase(MgO) is a reaction product formed in the
one-step pathway not formed in the two-step pathway.
Penclase
was detected in the powder residue only for Experiments 6,7 and 8 where the
magnesium to spodumene ratios of eight to one for Experiment 6 and ten to one
for Experiments 7 and 8 were used.
The free energy of this equation at 900°C, calculated by F*A*C*T,
is -865343 2 J which means that the reaction will precede to the right.
At magnesium to spodumene ratios of six to one and less, lithium was
produced by the two step reaction pathway and at higher magnesium to
spodumene ratios it is believed that both the one and two-step reaction
pathways contributed to lithium formation.
VIII. 11.
VACUUM R EFIN IN G OF LITHIUM FR O M ALUMINUM
In this thesis, an assumption has been made that it is possible to
vacuum refine lithium from aluminum
In this section, a brief explanation of
vacuum refining is given and it is investigated whether it is theoretically
possible to of vacuum refine lithium from aluminum.
Vacuum refining is based on the difference in vapour pressure between
two species in a melt
When the melt is exposed to vacuum, the species with
the higher vapour pressure, will preferentially evaporate from the species
91
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
which has the lower vapour pressure.
A description of the triads transfer phenomena and the series of equations
necessary to develop the equation which determines whether solute elimination
is possible via vacuum refining is beyond the scope of this thesis.
Excellent references are Dimayuga148'1 and
Harns(49).
The volatility coefficient, <f>, defined by Ollette(50) of a volatile
sohite,i , in a less volatile solvent, b, is delined as,
M.
18.17)
M
where,
7°
is the activity coefficient in the melt
P° is the equilibrium vapour pressure of pure species, (Pa)
M
is the molecular mass, kg kgmole'1
i, b denote the solute i and solvent b, respectively.
If a solute has a volatility coefficient greater than one, then vacuum
refining of the solute is possible.
Dimayuga(48)calculated the volatility coefficients for various elements
in liquid aluminum and a few are listed in Table 8.6.
Table
SOLUTE,
8.6.
i
VOLATILITY COEFFICIENTS OF VARIOUS
SOLUTES IN MOLTEN ALUMINUM
0
yi
T = 973 K
T = 1173 K
T = 1473 K
2.1
x
104
1.2
x
105
-4
10
Li
0 . 40
1.3
x
107
5.1 x
10J
Mg
0.7
1.5
x
10®
-8
10
4.2 x
106
Si
0 .04
3.6
x
-
7.0 x
10
7
1.6 x
The results state that lithium and magnesium would both be eliminated by
vacuum refining while silicon would not.
If spodumene reduction operation
92
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utilized an aluminum-magnesium alloy then magnesium would volatilize with the
lithium and the two would have to be separated.
t
This could be achieved by:
1) having different condensation characteristics in the reactor for
fractional condensation or 2) separating the lithium from the magnesium in a
bulk condensate by melting the condensate and utilizing lithium’s lower
melting point, 180°C vs. 648°C.
VIII. 12.
C O M PA R ISO N O F EX PERIM EN TA L
RESU LTS W ITH F*A*C*T CA LCU LA TION S
VIII. 12.1.
IN TRO D U C TIO N
The F*A*C*T analysis performed in Section IV. 1 had a great bearing on
the design of the experimental program.
The experimental results were
compared to the F*A*C*T calculations here.
T he goal o f the comparison was to
deternvne if a similarity existed between the lithium extraction values and
if so, then to use F*A*C*T to simulate the alumino-thermic reduction of
spodumene while varying other thermodynamic parameters such as temperature,
pressure and amount of excess liquid aluminum.
VIII.12.2.
CO M PARISO N O F TH ERM O D Y N A M IC
M OD EL AND EX PER IM EN TA L RESULTS
The graphs from Figures 8.11 and 3.2 tire presented here again in Figure
8.17 in order to compare the expenmental results to the thermodynamic
predictions.
Equation 8.11 was used to determine lithium extraction and
Input 3.1, shown here again as Input 8.17, was used for the F*A*C*T
calculations.
Li20 A l20 3'(SiO2)4 + 85.5 Al + <A> Mg
[8.17]
Figure 8.17 shows that g. od agreement existed between the lithium
extraction obtained experimentally and calculated by F*A*C*T .
At a
magnesium to spodumene ratio o f two to one, the lithium extraction in the
experiment was much larger than the predicted extraction by F*A*C*T.
This
may have been due to the less than perfect mixing of all the reactants which
«
would have resulted in localized, large, magnesium concentrations that would
93
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
have improved spodumene reduction.
