U.S. patent application number 10/587648 was filed with the patent office on 2008-02-14 for solvent extraction process for separating cobalt and/or manganese from impurities in leach solutions.
This patent application is currently assigned to Commonwealth Scientific And Industrial Research Organisation. Invention is credited to Chu Yong Cheng, Mark Daniel Urbani.
Application Number | 20080038168 10/587648 |
Document ID | / |
Family ID | 34830692 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080038168 |
Kind Code |
A1 |
Cheng; Chu Yong ; et
al. |
February 14, 2008 |
Solvent Extraction Process For Separating Cobalt And/Or Manganese
From Impurities In Leach Solutions
Abstract
A process for the separation of cobalt and/or manganese from
impurity elements selected from one or more of calcium and
magnesium contained in a leach solution, the process comprising the
step of subjecting the leach solution to solvent extraction using
an organic solution of a carboxylic acid such as Versatic 10 and a
hydroxyoxime such as LIX 63, optionally together with a
stabilzer.
Inventors: |
Cheng; Chu Yong; (South
Lake, AU) ; Urbani; Mark Daniel; (Wattle Grove,
AU) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Commonwealth Scientific And
Industrial Research Organisation
Campbell
AU
|
Family ID: |
34830692 |
Appl. No.: |
10/587648 |
Filed: |
January 28, 2005 |
PCT Filed: |
January 28, 2005 |
PCT NO: |
PCT/AU05/00088 |
371 Date: |
April 18, 2007 |
Current U.S.
Class: |
423/24 ; 423/109;
423/139; 423/49 |
Current CPC
Class: |
C22B 23/0453 20130101;
Y02P 10/234 20151101; C22B 3/0017 20130101; C22B 3/0028 20130101;
Y02P 10/20 20151101; C22B 47/0081 20130101 |
Class at
Publication: |
423/24 ; 423/109;
423/139; 423/49 |
International
Class: |
C22B 3/40 20060101
C22B003/40; C22B 23/00 20060101 C22B023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2004 |
AU |
2004900457 |
Jul 27, 2004 |
AU |
2004904165 |
Oct 29, 2004 |
AU |
2004906242 |
Claims
1. A process for the separation of cobalt and/or manganese from
impurity elements selected from one or more of calcium and
magnesium contained in a leach solution, or for separating cobalt
from manganese contained in a leach solution, the process
comprising the step of subjecting the leach solution to solvent
extraction using an organic solution of a carboxylic acid and an
aliphatic hydroxyoxime.
2. The process of claim 1, wherein cobalt poisoning as a result of
oxidation of cobalt(II) to cobalt(III) is avoided.
3. The process of claim 1, wherein the solvent extraction of the
leach solution with the organic solution produces an organic phase
and an aqueous raffinate, and wherein all of the organic phase is
subjected to stripping with an acid solution to strip cobalt from
the organic phase.
4. The process of claim 3, wherein the stripping with the acid
solution is preceded by scrubbing of the organic phase.
5. The process of claim 3, wherein the stripping with the acid
solution is preceded by a selective stripping stage.
6. The process of claim 1, wherein the organic solution displays
fast extraction kinetics for copper, cobalt, zinc and
manganese.
7. The process of claim 1, wherein the organic solution is in
contact with the leach solution for a period of 5 minutes or
less.
8. The process of claim 7, wherein the organic solution is in
contact with the leach solution for a period of 3 minutes or
less.
9. The process of claim 7, wherein the organic solution is in
contact with the leach solution for a period of 2 minutes or
less.
10. The process of claim 1, wherein the organic solution comprises
a stabilizer against hydroxyoxime degradation.
11. The process of claim 10, wherein the stabilizer reduces
oxidation and/or hydrolysis of the hydroxyoxime.
12. The process of claim 10, wherein the stabilizer is an
antioxidant.
13. The process of claim 10, wherein the stabilizer is an
alkylphenol.
14. The process of claim 1, wherein the leach solution contains
little nickel.
15. The process of claim 1, wherein the leach solution contains
cobalt and/or manganese, together with impurity elements selected
from one or more of calcium, magnesium, (manganese) and chloride,
optionally together with copper and/or zinc.
16. The process of claim 1, wherein, the leach solution contains
the following levels of elements: TABLE-US-00004 Ni: 0-100 ppm Co:
100 ppm-5 g/L Cu: 0-100 ppm Zn: 0.2-2 g/L Ca: 1 ppm-saturated Mn:
0.2-50 g/L Mg: 1 ppm-100 g/L
17. The process of claim 1, wherein the leach solution is a
solution that has been subjected to a preliminary iron and/or
aluminium precipitation step to precipitate out iron and/or
aluminium to leave an aqueous leach solution containing the target
elements and impurity elements.
18. The process of claim 1, wherein the carboxylic acid is
2-methyl, 2-ethyl heptanoic acid or a cationic exchange extractant
having extraction characteristics similar to 2-methyl, 2-ethyl
heptanoic acid.
19. The process of claim 1, wherein the hydroxyoxime is a chelating
.alpha.-hydroxyoxime.
20. The process of claim 1, wherein the leach solution contains
cobalt and manganese, and the pH of the aqueous phase in the
solvent extraction step is maintained in the range of from 5.5 to
7.0 to effect extraction of the cobalt and manganese into the
organic phase.
21. The process of claim 20, wherein the pH of the aqueous phase in
the solvent extraction step is maintained in the range of from 5.8
to 6.3.
22. The process of claim 20, wherein the organic phase containing
cobalt and manganese is subjected to selective stripping to
separate to a significant extent the cobalt from the manganese.
23. The process of claim 22, wherein the selective stripping
comprises contacting the organic phase from the solvent extraction
with an acidic aqueous solution to yield (a) a loaded strip liquor
containing manganese and (b) a selectively stripped organic
solution containing cobalt.
24. The process of claim 23, wherein the acidic aqueous solution
used in the selective stripping has a pH in the range of 4.0 to
5.0.
25. The process of claim 1, wherein the leach solution contains
cobalt and manganese, and the pH of the aqueous phase in the
solvent extraction step is maintained in the range of from 3.5 to
5.0 to effect extraction of cobalt into the organic phase and
rejection of manganese to the aqueous phase.
