CA1075474A

CA1075474A - Separation of cobalt and nickel

Info

Publication number: CA1075474A
Application number: CA250,059A
Authority: CA
Inventors: John E. Barnes; Terence G. Truscott
Original assignee: Vale Canada Ltd
Current assignee: Vale Canada Ltd
Priority date: 1975-04-24
Filing date: 1976-04-12
Publication date: 1980-04-15
Also published as: AU502904B2; FR2308596A1; GB1499406A; FR2308596B1; AU1317876A

Abstract

ABSTRACT
Cobalt is selectively removed from an aqueous acidic leach solution in a solvent extraction process using a nickel salt of an organophosphoric acid, preferably di-2-ethyl hexyl phosphoric acid. The nickel salt may be regenerated in a single continuous step.

Description

PC- ~AN '10759t'7f?~

This lnvention relates to the separation of cobalt values Erom nickel values in an aqueous solution in which they are dissolved.
It is known from Canadian Patent No. 795,724 to separate cobalt values from nickel values in an aqueous leach solution by liquid-liquid extraction by contacting the leach solution with a solution, in an inert orqanic water-immiscible solvent, of an alkali metal or ammonium salt of an organo-phosphoric acid having the formula (RO)2PO(OH), (wherein R
is hydrogen or substituted or unsubstituted alkyl, aryl or aralkyl; not more than one R is hydrogen; each R group other than hydrogen contains at least 8 carbon atoms; and the phosphoric acid molecule contains at least 12 carbon atoms), to extract the cobalt values from the aqueous phase to the organic phase, and separating the resultant cobalt-loaded phase from the remaining aqueous phase, which contains the major part of the nickel values. The cobalt is recovered from the cobalt-loaded phase, and the organophosphoric acid is reconverted to its alkali matal or ammonium salt and used to treat further amounts of leach solution.
When the leach solution is an inorganic salt solu~
tion, such as a sulphate, chloride or nitrate solution, it ma~
be desired to recover the nickel values from the aqueou~
raffinate phase remaining from the liauid-linuid extraction by crystallisation as the correspondin~ inorganic nickel salt. However, this remaining solution also contains sub-stantial amounts of alkali metal or ammonium ions, and to obtain inorganic nickel salt, such as nickel sulphate, of commercially acceptable purity, for example with a nickel plus cobalt to sodium [ (Ni ~ Co) : Na] weight ratio of at least 140:1, preferably at lea~t 400:1, requires several ~`v ,, ~6375~74 stages of recrystalli~ation, which is expensive ~oth in capital equipment and operating costs.
According to the present invention this disadvan-tage is overcome by performing the extraction with a solution oE the nickel salt of the organophosphoric acid in the inert organic solvent to give an aqueous phase from which some or all of the inorganic nickel salt is crystallised. In thi~
way it is possible to obtain an acceptable yield of crystals of the inorganic nickel salt, which have a commercially ac-ceptable purity without needing recrystallisation.
Accordingly the present invention provides a process for separating cobalt values from nickel values in an a~ueous acid sulphate, chloride or nitrate leach solution, which com-prises contacting the aqueous leach solution with a solution, in an inert substantially water-immiscible organic liquid, of the n.ickel salt of an organophosphoric acid of formula (R0)2PO(OH), wherein each R, which may be the same or dif-ferent, is hydrogen or substituted or unsubstituted alkvl, aryl or aralkyl, with the provisos that not more than one R is hydrogen, each R group other than hydrogen contains at least 8 carbon atoms and the phosphoric acid molecule contains at least 12 carbon atoms, so as to transfer cobalt values . from the aqueous leach solution to the organic solution;
: separating the organic solution containing transferred cobalt values from the aqueous raffinate solution thus ~ obtained; and crystalli~ing some or all of the aqueous ~ raffinate solution so as to produce crystals of nickel sulphate, chloride or nitrate.
To make the b.est use of reagents the organophos-. 30 phoric acid is preferably recovered from the cobalt-loaded solution and reconverted to its nickel salt, which is re-cycled for contacting with further aqueous leach solution.