Another discrepancy is the flattening o f the experimental curve at
higher MgiSpod ratios.
This was due to less than 100% efficiency of
reaction, possibly due to the less than 100% transformation o f a to P
spodumene
80
..... ........'"i ..
i
i
70
50
2
O
40
X
•
+
i
______ ________
+
60
EXP.
44
x
FACT
+
to
tr
+
>
x-----
UJ
zLU
2
3
a
O
a.
.......
K*
30
20
10 V---------
<
:
10
Mg:SPODUMENE MOLAR RATIO
Figure 8.17
Lithium extraction from experimental work and F*A*C*T
calculations vs. the magnesium to spodumene molar ratio.
Differences in a thermodynamic simulation and experimental work will
always exist because thermodynamic calculations are done for steady state,
ideal systems which were not attained in this study due to:
a) Argon flushing gas which earned lithium vapour out o f the vessel,
and lowered the amount of lithium in solution, offsetting the
equilibrium and permitting more lithium to enter the molten metal.
b) Imperfect mixing of the reactants.
c) Unknown wetting characteristics between the molten reductant and
spodumene.
94
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Other reasons for differences between experimental work and
thermodynamic simulated results in metallurgical processes are:
i
d) miscellaneous material losses.
e) analytical error.
f) The data used to create dissolved species is continually being updated
and until data for dissolved species is obtained which is unrefutable,
the thermodynamic predictions are not 100% accurate.
With all the possibilities for differences and the complexity of the
system, the c'ose resemblance of the experimental and computer modeled curves
is nevertheless an outstanding achievement of this thesis and suggests that
there is great value in using F*A*C*T as a simulation tool for further study
of this system.
VIII. 12.3.
F*A*C*T SIM U LA TIO N OF TH E ALUM INOTH E R M IC RED U C TIO N OF SPODUM ENE
The addition o f magnesium is a thermodynamic parameter in the reaction
between spodumene and aluminum.
Other parameters are temperature, pressure
and the amount of excess molten aluminum.
Using the F*A*C*T EQUILIB program
the alumino-thermic reduction of spodumene '»'as examined while varying the
above three parameters.
The Input supplied to F*A*C*T for the temperature
change simulation is shown in Input 8.18.
Li O A1 O -4SiO
2
2
3
2
+ 85.5A1 =
[s.isj
at a pressure of 1 Atm. and at temperatures ranging from 700°C to 1300°C by
increments o f 100°C.
The input to F*A*C*T for the pressure simulation also uses Input 8.18.
The temperature was fixed at 900°C and the pressure was lowered from 1 Atm.
to IE -5 Atm by orders of magnitude.
The simulation for the excess molten reductant used Equation 8.19 as the
Input,
Li OA1 O 4S i02 + <A>A1 =
[».i9]
«
95
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at a temperature of 900°C and a pressure of 1 Atm while increasing the number
of moles of aluminum from 50 to 739.
The results of the simulations are shown in Figures 8.18 - 8.22.
The F*A*C+T simulation of the lithium extraction from the ore vs.
temperature shown in Figure 8.18 increased exponentially as the temperature
was increased.
At a temperature of 1582°C, 100% recovery was obtained.
would not be a reasonable operating temperature.
Aluminum fuming would
occur, causing aluminum impurities in the condensate and there would be
serious attack on the refractories used.
100
>■
cr
LLI
>
8
LU
QC
1
800
1000
1200
1400
1600
TEMPERATUREC
Figure 8.18.
Lithium extraction from spodumene vs. temperature,
Input 8.18.
V
96
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This
The lithium extraction linearly increased as the amount of excess
aluminum was increased as shown in Figure 8.19.
One-hundred percent recovery
occurred when the ratio o f aluminum to spodumene was 739:1, corresponding
t
to an aluminum to spodumene mass ratio of 53.6:1.
% Li RECOVERY
100
200
600
400
800
MOLES Al
Figure 8.19.
Lithium extraction from spodumene vs. the amount of
excess liquid aluminum, Input 8.19.
97
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Figure 8.20 shows that the lithium recovery did not increase as the
pressure was lowered until a value of 1.2E-03 Atm was reached, whence 100%
recovery of the lithium occurred.
The recovery in this simulation is to the
gas phase as lithium vapour is formed.
This critical pressure could be
increased by increasing the temperature o f the system as shown in Figure
8.21.
The addition of more liquid aluminum was found to not have an effect
on the pressure required for 100% recovery.
100
r......
