U.S. patent application number 11/265684 was filed with the patent office on 2006-06-08 for processes for recovering metals from ores using organic solvent extraction and aqueous stripping at selected temperature differentials.
Invention is credited to Burrel Boley, Philip Crane, Dustin Gordon, Gary A. Kordosky, Andrew Nisbett, R. Brantley Sudderth, Michael J. Virnig.
Application Number | 20060117908 11/265684 |
Document ID | / |
Family ID | 36565585 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060117908 |
Kind Code |
A1 |
Virnig; Michael J. ; et
al. |
June 8, 2006 |
Processes for recovering metals from ores using organic solvent
extraction and aqueous stripping at selected temperature
differentials
Abstract
The disclosed invention concerns a process comprising: (a)
providing a pregnant leach solution comprising copper values; (b)
contacting the pregnant leach solution with an organic phase
comprising a copper extractant at an extraction temperature,
T.sub.ext, to form a loaded organic phase comprising the metal
values; (c) contacting the loaded organic phase with an aqueous
stripping solution at a stripping temperature, T.sub.strip, to form
a copper-enriched stripping solution; wherein the difference in
temperature (.DELTA.T) between the stripping temperature and the
extraction temperature according to equation (I):
.DELTA.T=T.sub.strip-T.sub.ext is less than or equal to about
10.degree. C. In other increasingly more preferred embodiments of
the invention, the difference in temperature (.DELTA.T) is less
than or equal to about 5.degree. C., less than or equal to about
2.5.degree. C., less than or equal to about 0.degree. C., less than
or equal to about -5.degree. C., and less than or equal to about
-10.degree. C. Also disclosed are economic means to manipulate the
extraction, strip, and electrowinning temperatures to achieve these
temperature differentials.
Inventors: |
Virnig; Michael J.; (Tucson,
AZ) ; Sudderth; R. Brantley; (Tucson, AZ) ;
Crane; Philip; (Victoria, AU) ; Nisbett; Andrew;
(Tucson, AZ) ; Boley; Burrel; (Tucson, AZ)
; Gordon; Dustin; (Tucson, AZ) ; Kordosky; Gary
A.; (Tucson, AZ) |
Correspondence
Address: |
COGNIS CORPORATION;PATENT DEPARTMENT
300 BROOKSIDE AVENUE
AMBLER
PA
19002
US
|
Family ID: |
36565585 |
Appl. No.: |
11/265684 |
Filed: |
November 2, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60632759 |
Dec 3, 2004 |
|
|
|
Current U.S.
Class: |
75/721 ; 75/740;
75/743 |
Current CPC
Class: |
C22B 15/0084 20130101;
C22B 15/0071 20130101; C22B 3/30 20210501; Y02P 10/20 20151101 |
Class at
Publication: |
075/721 ;
075/740; 075/743 |
International
Class: |
C22B 15/00 20060101
C22B015/00 |
Claims
1. A copper recovery process comprising: (a) providing a pregnant
leach solution comprising copper values; (b) contacting the
pregnant leach solution with an organic phase comprising a copper
extractant at an extraction temperature, T.sub.ext, to form a
loaded organic phase comprising the copper values; (c) contacting
the resulting loaded organic phase with an aqueous stripping
solution at a stripping temperature, T.sub.strip, to form a
copper-enriched stripping solution; wherein the difference in
temperature (.DELTA.T) between the stripping temperature and the
extraction temperature according to equation (I):
.DELTA.T=T.sub.strip-T.sub.ext (I) is less than or equal to about
10.degree. C.
2. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
7.5.degree. C.
3. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
5.degree. C.
4. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
2.5.degree. C.
5. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
0.degree. C.
6. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
-2.5.degree. C.
7. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
-5.degree. C.
8. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
-7.5.degree. C.
9. The copper recovery process according to claim 1, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
-10.degree. C.
10. The copper recovery process according to claim 1, wherein one
of more heat exchangers are utilized to lower the stripping
temperature of the aqueous stripping solution.
