Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1
PROCESS FOR THE EXTRACTION OF METALS FROM AMMONIACAL SOLUTION
The present invention concerns a solvent extraction process and especially a
process for the extraction of metals, particularly copper, from aqueous
ammoniacal
solutions, especially solutions obtained by leaching ores with ammonia.
It is known to extract metals, especially copper, from aqueous solutions
containing the metal in the form of, for example, a salt, by contacting the
aqueous
solution with a solution of a solvent extractant in a water immiscible organic
solvent and
then separating the solvent phase loaded with metal, i.e. containing at least
a part of the
metal in the form of a complex. The metal can then be recovered by stripping
with
solution of lower pH followed for example, by electrowinning. Most commonly,
the
1 o aqueous metal-containing solutions for extraction are the result of the
acid leaching of
ores. However it is known that copper can be preferentially leached from
certain ores
with ammoniacal solutions. This has the advantage that solutions containing
especially
high concentrations of copper are derived and that there is little
contamination of the
solution with iron.
Solvent extractants which have found favour in recent years particularly for
the
recovery of copper from aqueous acidic solutions include oxime reagents,
especially
o-hydroxyaryloximes. Whilst such reagents have been found to work extremely
well in
the recovery of copper from acidic solutions, problems have been encountered
in the
application of such reagents to extraction from ammoniacal solutions. One of
these
2o problems results from the high copper concentrations encountered in the
ammoniacal
solution. This can cause a very high copper loading in the organic solutions,
which
results in the viscosity of the organic solution increasing to a point where
the solution can
be difficult to process on an industrial scale. EP-A-0 036 401 solves this
problem by the
use of an extractant composition comprising two extractants, one being a
strong copper
extractant, such as an oxime, the other being a weak extractant, a beta-
diketone. The
use of beta-diketones is also taught by WO 93104208, where they are the
preferred
extractant, and the only type to be exemplified.
It has now been found that beta-diketones can suffer from poor chemical
stability
in the presence of the aqueous ammoniacal leach solution, and therefore
rapidly lose
their effectiveness and form undesirable impurities. Alternative extractants
contemplated
by WO 93104208, orthohydroxyaryl aldoximes, which have proved to be the most
effective extractants for copper from acidic solutions, also suffer problems
with stability
under ammoniacal leach conditions. Furthermore, most extractants are designed
for use
in acid leach systems, and operate at relatively low pH. WO 93104208 teaches
that
employing extractants designed for use with acidic solutions in an ammoniacal
system
leads to carry over of ammonia into the stripping solution and results in an
unacceptable
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2
loss of ammonia from the system. The carry over of ammonia is taught to
necessitate
the further treatment of the organic phase to remove the loaded ammonia.
Amongst the non-beta-diketone reagents contemplated by WO 93/04208 are
three ketoximes, 5-nonyl-2-hydroxyacetophenone oxime, 5-nonyl-2
hydroxybenzophenone oxime and 5-dodecyl-2-hydroxybenzophenone oxime. These
reagents are disclosed as being equivalent to aldoximes as less preferred
alternatives to
the beta-diketones.
The beta-diketone and oxime extractants contemplated by WO 93104208 are
taught to be soluble to the necessary extent in the water-immiscible solvents
commonly
employed in solvent extraction. WO 93/04208 discloses that for extractants
other than
beta-diketones and oximes, a solubility modifier such as an alcohol or ester
can be
employed where the solubility of the extractant needs to be increased.
During the course of the studies leading to the present invention, it was
found that
one or more of the problems of poor chemical stability, solution viscosity and
ammonia
transfer could be ameliorated by the use of a solvent extractant comprising an
orthohydroxyarylketoxime and a thermodynamic modifier.
According to a first aspect of the present invention, there is provided a
process for
the extraction of a metal from ammoniacal solution in which an aqueous
ammoniacal
solution containing a dissolved metal is contacted with a solvent extraction
composition
2 o comprising a water immiscible organic solvent and a water-immiscible
solvent extractant,
whereby at least a fraction of the metal is extracted into the organic
solution,
characterised in that the solvent extraction composition comprises an
orthohydroxyarylketoxime and a thermodynamic modifier.