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This reconversion may be done in two steps by first convert-ing the organophosphoric acid to its alkali metal or ammonium salt, advantageously its sodium salt, and then contactinq the solution of this salt in the inert organic solvent with mother liquor from the crystallisation of the inorganic nickel salt.
This method of reagent reconversion suffers from two disadvan-tages that it involves two separate steps, and that the first step must usually be per~ormed as a batch process which can, in practice, only be controlled by accurately measuring the volumes of organic and a~ueous phases used. However, if the reaction temperature in the first step rises too hi~h, or the reaction is carried on for too long, or both, there is a danger that the alkali metal or ammonium salt will be precipitated as a gel which would inhibit or prevent its transfer to the second step.
lso, i-t is usually necessary to analyse the product of the batch reaction to check that substantially complete (i.e.
not less than about 96~) conversion has occurred and excess neutralising agent has not been used because this excess can lead to undesirable precipitation of nickel hydroxide when the alkali metal or ammonium salt is converted to the nickel salt.
- Further disadvantages of the batch step are that it usually has to be carried out with a concentrated solu-tion o~ the neutralising agent, e.g. a 50% w/w caustic soda solution, and that it interrupts what may otherwise be a continuous process.
Another method for producing the nickel salt of the organophosphoric acid from the acid is to contact an _ 3 -.

~C~7~479L

organic solution of the acid with a suitable nickel base, Eor exan~ple nickel hydroxide or nickel carbonate, prefer-ably ~s an aqueous slurry. This method i5 also in essence a batch process, which is slow and difficult to use because it is difficult to separate the solid nickel base from the two liquid phases.
We have now found that the organophosphoric acid can be converted to its nickel salt in a single step, which may be carried out continuously with less ap~aratus and monitored simply, and thus provides savings in operative and capital costs.
~ccording to this feature of the invention, the nickel salt of the organophosphoric acid is prepared by thoroughly mixing an organic solution of organophosphoric acid, an aqueous solution of nickel sulphate, chloride or nitrate, and an aqueous alkaline solution, preferably an alkali metal, especially sodium, or ammonium hydroxide solution, to cause ~ransfer of nickel values from the aqueous nickel solution to the organic solution.
This reconversion reaction may be readily monitored by measurinq, with conventionl pH electrodes, the pH of the mixed phases, in which the aqueous phase should be the con~
; tinuous phase. Although the reaction i5 preferably carried out continuously, it can be carried out as a batch process.
Although the process of the present invention may be carried out with any of the organophosphoric acids refer-red to in Canadian Patent No. 795,724, it is preferably carried out using di-(2-ethylhexyl) phosphoric acid (hereinafter called D2E acid) as the organophosphoric acid and will be described hereinafter in more detail with reference to this acid.

~5~74 The requirement~ for the organic liquid which acts as a solvent or diluent for the organophosphoric acicl are set out in detail in the aforesaid Canadian Patent, and advantageously it is a kerosene or a naphtha. The concentration of organophosphoric acid in the organic solvent may be up to 40% v/v of the solvent; for example, to treat leach solution containing about 15 g/l of cobalt, a D2E acid concentration of about 30~ v/v is preferred.
Heretofore, as stated in Canadian Patent No.
795,724, it was believed desirable to incorporate an additive, such as 3 to 5% of tri-butyl phosphate or isodecanol, in the organic solvent to inhibit the forma-tion of emulsions and assist in phase sepaxation. However, we have now found that when, a~ in our invention, the nickel salt of the or~anophosphoric acid is used to extract cobalt from an aqueous leach solution it is possible, and indeed advantageous, to dispense throughout with the use of such an additive, and rely on intrinsic emulsion inhibition by the organic solvent and the organophosphoric acid and its salts used in the process. One advantage of omittin~
the additive is an approximately two-fold increase in the selectivity of the organic phase for cobalt as opposed to nickel, and so there is improved separation of cobalt from nickel. Other advantageY ar~ reduced loss of organic material to the various aqueous phases and increased ease in maintaining substantially constant composition in the - organic phase, which means that the process is easier to operate. If difficulty is experienced in obtaining satis-factory phase separation with a particular solvent in the absence of an additive, it i5 sometimes pos~ible to im~rove ~754'74 the phase separation by using a modified solvent obtained by removinq from the original solvent, for example by dis-tillation, material having a boiling point above about 250C, without having to resort to use of an additive.
However, if the organic and aqueous phase~ are to be used at temperatures below about 40C, it may be advantageous to include such an additive, as there is, for example, a tendency for the nickel and cobalt salts of the D2E acid to separate out from the solvent in the absence of tri-butyl phosphate.
The details of the apparatus and process techniques aro substantially as described in Canadian Patent No. 795,724.
The aqueous acid leach ~olution from which cobalt : is to be extracted in the process of the present invention is usually derived from leaching an ore, a metallurgical intermediate, such as a concentrate or residue from the extraction of nickel by formation of nickel carbonyl, or alloy scrap.
In carrying out the process of the present invention elements that tend to interfere with the extraction of cobal.t into the organic phase should, so far as nossible, be removed from the leach solution to be treated. These elements lnclude iron, arsenic, copper, calcium and :~ magnesium. Iron is especially undesirable, and should be kept below about 1 part per.million (ppm) in the aqueous solution, as it tends to build up in the organic phase. The arsenic content is frequently lowered to a satisfactory level`
simultaneously with reduction of the iron content. Calcium (and magnesium) should be kept below 80 ppm, and copper ~ 30 should preferably be kept below 5 ppm, as it tends to follow the cobalt.