11. The copper recovery process according to claim 10, wherein the
one or more heat exchangers transfer heat from a lean electrolyte
exiting an electrowinning stage to the copper-enriched stripping
solution such that a cooled lean electrolyte is formed and the
cooled lean electrolyte is used as at least a portion of the
aqueous stripping solution.
12. The copper recovery process according to claim 10, wherein the
one or more heat exchangers transfer heat from a lean electrolyte
exiting an electrowinning stage to a water source such that a
cooled lean electrolyte is formed and the cooled lean electrolyte
is used as at least a portion of the aqueous stripping
solution.
13. The copper recovery process according to claim 1, wherein one
or more heat exchangers are utilized to raise the extraction
temperature of the pregnant leach solution.
14. The copper recovery process according to claim 13, wherein the
one or more heat exchangers transfer heat from a lean electrolyte
exiting an electrowinning stage to the pregnant leach solution.
15. The copper recovery process according to claim 12, wherein the
one or more heat exchangers transfer heat from a heat source
selected from the group consisting of boilers and waste heat gases
to the pregnant leach solution.
16. A copper recovery process comprising: (a) providing a pregnant
leach solution comprising copper values; (b) contacting the
pregnant leach solution with an organic phase comprising a copper
extractant at an extraction temperature, T.sub.ext, to form a
loaded organic phase comprising the copper values; (c) contacting
the resulting loaded organic phase with an aqueous stripping
solution at a stripping temperature, T.sub.strip, to form a
copper-enriched stripping solution; wherein the difference in
temperature (.DELTA.T) between the stripping temperature and the
extraction temperature according to equation (I):
.DELTA.T=T.sub.strip-T.sub.ext (I) is less than or equal to about
10.degree. C., wherein one or more heat exchangers are utilized to
lower the stripping temperature of the aqueous stripping
solution.
17. The copper recovery process according to claim 16, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
-2.5.degree. C.
18. The copper recovery process according to claim 16, wherein the
one or more heat exchangers transfer heat from a lean electrolyte
exiting an electrowinning stage to the copper-enriched stripping
solution such that a cooled lean electrolyte is formed and the
cooled lean electrolyte is used as at least a portion of the
aqueous stripping solution.
19. The copper recovery process according to claim 16, wherein the
one or more heat exchangers transfer heat from a lean electrolyte
exiting an electrowinning stage to a water source such that a
cooled lean electrolyte is formed and the cooled lean electrolyte
is used as at least a portion of the aqueous stripping
solution.
20. A copper recovery process comprising: (a) providing a pregnant
leach solution comprising copper values; (b) contacting the
pregnant leach solution with an organic phase comprising a copper
extractant at an extraction temperature, T.sub.ext, to form a
loaded organic phase comprising the copper values; (c) contacting
the resulting loaded organic phase with an aqueous stripping
solution at a stripping temperature, T.sub.strip, to form a
copper-enriched stripping solution; wherein the difference in
temperature (.DELTA.T) between the stripping temperature and the
extraction temperature according to equation (I):
.DELTA.T=T.sub.strip-T.sub.ext (I) is less than or equal to about
10.degree. C., wherein one or more heat exchangers are utilized to
raise the extraction temperature of the pregnant leach
solution.
21. The copper recovery process according to claim 20, wherein the
difference in temperature (.DELTA.T) is less than or equal to about
-2.5.degree. C.
22. The copper recovery process according to claim 20, wherein the
one or more heat exchangers transfer heat from a lean electrolyte
exiting an electrowinning stage to the pregnant leach solution.
23. The copper recovery process according to claim 20, wherein the
one or more heat exchangers transfer heat from a heat source
selected from the group consisting of boilers and waste heat gases
to the pregnant leach solution.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
from U.S. Provisional application No. 60/632,759, filed Dec. 3,
2004.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] Most metals are obtained by removing those metals from the
ores in which they are found in the ground. One method to initially
separate metal from the ore is known as leaching. The first step in
the leaching process is to contact the mined ore with an aqueous
solution containing a leaching agent. For example, in copper
leaching operations, sulfuric acid in an aqueous solution is
contacted with the copper-containing ore. During this leaching
process, acid in the leach solution is consumed and copper is
dissolved, thereby increasing the copper content of the aqueous
solution.