—
--------1--------1------- -i—..... -
80
AU3AO03H
60
H %
40
20
-7
-4
-6
-3
-2
-1
LOG PRESSURE (ATM)
Figure 8.20.
Lithium extraction from the spodumene vs. pressure at 900°C,
Input 8.18.
1
98
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4
0.0
-
1.0
-
2.0
LU
QC
3
m
in
LU
EC
Q-
8
-3.0
-4.0
•5.0
900
1000
1100
1200
TEMPERATURE°C
Figure 8.21.
Pressure of 100% lithium extraction vs. temperature,
Input 8.18.
Magnesium addition to the system for each simulation would have the
effect of decreasing the required pressure, temperature or molar amount of
aluminum necessary to obtain 100% recovery.
8.22 for temperature.
This is illustrated in Figure
Input 8.17 was used with a constant pressure and the
temperature was increased from 1025°C to 1275°C by increments of 50°C
99
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0 Mg
(%)
2 Mg
4 Mg
Li RECOVERY
i----6 Mg
—
40
--- B---8 Mg
--- K---10 Mg
TEMPERATURE C
Figure 8.22.
The effect o f magnesium to spodumene ratio on the
lithium extraction from spodumene with temperature change.
I
-------------------------------------------The F*A*C*T analysis of the reduction of spodumene by aluminum under
various thermodynamic conditions showed that 100% extraction of lithium from
the spodumene is possible by either increasing the temperature, increasing
the amount of excess molten aluminum or by decreasing the pressure of the
system.
The amount by which one parameter has to be changed depends on the
levels of the other two parameters and the magnesium concentration.
This section demonstrated that complicated systems can be simulated and
the options available can be narrowed down to the best candidates: without
having to obtain and construct the different apparatus, perform a series of
experiments and analyze the products.
As a result enormous amounts of time,
money and effort are saved.
More importantly, this section also showed a good agreement in the
percent lithium extracted from spodumene obtained experimentally and from a
thermodynamic simulation.
100
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IX. CONCLUSIONS AND FUTURE WORK
t
IX. 1.
CONCLUSIONS
The main finding of this study was that magnesium addition to molten
aluminum increases the lithium extraction from (3 spodumene in a molten
metallo-thermic reduction process.
The effect of magnesium addition on the
extraction o f lithium from spodumene was similar to calculations made by a
computer thermodynamic program, F*A*C*T.
The lithium producing reactions at magnesium to spodumene ratios of less
than eight to one occurred by a two-step process,
Li O A1 0 -4SiO +
2
2
3
2
Li O-Al^O + 9Mg
A1
3
=
=
Li OA1 O
2
2
3
+ 4Si + ? A1 O
3
2
[9.1]
3
2Li + MgOAl^O^
[9.2]
In the first step the aluminum reduced the silica in the spodumene to
form silicon, lithium aluminate, and alumina.
In the second step
the magnesium reduced the lithium aluminate to form spinel and lithium.
At magnesium to spodumene ratios greater than o r equal to eight to
one a one-step reaction pathway occurred simultaneously,
Li20-A l70 3 4SiO + 9Mg
=
2Li + M g0-A l,O
+ 4Si + 8MgO
[9.3]
whereby the magnesium reduced the spodumene to form lithium, spinel, silicon,
and magnesium oxide.
The discovery that pure molten aluminum was able to reduce the silica
species in the spodumene indicated that sufficient wetting occurred between
the spodumene and the molten aluminum for reaction to occur.
Therefore
magnesium’s role in the system was thermodynamic in nature.
The presence of lithium in the condensed metal vapours indicated that
lithium was produced and volatilized.
This suggests that at sufficiently low
pressures all the lithium present in the molten ingot could be volatilized
101
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from the ingot.
This concurs with the vacuum refining theory o f lithium in
aluminum.
F*A *C*T predicted that one hundred percent extraction o f lithium from
spodumene can be obtained without magnesium addition, by altering the
thermodynamic parameters of the system, such as, the amount o f excess
aluminum, the pressure or temperature.
These parameters could be varied
individually or in combination to result in ideal operating conditions.
The rate of reaction was high in the first twenty minutes o f the
experiments and in that time period the majority of the lithium was extracted
from the spodumene
Previous claims that lime was an absolutely necessary reactant in the
alumino-thermic reduction of spodumene does not apply to a M LE process.
The conversion of a to J3 spodumene is a necessity because it produces a
more reactive charge material w ith a larger surface area.
IX.2.