~75~7~

However, copper need not be kept below 5 ppm, if a subse~uent purlfication is to be undertaken to separate the copper ~rom the cobalt. Because the process of the present invention is used so that the concentration of alkali metal or am-monium ions in the aqueous raffinate solution is not high enough to interfere with the crystallisation of commercially acceptably pure nickel qulphate, chloride or nitrate in a single crystallisation, the concentrations of alkali metal, especially sodium, and ammonium ions in the leach solution must not be such as to lead to an undesirably high concentra-tion thereof in the raffinate.
For efficient operation of the cobalt extraction - step of the process the pH of the leach solution should first be adjusted to from ~bout 4.0 up to ahout 6.0 and pre-ferably to about 5. If the pH is below 4, the loading of cobalt produced in the organic phase is generally too low for practical use of the process, and, if the pH is greater than 6, phase separation after extraction is generally poor and there is a danger of precipitating nickel hydr-; 20 oxide, which would interfere further with the phase separation. The temperature o~ the extraction may be - from 65 to 90C, but is preferably about 85C.
~- The cobalt-loaded organic e~tract obtained con-tains some nickel (and copper) and should preferably be scrubbed to increase the cobalt to nickel ratio therein, for example as described in Canadian Patent No. 795,724.
This scrubbing may be carried out using aqueous sulphuric, ~`
; hydrochloric, or nitric acids or an aqueous solution of cobalt sulphate, chloride or nitrate, which preferentially ; 30 displace nickel rather than cobalt or any copper present.

113754~

The scrubbing may be continued until, for exam~le, the cobalt to nickel weight ratio is at least 100:1. The aqueous pro-duct from the scrubbing may be returned to an earlier point in the process, such as to a leaching reaction producing the leach solution feed or to the aqueous leach solution itself.
The scrubbed organic phase obtained may be strip-ped to recover substantiall~ all the cobalt value~, for example, as described in the above-mentioned Canadian Patent. The cobalt salt of D2E acid is preferablv converted by the stripping into an organic solution of D2E acid i-tself and an aqueous solution of a cobalt salt. The stripping may be effected to produce D2E acid by usinq aqueous sulphuric, hydrochloric or nitric acid, but usually the acid corresponding to the acid radical of the original nickel salt lS used. If aqueous sulphuric, hydrochloric or nitric acid was used to scrub the organic phase, the same acid may also be used to strip the cobalt, but the volume of stripping agent used is then generally greater than the volume of the scrubbing agent. Although the aqueous cobalt sulphate, chloride or nitrate solution produced by the stripping contains some nickel and coPper simultaneously stripped, it may be crystallised, optionally after further purification, e.g. to remove copper, to produce cobalt sulphate, chloride or nitrate crystals having a cobalt to nickel weight ratio of 250:1 or more.
The D2E acid formed by the stripping is, in turn, readily converted to its nickel salt either by the two-step con-version or by the single step conversion, both of which are described in more detail hereinafter.
The nickel sulphate, chloride or nitrate in the aqueous raffinate solution from the initial extraction of ~7~74 the le~ch solution may be completely converted to crystals, but this is undesirable because any dissolved solid im-purities present in the raffinate would find their way in-to the crystals and could lead to the crystals being unacceptably impure and because there would be no mother liquor left to convert to the nickel salt of the organo-phosphoric acid. Preferably the whole of the aqueous raffinate is partially crystallised to recover some of the inorganic nickel salt as crystals and the mother liquor used to prepare the nickel salt of the organo-phosphoric acid. The crystals from this partial crystal-lisation are of better quality than would be obtained if an equal quantity of crystals were produced by partially - or completely crystallising only a part of the raffinate or completely crystallising all the raffinate. The reason the crystals obtained from the partial crystallisation of ~he whole of the raffinate are of better quality than the others is that more water can be left in the mother liquor to hold sodium and other impurities in solution. It is possible to divide the raffinate into two parts, one of which is completely or partially crystalllsed and the other used to make the nickel salt of D2E acid.
- In any event, the crystallisation of the aqueous raffinate is preferably carried out so as to leave sufficient mother liquor ~and washings~, together with any uncrystallised -` raffinate to prepare the required amount of nickel salt of the organophosphoric acid, e.g. D2E acid~ --D2E acid formed by stripping cobalt from cobalt loaded organic phase is, in the two-step reconversion, ~0 readily converted to its alka~i metal or ammonium salt by ~ .