[0004] The aqueous solution then contains the leached metal in a
dilute form together with other impurities, for example iron. This
aqueous solution (also known as the Pregnant Leach Solution--PLS)
can then be treated via a process referred to as solvent extraction
in which the leach solution is contacted with a non-aqueous
solution containing a metal extraction reagent. The metal
extraction reagent extracts the metal from the aqueous phase into
the non-aqueous phase.
[0005] For example, copper in a dilute aqueous sulfuric acid
solution is commonly extracted in a solvent extraction process by
an oxime based extractant in an organic medium according to the
chemical reaction;
[2R--H].sub.org+[Cu.sup.2++SO.sub.4.sup.2-].sub.aq[R.sub.2Cu].sub.org+[2H-
.sup.++SO.sub.4.sup.2-].sub.aq (1) where R--H is the oxime
extractant. The resultant aqueous solution (also known as
raffinate), depleted in copper and enriched in sulfuric acid, is
returned to the leaching process for further leaching of
copper.
[0006] Since the above chemical reaction (1) is reversible, it
follows that the copper loaded onto the oxime reagent in the
organic medium can then be re-extracted into another aqueous
medium, provided there is sufficient acid in this aqueous medium to
drive the reverse chemical reaction. This is accomplished in a
stage in the overall process known as stripping. The stripping
process involves contacting the organic phase with an aqueous
solution (also referred to as the Lean Electrolyte--LE) having a
high sulfuric acid concentration with some copper. Copper is then
re-extracted from the organic phase into the aqueous solution (also
referred to as Rich Electrolyte--RE) which then has a relatively
high concentration of copper and a lower level of sulfuric
acid.
[0007] The Rich Electrolyte solution is then subjected to a process
referred to as electrowinning, which takes place in what is called
a tankhouse. In electrowinning, the Rich Electrolyte solution is
passed through an electrolytic cell between an anode and a cathode.
The electrical potential placed between the two electrodes causes
copper to be deposited on the surface of the cathode as copper
metal. Sulfuric acid is generated in this process. The aqueous
solution (now available for recycling as the Lean Electrolyte),
somewhat depleted in copper and somewhat enriched in sulfuric acid,
can be returned to the solvent extraction strip stage to again
strip more copper off the organic medium. The leaching, solvent
extraction/stripping and electrowinning of copper is a common,
continuous practice as a method to recovery copper from ores.
[0008] The solvent extraction process effectively concentrates the
leached copper species into an aqueous solution (electrolyte) that
is relatively high in copper and relatively low in other
impurities, for example iron. This allows the electrowinning
process to produce high quality copper metal at a high electrical
current efficiency.
[0009] Leaching of low grade copper ores is typically carried out
in heap or dump leaching operations. In dump leaching operations,
the ore is typically placed in a natural geological feature such as
a canyon. The depth of the ore in the dump can range from
relatively shallow to a few hundred meters in thickness. Heap
leaching is carried out on permanent pads or on on-off pads. In the
case of permanent pads, the depth of the ore can be similar to that
in a dump. On-Off pads are designed so that the ore is placed on
the prepared pad in a layer several meters thick, leached, allowed
to drain and then removed from the pad. In these types of leaching
systems, fresh aqueous leaching agent and/or recycled acidic
raffinate solution is applied to the tops of the heaps or dump and
allowed to drain down through the ore. It is then collected at the
bottom of the heap or dump and fed as PLS to the solvent extraction
operation.
[0010] The temperature of the PLS exiting the copper leaching
system will be dependent on the heat build up in the dump or heap.
