ZINC STRIPPING
FROM STEELWORK DUST
Kamil Wichterle, Jan Cieslar, Jana Wichterlová
VSB-Technical University of Ostrava,
70833 Ostrava Poruba, Czech Republic
kamil.wichterle@vsb.cz
What is the steelwork dust ?
World steel production
Iron ore
Scrap
60%
40%
Blast furnace
Pig iron
Fe, C, (Si,P,S,…)
O2
CaO
Direct reduction
Sponge iron
Fe, (Si,P,S,…)
Oxygen steelmaking
BOF (basic oxygen furnace)
Steelmaking
slag
Fe
0,5%Zn, 0,03%Pb,
Electric steelmaking
EAF (electric arc furnace)
Steel
1 400 mil. t /year
Dust
30 mil. t /y
2-5 mil. t Zn /y
Dust composition depends mostly on the quality of scrap
Statistics for USA and Canada (year 2000) for EAF mostly (50%):
Fe
15-30%
Zn
12-25%
Pb
1-2%
Cd
0,02-0,05%
Percentage of iron is higher and percentage of the heavy metals is lower in
the dust from BOF process (as the heavy metals are absent in the entering
pig iron)
In particular our samples from the tandem furnaces Arcelor Mittal
contained
Fe
about 50%
Zn
8-16%
Pb
1%
Cd
0,02%
Dust as a basic neutralizing agent
1 tonne
PRICE
NaOH
CaO
ZnFe2O4
$ 400
$ 25
$ -20
Steelmaking dust processing
Pyrometalurgy:
Reduction roasting at 1000-2000°C
problems:
Distillation of Zn (boiling point 907°C) and its condensation in oxidizing
environment in form of ZnO
Hydrometalurgy:
problems:
Total dissolution (both Fe and Zn oxides) in conc. H2SO4 or HCl
Hydrolysis at increasing pH in large volume of water leads to iron
precipitation = haematite, goethite, or jarosite
Filtration
problems:
Chlorine metalurgy:
Reaction of Cl2 or HCl with the dust –chlorides formation
The iron chlorides decompose at higher temperature to oxides and HCl
ZnCl2 (boiling point 756°C) is volatile and it condenses as a watersoluble salt
Experimental studies
of the reactions of HCl with
metallurgy dust
VŠB -Technical University of Ostrava
Faculty of Metallurgy and Material Engineering
Department of Chemistry
Jan Cieslar
Šárka Langová
Juraj Leško
Dalibor Matýsek
Radim Škuta
Jana Wichterlová
Kamil Wichterle
Arcelor Mittal Steel – Tandem Furnaces
The dust in Arcelor Mittal Steel plant is separated by textile filtres and
collected as a water suspension
– after a sedimenttion in Dorr thickenners the mud is dumped in deposits
The dust in Arcelor Mittal Steel plant is collected by textile filtres and
transferred to water suspension
– after a sedimenttion in Dorr thickenners the mud is dumped in deposits
Distribution of particle size for the TP dust sample
Mineralogy of the sample TP
%
w/w
Hematit
3,2
Magnetit
35,6
Wuestit
3,2
Franklinit
36,6
Grafit
4,4
Zinkit
5,6
amorphous
11,4
%
Zn
distribution
Zn %
9,9
69,0
4,5
31,0
Inlet HCl
Quartz
tube
Oven
Condenser
Laboratory equipment
EQUILIBRIUM DATA
2 HCl(g) + 1/3 Fe2O3(s) = 2/3 FeCl3(s,l,g) + H2O(g)
2 HCl(g) + 1/4 Fe3O4(s) = 1/4 FeCl2(s,l,g) + 1/2 FeCl3(s,l,g) + H2O(g)
2 HCl(g) + FeO (s) = FeCl2(s,l,g) + H2O(g)
2 HCl(g) + ZnO (s) = ZnCl2(s,l,g) + H2O(g)
2 HCl(g) + 1/4 ZnFe2O4(s) = 1/4 ZnCl2(s,l,g) + 1/2 FeCl3(s,l,g) + H2O(g)
2 HCl(g) + ZnFe2O4(s) = ZnCl2(s,l,g) + Fe2O3(s) + H2O(g)
FeCl2(s,l,g) + ZnFe2O4(s) = ZnCl2(s,l,g) + Fe2O3(s) + FeO (s)
2/3 FeCl3(s,l,g) + ZnFe2O4(s) = ZnCl2(s,l,g) + 4/3 Fe2O3(s)
Gibbs energy, kJ/mol
80
40
0
200
Eq.(1)
Eq.(4)
Eq.(7)
Eq.(2)
Eq.(5)
Eq.(8)
400
Eq.(3)
Eq.(6)
600
800
Temperature, °C
-40
-80
1000
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Evidently, iron chlorides are unstable at
temperatures higher than 300°C.
Zinc chloride is generally chemically
stable up to 700°C
However, ZnCl2 at higher temperatures
leaves the reaction space as a vapor
(its boiling point is 756°C)
which affects the equilibrium
Therefore, higher temperatures
are suitable to separate ZnCl2
vapors from the solid residuum
of iron oxides
90
80
70
X [%]
60
50
40
30
X(Zn)
20
X(Fe)
X(HCl)
10
X(Zn)+X(Fe)
0
100
200
300
400
500
600
700
800
T [°C]
Zn, Fe, and HCl conversions as functions of temperature
for the TP dust sample (45 minutes reaction)
900
100,0
X(Zn)
X(Fe)
X [%]
80,0
X(HCl)
60,0
40,0
20,0
0,0
0
10
30
20
40
t [min]
Zn, Fe, and HCl conversions as functions of reaction time
for the TP dust sample (temperature 900°C)
50
World steel production
Iron ore
Scrap
60%
40%
Blast furnace
Pig iron
Fe, C, (Si,P,S,…)
O2
CaO
Direct reduction
Sponge iron
Fe, (Si,P,S,…)
Oxygen steelmaking
BOF (basic oxygen furnace)
Steelmaking
slag
Fe
0,5%Zn, 0,03%Pb,
Electric steelmaking
EAF (electric arc furnace)
Steel
1 400 mil. t /year
Dust
30 mil. t /y
2-5 mil. t Zn /y
World zinc production
2009
8 millions tonnes Zn
China (continental)
2.9
Peru
1.4
Australia
1.3
United States
0.7
Canada
0.7
Zinc lossed in steelmaking dust:
3 millions tonnes of Zn
1 tonne of Zn = $ 1500 - $ 2500
!!!!!!
(2009-2010)
Efficient way of zinc recycling is
worth to be studied
Thank you for the attention