Metals that may be extracted in the process according to the present invention
include copper, cobalt, nickel and zinc, most preferably copper.
The orthohydroxyarylketoxime compounds employed in the present invention are
substantially water insoluble and have the formula:
NOH
2/ ' 1
R R
3o Formula (1)
wherein
R' is an optionally substituted hydrocarbyl group
R2 is an optionally substituted ortho-hydroxyaryl group,
and salts thereof.
Whilst the invention is described herein with reference to a compound of
Formula
(1), it is understood that it relates to said compound in any possible
tautomeric forms,
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3
and also the complexes formed between orthohydroxyarylketoximes and metals,
particularly copper.
Optionally substituted hydrocarbyl groups which may be represented by R'
preferably comprise optionally substituted alkyl and aryl groups including
combinations of
these, such as optionally substituted aralkyl and alkaryl groups.
Examples of optionally substituted alkyl groups which may be represented by R'
include groups in which the alkyl moieties can contain from 1 to 20,
especially from 1 to
4, carbon atoms. A preferred orthohydroxyarylketoxime is one in which R' is
alkyl,
preferably containing up to 20, and especially up to 10, and more preferably
up to 3
1 o saturated aliphatic carbon atoms. Most preferably R' is a methyl group.
Examples of optionally substituted aryl groups include optionally substituted
phenyl groups. When R' is an aryl group, it is preferably an unsubstituted
phenyl group.
Optionally substituted ortho-hydroxyaryl groups which may be represented by R2
include optionally substituted phenols. Examples of optionally substituted
phenols which
may be represented by RZ include those of formula:
OH
R3
Ra ~ Rs
R5
wherein R3 to Rs each independently represent H or a C, to C22, preferably a
C~ to
C,5, linear or branched alkyl group. Particularly preferably only RS
represents a C,_ZZ alkyl
2 o group, most preferably a C, to C,5 alkyl group, with R3; R° and Rfi
representing H.
When R' or Rz is substituted, the substituent{s) should be such as not to
affect
adversely the ability of the orthohydroxyarylketoxime to complex with metals,
especially
copper. Suitable substituents include halogen, nitro, cyano, hydrocarbyl, such
as
C,_~-alkyl, especially C,_,o-alkyl; hydrocarbyloxy, such as C,_~-alkoxy,
especially
2 5 C,_,o-alkoxy; hydrocarbyloxycarbonyl, such as C,_ZO-alkoxycarbonyl,
especially
C,_,o-alkoxycarbonyl; aryl, such as C,_ZO-alkylcarbonyl and arylcarbonyl,
especially
C,_,o-alkylcarbonyl and phenylcarbonyl; and acyloxy, such as C,_ZO-
alkylcarbonyloxy and
~rylcarbonyloxy, especially C,_,o-alkylcarbonyloxy and phenylcarbonyloxy.
There may be
more than one substituent in which case the substituents may be the same or
different.
3o In many preferred embodiments, the orthohydroxyarylketoxime employed is a
5-(C8 to C,4 alkyl)-2-hydroxyacetophenone oxime, particularly 5-nonyl-2-
hydroxyacetophenone oxime.
The composition may comprise one or more different orthohydroxyarylketoximes
in which the nature of the substituent groups represented by R' and R2 differ
between
35 component orthohyd~oxyarylketoximes, especially where the component
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orthohydroxyarylketoximes are isomeric. Such isomeric mixtures may have better
solubility in organic solvents than a single orthohydroxyarylketoxime.
The orthohydroxyarylketoximes are often present in an amount of up to 60% by
weight of the composition, commonly no more than 50%, and usually no more than
40
wlw. Often, the orthohydroxyarylketoxime comprises at least 5% by weight,
commonly at
least 10% by weight and usually at least 20% by weight of composition, and
preferably
comprises from 25 to 35%, such as about 30%, by weight of the composition.
Thermodynamic modifiers employed in the present invention are substantially
water insoluble. Suitable thermodynamic modifiers can be alkyiphenols,
alcohols, esters,
to ethers and polyethers, carbonates, ketones, nitrites, amides, carbamates,
sulphoxides,
and salts of amines and quaternary ammonium compounds.