FU TU R E W O RK
This first investigation on the metallo-thermic reduction of spodumene
was successful in achieving its goals of a reducing spodumene to produce a
lithium bearing molten ingot.
There is great potential for this process
commercially, but more work is necessary for further development.
In this
section projects and tasks that w ould aid in the further development of this
process are proposed below:
The theory and the experimentation o f the condensation of pure metal
vapours, preferably to the liquid phase.
These models would be used in a
lithium condensing apparatus in the alumino-thermic reduction of spodumene.
T he surface chemistry of (3 spodumene and liquid metals.
The vacuum refining of lithium from molten aluminum.
The kinetics of the reduction of spodumene by metallo-thermic reduction.
102
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T he reaction mechanisms between liquid metals and oxide particles and
their effect on the kinetics.
The process, ideally would not include magnesium as a reactant due to
its similar vapour pressure to lithium and its high cost.
Therefore an all
important task would be the reduction of (3 spodumene by molten aluminum under
conditions specified F*A*C*T at which 100% lithium extraction was predicted.
A vital task would be to design and construct a reactor suitable for
future tests. The reactor would have to: charge all the materials
simultaneously in an inert atmosphere or vacuum, have intense mixing between
the ore and the molten reductant, control of fine powder emissions, a method
o f powder removal from the molten metal, materials unreactive with lithium,
and an option for the development of a continuous process.
1
103
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
X. CONTRIBUTIONS
This work examined four original topics which were:
1) the production of lithium via the molten metallo-thermic
reduction of spodumene.
2) the production of lithium via metallo-thermic reduction at
at atmospheric pressure.
3) the reduction of spodumene by molten metallo-thermic reduction.
4) the reduction of an oxide ore by a molten alloy.
The findings from this study were extremely useful and provided new
information on the chemistry and physical phenomena on MLE processes and more
specifically on the spodumene, aluminum and magnesium system.
The
encouraging results indicate that the development of a process for lithium
production from spodumene by molten metal reduction is worth pursuing.
1
I
104
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REFERENCES
R. Harris, A.E. Wraith, and J. Togun, "Producing Volatile Metals",
Canadian Patent Application, Ser.No.: 539,058, June 8, 1987, U SA Patent
Application, SerNo.. 201,446, June 2, 1988
E.P. Comer " The Lithium Industry Today ”,
Energy, 3 (1978)
pp.237-240
Ricardo Bach, J.R. Wasson "Lithium and Lithium Compounds",Kirk-Othmer
Encyclopedia of Chemical Technology, Vol. 14., New York, Wiley & Sons,
1981, pp.449-476.
4
D. Linden, Battenes and Fuel Cells, McGraw Hill Book Co., Montreal,
1984, p. 11.6.
5
M. Hunt, " New Frontiers in Superlight Alloys ", Materials Eng.,
Aug (1988), pp 29-32.
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1
T.R. Crompton, Small Battenes- Primary Cells, The McMillan F*ress
Ltd, Vol 2, London, 1986, p. 147
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David Linden, Handbook of Batteries and Fuel Cells, McGraw H ill Book
Co., Montreal, 1984, pp 11.1-11.87.
s
SR
Taylor, "Abundance of Chemical Elements m the Continental Crust: A
New Table," Geochimica et Cosmochemica Acta 1^64, Vol. 28, pp.1273-1285.
9
L. Crocker, R H Lien, "Lithium and its Recovery From Low-Grade Nevada
Clays", U S Bureau of Mines Bulletin 691, 1987
10
J.D. Vine, "The Lithium Resource Enigma", Lithium Resources and
Requirements by the Year 2000, U.S G S. Prof. Paper 1005, 1976.
11
J. Norton, "Lithium Resource Estimates - What Do They Mean?", Lithium
Resources and Requirements by the Year 2000, U.S.G.S. Prof. Paper 1005,
1976.
12
J.E. Ferrel, "Lithium", Mineral Facts and Problems, U.S, Bureau o f Mines
Bulletin 675, U S. Department o f the Interior, 1985, pp.461-470.
1
105
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13
J. Searls, "Lithium", Mineral Facts and Problems, U.S. Bureau o f Mines
Bulletin 671, U.S. Department o f the Intenor, 1980, pp.521-534.
14
A.T. Kuhn, Industrial Electrochemical Processes, Elsevier, London,
U.K., 1971.
15
C.L. Mantell, Electrochemical Engineering, McGraw-Hill, London, U.K.,
1960.
16
17
Mining Journal, Vol. 312, No. 8002, A pnl 7, 1989, p.35.