26. The process of claim 23, wherein the cobalt is recovered from
the organic phase by bulk stripping.
27. The process of claim 1, wherein the leach solution comprises
zinc and/or copper, the zinc and/or copper are extracted into the
organic phase with the cobalt in the solvent extraction step, and
the zinc and/or copper are separated from the cobalt by ion
exchange.
28. The process of claim 1, wherein the leach solution comprises
manganese and a low level or no cobalt, and the manganese is
extracted into the organic phase to effect separation of manganese
from the impurity elements calcium and/or magnesium.
29. The process of claim 1, wherein scrubbing is conducted on the
organic phase after each solvent extraction.
30. A process for the separation of zinc, copper and cobalt from
impurity elements selected from one or more of manganese, calcium
and magnesium contained in a leach solution, the process comprising
the step of subjecting the leach solution to solvent extraction
using an organic solution of a carboxylic acid and an aliphatic
hydroxyoxime.
31. The process of claim 30, wherein cobalt poisoning as a result
of oxidation of cobalt(II) to cobalt(III) is avoided.
32. The process of claim 30, wherein the solvent extraction of the
leach solution with the organic solution produces an organic phase
and an aqueous raffinate, and wherein all of the organic phase is
subjected to stripping with an acid solution to strip cobalt from
the organic solution.
33. The process of claim 30, wherein the organic solution displays
fast extraction kinetics for copper, cobalt, zinc and
manganese.
34. A product recovered by the process according claim 1.
Description
[0001] The present invention relates to a process for separating
cobalt and/or manganese from calcium and magnesium contained in an
aqueous solution such as an aqueous leach solution, and for
recovering the cobalt and/or manganese where desired.
[0002] The world mineral industry is experiencing an unprecedented
interest in metal extraction from laterite and sulphide ores
through hydrometallurgical processes. Commonly, the
hydrometallurgical process involves grinding, leaching and solvent
extraction (SX), with recovery of product via precipitation or
reduction processes. The intensity of the leaching process
(temperature, pressure, bio) depends on the nature of the ore
(mineralogy, grade), the distribution of the metal(s) to be
recovered and the particle size reduction achieved during grinding.
Leach solutions often contain copper, nickel, cobalt and zinc
(and/or manganese) as metals to be recovered (target metals), with
calcium, magnesium, iron and aluminium (and manganese if not to be
recovered) as impurity metals to be rejected. Iron (as ferric) and
aluminium are often removed by precipitation at low pH (pH 2.5-5.0)
prior to SX.
[0003] Separations of industrial significance that have proven to
be particularly troublesome include: [0004] the separation of
cobalt (and optionally nickel) from manganese (and calcium and
magnesium), where manganese is to be rejected, and [0005] the
separation of manganese (and cobalt and nickel) from calcium and
magnesium, where manganese is to be recovered.
[0006] Traditionally, sulphide or hydroxide precipitation followed
by re-leach processes have been used by industry to effect these
separations.
[0007] Drawbacks of sulphide precipitation include: [0008] The
separation of manganese from cobalt by sulphide precipitation is
incomplete and causes problems in the downstream processes. [0009]
The re-leaching of sulphides needs high temperature and pressure,
indicating high capital and operating costs. [0010] The separation
of copper and zinc from nickel and cobalt needs separate
processes.
[0011] The drawbacks of the hydroxide precipitation process
include: [0012] The use of magnesia as precipitation agent (if used
to prevent gypsum formation) adds cost to the operation. [0013]
Manganese is partially precipitated. [0014] The use of ammoniacal
leaching (if used) to separate cobalt from manganese results in
complexity of the flowsheet and causes serious problems in the
downstream processes. [0015] Ammonia is expensive and the scrubbing
and recovery of ammonia are difficult. [0016] The separation of
copper and zinc from nickel and cobalt needs separate
processes.
[0017] It is an object of the invention to provide alternative
processes for: [0018] Separating cobalt from calcium and magnesium,
and optionally manganese, especially for solutions deficient in
nickel, and [0019] Separating manganese from calcium and magnesium,
especially for solutions deficient in cobalt and nickel.
SUMMARY OF THE INVENTION
[0020] The present invention is generally based on the development
of an organic solution of a carboxylic acid and a hydroxyoxime
which is effective in shifting the pH isotherms of nickel, cobalt,
copper, zinc, magnesium, manganese and calcium in such a way as to
enable separation of certain groups of these elements from each
other. In particular, the isotherms of the elements copper, zinc,
nickel and cobalt are separated from the isotherm of manganese to
allow effective separation of manganese from these elements.
Further, the isotherm of manganese is sufficiently separated from
the isotherms of calcium and magnesium to allow effective
separation of manganese from calcium and magnesium. Thus, when used
in combination with certain leach solutions containing appropriate
levels of elements, and in appropriate pH conditions, it becomes
possible to separate (and optionally thereafter recover) cobalt
and/or manganese from (manganese) calcium and magnesium. Under some
conditions, the organic solution of carboxylic acid and
hydroxyoxime may be susceptible to degradation, particularly with
respect to the hydroxyoxime component. Accordingly, a stabilizer
may advantageously be added.
[0021] According to the present invention there is provided a
process for the separation of cobalt and/or manganese from impurity
elements selected from one or more of calcium and magnesium
contained in a leach solution, the process comprising the step of
subjecting the leach solution to solvent extraction using an
organic solution of a carboxylic acid and a hydroxyoxime. In some
situations there is a need to separate cobalt from manganese only
and therefore there is also provided a process for the separation
of cobalt from manganese contained in a leach solution, the process
comprising the step of subjecting the leach solution to solvent
extraction using an organic solution of a carboxylic acid and a
hydroxyoxime. The organic solution may optionally further comprise
a stabilizer.
[0022] The present invention is a particular example of a more
general process for separating one or more of nickel, cobalt and
manganese from the impurity elements (manganese) calcium and
magnesium contained in a leach solution, which process comprises
the steps of subjecting the leach solution to solvent extraction
using a carboxylic acid and a hydroxyoxime. The process of the
invention that is the subject of this application is particularly
suited to leach solutions containing low levels of nickel, since
nickel has slow extraction and stripping kinetics in the absence of
further additives.