Alkylphenols which may be used as modifiers in conjunction with the extractant
include alkylphenols containing from 3 to 15 alkyl carbon atoms, for example 4-
tert-
butylphenol, 4-heptylphenol, 5-methyl-4-pentylphenol, 2-chloro-4-nonylphenol,
2-cyano-
1 s 4-nonylphenol, 4-dodecylphenol, 3-pentadecylphenol and 4-nonylphenol and
mixtures
thereof. The preferred phenols contain alkyl groups having from 4 to 12 carbon
atoms,
especially the mixed 4-nonylphenols obtained by condensation of phenol and
propylene
trimer.
Alcohols which may be used as modifiers in conjunction with the extractant
2 o include saturated and unsaturated hydrocarbon alcohols and polyols
containing 14 to 30,
preferably 15 to 25 carbon atoms. The alcohols are preferably highly branched
with the
hydroxyl group located approximately midway along the hydrocarbon backbone.
Especially preferred are the branched chain alcohols that may be made by
condensation
of short chain alcohols by the Guerbet process, such alcohols sometimes being
referred
25 to as Guerbet alcohols. Optionally, the alcohols may contain an aromatic
group or other
functional group, particularly an ester group.
Especially useful alcohols may be synthesised from highly branched precursors
leading to very highly branched Guerbet alcohols containing a large number of
terminal
methyl groups. Examples of particularly efficient alcohol modifiers include
highly
3o branched isohexadecyl alcohol and iso-octadecyl alcohol, the latter being
2-(1,3,3-trimethylbutyl)-5,7,7-trimethyloctan-1-ol.
Esters which may be used as modifiers in conjunction with the extractant
include
saturated and unsaturated aliphatic and aromatic-aliphatic esters containing
from 10 to
30 carbon atoms. The esters may be mono-esters or polyesters, especially di-
esters.
35 The esters are preferably highly branched. Optionally, the esters may
contain other
functional groups, particularly a hydroxyl group or ether group. Where the
ester is a
product of the reaction of an alcohol and a mono-carboxylic acid, it is
preferred that the
alcohol is an alkyl alcohol and comprises from 1 to 6 carbon atoms, and the
mono-
carboxylic acid comprise from 2 to 16 carbon atoms. Where the ester is a
product of the
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reaction of an alcohol and a di-carboxylic acid, it is preferred that the
alcohol is an alkyl
alcohol and comprises from 1 to 6 carbon atoms, and the di-carboxylic acid
comprises
from 4 to 12 carbon atoms. Where the ester is a product of the reaction of a
diol and a
mono-carboxylic acid, it is preferred that the diol is an alkyl diol and
comprises from up to
5 6 carbon atoms, and the mono-carboxylic acid comprises from 6 to 16 carbon
atoms.
Where the ester is a tri-alkyl phosphate, the alkyl groups each commonly
comprise from
4 to 14 carbon atoms. Examples of useful esters include isodecyl acetate,
methyl
decanoate, 2-pentyl octanoate, n-hexyl hexanoate, methly isooctanoate, 1,4-
butanediol
dihexanoate, butyl adipate, isobutyl adipate, bis-2-ethoxyethyl adipate,
dipropylene glycol
1 o dibenzoate, propylene glycol dibenzoate, tributyl phospate,
trioctylphosphate and
triethylhexylphosphate, and particularly 2,2,4-trimethyl-1,3-pentanediol
isobutyrate and
2,2,4-trimethyl-1,3-pentanediol benzoate.
Ethers which may be used as modifiers in conjunction with the extractant
include
hydrocarbon ethers and polyethers containing 12 to 30, preferably 15 to 25
carbon
atoms. Examples of useful ethers and pofyethers include benzyl 2-(2-
butoxyethoxy)ethyl
ether and benzyl 2-butoxyethyl ether.
Carbonates which may be used as modifiers in conjunction with the extractant
include carbonates containing from 4 to 16 carbon atoms. Commonly, the
carbonates
are alkyl carbonates. Examples of useful carbonates include isobutylcarbonate,
isotridecylcarbonate and a carbonate mixture comprising a mixture of Ce and
C,o alkyl
groups.
