TSINGHUA SCIENCE AND TECHNOLOGY
I S S N 1 0 0 7 - 0 2 1 4 0 3 / 1 8 p p 1 6 0 -164
Volume 11, Number 2, April 2006
Equilibrium Copper Strip Points as a Function of Temperature
and Other Operating Parameters: Implications for Commercial
Copper Solvent Extraction Plants
Gary Kordosky**, Michael Virnig, Burrel Boley
Cognis Corporation, Tucson, Arizona, USA
Abstract: The development of pressure and bioleaching processes for high grade copper ores and concentrates will result in copper solvent extraction plants treating solutions with high copper and acid concentrations at temperatures up to 45℃ and these copper solvent extraction plants will run with reagent concentrations up to 40 vol.%. There is also a trend to use copper stripping solutions with less acid than typically used
in recent years. Cognis has developed a model that accurately predicts the copper strip point for virtually
any copper solvent extraction reagent or combination of reagents under a wide variety of conditions.
The
equilibrium strip points for several well known commercial copper solvent extraction reagents are given as a
function of reagent concentration, the copper and acid concentration of the strip aqueous, and the temperature. It is shown that the equilibrium strip point is not a straight line function of reagent concentration and
that the equilibrium strip point increases with an increase in temperature. Copper extraction also increases
as the temperature increases.
Key words: equilibrium strip point; solvent extraction plants; bioleaching process
Introduction
Copper solvent extraction (SX) is a well known process for copper recovery from a wide variety of leach
solutions. Until recently, typical leach solutions contained 0.5 to 8 g/L Cu at 15 to 25℃. In the past 5 years
there has been significant progress in leaching high
grade copper sulfide ores[1] and copper concentrates[2]
resulting in leach solutions having 15-60 g/L Cu and 250 g/L sulphuric acid at high temperatures. These more
concentrated, high temperature leach solutions require
that copper SX plants run at higher reagent concentrations and at higher temperatures than in the past. While
testing a high grade leach solution, Cognis ran a rouReceived: 2005-10-09
﹡﹡ To whom correspondence should be addressed.
E-mail: Gary.Kordosky@cognis-us.com
tine room temperature isotherm with 35 vol.% reagent
and then followed this with a continuous mini-plant
run at 40℃. Copper recovery in the mini-plant was
higher than theoretically possible using a McCabeThiele diagram based on the room temperature isotherm.
This led Cognis to investigate the effect of temperature on
the extraction and stripping of copper.
In addition, several copper SX plants have found
that copper cathode quality improves as the sulphuric
acid concentration in the stripping aqueous is decreased over the range 200 to 160 g/L Cu providing an
impetus to use a lower acid concentration in stripping.
1
Stripping of Copper
1.1 Equilibrium stripping data for the stripping
model
Equilibrium strip points were generated by a vigorous
Gary Kordosky et al：Equilibrium Copper Strip Points as a Function …
3-min contact of the respective organic solution 3
consecutive times with a fresh aqueous strip solution at
an organic/aqueous ratio (O/A) of 0.2. During the
course of this work, it was found that these conditions
gave an equilibrium stripped organic versus the particular
aqueous strip solution. The equilibrated stripped organic
phase was filtered and analyzed for copper.
The conditions under which the respective organic
and aqueous solutions were equilibrated were
generated by a proprietary statistical design program.
The components in the organic phase included
aldoxime and ketoxime extractant, various modifiers,
and diluent such that the total reagent concentration is
5 vol.% to 45 vol.% as reagents are formulated today
with a modifier content from zero to the highest level
available in commercial copper SX reagents. The
aqueous strip solutions contained 30 to 55 g/L Cu and
120 to 210 g/L H2SO4. The temperature was 20 to 45℃.
These conditions cover the operational range found for
most, if not all, copper SX plants coupled with copper
electrowinning. The data was entered into the
statistical design program. The program generated an
equation from which the stripped organic value for any
reagent can be obtained at any copper and acid
concentration and at any temperature within the range
of conditions given above.