[0023] The solvent extraction step described above achieves very
good separation of cobalt (and/or manganese) present in the leach
solution from (manganese,) calcium, magnesium and chloride impurity
elements which may be present, and good separation of cobalt from
manganese if cobalt is to be recovered and manganese is to be
rejected as an impurity element. If zinc and copper are present,
the process comprises separation of zinc, copper, cobalt (and/or
manganese) from impurity elements selected from one or more of
calcium, magnesium (and manganese) contained in a leach solution,
the process comprising the step of subjecting the leach solution to
solvent extraction using an organic solution comprising a
carboxylic acid and a hydroxyoxime. According to a preferred
embodiment, the organic solution further comprises a
stabilizer.
[0024] According to one embodiment, the elements cobalt and/or
manganese extracted into the organic phase during solvent
extraction are recovered therefrom. Where the organic phase of the
extraction step contains primarily cobalt or manganese alone, the
recovery step may comprise bulk stripping of the element from the
organic phase. The bulk stripping may optionally be combined with
ion exchange to remove any minor amounts of impurity elements, such
as zinc, copper and nickel to improve the purity of the recovered
elements. Another optional process for improving the purity of the
recovered element is sulphide precipitation. Sulphide precipitation
is more suited to precipitation of any minor amounts of copper,
zinc, cobalt and nickel present in the manganese recovered from
stripping.
[0025] In the situation where the leach solution contains both
cobalt and manganese, and these are both extracted into the organic
phase, the recovery step may comprise selective stripping of the
organic phase to separate the manganese from the cobalt. The
manganese may thereafter be recovered from the loaded strip liquor,
and the cobalt recovered from the selectively stripped organic
solution by bulk stripping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention will be described in further detail with
reference to the following figures which relate to preferred
embodiments of the invention.
[0027] FIGS. 1 and 2 are graphs comparing extraction pH isotherms
of metals using a comparative extraction system (FIG. 1) and the
extraction system of one embodiment of the invention (FIG. 2).
[0028] FIG. 3 is a graph showing the extraction kinetics of metals
from a leach solution using the extraction system of one embodiment
of the invention.
[0029] FIG. 4 is a graph showing the stripping kinetics of metals
from a loaded organic phase from the extraction system of one
embodiment of the invention.
[0030] FIG. 5 is a graph comparing stripping kinetics of cobalt
using a comparative extraction system and the extraction system of
one embodiment of the invention.
[0031] FIGS. 6 and 7 are graphs comparing extraction pH isotherms
of metals using a comparative extraction system (FIG. 6) and the
extraction system of one embodiment of the invention (FIG. 7).
[0032] FIG. 8 is a graph showing the extraction kinetics of
manganese from a leach solution using the extraction system of one
embodiment of the invention.
[0033] FIG. 9 is a graph showing the stripping kinetics of
manganese from a loaded organic phase from the extraction system of
a one embodiment of the invention.
[0034] FIG. 10 a schematic flow chart of the steps of the process
of one embodiment of the invention.
[0035] FIG. 11 is a schematic flow chart of the steps of the
process of a second embodiment of the invention.
[0036] FIG. 12 is a schematic flow chart of the steps of the
process of a third embodiment of the invention.
[0037] FIG. 13 is a schematic flow chart of the steps of the
process of a fourth embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0038] At the core of the present invention is a synergistic
solvent extraction step which effects extraction of a large
proportion of the nickel, cobalt, copper, and zinc into an organic
phase (to the extent that these elements are present), with a large
proportion of the calcium, magnesium, and chloride being rejected
to the aqueous phase. Depending on the pH selected, the manganese
can report to either the organic phase or the aqueous phase, as is
chosen for a particular leach solution. The solvent extraction is
conducted with a combination of carboxylic acid and a hydroxyoxime
synergist, and optionally a stabilizer.
[0039] The hydroxyoxime synergist is capable of increasing the pH
gap, .DELTA.pH.sub.50, between isotherms for nickel and cobalt and
that for manganese, and between the isotherm for manganese and
those for calcium and magnesium. This results in advantageous
selectivity of nickel and cobalt and optionally manganese, over the
impurities (manganese), calcium, magnesium and chloride.
[0040] The pH.sub.50 value is the pH at which 50% metal extraction
is achieved. Thus, .DELTA.pH.sub.50 is the difference between the
pH.sub.50 values for two metals, or the difference between the
pH.sub.50 values for the same metal under different extraction
conditions.
[0041] Carboxylic Acid
[0042] In the most preferred embodiment of the invention, the
carboxylic acid is 2-methyl, 2-ethyl heptanoicic acid (commercially
available as Versatic 10) or a cationic exchange extractant having
extraction characteristics similar to 2-methyl, 2-ethyl heptanoic
acid could be used. Cationic exchange extractants have hydrogen
ions which are exchanged with metal ions in the aqueous solution.
The term carboxylic acid is used in its broadest sense to refer to
any organic carboxylic acid. Carboxylic acids have the formula
RCOOH, in which R represents any optionally substituted aliphatic
or aromatic group, or combinations of these groups, including
optionally substituted alkyl, alkenyl, alkynyl, aryl, or heteroaryl
groups (and combinations thereof). Preferably R represents a
relatively bulky group containing at least 4 carbon atoms, and
preferably between 4 to 18 carbon atoms. The term "alkyl" used
either alone or in a compound word such as "optionally substituted
alkyl" or "optionally substituted cycloalkyl" denotes straight
chain branched or mono- or poly-cyclic alkyl, preferably C1-30
alkyl or cycloalkyl, most preferably C4-18 alkyl. Examples of
straight chain and branched alkyl include methyl, ethyl, butyl,
isobutyl, tert-butyl, 1,2-dimethylpropyl, 1-methylpentyl,
5-methylhexyl, 4,4-dimethylpentyl 1,2-dimethylpentyl,
1,3-dimethylpentyl, 1,1,2-trimethylbutyl, nonyl, 1- 2- or
3-propylhexyl, decyl, 1-, 2-, 3-, 4-, 5- or 6-ethyloctyl, 1-, 2-,
3-, 4- or 5-propyloctyl, 1-, 2- or 3-butylheptyl, 2-hexyl
2-methyloctyl and the like. Examples of cyclic alkyl include
cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl and cyclodecyl and
the like. The alkyl may optionally be substituted by any
non-deleterious substituent.