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Nac. La Plata, La Plata, Argentina) Bol Soc Esp. Ceram. Vidrio,
15(1)(1976), p p.5-10.
18
Friednch Liebau, Structural Chemistry o f the Silicates, Springer
Verlag, New York, 1985, p.260.
19
Friedrich Liebau, Structural Chemistry o f the Silicates, Springer
Verlag, New York, 1985, p.265.
20
Friedrich Liebau, Structural Chemistry o f the Silicates, Springer
Verlag, New York, 1985, p.254.
21
L.M. Pidgeon and W A. Alexander, "Thermal Production o f Magnesium:
Pilot Plant Studies on the Retort Ferrosilicon Process", Trans. AIME,
159, 1944, pp.315-352.
22
O. Kubaschewski, C.B. Alcock, Metallurgical Thermochemistry, 5th Ed.,
Pergamon Press, Toronto, pp.212-214.
23
R.H. Parker, An Introduction to Chemical Metallurgy, Pergamon
Press, Toronto, 1967, pp 272-273
24
C.J. Kunesh, "Calcium and Calcium Alloys", Kirk Qthmer Encyclopedia o f
Chemical Technology, Vol. 14, New York, Wiley & Sons, 1981, pp.414-415.
25
W.J. Kroll, and A W. Schlechten, "Laboratory Preparation o f Lithium
Metal by Vacuum Metallurgy", Trans AIME, 182, 1948, pp.266-274.
26
R.A. Stauffer, "Vacuum Process for Preparation o f Lithium Metal from
Spodumene", Trans. AIME, 182, 1948, pp 275-285.
I
106
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27
W . Morris and L.M. Pidgeon, "The Vapor Pressure of Lithium in the
Reduction of Lithium Oxide by Silicon," Can J. Chem., 36, 1958,
pp.910-914.
28
T.F. Fedorov and F.I. Sharmai, "The Physico-Chemical Principles o f the
Vacuum Thermite Reduction of Lithium", The Uses of Vacuum in Metallurgy,
Oliver & Boyd, Edinburgh, U.K., 1964, pp. 126-132.
Mikulinski et al, "Kinetics and Conditions o f Condensation During the
Preparation of Alkali Metals by a Vacuum-Thermal Method", Redk.
Shchelochnye Elem., Sb D okl Vses Soveechch
2nd. Novosibirsk, 1964,
p p .350-360.
30
A.S. Kozhevnikov, " Reduction of Lithium Oxide With Aluminum", Redk.
Shchelochnye Elem., Sb D okl. Vses. Soveechch., 2nd. Novosibirsk, 1964,
pp 343-349.
31
Mikulinski, A.S. and Efremkin, V.V., "Lithium Ores as Complex Raw
Materials", Redk. Shchelochnye Elem , Sb. Dokl. Vses. Soveechch., 2nd.
Novosibirsk, 1964, pp.339-342.
32
A.I. Lainer, A. Kh. Nazirov, "Mineral Composition o f Lime Spodumene
Sinters", Izv. Akad. Nauk SSSR, Metal. 6(1966), pp.36-39.
33
34
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B C. Allen, Liquid Metals, Marcel Dekker, New York, 1973, p. 161.
R.H. Ewing, Phil Mag. , Vol. 25, 1979.
A.M. Korol’kov, "Casting Properties o f Metals and Alloys", Consultants
Bureau, 1960, p.37.
36
W .T. Thompson, A.D. Pelton and C.W . Bale,
F*A*C*T- Facility for the
Analysis of Chemical Thermodynamics, (CRCT) Centre for Research in
Computational Thermochemistry, Ecole Polytechnique, Montreal, 1988.
37
G.K. Sigworth, T.A. Engh, "Refining o f Liquid Aluminum - a Review of
Important Chemical Factors", Scandinavian Journal o f Metallurgy, 11.
1982, pp. 143-149.
38
CRC Handbook of Chemistry and Physics, 64ih Ed., CRC Press Ltd., Boca
Raton, Florida, p.d-46.
<
107
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Richardson, F.D., Physical Chemistry o f Melts in Metallurgy, Vol. 1,
Academic Press, New York, 1974, pp. 141-143.
R.S. Boy ton, "Chemistry and Technology of Lime and \ imestone",
John Wiley & Sons Inc., Toronto, 1980, p.358.
Software for Automated Powder Diffraction, APD 1700, Operation
Manual, 1st Ed. Philips Corp, The Netherlands, 1984.