Ketones which may be used as modifiers in conjunction with the extractant
include alkyl ketones in which the alkyl group contains from 1 to 20 carbon
atoms.
Examples of useful ketones include isobutyl heptylketone, diundecyl ketone and
5,8
diethyldodecane-6,7-dione.
Nitrites which may be used as modifiers in conjunction with the extractant
include
aliphatic and arafiphatic hydrocarbonitriles which comprise from 10 to 36
carbon atoms.
Examples of useful nitrites include undecylnitrile and oleonitrile.
Amides which may be used as modifiers in conjunction with the extractant
include
3o amides containing from 8 to 20 carbon atoms. Amides comprise products which
may be
derived from the reaction of a primary or secondary amine with a mono- or di
carboxylate
acid or equivalent, in particular phosgene or equivalents. Examples of useful
amides
include N,N'-bis-2-ethylhexyl urea, N,N'-bis-2-ethylhexyl 2-ethylhexanamide, N-
hexyl 2-
ethylhexanamide, N,N'-dibutyl benzamide, N,N'-dibutyl octanamide, N,N'-
dimethyl
octanamide and N,N'-bis-2-ethylhexyl versatamide.
Carbamates which may be used as modifiers in conjunction with the extractant
include alkyl and aryl carbamates. Examples of useful carbamates include N-
octyl
isotridecylcarbamate and isotridecyl N-tolylcarbamate.
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Sulphoxides which may be used as modifiers in conjunction with the extractant
include alkyl sulphoxides. An example of a useful sulpoxide is di-2-ethylhexyl
sulphoxide.
Salts of amines and quaternary ammonium compounds which may be used as
modifiers in conjunction with the extractant include tertiary amines and
quaternary
ammonium compounds containing alkyl groups having from 8 to 18 carbon atoms
and
sulphonic acid salts thereof. Examples of sulphonic acids include
dinonylnapthalene
sulphonic acid and toluene sulphonic acid.
In the context of the present invention, 'highly branched' as applied to the
alcohols
and esters means that the ratio of the number of methyl carbon atoms to non-
methyl
1 o carbon atoms is higher than 1:5 and preferably higher than 1:3.
If desired, mixtures of compounds selected from the group consisting of
alkylphenols, alcohols, esters, ethers, polyethers, carbonates, ketones,
nitrites, amides,
carbamates, sulphoxides, and salts of amines and quaternary ammonium compounds
may be employed as modifiers. Particularly preferred are mixtures comprising a
first
compound selected from the group consisting of alkylphenols, alcohols, esters,
ethers,
polyethers, carbonates, ketones, nitrites, amides, carbamates, sulphoxides,
and salts of
amines and quaternary ammonium compounds and a second compound selected from
the group consisting of alkanols having from 6 to 18 carbon atoms, an alkyl
phenol in
which the alkyl group contains from 7 to 12 carbon atoms, and
tributylphosphate.
2o The modifiers often comprise up to 20% w!w of the composition, preferably
from 5
to 15 % w/w, and most preferably from 8 to 12% wlw. The weight ratio of
modifier to
ketoxime is often in the range of from 10:1 to 1:10, commonly from 5:1 to 1:5,
and
preferably from 1:1 to 1:4.
The aforementioned modifiers may be used in the preparation of extractant
compositions containing one or more extractants and one or more modifiers.