[0043] In this specification "optionally substituted" means that a
group may or may not be further substituted with one or more groups
selected from alkyl, alkenyl, alkynyl, aryl, halo, haloalkyl,
haloalkenyl, haloalkynyl, haloaryl, hydroxy, alkoxy, alkenyloxy,
aryloxy, benzyloxy, haloalkoxy, haloalkenyloxy, haloaryloxy, nitro,
nitroalkyl, nitroalkenyl, nitroalkynyl, nitroaryl,
nitroheterocyclyl, amino, alkylamino, dialkylamino, alkenylamino,
alkynylamino, arylamino, diarylamino, benzylamino, dibenzylamino,
acyl, alkenylacyl, alkynylacyl, arylacyl, acylamino, diacylamino,
acyloxy, alkylsulphonyloxy, arylsulphenyloxy, heterocyclyl,
heterocycloxy, heterocyclamino, haloheterocyclyl, alkylsulphenyl,
arylsulphenyl, carboalkoxy, carboaryloxy, mercapto, alkylthiom
benzylthio, acylthio and the like.
[0044] Suitable optional substituents will be chosen on the basis
that the carboxylic acid have the desired extraction
characteristics, and the substituents do not react with any other
component of the mixture under the given extraction conditions.
[0045] Hydroxyoxime
[0046] A hydroxyoxime is used as a synergist with the carboxylic
acid in the solvent extraction step. A hydroxyoxime is a compound
containing an oxime group and a hydroxy group. Preferably, the
groups are in an .alpha.-position with respect. to each other. Such
.alpha.-hydroxyoximes are chelating, whereas oximes are generally
non-chelating and thus behave differently. The "oxime" functional
group contains a carbon to nitrogen double bond, with the nitrogen
atom being attached to an oxygen atom. Accordingly, the term oxime
includes within its scope oximes with a hydroxy group attached to
the nitrogen atom, and oxime ethers, although hydroxime
(>C.dbd.N--OH) is preferred. The hydroxyoxime may be a C8-C26
hydroxyoxime. Preferably, the hydroxyoxime is an aliphatic
hydroxyoxime. Preferably, the hydroxyoxime is of the formula:
##STR00001##
[0047] in which R' and R'' are each selected from an optionally
substituted, straight chain, branched or cyclic alkyl, group
containing from 2 to 12 carbon atoms. Preferably each of R' and R''
are unsubstituted alkyl groups, most preferably a heptyl group. An
example of such a compound is 5,8-diethyl-7-hydroxy-6-dodecanone
oxime (the active component of a commercial agent LIX 63). This has
the following structure:
##STR00002##
Stabilizer
[0048] Under some conditions, the reagent mixture of carboxylic
acid and hydroxyoxime may be susceptible to degradation,
particularly with respect to the hydroxyoxime component.
Accordingly, a suitable stabilizer may advantageously be used to
slow any degradation reaction. Degradation may take place via a
number of mechanisms, including oxidation and hydrolysis. Hence the
stabilizer is suitably one that mitigates against oxidation and/or
hydrolysis of the hydroxyoxime. Such stabilsers include, but are
not limited to, esters (e.g. TXIB), ethers, ketones, alcohols (e.g.
isodecanol, TDA) and alkylphenols (e.g. nonylphenol, dodecylphenol,
BHT, Ionol). Preferably the stabilizer is an anti-oxidant. Of
these, we have found the alkylphenol anti-oxidants to be particular
useful. The term "alkylphenol" encompasses all alkyl derivatives of
phenol, and in particular those derivatives with one or more
straight chain, branched or cyclic alkyl substituents. The
alkylphenol 2,6-bis(1,1-dimethylethyl)-4-methyl phenol
(commercially available as BHT and Ionol) or reagents with similar
anti-oxidant characteristics to 2,6-bis(1,1-dimethylethyl)-4-methyl
phenol are particularly useful.
[0049] Leach Solution
[0050] The leach solution subjected to the synergistic solvent
extraction with the organic solution of carboxylic acid,
hydroxyoxime and optionally a stabilizer may be any type of leach
solution containing cobalt and/or manganese, together with impurity
elements selected from one or more of calcium, magnesium,
(manganese) and chloride, optionally together with copper and zinc.
Preferably, the leach solution is one containing little nickel.
[0051] In this respect, the leach solution suitably contains less
than 100 ppm nickel, or any other low level that does not warrant
recovery for economic reasons. Where cobalt is to be recovered, the
nickel is suitably present in any amount of less than 50% of that
of cobalt (for example, <100 ppm nickel, >200 ppm
cobalt).
[0052] According to one embodiment, the leach solution may contain
the following levels of elements:
TABLE-US-00001 Ni: 0-100 ppm Co: 100 ppm-5 g/L Cu: 0-100 ppm Zn:
0.2-2 g/L Ca: 1 ppm-saturated, for instance between 0.5-0.7 g/L Mn:
0.2-50 g/L, or 1-50 g/L Mg: 1 ppm-100 g/L, or 2-100 g/L.
[0053] The leach solution may for instance be a pregnant leach
solution obtained from the pressure acid leaching of any suitable
ore type, such as a laterite or sulphide ore. It may alternatively
be a solution from bio-leach, atmospheric acid leach, oxidative
leach, reductive leach, chloride leach or any combination of these
leach processes. The steps involved in producing such leach
solutions are well known in the art.
[0054] The leach solution is preferably a solution that has been
subjected to a preliminary iron and/or aluminium precipitation step
to precipitate out iron and/or aluminium to leave an aqueous leach
solution containing the target elements and impurity elements
identified above. The leach solution may alternatively or further
have been subjected to one or more additional treatment or
processing stages.