161
for 20 vol.% solutions of LIX 8180 and LIX 622N
when the organic phase is in equilibrium with an
aqueous phase having 50 g/L Cu and 130 to 180 g/L
sulphuric acid. The stripped organic values for both
reagents increase with temperature. The stripped
organic value lines for LIX 8180 have a slight upward
bow while the stripped organic value lines for LIX
622N are all straight lines over the conditions selected.
As expected stripped organic values for both reagents
increase as the acid concentration in the aqueous strip
solution decreases. The respective stripped organic
values for LIX 8180 increase to a greater extent as the
acid concentration decreases from 180 to 130 g/L Cu.
For example, the increase in the stripped organic value
for 20 vol.% LIX 8180 equilibrated with 180 g/L acid
and 50 g/L Cu and then with 170 g/L acid and 50 g/L
Cu is about 0.09 g/L Cu at 20℃ while the increase in
the stripped organic value for 20 vol.% LIX 8180
equilibrated with 140 g/L acid and 50 g/L Cu and then
with 130 g/L acid and 50 g/L Cu is about 0.22 g/L Cu
at 20℃. The respective stripped organic value lines for
LIX 622N are almost parallel as the acid concentration
in the strip aqueous varies from 180 to 130 g/L
sulphuric acid and differ by about 0.31 g/L Cu for each
1.2 Equilibrium stripped organic values
Equilibrium strip organic values for the copper
extraction reagents, LIX 622N and LIX 8180, were
generated with the statistical design program under a
variety of conditions. LIX 622N, which contains the
extractant 5-nonlysalicylaldoxime modified with
tridecanol, is a copper extraction reagent whose copper
extraction stripping chemistry is representative of the
family of modified aldoxime copper extraction
reagents. LIX 622N is the strongest copper extraction
reagent that a copper SX plant is likely to use. LIX
8180, which contains the extractant 5-nonyl-2hydroxyacetophenone oxime and no modifier, is a
moderately strong, easy to strip copper extraction
reagent. LIX 8180 is the least strong copper extraction
reagent that a copper SX plant is likely to use. Both
reagents load 5.6 g/L Cu at 10 vol.% using the
standard quality control test of Cognis.
Figures 1a and 1b show the equilibrium stripped
organic values over the temperature range 20 to 45℃
Fig. 1 Stripped organic values for 20 vol.% reagent
as a function of temperature and sulphuric acid concentration at 50 g/L Cu.
162
10 g/L change in the sulphuric acid concentration.
Figures 2a and 2b show equilibrium stripped organic
values over 20-45℃ for 20 vol.% solutions of LIX
8180 and LIX 622N, respectively, when the organic
phase is in equilibrium with an aqueous phase having
30 to 55 g/L Cu and 160 g/L sulphuric acid. Again the
stripped organic values for both reagents increase with
temperature. The stripped organic value lines for LIX
8180 have a slight upward bow, while those for LIX
622N are straight. As expected, the respective strip
organic values increase as the copper concentration in
the strip aqueous phase increases. For LIX 8180, the
stripped organic value is somewhat sensitive to the
copper content in the strip aqueous at 45℃, but much
less sensitive at 20℃. Contrast this with LIX 622N
where the stripped organic value is quite sensitive to
the copper concentration at 20℃ and only slightly
more sensitive at 45℃.
Tsinghua Science and Technology, April 2006, 11(2): 160-164
sulphuric acid. As expected, the stripped organic
values for each reagent increase as the reagent
concentration increases. Note that for both reagents the
stripped organic value line has a slight downward bow
as the reagent concentration increases. For LIX 8180
the bow appears to be about the same at both high and
low sulphuric acid concentrations while for LIX 622N
the bow is slightly greater at higher acid concentration
than at lower acid concentration.
Fig. 3 Stripped organic values for LIX 8180 and LIX
622N as a function of reagent concentration and sulphuric acid concentration at 50 g/L Cu and 35℃.