Organic solvents which may be used for the extraction include any mobile
organic
solvent, or mixture of solvents, which is immiscible with water and is inert
under the
extraction conditions to the other materials present. Examples of suitable
solvents
include aliphatic, alicyclic and aromatic hydrocarbons and mixtures of any of
these as
well as chlorinated hydrocarbons such as trichforoethylene, perchioroethylene,
trichloroethane and chloroform. Examples of suitable hydrocarbon solvents
include low
aromatic (<1% wlw) content hydrocarbon solvents such as ESCAID 110
commercially
available from Exxon (ESCAID is a trade mark), and ORFOM SX11 commercially
available from Phillips Petroleum (ORFOM is a trade mark). Preferred solvents
are
hydrocarbon solvents including high flash point solvents with a high aromatic
content
such as SOLVESSO 150 commercially available from Exxon (SOLVESSO is a trade
mark) and includes solvents which consist essentially of a mixture of
trimethylbenzenes
such as AROMASOL H, commercially available from Imperial Chemical Industries
PLC
(AROMASOL is a trade mark). Especially preferred, however, on grounds of low
toxicity
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and wide availability are hydrocarbon solvents of relatively low aromatic
content such as
kerosene, for example ESCAID 100 which is a petroleum distillate comprising
20°~
aromatics, 56.6% paraf~ns and 23.4% naphthenes commercially available from
Exxon
(ESCAID is a trade mark), or ORFOM SX7, commercially available from Phillips
Petroleum (ORFOM is a trade mark).
In many embodiments, the composition comprises at least 35%, often at least
45% by weight, preferably from 50 to 70% w!w of water-immiscible hydrocarbon
solvent.
The composition will comprise at least ane orthohydroxyarylketoxime which may
be
present in an amount up to 54% w/w, and preferably from 25 to 35% .w/w. A
modifier,
1 o particularly an alkylphenol, alcohol or ester modifier may also be present
in an amount up
to 20%, preferably from 5 to 15%, w/w. Compositions comprising an
orthohyrdoxyarylketoxime which is present in an amount from 25 to 35% w/w and
an
alkylphenol, alcohol or ester mod~er which is present in an amount of from 5
to 15% wlw
are particularly preferred.
Particularly preferred solvent extraction compositions are those comprising
from
to 35% wlw of 5-(C8 to C,4 alkyl)-2-hydroxyacetophenone oxime, 5 to 15% wlw of
tridecanol, tributyphosphate, or 2,2,4-trimethyl-1,3-pentanediol isobutyrate
or the benzoic
acid ester thereof, and from 50 to 70% of water-immiscible hydrocarbon
solvent.
The aqueous ammoniacal solution from which metals are extracted by the
2 o process of the present invention often has a pH in the range of from 7 to
12, preferably
from 8 to 11, and most preferably from 9 to 10. The solution can be derived
from the
leaching of ores, particularly chalcocite ores, or may be obtained from other
sources, for
example metal containing waste streams such as from copper etching baths.
The concentration of metal, particularly copper, in the aqueous ammoniacal
2 5 solution will vary widely depending for example on the source of the
solution. Where the
solution is derived from the leaching of ores, the metal concentration is
often up to 758/1
and most often from 10 to 408/1. Where the solution is a waste stream, the
metal
concentrations are often somewhat higher than those from the leaching of ores,
for
example up to 150811, usually from 75 to 130811.
3 o The process of the present invention can be carried out by contacting the
solvent
extractant composition with the aqueous ammoniacal solution. Ambient or
elevated
temperatures, such as up to 75°C can be employed if desired. Often a
temperature in
the range of from 15 to 60°C, and preferably from 30 to 50°C, is
employed. The aqueous
solution and the solvent extractant are usually agitated together to maximise
the
interfacial areas between the two solutions. The volume ratio of solvent
extractant to
aqueous solution are commonly in the range of from 20:1 to 1:20, and
preferably in the
range of from 5:1 to 1:5. In many embodiments, to reduce plant size and to
maximise
the use of solvent extractant, organic to aqueous volume ratios close to 1:1
are
employed, such as 1.5:1 or less, and preferably 1.3:1 or less.
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The mole ratio of orthohydroxyarylketoxime to copper transferred is often
selected
to be in the range of from 2.7:1 to 2:1. Preferably, to achieve improved
hydrometallurgical properties, such as reduced viscosity and improved phase
disengagement, the mole ratio of oxime to copper transferred is from 2.3:1 to
2.0:1.
After contact with the aqueous ammoniacal solution, the metal can be recovered
from the solvent extractant by contact with an aqueous strip solution having a
pH lower
than that from which the metal was extracted.