[0055] Synergistic Solvent Extraction Conditions
[0056] The solvent extraction step involves contacting an organic
solvent containing the carboxylic acid, hydroxyoxime and optionally
stabilizer with the (aqueous) leach solution. The organic solvent
may be any suitable organic solvent known in the art. Kerosene is
the most common solvent/diluent used for this purpose due to its
low cost and availability. Shellsol 2046 is one specific
example.
[0057] The amount of carboxylic acid and hydroxyoxime (and
stabilizer) in the organic solution used in the solvent extraction
step will depend on the concentration of the (nickel), cobalt (and
optionally manganese) or both to be extracted and the A/O
(aqueous/organic) flow rate ratio. The concentration would
typically be in the range of from 0.1 to 2.0 M for carboxylic acid,
with a preferred range of 0.1 to 1.0 M, and 0.05 to 1.0 M for
hydroxyoxime. The concentration of stabilizer may be in the range
of from 0 to 0.1 M, typically 0.005 to 0.1 M.
[0058] Preferably, the pH of the aqueous phase is maintained in a
range from 3.5 to 5.0 and more preferably 4.0 to 4.5 in the
extraction step if manganese is to be rejected. Preferably, the pH
of the aqueous phase is maintained in a range from 5.5 to 7.0 and
more preferably 5.8 to 6.3 in the extraction step if manganese is
to be recovered. The temperature is preferably maintained in the
range of from 10.degree. C. to 60.degree. C., more preferably from
20 to 40.degree. C. Whilst temperatures as low as 10.degree. C. are
achievable, a temperature lower than 15.degree. C. results in high
viscosity. At temperatures higher than 60.degree. C. there is a
risk of increased evaporation and degradation of the organic
phase.
[0059] The aqueous to organic ratio (A/O) in the extraction step is
most suitably 1:1, but may lie in the range from 10:1 to 1:10, and
preferably 1:5 to 5:1. The aqueous to organic ratio maintained in
the scrubbing step may lie within the range from 1:5 to 1:200, but
preferably it is in the range of 1:5 to 1:20.
[0060] The cobalt and/or manganese extracted into the loaded
organic phase in the synergistic solvent extraction can be
recovered in downstream processing stages.
[0061] Scrubbing
[0062] The organic phase from the synergistic extraction step of
the invention is suitably subjected to scrubbing. The scrub
solution may suitably be a process stream recycled from the
process, and is preferably derived from an aqueous stream of a
stripping stage (which may be a selective stripping stage)
following the scrubbing stage.
[0063] Recovery of Cobalt, Manganese or Both from Scrubbed Organic
Solution
[0064] There are a number of options envisaged by the applicants
for the recovery of cobalt, manganese or both from the scrubbed
organic solution. One example for the situation where both cobalt
and manganese are extracted (i.e. pH of aqueous phase in extraction
is 5.5 to 7.0) is set out below. It is noted that other options
within the skill and knowledge of those in the art could be used in
place of the following, and are within the scope of the present
invention. Moreover, different steps would be used for different
leach solutions containing different levels of elements, or when
other elements are desired to be recovered or removed.
[0065] Selective Stripping to Separate Cobalt and Manganese
[0066] According to one embodiment of the invention, the organic
phase containing cobalt and manganese is subjected to selective
stripping to separate to a significant extent the cobalt and the
manganese. The selective strip suitably involves contacting the
organic phase from the synergistic extraction with an acidic
aqueous solution to yield (a) a loaded strip liquor containing
manganese and (b) a selectively stripped organic solution
containing cobalt (and zinc, nickel and copper, if they were
present in the organic phase from the synergistic extraction).
[0067] The acidic aqueous solution for the selective strip is
suitably sulphuric acid solution, although other aqueous acid
solutions known in the art (such as hydrochloric) may be used. The
pH of the acidic aqueous solution is suitably in the range of about
4.0 to 5.0, depending on the level of separation desired. Most
preferably, the pH is about 4.5.
[0068] The combination of the described synergistic extraction with
the selective strip of manganese from cobalt is a very useful
combination, enabling the recovery of manganese and cobalt using
only one solvent extraction circuit (although more than one circuit
could be used if so desired with other process steps).
[0069] Other Process Details
[0070] The synergistic extraction step of the present invention may
be combined with different preliminary and following process steps
for the development of processes suitable for the recovery of
cobalt and/or nickel when different impurity elements may be
present.
[0071] It will be well understood to persons skilled in the art of
the invention that scrubbing stages of the type well known in the
art may be used for recovering elements even if the scrubbing
stages are not specifically mentioned. The design of the optimum
arrangement of scrubbing stages will depend on the specific aqueous
leach solution and the elements desired to be recovered therefrom
(and target percentage recovery levels).
[0072] It is also an advantage of the present invention that cobalt
can be separated from impurities contained in leach solutions
without intermediate precipitation of the cobalt with other
impurity elements and re-leaching of the precipitate to
subsequently enable the removal of the impurities. Thus, in a
preferred embodiment of the invention, the process does not include
a precipitation step involving precipitation out of the target
elements and re-leaching of the precipitate.
EXAMPLES
[0073] The present invention will now be described in further
detail with reference to the following examples which demonstrate
the underlying theory behind the invention, and how the invention
is put into practice.
[0074] Batch Test Work
Example 1
Extraction pH Isotherms of Metals with Versatic 10/LIX63
Synergistic System
[0075] This example illustrates that when carboxylic acid 25
Versatic 10 is used as the extractant with no added synergist, the
pH isotherms of the "valuable" elements Zn, Ni, and Co are too
close to the isotherms of the "impurity" elements Mn, Ca and Mg for
effective separation. However when a synergistic system comprising
Versatic 10 and hydoxyoxime LIX 63 is used, the isotherms of the
"valuable" elements Cu, Zn, Ni, and Co are sufficiently separated
from the isotherm of Mn to allow effective separation. Further, the
isotherm of Mn is sufficiently separated from the isotherms of Ca
and Mg to allow effective separation.
[0076] The aqueous solution was a synthetic solution to simulate a
typical laterite leach solution containing 3 g/L Ni, 0.3 g/L Co,
0.2 g/L Cu and Zn, 2 g/L Mn, 10 g/L Mg and 0.5 g/L Ca.