This in turn is dependent on the size of the dump or heap. The
larger and deeper the size of the leaching system the less heat
that will be lost by radiation to the environment. Heat loss will
also be dependent on the local climatic conditions. If sulfide ores
are present, bioleaching of these sulfide minerals will contribute
significant amounts of heat to the dump or heap. In general, the
temperature of the PLS exiting the leaching system will typically
vary from about 8.degree. C. to about 30.degree. C.
[0011] In agitation leaching, which is commonly carried out in
large vats where an ore is mixed with fresh aqueous leaching agent
and/or recycled acidic raffinate solution, the resulting PLS can
then be separated from the leached residue via a series of
clarification operations and fed to solvent extraction. The ore
grade is typically higher than in the case of ores fed to heap or
dump leaching. Due to the nature of the operation, the temperature
of the copper PLS will typically vary from about 15.degree. C. to
about 30.degree. C. The solvent stripping step is normally carried
out at temperatures above 30 deg. C. Therefore, existing solvent
extraction plants generally operate with a lower temperature in the
extraction stages than in the stripping stage(s).
[0012] Electrowinning of copper is typically maintained at
temperatures in the 40.degree. C. to 50.degree. C. range to insure
the production of high grade copper cathode. As a result,
electrowinning tankhouses are typically outfitted with boilers to
allow for some heat input into the electrolyte to insure that the
electrolyte temperature is maintained in the correct range. To
minimize heat loss from the electrowinning tankhouse, the Lean
Electrolyte line going to stripping and the Rich Electrolyte return
line from stripping are passed through interconnected heat
exchangers so that the warm Lean Electrolyte is used to warm the
Rich Electrolyte returning to the electrowinning tankhouse, thus
minimizing energy losses from the tankhouse.
BRIEF SUMMARY OF THE INVENTION
[0013] It has now been surprisingly found that there are
significant advantages in copper recovery operations with elevated
temperatures during the extraction stage and/or lowered
temperatures during the stripping stage. More particularly,
advantages in copper recovery operations are realized according to
the present invention by decreasing the temperature differential
between the temperature during stripping and the temperature during
extraction.
[0014] In general, the present invention can also be described in
terms of the following equation: T.sub.Strip-T.sub.Ext=.DELTA.T
where T stands for the temperature in .degree. C. To maximize the
advantages achieved in a solvent extraction process, the value of
.DELTA.T is minimized, or preferably driven to a negative value
.DELTA.T is no more than 15.degree. C. A preferred value of
.DELTA.T is </=10.degree. C., a more preferred value is
</=7.5.degree. C., a still more preferred value is
</=5.degree. C., a still more preferred value is
</=2.5.degree. C., a still more preferred value is
</=0.degree. C., a still more preferred value is
</=-2.5.degree. C., a still more preferred value is
</=-5.degree. C., a still more preferred value is
</=-7.5.degree. C., and the most preferred value is
</=-10.degree. C.
[0015] One embodiment of the present invention includes a process
comprising: (a) providing a pregnant leach solution comprising
copper values; (b) contacting the pregnant leach solution with an
organic phase comprising a copper extractant at an extraction
temperature, T.sub.ext, to form a loaded organic phase comprising
the metal values; (c) contacting the loaded organic phase with an
aqueous stripping solution at a stripping temperature, T.sub.strip,
to form a copper-enriched stripping solution; wherein the
difference in temperature (.DELTA.T) between the stripping
temperature and the extraction temperature according to equation
(I): .DELTA.T=T.sub.strip-T.sub.ext (I) is less than or equal to
about 10.degree. C. In other increasingly more preferred
embodiments of the present invention, the difference in temperature
(.DELTA.T) is less than or equal to about 7.5.degree. C., less than
or equal to about 5.degree. C., less than or equal to about
2.5.degree. C., less than or equal to about 0.degree. C., less than
or equal to about -2.5.degree. C., less than or equal to about
-5.degree. C., less than or equal to about -7.5.degree. C., and
less than or equal to about -10.degree. C.
[0016] The phrases "difference in temperature", "(.DELTA.T)" and
"temperature differential", as used herein, are synonymous and
interchangeable with reference to the difference, in degrees
Celsius, between the temperature during the stripping stage and the
temperature during the extraction stage.