G.F Bell, "The Analysis of Aluminum Alloys by Means of Atomic
Absorption Spectrophotometry", Atomic Absorption Newsletter,
Vol. 5, No. 73, 1966, pp.73-76.
J. Soters and R. Stux, "Atomic Absorption Methods Manual", Vol. 1,
Instrumentation Lab Inc , Wilmington Ma., 1979.
Tracor Northern, 2551 West Beltline, Middleton, Wis., 1985.
Lotus 123, Release 2,
Lotus Development Corporation, SeattleWash.,
1985.
Peter Hayes, Process Selection in Extractive Metallurgy, Hayes
Publishing Co., Brisbane, Aus., 1985, p.276.
M.A. Filyand, E.I. Semenova,
Handbook of the Rare Elements, Edited by
M.E. Alfeneff, Boston Technical Publishers, Cambridge Mass., 1968,
p.162.
Dimayuga, F., "Vacuum Refining of Molten Aluminum", Ph.D.
Thesis, McGill University, 1980, pp. 18-45.
H am s, R.L., "Vacuum Refining o f Molten Steel", Ph.D. Thesis,
McGill University, 1980, pp. 14-38.
Olette, M., "Vacuum Distillation o f Minor Elements from Liquid Ferrous
Alloys", Physical Chemistry of Process Metallurgy ; Part 2, Edited by
G. St. Pierre, Interscience, N.Y., 1961, pp. 1065-1087.
!
108
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
APPENDIX A
The F*A*C*T simulation of the addition of magnesium to the
alumino-thermic reduction of spodumene is shown below.
The product species identified with
’ were drawn from the private
data created for the dissolved species in molten aluminum.
The gaseous
magnesium identified with a T was extrapolated from its normal temperature
range, the value given would be the magnesiums’s partial pressure over the
system.
T he cutoff concentration was set at 1 x 10'5, species with a
concentration or activity less than that were not listed.
MgrSpod ratio = 0
(LI20)*(A L203)*(SI102)4 + 85.5 AL + <A> MG =
80.318
( 0.99720
+ 0.17424E-02
+ 0.9796 IE-03
( 1173.0, 1.00
A1
Li
Li)
,SOLN 2)
+
3.9939
( 1173.0, 1.00
Si
,S1,
1.0000
)
2.8124
( 1173.0, 1.00
A1203
,S1, 1.0000
)
1.7814
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
+
+
<—
WHERE ’A ’ ON TH E REACTANT SIDE IS 0.000E+00
Mg:Spod ratio = 1
(L I20)*(A L203)*(SI102)4 + 85.5 AL + <A> MG =
81.055
( 0.99467
+ 0.20963E-02
+ 0.17409E-02
+ 0.97878E-03
+ 0.43586E-03
( 1173.0, 1.00
A1
Mg
Li
Li
Mg)
,SOLN 2)
+
Si
,S1,
3.9939
( 1173.0, 1.00
1.0000
< <—
)
109
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
+
+
1.7796
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
1.7540
( 1173.0, 1.00
A1203
,S1, 1.0000
)
+ 0.79476
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000 )
+ O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.22977E-01)
CTANT SIDE IS
1.00
Mg:Spod ratio = 2
85.5 AL + <A> MG
81.723
( 0.99467
+ 0.20963E-02
+ 0.17409E-02
+ 0.97878E-03
+ 0.43586E-03
( 1173.0, 1.00
A1
Mg
Li
Li
Mg)
,SOLN 2)
+
3.9938
( 1173.0, 1.00
Si
,S1,
+
1.7931
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000 )
+
1.7777
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
+ 0.42409
( 1173.0, 1.00
A1203
,S1, 1.0000
)
+ O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.22977E-01)
WHERE ’A ’ ON THE REACTANT SIDE IS
1.0000
<< ---
)
2.00
Mg:Spod ratio = 3
(LI20)*(AL203)*(SI 102)4 + 85.5 AL + <A> MG
+
O.OOOOOE+OO
( 0.25912E-03