[0077] The metal extraction pH isotherms with the 0.5 M Versatic 10
(carboxylic acid) alone were determined and plotted, as shown in
FIG. 1. The metal extraction pH isotherms using the combination of
0.5 M Versatic 10 and 0.35 M LIX63 (hydroxyoxime) were also
determined and plotted in FIG. 2. Comparison of the two figures
reveals that the combination of LIX63 with Versatic 10 resulted in
significant synergistic extraction isotherm shifts (to lower pH)
for nickel, cobalt, copper, zinc, and manganese and antagonistic
shifts (to higher pH) for calcium and magnesium. As shown in FIG.
2, with the 0.5 M Versatic 10/0.35 LIX63 system, the
.DELTA.pH.sub.50 values of nickel, cobalt, copper, zinc, manganese
and Ca were found to be 2.8, 3.5, >2.0, 2.0, 1.2 and -0.5 pH
units, respectively.
TABLE-US-00002 pH.sub.50 of metals from pH isotherms in FIGS. 1 and
2 pH.sub.50 0.5 M Versatic 10 + Metal 0.5 M Versatic 10 0.35 M LIX
63 .DELTA.pH.sub.50 Ni 6.2 3.4 2.8 Co 6.3 2.8 3.5 Cu 4.1 <2.0
>2.0 Zn 5.7 3.7 2.0 Mn 6.5 5.3 1.2 Ca 7.0 7.5 -0.5
[0078] The .DELTA.pH.sub.50(Mn--Ni) value for the 0.5 M Versatic
10/0.35 M LIX63 system was found to be 1.9 pH units and the
.DELTA.pH.sub.50 (Mn--Co) value 2.5 pH units, indicating easy
separation of nickel and cobalt from manganese, calcium and
magnesium. The .DELTA.pH.sub.50(Ca--Mn) value for the 0.5 M
Versatic 10/0.35 M LIX63 system was found to be 2.2 pH units,
indicating easy separation of manganese from calcium and
magnesium.
Example 2
Extraction Kinetics with Versatic 10/LIX63 synergistic system.
[0079] This example illustrates that when the synergistic system
comprising Versatic 10 and LIX 63 is used, Cu, Co, Zn and Mn
display fast extraction kinetics, while the extraction kinetics for
Ni are slow. Hence this system is potentially suitable for Cu, Co,
Zn and Mn recovery when the leach solution contains little Ni.
[0080] Tests were conducted to establish the extraction kinetics of
the metals in the synthetic laterite solution using Versatic
10/LIX63. The extraction kinetics of copper, cobalt, zinc (and
manganese--see Example 6 and FIG. 8) were found to be fast and the
extraction kinetics of nickel were found to be relatively slow
(FIG. 3). Within 30 seconds, only 55% Ni was extracted and within 2
minutes, only 74%. It is noted that Mn and Zn are crowded out as Ni
extracts.
Example 3
Stripping Kinetics with Versatic 10/LIX63 Synergistic System
[0081] This example illustrates that when the synergistic system
comprising Versatic 10 and LIX 63 is used, Cu, Co, Zn and Mn
display fast stripping kinetics, while the stripping kinetics for
Ni are slow. Hence this system is potentially suitable for Cu, Co,
Zn and Mn recovery when the leach solution contains little Ni.
[0082] Tests were conducted to determine the stripping kinetics of
the metals from the 0.5 M Versatic 10/0.35 M LIX63 system using a
strip solution containing 5 g/L Ni and 10 g/L sulphuric acid (FIG.
4). The stripping kinetics of copper, cobalt and zinc were fast.
The stripping kinetics of nickel were slow, with only 18% of the
nickel being stripped after 2 minutes of mixing.
Example 4
Stripping of Cobalt from LIX63 Alone and Versatic 10/LIX63
Systems
[0083] This example illustrates that when the synergistic system
comprising Versatic 10 and LIX 63 is used, Co displays fast
stripping kinetics, however when LIX 63 alone is used, Co cannot be
readily stripped thus making LIX 63 alone an unsuitable extractant
for Co-containing solutions.
[0084] Cobalt(II) can poison hydroxyoxime reagents such as LIX63.
This means that once cobalt(II) is extracted by hydroxyoxime
reagents (and oxidises to Co(III)), it cannot be stripped with
concentrated acids. Tests were conducted to see whether the new
system results in cobalt poisoning of the extractant/synergist.
[0085] Parallel tests were conducted with 0.35 M LIX63 alone and
0.5 M Versatic 10/0.35 M LIX63 systems by mixing the organic
solutions with aqueous solution containing cobalt (FIG. 5). The
organic and aqueous solutions were left in contact with air
bubbling for 76 hours. Thereafter, a sulphuric acid solution of 100
g/l sulphuric acid was used to strip cobalt from the loaded organic
solution sample. The cobalt stripping efficiency from the 0.35 M
LIX63 alone system was only 29.2% after 10 minutes stripping. The
cobalt stripping efficiency for the 0.5 M Versatic 10/0.35 M LIX63
system was 99.5%. This indicates that cobalt(II) does not poison
the Versatic 10/LIX63 system.
Example 5
Extraction pH Isotherms of Metals with Versatic 10/LIX63 System
[0086] This example illustrates that when Versatic 10 is used as
the extractant with no added synergist, the pH isotherm of Mn is
too close to the isotherms of the "impurity elements" Ca and Mg for
effective separation. However when the synergistic system
comprising Versatic 10 and LIX 63 is used, the isotherm of Mn is
sufficiently separated from the isotherms of Ca and Mg to allow
effective separation.
[0087] The aqueous solution was a synthetic solution to simulate a
typical waste laterite leach solution containing 1.46 g/L Mn, 17.6
g/L Mg and 0.54 g/L Ca.
[0088] The extraction pH isotherms were determined for 0.5 M
Versatic 10 alone and 0.5 M Versatic 10/0.2 M LIX63 systems and
shown in FIGS. 6 and 7, respectively. The pH.sub.50 (Mn) decreased
from 6.9 to 5.6 pH units while the positions of isotherms of
magnesium and calcium remained virtually unchanged. At pH 6.5, the
extractions of manganese, calcium and magnesium were 17.9%, 2.84%
(or 46 ppm)and 0.16% (or 82 ppm), respectively, for the Versatic 10
alone system while the extractions of manganese, calcium and
magnesium were 87.3%, 2.41% (or 39 ppm) and 0.05% (or 26 ppm),
respectively, for the Versatic/LIX63 system. This indicates that
the selectivity of Versatic 10 for manganese over magnesium and
calcium was very greatly improved.