[0017] Lowering the temperature during the stripping stage results
in more efficient stripping of the organic phase as evidenced by a
lower copper concentration in the stripped organic. On the other
hand, increasing the temperature during the extraction stage
results in more efficient use of the oxime extractant as evidenced
by a higher copper concentration in the loaded organic. Lowering
the temperature during the stripping stage and/or increasing the
temperature during the extraction stage increases the net transfer
of copper per unit time, assuming that fiords are constant.
[0018] Thus, processes according to the present invention can be
used to (1) increase overall copper production, (2) decrease
overall oxime extractant concentration while maintaining copper
production constant, or (3) decrease sulfuric acid concentration in
the electrolyte while maintaining copper production constant or (4)
some combination of two or more of these beneficial effects.
[0019] In another aspect, the invention provides economic means to
manipulate the extraction, strip, and electrowinning
temperatures.
DETAILED DESCRIPTION OF THE INVENTION
[0020] All numbers expressing quantities of ingredients or reaction
conditions used herein are to be understood as modified in all
instances by the term "about".
[0021] The following detailed description provides an explanation
of the present invention in terms of certain preferred embodiments
involving the recovery of copper from copper ores. However, it is
to be understood that the present invention applies to various
metal recovery processes employing leaching, extraction and
stripping operations, and may be advantageously employed in the
recovery of various different metals from a variety of ores, and in
metal recovery plants utilizing any configuration of multiple
extraction and stripping stages arranged in series, in parallel,
nested, or any combination thereof.
[0022] In certain preferred embodiments of the present invention
directed to processes for recovering copper from copper-containing
ores, the ores may be either primarily oxide type copper minerals,
a mixture of oxide and sulfide type copper minerals, or sulfide
type copper minerals. For a more complete description of the
minerals including leaching chemistry, see the 1996 SME Short
Course--Copper Heap Leach Notes, 1996 SME Annual Meeting, Phoenix,
Ariz.
[0023] The preferred copper extractants are those based on phenolic
oximes (such as those disclosed in U.S. Pat. Nos. 4,978,788,
5,176,843 and 6,395,062) including ketoximes such as
2-hydroxy-5-nonylacetophenone oxime and the aldoximes such as
5-nonylsalicylaldoxime, by themselves or as mixtures with one
another or with a modifier (such as those modifiers and oxime
combinations disclosed in U.S. Pat. No. 6,231,784). Also preferred
would be mixtures of an aldoxime with a modifier present.
[0024] To illustrate some of the advantages of the present
invention, as applied to copper recovery operations, one can first
look at the effect of lowering the temperature during the stripping
stage. A case study was carried out using the ISOCALC.RTM. Solvent
Extraction Modeling Software developed by Cognis Corporation. Using
this software allows one to predict with great accuracy the
performance that can be achieved in a continuous solvent extraction
plant. The program is based on a very large set of actual isotherm
data determined at 25.degree. C. for a variety of LIX.RTM.
reagents, which are generally oxime-containing metal extraction
reagents, from which an algorithm was determined which serves as a
foundation for the modeling. The model was used to determine an
extraction isotherm for a conventional plant consisting of 2 stages
of extraction in series and 1 stage of stripping. Using an average
set of values from commercially operating plants, the PLS was
assumed to contain 6 gpl of copper, 70 gpl of sulfate and have a pH
of 1.9. Similarly, the organic phase was assumed to be 25% (v/v)
LIX.RTM. 984N in a typical aliphatic hydrocarbon diluent. LIX.RTM.
984N is 0.77 M in 2-hydroxy-5-nonylacetophenone oxime and 0.88 M in
5-nonylsalicylaldoxime. The level of the copper on the stripped
organic at a given temperature was taken from a mathematical model
derived from a collection of stripping isotherms determined at
different temperatures and reagent concentrations. The stripped
organic value was plugged into the ISOCALC.RTM. Solvent Extraction
Modeling Software and used to model the performance of a plant
operating within these parameters.