( 1173.0, 1.00
Mg
,G ,0.284E-03)
82.724
( 0.98521
+ 0.78317E-02
+ 0.33649E-02
A1
Mg
Li
110
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
T)
<—
<—
«
+
+
0.18919E-02
0.16284E-02
( 1173.0, 1.00
Li
Mg)
,SOLN 2)
+
3.9937
( 1173.0, 1.00
Si
,S1,
+
2.2174
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000 )
+
1.5651
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
0.00000E+00
( 1173.0, 1.00
A1203
,S1, 0.37036
)
+
O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.62040E-01)
+
O.OOOOOE+OO
( 1173.0, 1.00
Mg2Si
,S1, 0.63224E-03)
+
WHERE ’A’ ON THE REACTANT SIDE IS
1.0000
)
3.00
Mg:Spod ratio = 4
(LI20)*(A L203)*(SI102)4 + 85.5 AL + <A> MG
I
+
O.OOOOOE+OO
(
83.827
( 0.97224
+ 0.16585E-01
+ 0.48968E-02
+ 0.34485E-02
+ 0.2753 IE-02
( 1173.0, 1.00
A1
Mg
Li
Mg
Li)
,SOLN 2)
+
3.9937
( 1173.0, 1.00
Si
,S1,
+
2.3206
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000 )
+
1.3587
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
0.00000E+00
( 1173.0, 1.00
A1203
,S1, 0.20958
)
0.00000E+00
( 1173.0, 1.00
MgO
,S1, 0.10964
)
+
+
0.54874E-03
( 1173.0, 1.00
Mg
,G ,0.585E-03)
1.0000
T)
<-<—
)
111
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
+
O.OOOOOE+OO
( 1173.0, 1.00
WHERE ’A’ ON THE REACTANT SIDE IS
Mg2Si
,S1, 0.28354E-02)
4.00
Mg:Spod ratio = 5
(LI20)*(AL203)*(SI102)4 + 85.5 AL + <A> MG =
+
O.OOOOOE+OO
(
84.908
( 0.95986
+ 0.25337E-01
+ 0.60523E-02
+ 0.5268 IE-02
+ 0.34028E-02
( 1173.0, 1.00
A1
Mg
Li
Mg
Li)
,SOLN 2)
+
3.9936
( 1173.0, 1.00
Si
,S1,
+
2.4014
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000 )
+
1.1972
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.15162
)
0.00000E+00
( 1173.0, 1.00
A1203
,S1, 0.15154
)
O.OOOOOE+OO
( 1173.0, 1.00
Mg2Si
,S1, 0.66173E-02)
+
+
+
Mg
,G ,0.883E-03)
0.83830E-03
( 1173.0, 1.00
WHERE ’A’ ON THE REACTANT SIDE IS
1.0000
T)
<-<—
)
5.00
Mg:Spod ratio = 6
(LI20)*(AL203)*(SI102)4 + 85.5 AL + <A> MG =
+
O.OOOOOE+OO
(
85.977
( 0.94793
+ 0.33983E-01
+ 0.70658E-02
+ 0.70094E-02
+ 0.39409E-02.
0.11244E-02
( 1173.0, 1.00
Mg
,G .0.118E-02)
A1
Mg
Mg
Li
Li)
112
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
T)
<—
( 1173.0, 1.00
.SOLN 2)
3.9935
( 1173.0, 1.00
Si
,S1,
+
2.4707
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000 )
+
1.0585
( 1173.0, 1.00
LiA102
,S1, 1.0000 )
+
O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.19015
)
O.OOOOOE+OO
( 1173.0, 1.00
A1203
,S1, 0.12083
)
+
+
WHERE ’A ’ ON THE REACTANT SIDE IS
1.0000 )
6.00
Mg:Spod ratio = 7
(LI20)*(AL203)*(SI102)4 + 85.5 AL + <A> MG =
+
0.14058E-02
( 1173.0, 1.00
O.OOOOOE+OO
(
87.039
( 0.93636
+ 0.42489E-01
+ 0.88344E-02
+ 0.78376E-02
+ 0.44065E-02
( 1173.0, 1.00
A1
Mg
Mg
Li
Li)
,SOLN 2)
+
3.9934
( 1173.0, 1.00
Si
,S1,
+
2.5329
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000
+
0.93427
( 1173.0, 1.00
LiA102
,S1, 1.0000
+
O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.22622
+
O.OOOOOE+OO
( 1173.0, 1.00
A1203
,S1, 0.10157
WHERE ’A’ ON THE REACTANT SIDE IS
Mg
,G .0.146E-02)
1.0000
7.00
«
113
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
T)
<<—
Mg:Spod ratio = 8
(LI20)*(AL203)*(S1102)4 + 85.5 AL + <A> MG =
+
0.1682 IE-02