Example 6
Extraction Kinetics with Versatic 10/LIX63 System
[0089] This example illustrates that when the synergistic system
comprising Versatic 10 and LIX 63 is used, Mn displays fast
extraction kinetics. Hence this system is suitable for Mn
recovery.
[0090] The extraction kinetics of the metals in the synthetic waste
laterite leach solution using the 0.5 M Versatic 10/0.2 M LIX63
system were determined and graphed in FIG. 8. As shown, the
extraction kinetics of manganese were fast. Within 0.5 minutes, the
system almost reached equilibrium with manganese extraction of
80%.
Example 7
Stripping Kinetics with Versatic 10/LIX63 System
[0091] This example illustrates that when the synergistic system
comprising Versatic 10 and LIX 63 is used, Mn displays fast
stripping kinetics. Hence this system is suitable for Mn
recovery.
[0092] The stripping kinetics of the manganese in the loaded 0.5 M
Versatic 10/0.2 M LIX63 system were determined using a strip
solution containing 60 g/L Mn and 35 g/L sulphuric acid and graphed
in FIG. 9. As shown, the stripping kinetics of manganese were fast.
Within 0.5 minutes, the system almost reached equilibrium with
manganese extraction of 99%.
[0093] Process Flowcharts
Example 8
Process for Separation and Recovery of Cobalt and Manganese from
Leach Solutions
[0094] Based on the above findings, a new direct solvent extraction
(DSX) process flow sheet was designed. The flow sheet is shown in
FIG. 10.
[0095] Leach Solution
[0096] The leach solution contains manganese and cobalt, as well as
the impurity elements calcium and magnesium, but little or no
copper, zinc or nickel. A suitable solution composition for this
flow sheet may comprise Co>200 ppm, Mn>1 g/L, Ca<50 g/L
(Ca will be<1 g/L in sulphate solutions), Mg<100 g/L, Cu, Zn
and Ni<100 ppm (or of no economic value). It is noted that the
flow sheet is not limited to such leach solutions, and the leach
solutions may comprise different levels of the given elements,
optionally together with further impurity elements. This leach
solution is one that may have been subjected to preliminary
neutralisation with limestone at pH 4.5-5.0 to precipitate impurity
elements Fe (III), Al, Si and Cr.
[0097] Synergist Solvent Extraction (SSX EX)
[0098] In the synergistic solvent extraction step, an organic
solution of carboxylic acid (Versatic 10), a hydroxyoxime (LIX 63)
and a stabilizer (Ionol) in organic diluent Shellsol 2046 is
contacted with the leach solution at pH 6-6.5 to obtain (a) an
aqueous raffinate containing magnesium and calcium, and (b) a
loaded organic solution containing almost all of the cobalt and
manganese, and only minor levels of calcium and magnesium.
[0099] Scrubbing (SSX SC)
[0100] The organic solution from the extraction step is subjected
to scrubbing at pH 5.5-6 using a sulphate solution containing a
small amount of manganese from the next step of stripping 1,
resulting in (a) a scrubbed organic solution containing cobalt and
manganese, and (b) a scrub liquor which is recycled to the
synergistic solvent extraction step.
[0101] Selective Stripping (SSX ST1)
[0102] The scrubbed organic solution is subjected to stripping 1
(selective strip) using a sulphuric acid solution at pH between
4.0-5.0 resulting in (a) a loaded strip liquor containing
manganese, and (b) a stripped organic solution containing mainly
cobalt and only a very small amount of manganese.
[0103] The loaded strip liquor is sent to manganese recovery, with
one stream returning to the previous scrubbing stage.
[0104] Scrubbing (SSX SC2)
[0105] The organic solution from stripping 1 is subjected to
scrubbing 2 at a pH of 3.5-4.0 using the aqueous strip liquor from
a subsequent stripping stage (stripping 2). This step results in
(a) a scrubbed organic solution containing cobalt, and (b) a scrub
liquor which is recycled to the original synergistic solvent
extraction stage to maximize cobalt recovery.
[0106] Stripping (SSX ST2)
[0107] The scrubbed organic solution is subjected to stripping 2
using sulphuric acid solution at pH between 2.0-2.5. The cobalt
recovered in this stripping stage is optionally subjected to
zinc/copper/nickel ion exchange to enable removal of any zinc,
copper and nickel impurities present. The zinc, copper and nickel
is disposed of, and the cobalt is sent to cobalt recovery by any
process known in the art. One example is cobalt precipitation using
base or sulphide.
Example 9
Process for Separation and Recovery of Cobalt from Leach
Solutions
[0108] An alternative solvent extraction process flow sheet was
formulated for the recovery of cobalt from leach solutions 25
containing impurity elements manganese, calcium and magnesium, with
little or no copper, zinc or nickel. This flow sheet is shown in
FIG. 11. A typical solution composition for which this flow sheet
could be applicable comprises Co>200 ppm, Mn<100 g/L,
Ca<100 g/L (Ca will be<1 g/L in sulphate solutions),
Mg<100 g/L, Cu, Zn and Ni<100 ppm (or of no economic value).
Of course, variations in this solution composition are
possible.
[0109] The plant leach solution (PLS) is adjusted to a pH between
4.0-5.0 and subjected to the synergistic solvent extraction (SSX)
described in relation to Example 8 above. The organic phase
contains the cobalt (as well as zinc, copper and nickel to the
extent that these are present) and a minor level of manganese. The
aqueous raffinate contains magnesium, calcium and manganese.
[0110] Scrubbing is conducted as described above in relation to
Example 8, at pH 3.5-4.5, yielding (a) a scrubbed organic solution
containing principally cobalt, but also zinc, copper, and nickel in
very low quantities if present at all in the plant leach solution,
and (b) a scrub liquor which is recycled to the original
synergistic solvent extraction stage to maximize cobalt recovery.