[0025] Using an average set of values from commercially operating
plants, the Lean Electrolyte composition was assumed to be 170 gpl
sulfuric acid and 36 gpl copper. The Rich Electrolyte likewise
contained 45 gpl copper and the temperature in stripping was
assumed to be 45.degree. C. For the base case, the targeted copper
recovery was assumed to be 90% to achieve a total annual copper
production of 40,000 metric tons per year. The results summarized
in Table 1 illustrate the benefits in copper production, afforded
by the invention simply by lowering the temperature in the strip
stage while keeping all the other process parameters the same.
TABLE-US-00001 TABLE 1 Stripped Cu Cu NT* T.sub.Strip Org Recovery
(gpl Cu/% (v/v) .DELTA. T Cu Prod Case (.degree. C.) (gpl Cu) (%)
Extract) (.degree. C.) (tons/yr) 1 45 5.36 90.08 0.216 +20 40,000 2
40 5.18 90.75 0.218 +15 40,306 3 35 4.99 91.43 0.219 +10 40,608 4
30 4.80 92.08 0.221 +5 40,897 5 25 4.58 92.75 0.223 0 41,195 6 20
4.36 93.36 0.224 -5 41,466 *NT is net transfer by the organic
phase. The greater the value of NT, the more efficiently the
extractant is being used and the greater the copper recovery.
[0026] According to the invention, lowering the stripping
temperature from 45.degree. C. to 40.degree. C. (Table 1, Case 1
vs. Case 2) results in an increase of 306 tons of copper. At
current copper prices of .about.$1.30/lb, this represents an
additional $876,751 of revenue.
[0027] Depending on the site specific circumstances of a copper
solvent extraction plant, it may not be feasible to produce more
copper as described in the above paragraph. As can be seen in Table
1, lowering the temperature in strip results in an increase in
copper NT. If it is not feasible to increase the amount of copper
transferred to electrowinning, according to the invention one is
alternatively able to lower the concentration of the oxime
extractant in the organic phase while still maintaining the overall
copper recovery at 90%. This is a significant advantage in terms of
cost of the organic phase.
EXAMPLE 1
[0028] Using the ISOCALC.RTM. Solvent Extraction Modeling Software
one can also evaluate the effect of lowering the reagent
concentration and strip temperature while maintaining copper
recovery and all other factors constant. The results are summarized
in Table 2. TABLE-US-00002 TABLE 2 Stripped Cu Cu NT* T.sub.Strip
Org Recovery (gpl Cu/%(v/v) .DELTA. T [Oxime] Case (.degree. C.)
(gpl Cu) (%) Extract) (.degree. C.) (% (v/v)) 1 45 5.36 90.08 0.216
+20 25 2 40 5.03 90.08 0.223 +15 24.2 3 35 4.70 90.07 0.231 +10
23.4 4 30 4.38 90.03 0.239 +5 22.6 5 25 4.07 90.08 0.247 0 21.9 6
20 3.75 90.04 0.256 -5 21.1
Every 5.degree. C. decrease in the strip temperature allows one to
reduce the extractant concentration by 0.8% (v/v), a reduction of
.about.3.2-3.8% relative.
[0029] According to the invention, there is another potential
benefit to lowering the temperature during the stripping stage.
Since the organic strips more readily at lower temperature, one can
also effectively lower the acid concentration and still achieve the
desired copper recovery. Lowering the acid concentration in the
electrolyte has a couple of benefits. Due to the build up of
impurities in the electrolyte, it is necessary to bleed a portion
of the electrolyte from the tankhouse periodically to control the
level of these impurities. The acid lost in the bleed must be
replaced with fresh acid representing a cost. Lowering the acid
content of the electrolyte lowers this cost. Additionally, one can
produce higher quality copper cathode when plating is carried out
at lower acid concentrations.
EXAMPLE 2
[0030] To further illustrate the invention, one can look at an
additional set of case studies using the ISOCALC.RTM. Solvent
Extraction Modeling Software with actual extraction isotherm data
and experimentally determined strip data. Two sets of extraction
isotherm data were determined at 25.degree. C. and 45.degree. C.
along with the corresponding strip points at these
temperatures.