The aqueous lower pH strip solution employed in the process according to the
present invention is usually acidic, commonly having a pH of 2 or less, and
preferably a
pH of 1 or less, for example, a pH in the range of from -1 to 0.5. The strip
solution
commonly comprises a mineral acid, particularly sulphuric acid, nitric acid or
hydrochloric
acid. In many embodiments, acid concentrations, particularly for sulphuric
acid, in the
range of from 130 to 200g/l and preferably from 150 to 180g/l are employed. A
low acid
concentration but at least 4M chloride containing strip solution as described
in European
Patent application no. 93301095.1 (publication no. 0 562 709 A2) or
fntemational
application publication No. W095104835 (both of which are incorporated herein
by
reference) can be employed. When the extracted metal is copper or zinc,
preferred strip
solutions respectively comprise stripped or spent electrolyte from a copper or
zinc
electro-winning cell, typically comprising up to 80g/l copper or zinc, often
greater than
2 0 40g11 copper or zinc and preferably from 50 to 70g/l copper or zinc, and
up to 200g/l
sulphuric acid, often greater than 130g/l sulphuric acid, and preferably from
150 to 180811
sulphuric acid.
The volume ratio of organic solution to aqueous strip solution in the process
of the
present invention is commonly selected to be such so as to achieve transfer,
per litre of
strip solution, of up to 50811 of metal, especially copper into the strip
solution from the
organic solution. In many industrial copper electrowinning processes often at
least 108/1,
preferably from 25 to 358/1 and especially about 30811 of copper per litre of
strip solution
is transferred from the organic solution. Volume ratios of organic solution to
aqueous
solution of from 1:2 to 15:1 and preferably from 1:1 to 10:1, especially less
than 3:1 are
3o commonly employed.
A preferred embodiment of the present invention comprises a process for the
extraction of a metal from aqueous ammoniacal solution in which:
in step 1, a water-imrniscible solvent extraction composition comprising a
orthohydroxyarylketoxime and a thermodynamic modifier is first contacted with
the
aqueous ammoniacal solution containing metal,
in step 2, separating the solvent extraction composition containing metal-
solvent
extractant complex from the aqueous ammoniacal solution;
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9.
in step 3, contacting the solvent extraction composition containing metal-
solvent
extractant complex with an aqueous strip solution of lower pH than the
ammoniacal
solution to effect the stripping of the copper from the water immiscible
phase;
in step 4, separating the metal-depleted solvent extraction composition from
the
lower pH aqueous solution.
The metal can be recovered from the aqueous strip solution by conventional
methods, for example by electrowinning.
The invention is further illustrated, but not limited, by the following
examples.
1 o Examples 1 and 2 and Comparison A
A mini-rig trial was carried out to investigate the performance of different
solvent
extraction compositions in the extraction of copper from a typical ammoniacal
copper
solution. The process comprised two extraction stages, one wash stage and one
strip
stage. 500 ml counter-current mixer-settlers stirred at 1000 rpm were employed
in each
stage. The extraction stages were operated at an organic:aqueous (O:A) ratio
of 1.2:1,
and the wash and strip stages were operated at an organic:aqueous (O:A) ratio
of 1:1.
Residence times in each stage were about 3 minutes. The ammoniacal copper
solution
comprised 30g/l copper, 45g1f ammonia and 75g/l sulphate. The wash solution
was a
dilute sulphuric acid solution having a pH of 2. The strip solution was an
aqueous copper
2o sulphate solution comprising 30g/l copper and 180g11 sulphuric acid. Three
different
solvent extraction compositions were employed. In Example 1, the extractant
comprised
282g/1 of 5-nonyl-2-hydroxyacetophenone oxime and 11 % w/w 2,2,4-trimethyl-1,3-
pentanediol isobutyrate in the hydrocarbon solvent ORFOMT"" SX7. In Example 2,
the
extractant comprised 247g/l of 5-nonyl-2-hydroxyacetophenone oxime and 9.7%
wlw
2,2,4-trimethyl-1,3-pentanediol isobutyrate in the hydrocarbon solvent
ORFOMT"" SX7. In
Comparison A, the extractant comprised 282g/l of 5-nonyl-2-hydroxyacetophenone
oxime
in the hydrocarbon solvent ORFOMT"" SX7. During each of the trials, the copper
content
of the advance electrolyte produced from the strip solution was determined at
periodic
intervals and used to calculate the percentage copper recovery based on the
copper
content of the aqueous ammoniacal solution. The percentage copper recoveries
achieved were as follows:
Trial % copper recovery
Example 1 100 (average of 7 determinations)
Example 2 100 (average of 4 determinations)
Comparison A 90.3 (average of 3 determinations)
The results of Examples 1 and 2 clearly demonstrate the improved performance
of the process according to the present invention, compared with the results
for
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Comparison A (not according to the present invention) in which a process
omitting the
thermodynamic mod~er was employed.