The organic phase of the scrubbing step contains cobalt, and
possibly zinc, nickel and copper, which is then subjected to
stripping with sulphuric acid at pH between 2.0 and 2.5. The loaded
strip liquor is sent to cobalt recovery (with one stream returning
to the previous scrubbing stage), optionally via ion exchange, with
the organic phase returned to the synergistic solvent
extraction.
Example 10
Process for Separation and Recovery of Cobalt, Copper and Zinc
[0111] FIG. 12 details a process flow sheet which is a variation on
that illustrated in FIG. 11, and described in Example 9 above.
[0112] The process of FIG. 12 is suitable for recovering copper,
cobalt and zinc from leach solutions that contain impurity elements
manganese, calcium and magnesium, with little or no nickel. A
solution composition to which this process may suitably be applied
contains the following: Cu>500 ppm, Co>200 ppm, Zn>500
ppm, Mn<100 g/L, Ca<100 g/L (Ca will be<1 g/L in sulphate
solutions), Mg<100 g/L and Ni<100 ppm (or of no economic
value). Of course, variations in this solution composition are also
envisaged.
[0113] The plant leach solution is subjected to copper solvent
extraction and copper electrowinning. The leach solution containing
reduced levels of copper, and all other elements, is then subjected
to iron and aluminium precipitation (Fe/Al PPT) by neutralising the
leach solution with limestone to a pH of between 4.0-5.0 to
precipitate iron and aluminium. The leach solution is then
subjected to the synergistic solvent extraction, scrubbing and
stripping as described in relation to Example 9 and FIG. 11 above.
As will be appreciated, any copper and zinc still present reports
to the phases to which the cobalt reports.
[0114] The aqueous phases collected from scrubbing and stripping
contain cobalt, zinc and minor levels of copper, together with any
levels of nickel which may be present. The aqueous liquor is
subjected to zinc solvent extraction to remove zinc therefrom for
recovery. Thereafter, the cobalt (and nickel and copper) containing
solution is subjected to nickel and copper ion exchange to enable
nickel and copper removal and disposal. Thereafter, the cobalt is
recovered.
Example 11
Process for Separation and Recovery of Manganese from Leach
Solutions
[0115] A new solvent extraction process flow sheet was developed
for recovering manganese from leach solutions that contain the
impurity elements calcium and magnesium, with little or no copper,
zinc, cobalt or nickel. This is set out in FIG. 13. A typical
solution composition which may be subjected to this process may
comprise Mn>1 g/L; Ca<50 g/L (Ca will be<1 g/L in sulphate
solutions); Mg<100 g/L; Cu, Zn, Co and Ni<100 ppm (or of no
economic value). Of course, variations in this solution composition
are envisaged.
[0116] The leach solution, which may have been subjected to
preliminary processing steps, is subjected to synergistic solvent
extraction with the Versatic 10/LIX 63/Ionol synergistic system,
with the aqueous phase adjusted to a pH between 6.0-7.0. The
aqueous raffinate contains calcium and magnesium, and the organic
phase contains manganese, with minor levels of calcium of
magnesium. The organic phase is subjected to scrubbing using a
scrub solution at pH between 6.0-6.5. The scrub solution is a
stream of the manganese sulphate solution generated in a subsequent
stripping stage. The organic phase from the scrubbing stage
containing manganese is sent to stripping, and the aqueous scrub
liquor is recycled to the synergistic solvent extraction stage.
[0117] Stripping is performed on the organic phase using sulphuric
acid at pH between 3.0-4.0. The aqueous strip liquor is optionally
subjected to sulphide precipitation to remove any copper, zinc,
cobalt or nickel impurities present, and the manganese sent to
manganese recovery. A stream of the strip liquor is recycled to the
scrubbing stage. This process is particularly suited for situations
where the manganese value is acceptable, making it desirable to
recover the manganese from a leach solution. If the leach solution
contains appreciable levels of cobalt, and other elements having pH
isotherms similar to cobalt, then the process of Example 8 and
FIGS. 10 would be more suited.
Example 12
Effect of Stabilizer (Ionol) on Degradation of Hydroxyoxime (LIX63)
in Versatic 10/LIX63 System
[0118] This example shows how addition of an anti-oxidant
stabilizer (Ionol) slows the rate of degradation of the
hydroxyoxime LIX63 in the Versatic 10/LIX63 extraction system.
[0119] An organic extractant solution (25 mL) containing 0.4 M
LIX63 and 0.5 M Versatic 10 in Shellsol D70 diluant was loaded with
a synthetic leach solution (50 mL) containing 0.5 g/L Ca, 9 g/L Na,
24 g/l Mg, 45 g/L Mn, 0.2 g/L Co, 1 g/L Zn and 0.15 g/L Cu, at pH
4.5 and left to stand in a water bath at 25.degree. C. Two further
(duplicate) systems, each containing 10 g/L Ionol were prepared and
treated similarly. After 18 days, the organic solution was sampled
and analysed for LIX63 using gas chromatography. The results are
shown in the table below. After 18 days in the Ionol-free system,
5.2% of the LIX63 had been degraded. After 18 days in the duplicate
systems initially containing 10 g/L Ionol, 0.7% and 1.6% of the
LIX63 had been degraded.
TABLE-US-00003 TABLE 1 Oxime concentration in the loaded organic
solutions as a function of contact time. LIX63 (%) relative to
initial concentration Contact time Versatic 10 + Versatic 10 +
Versatic 10 + (days) LIX63 LIX63 + Ionol LIX63 + Ionol 0 100.0
100.0 100.0 8 97.0 99.6 99.2 18 94.8 99.3 98.4
[0120] It will be understood to persons skilled in the art of the
invention that many modifications may be made to the embodiments
described without departing from the spirit and scope of the
invention.
[0121] In the claims which follow and in the preceding description
of the invention, except where the context requires otherwise due
to express language or necessary implication, the word "comprise"
or variations such as "comprises" or "comprising" is used in an
inclusive sense, i.e. to specify the presence of the stated
features but not to preclude the presence or addition of further
features in various embodiments of the invention.
* * * * *