[0031] The organic solution was 0.093 M in 5-nonylsalicylaldoxime
and 0.189 M in 2-hydroxy-5-nonylacetophenone oxime in a typical
aliphatic hydrocarbon diluent. The PLS contained 3.08 gpl Cu at a
pH of 1.8. The above organic solution was contacted vigorously with
the PLS solution at various organic to aqueous ratios for
sufficient time to achieve equilibrium. The resulting equilibrated
organic phases and the corresponding aqueous phases were analyzed
for copper by atomic absorption spectroscopy. The results are
summarized in Tables 3 and 4.
[0032] The copper max load against the PLS was determined by
successively contacting the organic phase 3 times with fresh
volumes of PLS at an O/A=1 at the desired temperature. The organic
was assayed for copper by atomic absorption spectroscopy. The
stripped organic representing 1 stage of stripping was determined
in a similar fashion by equilibrating the organic with a synthetic
rich electrolyte containing 55 gpl of copper and 157 gpl of
sulfuric acid. The data is summarized in Table 5. TABLE-US-00003
TABLE 3 Extraction isotherm at 25.degree. C. Organic/Aqueous
[Cu].sub.Aq (gpl Cu) [Cu].sub.Org (gpl Cu) 7/1 0.05 1.98 2/1 0.08
3.13 1/1 0.16 4.66 1/1.5 0.32 6.08 1/2 0.54 6.83 1/2.5 0.80 7.31
1/3.5 1.27 7.97 1/6 1.94 8.37
[0033] TABLE-US-00004 TABLE 4 Extraction isotherm at 45.degree. C.
Organic/Aqueous [Cu].sub.Aq (gpl Cu) [Cu].sub.Org (gpl Cu) 7/1 0.04
1.98 2/1 0.05 3.10 1/1 0.10 4.66 1/1.5 0.22 6.07 1/2 0.44 7.16
1/2.5 0.75 7.83 1/3.5 1.30 8.41 1/6 2.01 8.89
[0034] TABLE-US-00005 TABLE 5 Summary of Copper Max Load and
Stripped Organic Values Temperature Cu Max Load Stripped Organic
(.degree. C.) (gpl Cu) (gpl Cu) 25 8.76 2.21 45 9.46 2.91
[0035] Using the above data in the ISOCALC.RTM.Solvent Extraction
Modeling Software, the performance of a copper solvent extraction
plant consisting of 2 stages of extraction in series
(counter-current), 1 stage of extraction in parallel and 1 stage of
stripping. The results are summarized in Table 6. TABLE-US-00006
TABLE 6 Cu Cu NT* Cu T.sub.Strip Recovery (gpl Cu/% (v/v) .DELTA. T
Production Case (.degree. C.) T.sub.Extract (%) Extract) (.degree.
C.) (tons/yr) 1 45 25 84.87 0.299 +20 40,000 2 25 25 90.02 0.317 0
42,408 3 45 45 89.54 0.316 0 42,274 4 25 45 93.01 0.328 -20
43,879
Case 1 represents the base case which is typical of current
practice. Cooling the strip from 45.degree. C. to 25.degree. C.
while maintaining the extraction temperature 25.degree. C. (Case 1
vs Case 2) results in an additional 2,408 tons of copper production
(a 6% increase) similar to what was seen in the first example.
Increasing the temperature of extraction from 25.degree. C. to
45.degree. C. while maintaining the strip temperature at 45.degree.
C. (Case 1 vs Case 3) results in a similar increase in production
as in Case 1 vs Case 2.
[0036] The effect of lowering the strip temperature from 45.degree.
C. to 25.degree. C. and at the same time increasing the temperature
of extraction from 25.degree. C. to 45.degree. C. is seen in
comparing Case 1 with Case 4, results in a 3,879 ton (9.7%
relative) increase in copper production. Clearly, there are
significant benefits associated with minimizing the value of
.DELTA.T to the point of driving it towards a negative value.