( 1173.0, 1.00
Mg
,G ,0.174E-02)
O.OOOOOE+OO
(
88.097
( 0.92512
+ 0.50840E-01
+ 0.10571E-01
+ 0.85733E-02
+ 0.48202E-02
( 1173.0, 1.00
A1
Mg
Mg
Li
Li)
,SOLN 2)
+
3.9933
( 1173.0, 1.00
Si
,S1,
+
2.5900
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000
+
0.82008
( 1173.0, 1.00
LiA102
,S1, 1.0000
+
O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.26037
+
O.OOOOOE+OO
( 1173.0, 1.00
A1203
,S1, 0.88246E-01
+
O.OOOOOE+OO
( 1173.0, 1.00
Mg2Si
,S1, 0.26643E-01
WHERE ’A’ ON THE REACTANT SIDE IS
T)
<—
<—
1.0000
8.00
MgrSpod ratio = 9
(LI20)*(AL203)*(SI102)4 + 85.5 AL + <A> MG =
+
0.19531E-02
( 1173.0, 1.00
Mg
,G .0.202E-02)
O.OOOOOE+OO
(
89.150
( 0.91419
+ 0.59030E-01
+ 0.12274E-01
+ 0.9238 IE-02
+ 0.51939E-02
( 1173.0, 1.00
A1
Mg
Mg
Li
Li)
,SOLN 2)
+
3.9933
( 1173.0, 1.00
Si
,S1,
2.6433
(Mg0)(A1203)
+
1.0000
T)
<—
<—
)
114
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
( 1173.0, 1.00
,S1,
1.0000
)
0.71338
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.29298
)
+
O.OOOOOE+OO
( 1173.0, 1.00
A1203
,S1, 0.78426E-01)
+
O.OOOOOE+OO
( 1173.0, 1.00
LiAl
,S1, 0.76319E-01)
+
O.OOOOOE+OO
( 1173.0, 1.00
M g2Si
,S1, 0.35918E-01)
+
+
WHERE ’A’ ON THE REACTANT SIDE IS
9.00
MgrSpod ratio = 10
(LI20)*(AL203)*(SI 102)4 + 85.5 AL + <A> MG
+
0.22187E-02
( 1173.0, 1.00
Mg
,G .0.229E-02)
O.OOOOOE+OO
(
90.201
( 0.90354
+ 0.67057E-01
+ 0.13943E-01
+ 0.98462E-02
+ 0.55359E-02
( 1173.0, 1.00
A1
Mg
Mg
Li
Li)
,SOLN 2)
+
3.9932
( 1173.0, 1.00
Si
,S1,
2.6937
( 1173.0, 1.00
(Mg0)(A1203)
,S1, 1.0000
)
0.61253
( 1173.0, 1.00
LiA102
,S1, 1.0000
)
O.OOOOOE+OO
( 1173.0, 1.00
MgO
,S1, 0.32427
)
+
O.OOOOOE+OO
( 1173.0, 1.00
A1203
,S1, 0.70858E-01)
+
O.OOOOOE+OO
( 1173.0, 1.00
Mg2Si
,S1, 0.46352E-01)
+
+
+
W H E R E ’A ’ O N THE R E A C T A N T SID E IS
1.0000
10.0
115
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
T)
<—
<—
)
APPENDIX B
In this study the reductant was a mixture o f molten aluminum with
dissolved magnesium, lithium and silicon. Figures B.l, B.2, and B.3 show the
cs
phase diagrams
for aluminum with magnesium, lithium and silicon
respectively, with the intention of showing that at 900°C and the weight
percents incurred, that no precipitation of intermetallic species would
occur.
20
700
Weight P e r c e n t M a g n e s i u m
BO
60
ion
600
0U
500
uv
(At)
3
u 400
V
a
E
41
300
200-
100
20
A1
Figure B.l.
30
40
50
60
7C
BO
Atomic Percent Magnesium
100
Mg
Aluminum-magnesium phase diagram
T. Massalski, Ed., "Binary Alloy Phase Diagrams", AS ME, Metals Park,
Ohio, 1985.
?
116
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
W eight
P ercent L ith iu m
ao
800
30
40
too
50
700 -
600
(AI)
u
O
) 500U
3
C
3
ud>
o
e£ 400
tu
t-
330°C
300
200
(Ll)
100
0
A1
Figure B.l.
10
20
30
40
50
60
70
eo
90
A tom ic Percent L ith iu m
Aluminum-Lithium phase diagram
117
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
100
Li
W eight P e rc e n t S ilic o n
eo
20
1500
i
too
1300
0
CD
U
3
co
1100
900
0CL>
sa>
5 0 o jf < A‘)
300
20
A1
Figure B.3.
(S i)
^
40
50
60
A to m ic Percent Silicon
Aluminum-silicon phase diagram.
118
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
90
too