_ g _ ~754~7~

a suit~ble alkali, for example to its sodium salt by a 50~ w/w solution of sodium hydroxide.
The nickel salt of D2E acid (hereinafter nickel D2E) may then be prepared by contacting mother liquor from the inorganic nickel salt crystallisation with, for example, a solution of the sodium salt of D2E acid (hereinafter sodium D2E) in the inert organic solvent. This conversion to nickel D2E may be carried out at a temperature o from about 35 to 85C.
This conversion of the sodium D2E to nickel D21~ may be carried out in a single stage, if desired, as this is usually sufficient to decrease the sodium content o~ the organic phase by a factor of about 20, which may be adequate. This 20-fold reduction, in turn, leads to a reduction in the sodium content of the inorganic nickel salt raffinate from the nickel/cobalt separation also by a factor of about 20 (as compared with the use of sodium D2E in Canadian Patent No. 795,724), which is usually su-fficient to enable commercially saleable nickel sulphate, chloride or nitrate to be crystallised in one crystallisation.
Preferably, however, the organic solution of nickel D2E is prepared by the single-step conversion.
This single step conversion is conveniently performed continuously in a single stage in a conventional mixer-settler. Whether the conversion is done continuously or as a batch process, a thorough mixture of an organic solution of D2E acid and aqueous mother liquor should pre-ferably first be established before the alkaline solution, preferably a 10 or more w/w % aqueous sodium hydroxide 501u-tion, is added, as this reduces any tendency to precipitate :
, ~6~75~

nickel hydroxide. The single step preparation will hereinafter be described ;n terms of sodium hydroxide (cau~tic soda) a~
this is the preferred reagent, although ammonium hydroxide and other alkali metal h~droxides may be used. Once the initial mixture of organic solution of D2E acid and mother liquor has been established it iR, of couxse, possible to run in all three solutions simultaneously. The rate of adding the caustic soda solution should be chosen so that the pH of the mixed phases is, for a continuous reconversion, in the ranqe of from about 5.0 to 6Ø If the pH is less th~n 5.0, the clegree of replacement, in the organic phase, of hydrogen by nickel is generally too low, in practical terms, for the nickel D2E solution obtained to be ~uitable for extracting cobalt from the leach solution. If the pH
is greater than 6.0, it may be difficult to separate the - organic and aqueous phases after the reconversion.
For the pH measurement~ to be meaningful the - aqueous phase must be substantially continuous in the mix-ture; the pH cannot generally be measured with a continuous organic phase. A suitable electrode system for measuring ~ the pH is a glass hydrogen ion electrode with a calomel - reference electrode.
This single-step convèrsion of D2E acid to nickel D2E may be carried out at a temperature of from about 35 to 85C., perferably 70 to 80C.
The separation of the aqueous and organic phases from the single step conversion of D2E acid to nickel D2E
can conveniently be carried out in the settler part of a conventional mixer-settler. The pH of the aqueous phase in the settler is not generally suitable for monitoring - the reaction as it responds too slowly to change~ in the pH in the mixer where the conversion is occurring.