[0037] As previously discussed, manipulating the temperatures in
stripping can provide the overall copper recovery operation with
the flexibility to operate with lower reagent concentrations or
with lower acid concentrations in the Lean Electrolyte while
maintaining copper recovery/production constant. Increasing the
temperature in extraction also provides the operation with the
flexibility to operate at lower reagent concentrations. It also
offers the possibility of treating a PLS with a higher acid
concentration while maintaining copper recovery/production
constant. It also provides the flexibility to permit treating a PLS
with a higher copper content without increasing reagent
concentration while maintaining copper recovery constant.
[0038] Another aspect of the invention provides economic means to
manipulate the extraction temperature (T.sub.Ext) and the strip
temperature (T.sub.strip). The exact processes by which one lowers
the temperature of the electrolyte prior to the stripping stage or
increases the temperature of the PLS prior to the extraction stage
will depend on site specific considerations. Some suitable
mechanisms include, but are not limited to the following.
EXAMPLE 4
[0039] (A) The temperature of the electrolyte can be lowered using
an external cooling source. Current practice involves using
interconnected heat exchangers to transfer heat from the Lean
Electrolyte as it exits the electrowinning tank house to the
incoming Rich Electrolyte coming from stripping to minimize heat
loss from the electrowinning tank house. This results in cooling
the Lean Electrolyte a few degrees. The Lean Electrolyte can be
cooled more effectively by either coupling the current heat
exchanger with an external cooling source such as an evaporative
cooler, a compressor based refrigeration unit or using a low
temperature fluid stream, for example, the PLS or makeup water.
Since heat must be returned to the tank house, it may be
advantageous to install a second heat exchanger on the Lean
Electrolyte line downstream from that used to transfer heat to the
Rich Electrolyte. This second heat exchanger would then be coupled
with an external cooling source such as an evaporative cooler, a
mechanical refrigeration unit, or using a low temperature fluid
stream such as PLS or makeup water. The Rich Electrolyte must be
reheated prior to return to the electrowinning tank house. This can
be done partially by passing through a heat exchanger coupled to
the Lean Electrolyte as previously discussed. It can be reheated
using an external energy source such as a boiler, solar heating, or
alternatively by interchanging heat between a high temperature
fluid stream such as an stream from a copper concentrate leach
system, for example, an autoclave or a bioreactor leach system. The
advantage of using the autoclave leach system or the bioreactor
leach system is that it also produces additional copper that can be
recovered in addition to the heat. One could also use the waste
heat from a sulfur burner, which would also allow one to produce
sulfuric acid for use in the process.
[0040] (B) The temperature of the PLS can be increased by using it
as the cooling fluid in a heat exchanger with the Lean Electrolyte
before passing it to extraction. It can be heated using an external
energy source such as a boiler, solar heating, or alternatively by
interchanging heat between a high temperature fluid stream such as
an stream from a copper concentrate leach system, for example, an
autoclave or a bioreactor leach system. The advantage of using the
autoclave leach system or the bioreactor leach system is that it
also produces additional copper that can be recovered in addition
to the heat. One could simply dilute cold PLS from a heap or dump
leaching operation with the hot discharge from a copper concentrate
leach system. One could also use the waste heat from a sulfur
burner, which would also allow one to produce sulfuric acid for use
in the process.
[0041] (C) One could also take steps to minimize heat loss from the
PLS by covering PLS ponds and catchments to minimize evaporation
and radiant heat loss.
[0042] Clearly, as described above, there are a number of potential
ways to alter the temperature balance in a solvent extraction
plant. There are undoubtedly others that would be understood by one
of ordinary skill in the art based upon the foregoing
description.
[0043] A further extension of this invention is the concept of
simply replacing the current boilers used to heat the electrolyte
by use of the waste heat from copper concentrate leaching systems
such as autoclave leach systems or bioreactor leach systems. One
could also use the waste heat from a sulfur burner.
[0044] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
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