Examples 3, 4, 5, 6, 7 and 8, and Comparisons B and C
5 In a separate test, extraction and stripping isotherms were determined for
the
solvent extraction compositions. In each case, the extractant comprised 118811
(0.56M)
of 5-nonyl-2-hydroxyacetophenone oxime, the Comparison compositions (B and C)
had
no modifier and the Examples compositions contained 85811 of modifier chosen
from
tridecanol (Examples 3 and 6), 2,2,4-trimethyl-1,3-pentanediol isobutyrate
(Examples 4
to and 7) or tributylphosphate (Examples 5 and 8), in the hydrocarbon solvent
ORFORMT""
SX7.
The loading isotherm was generated using a feed composition comprising 30811
copper and 45811 ammonia (2-3811 free ammonia) at 40°C. This was
carried out by
contacting the formulated reagent at different organic:aqueous (O:A) ratios,
allowing the
phases to reach equilibrium and then separating the phases and analysing each
phase
for metal values. The stripping isotherm was generated by contacting an
organic phase
loaded with copper with a stripping acid composition comprising 35811 copper
and 150811
sulphuric acid at 40°C. This was carried out at different
organic:aqueous (O:A) ratios,
allowing the phases to reach equilibrium and then separating the phases and
analysing
2 o each phase for metal values. For Examples 3 and 6, the stripping isotherm
was
measured at O:A ratios of 2:1, 1.5:1, 1:1, 1:2, 1:6, 1:10 and the extract
isotherm was
measured at O:A ratios of 1:2, 1:3, 1:5, 1:10. For Examples 4 and 7, the
stripping
isotherm was measured at O:A ratios of 3:1, 2:1, 1.5:1, 1:1, 1:2, 1:4, 1:10
and the extract
isotherm was measured at O:A ratios of 1:2, 1:3, 1:10. For Examples 5 and 8,
the
stripping isotherm was measured at O:A ratios of 2:1, 1.5:1, 1:1, 1:2, 1:5 and
the extract
isotherm was measured at O:A ratios of 1.5:1, 1:1, 1:1.5, 1:3. For Comparisons
B and C,
the stripping isotherm was measured at O:A ratios of 3:1, 2:1, 1.5:1, 1:1,
1:1.5, 1:5 and
the extract isotherm was measured at O:A ratios of 1.5:1, 1:1, 1:2, 1:3.
The expected recoveries were then predicted by iterative means using a McCabe-
Thiele construction, utilising the isotherm data generated from the
experimental data.
The expected recoveries for a 2 extract, 1 strip process at the quoted O:A
ratios for
extract and strip stages were:
i '
CA 02302353 2000-02-25
WO 99/10546 PCT/US98/17712
11
Modifier OlA Ratio h
Ext Strip Recovery
Comparison B -- 1:1 1:1 51.45
Example 3 TDA 1:1 1:1 55.75
Example 4 TXIB 1:1 1:1 55.73
Example 5 TBP 1:1 1:1 56.42
Comparison C - 2.02:1 1:1 96.68
Example 6 TDA 2.17:1 1:1 99.68
Example 7 TXIB 1.97:1 1:1 99.91
Example 8 TBP 2.14:1 1:1 98.33
TDA = Tridecanol
TXIB = 2,2,4-Trimethyl-1,3-pentanediol isobutyrate
TBP = Tributylphosphate
The results clearly demonstrate that improved pertormance
of the process can be
achieved according to the present invention, for a
range of modifiers, compared with the
results for Comparisons B and C (not according to
the present invention) in which a
process omitting the thermodynamic modifier was employed.