Fig. 2 Stripped organic values for 20 vol.% reagent
as a function of temperature and copper concentration
at 160 g/L sulphuric acid.
Figures 3a and 3b show the equilibrium stripped
organic values for LIX 8180 and LIX 622N,
respectively, at 35℃ as reagent concentration is
increased from 5 vol.% to 45 vol.% when the aqueous
strip solution has 50 g/L Cu and 130 to 180 g/L
Figures 4a and 4b show the equilibrium stripped
organic values for LIX 8180 and LIX 622N,
respectively, at 35℃ as reagent concentration is
increased from 5 vol.% to 45 vol.% when the aqueous
strip solution has 30 to 55 g/L Cu and 160 g/L
sulphuric acid. As expected, the stripped organic
copper concentration increases as the reagent
concentration increases. It is interesting to note the
much greater downward bow in the stripped organic
value line for LIX 8180 at low copper concentration in
the strip aqueous compared to high copper
concentration. Contrast this with LIX 622N where the
downward bow is only slightly greater at low copper
concentration than at high copper concentration.
163
Gary Kordosky et al：Equilibrium Copper Strip Points as a Function …
the actual and predicted stripped organic values are
remarkably close. LIX 860N-I contains the extractant
5-non-lysalicylaldoxime in diluent with no added
modifier.
The reagents and reagent blends shown in Table 1
vary over a wide range from the strong modified
aldoxime reagent LIX 612N-LV to various blends of
aldoxime and ketoxime with varying amounts of
modifier to the blend of LIX 860N-I and LIX 8180
containing no modifier. Table 1 is only a small
representation of the many reagents and reagent blends
where actual and predicted stripped organic values
have been compared. In all cases, the agreement
between the actual experimentally determined stripped
organic value and that predicted by the model is very
good.
3
Fig. 4 Stripped organic values for LIX 8180 and LIX
622N as a function of reagent concentration and copper concentration at 160 g/L sulphuric acid and 35℃.
2
Accuracy of Model
Table 1 shows experimentally determined (actual) and
predicted (model) stripped organic values for 6 different reagent or reagent blends. The 17 vol.% organic solutions were equilibrated by 3 consecutive, 3-min contacts at an O/A of 0.2 with an aqueous solution having
44 g/L Cu and 190 g/L sulphuric acid at 41℃. The 27
vol.% organic solutions were equilibrated by 3 consecutive, 3-min contacts at an O/A of 0.2 with an
aqueous solution having 45 g/L Cu and 185 g/L sulphuric acid at 35℃. Considering experimental error,
Extraction of Copper
Figure 5 shows extraction isotherms at 25℃ and 40℃
for a solution obtained from the leaching of copper
sulfide concentrates. This copper leach solution
contained 24.8 g/L Cu and 40 g/L sulfuric acid. The
reagent is 40 vol.% LIX 612N-LV, a modified
aldoxime reagent. Figure 6 shows extraction isotherms
at 25℃ and 45℃ for a leach solution containing 3.12
g/L Cu at pH 1.8. The reagent is 17.5 vol.% LIX 937N,
an aldoxime/ketoxime blend having more ketoxime
than aldoxime. In both cases, copper extraction
increases as the temperature increases which is
consistent with previous work[3].
Also, shown in each figure is the stripped organic
values for the reagent at the higher and lower
temperature. For LIX 937N, the stripped organic value
is in equilibrium with an electrolyte having 156 g/L
Table 1 Actual and predicted stripped organic values for various reagents and blends of reagents
Reagent composition (%)
Stripped organic values for
Stripped organic values for
17 vol.% reagent at 41℃
27 vol.% reagent at 35℃
(g/L Cu)
(g/L Cu)
LIX 860N-I
LIX 8180
LIX 612N-LV
Diluent
Actual
Model
Actual
Model
38.3
30.0
26.7
5.0
2.82
2.83
4.44
4.45
54.6
20.3
21.7
3.4
3.43
3.48
5.47
5.52
0.0
0.0
100.0
0.0
2.89
2.90
4.22
4.31
25.0
64.3
0.0
10.7
1.44
1.52
2.30
2.36
12.5
32.1
50.0
5.4
2.30
2.28
3.50
3.54
8.3
21.4
66.7
3.6
2.51
2.51
3.81
3.84
Tsinghua Science and Technology, April 2006, 11(2): 160-164
164
extraction, lower reagent concentration or some
combination of both. However, cooling and heating
aqueous solutions are energy intensive and this could
only happen where energy was essentially free and
easily moved around the circuit for a very low cost.