:;

~75~79~

The aqueous products of the hydrogen/nickel and sodium/nickel exchanges contain less residual cobalt than does the mother liquor because some of this cobalt is ex-tracted into the organic phase during the hydrogen/nickel and sodium/nickel exchanges. The nickel remaining in these aqueous products may be precipitated as nickel carbonate or hydroxide, which may be converted to other nickel com-pounds. The nickel to cobalt weight ratio in these compounds can be 200:1 or more.
The nickel D2E produced from either the sodium/
nickel or hydrogen/nickel exchanga contains some cobalt which has been extracted from the residua~l cobalt in the nickel raffinate, the concentration of this cobalt having been increased by the evaporation of water during the crystallisation. This further cobalt recovery (about half of the cobalt content of the raffinate) is a valuable advantage of the process of the present invention over the process described in Canadian Patent No. 795,724. The nickel ` concentration in the organic solution produced in either the sodium/nickel or hydrogen/nickel exchanges is substantially independent of the temperature, but the cobalt recovery increases and the amount of any sodium in the organic solu-tion decreases with increasing temperature, and so tempera tures of 50C or above are preferred.
The organic solution of nickel D2E obtained from either of these exchanges is recycled to the initial cobalt/
nickel separation.
As the various steps in the process are carried out at various temperatures,means should be provided for heating or cooling the various streams as necessary.
~'` , ..

: , . - .

5479~

Two preferred ways of carrying out the process of the present invention are illustrated ~chematically in the two flowsheets shown in the accompanying drawings, in which:
Figure 1 shows an embodlment in which the D2E acid is converted vla sodium D2E to nickel D2E, and ;
Fic3ure 2 shows an embo~iment in which the D2B acid is converted in a single step to nickel D2E.
Referring to Figs. 1 and 2 of the drawings since much of the process illustrated is common to both, an aqueous sulphate leach solution 1 containing nickel and cobalt and having a pH of about 5.0 is contacted, as aqueous phase, in a nickel-cobalt separation steP 2 with an organic phase comprising a solution of the nickel salt of D2E in a hydrocarbon solvent, e.g. Esso Mentor 28 or Shell Catenex Oil 11. (According to their manufacturers' literature Esso Mentor 28 contains,''by weight, 95% of a mixture of aliphatic and naphthenic hydrocarbons and 5~ of ' ~romatic hydrocarbons and Shell Catenex Oil 11, by weight, 5% aromatic hydrocarbons, ~6~ allphatic hYdrocarbons and 29% naphthenic hydrocarbons.) The organic phase may also contain an emulsification inhibitor, such as tri-n-butyl phosphate. The amount of organic extractant (nickel D2E) used is preferably sufficient to remove substantially all the cobalt from the leach solution feed, whilst minimi~ing . .
the amount of residual nickel in the organic phase. When the nickel D2E is prepared, as described hereinafter, from the mother liquor from the nickel sulphate crystallisation, the organic solution of nickel D2E may contain a iittle - 30 sodium D2E and cobalt D2E (cobalt salt of D2E acid).

, .

1~37547~

The contacting of the aqueous and organic phases in the nickel/cobalt separation 2 may be performed in known manner, for example, as a five-stage countercurrent extrac-tion. Cobalt values in the aqueous leach solution transfer into the organic layer and displace nickel (and residual sodium) vaLues into the aqueous phase.
The aqueous phase 13 leaving the separation 2 contains nickel and traces of cobalt and sodium and is sent to the nickel sulphate crystallisation 15, described in more detail hereinafter.
The organic phase 3 leaving the separation 2, contains cobalt (as cobalt D2E) and some residual nickel (as nickel D2E), but substantially no sodium. The nickel content of this organic phase is substantially removed by scrubbing with aqueous sulphuric acid in a sulphuric acid scrub 4, which may be a three or more stage countercurrent scrub. This scrub 4 may be carried out at a temperature in the range of ~rom about 65 to 75C using aqueous sulphuric acid containing 90 g/l of sulphuric acid and an overall organic 20- to aqueous volume ratio of about 5:1, but the aqueous phase . .
20 is preferably recycled to give an effective organic to aqueous volume ratio of about l:l. The aqueous phase 21 - leaving the scrub 4 contains nickel and some cobalt and may be recycled to the leach solution feed l, or less desirably, to the leach reaction itself.
The organic phase 5 leaving the scrub 4 is pas-sed to a sulphuric acid stripping step 6 and contains some D2E acid, cobalt and only a little residual nickel.
The sulphuric acid strip 6 may be a three-stage countercurrent stripping of cobalt and may be carried out ~L~375474 at a temperature in the range of from 60 to 95C., preferably not above 85C. The aqueous solution of sulphuric acid 7 may be used at a concentration of 90 g/1 of sulphuric acid in an organic to aqueous volume ratio of about 2.7:1.
The aqueous phase 8 leaving the strip 6 is a cobalt sulphate solution containing only a small amount of residual nickel. This cobalt sulphate li~uor ma~ be crystallised to form crystals having a Co~Ni weight ratio of at least 100:1, e.g. 250:1. Any remaining mother liquor may be further treated to produce other cobalt compounds.
The organic phase 9 leaving the strip 6 comprises subs'cantially only D2E acid dissolved in the hydrocarbon solvent and containing, if used, the emulsification in-hibitor. Only very small amounts of nickel and cobalt are present in this phase, the D2E acid of which has to be con-verted to its nickel salt by use of mother liquor 17 from a nickel sulphate crystallisation 15.
The crystallisation 15 is of the aqueous phase product of the separation 2 which is a nickel sulphate raf-finate solution 13 containing traces of residual cobalt.
The crystallisation 15 can be carried out in conventional evaporation/crystallisation equipment, such as a climbing film evaporator and a continuous crystalliser (not indicated), for example by concentrating the nickel raffinate 13 to about 105Tw !twaddell) and crystalllsing the liquor at about 32 to 34~C. The NiSO4.6H2O crystals 16 formed are d~scharged, together with some mother liquor, filtered, washed and dried.
; The crystals 16 have an improved nickel to cobalt weight - ratio as compared with the nickel raffinate 13. For example, a nickel raffinate with a nickel to cobalt weight ratio of .