4
Fig. 5
Fig. 6
Extraction isotherm LIX 612N-LV.
Extraction isotherm LIX 937N.
sulfuric acid and 55g/L Cu which is representative for
1 strip stage. For LIX 612N-LV the organic value is in
equilibrium with an electrolyte having 175 g/L H2SO4
and 39.5 g/L Cu which is representative for 2
countercurrent strip stages.
The isotherm data and strip data were entered into
the Cognis Isocalc® modeling program and circuit
simulations were run. The LIX 612N-LV circuit had 3
countercurrent extraction stages at an advance O/A of
2 using mixer efficiencies of 90%, 92%, and 95% for
extraction stages 1, 2, and 3, respectively. The copper
recovery was 63% at both 25℃ and 40℃. When mixer
efficiencies of 99% were used in the model at 40℃,
the copper recovery increases to 65%.
The LIX 937N circuit was a series parallel design
with a single parallel stage treating half the leach
solution followed by 2 countercurrent extraction stages
treating the other half of the leach solution at an
advance O/A ratio of 1. Mixer efficiencies were 98%,
96%, and 94% for E parallel, E-2 series, and E-1 series,
respectively. Copper recovery was essentially the same
at 25℃ (90%) and at 45℃ (90.05%). When mixer
efficiencies of 99% were used in the model at 45℃,
the copper recovery increases to 91.3%.
In most copper solvent extraction plants the
temperature in stripping is warmer than the
temperature in extraction. If the temperatures could be
reversed, some benefit would result: higher copper
Conclusions
The Cognis strip model can be used to predict the
stripped organic value for almost any oxime copper
solvent reagent or blend of reagents under a wide variety of conditions. An increase in temperature favors
copper extraction and this results in a higher stripped
organic and a steeper extraction isotherm. In an actual
SX plant, the increase in copper extraction is offset by
the higher stripped organic and copper recovery does
not change provided the mixer efficiencies are the
same. Since higher mixer efficiencies can be expected
at higher temperatures, plants operating at higher temperatures will achieve slightly higher copper recovery
than they would at lower temperatures, all other conditions remaining the same. Cognis has run several other
continuous mini-plant circuits on leach solutions at
room temperature and at 40℃ to 45℃. In all cases,
greater copper recovery was achieved at higher temperature. In some cases copper recovery was slightly
above what is theoretically possible based on a roomtemperature isotherm. This indicates that there may be
circumstances where the increased copper extraction at
higher temperature more than overcomes the increased
strip organic value, but not by much in any case.
Acknowledgements
The authors are grateful to Cognis for permission to publish this
paper.
References
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ALTA 2002 Copper-7, Treatment of Sulfide Concentrates
and Ores. ALTA Metallurgical Services, Melbourne,
Australia, 2002.
[2] Marsden J O, Brewer R E, Hazen N. In: Young C A,
Alfantazi A M, Anderson C G, Dreisinger D B, Harris B,
James A, eds. Hydrometallurgy, Fifth International Conference in Honor of Professor Ian Ritchie, Vol. 2: Electrometallurgy and Environmental Hydrometallugy. TMS, 2003.
[3] Alguacil F J, Cobo A, Alonso M. Copper separation from
nitrate/nitric acid media using Acorga M5640 extractant
(Part 1): Solvent extraction study. Chemical Engineering
Journal, 2002, 85: 259-263.