1~7~7~

165:1 gave rise to crystals with a ratio of 205:1 and a mother liquor with a ratio of 121:1.
The mother liquor 17 ~and washings of the crystals) from the crystallisation 15 i5 pagsed to the nickel D2E pre-paration 18.
Referring to only Fig. 1 of the accompanying draw-ings this nickel D2E preparation 18 i5 fed with sodium D2E
prepared in the sodium salt preparation 10. In the pre-paration 10, the D2E acid in the organic phase 9 from the sulphuric acid strip 6 is converted to sodium D2E by a batch method in which aqueous sodium hydroxide solution 11 is vigorously stirred with the organic phase 9, at a tempera-ture which is preferably about 70C, the concentration of sodium hydroxide being preferably chosen so that a single, organic, phase is formed. Care is taken to ensure that the sodium hydroxide does not separate out, so that conversion can be substantially complete. Excess sodium hydroxide should be avoided to prevent precipitation of nickel hydroxide during the preparation of the nickel D2E
(18). The single phase product 12 of the preparation 10 contains sodium D2E and is preferably analysed for its sodium or acid content to assess the completeness of the conversion before it is sent to the preparation 18.
In the preparation 18 of nickel D2E this organic phase 12 iS contacted with the mother liquor 17 rom the recrystallisation 15 of the nickel sulphate raffinate 13, which contains some residual cobalt. The preparation 18, which is usually carried out at a temperature of about 50 to 85C, preferably above 65C, replaces the sodium in the sodium D2E by nickel from the mother liquor. The preparation 18 is conveniently a two-stage countercurrent exchange, e.g. with an organic to aqueous phase volume ratio of about 2.4:1, as this gives a better overall .

S4~4 exchange, although a single stage would generally be satisfactory.
In contrast to the two-step reconversion ~ust described with reference to Fig. 1 of the accompanying drawings, Fiq. 2 shows a single step conversion of D2E
acid to nickel D2E. Referring to Fig. 2, mother liquor 17 (and washings of the NiSO4.6H2O crystals) from the ; crystallisation 15 is passed to the nickel D2E preDaration 18 where it meets sodium hydroxide solution 11 and the already described organic phase 9 carrying D2E acid from the sulphuric acid strip 6. In the preParation 18, which is usually carried out at a pH in the range of 5.0 to 6.0 and a temperature in the range of from about 50 to 85C, preferably above 65C, e.g. 70 to 80C, the acid-hydrogen in the D2E acid is replaced by nickel from the mother liquor. The reaction is conveniently a single-step ex-change, e.g. with an organic to nickel sulphate solution ` to caustic soda solution volume ratio of about 4:1:about 1, as this gives a good overall exchange.
Referring again to both Figs. 1 and 2 as the process is now common to both, the organic phase 14 pro-duced by preparation 18 contains nickel, a little cobalt and a trace of sodium. This organic phase is recycled to the separation 2.
The aqueous phase 19 produced by preparation 18 -- contains nickel, sodium and little cobalt. The nickel in this aqueous phase 19 may be converted into nickel carbonate Qr hydroxide for sale or for conversion to further nickel compounds. ,-All the exchange reactions may be carried out in conventional mixer-settlers, or other solvent extraction 75~7~

contactors usinq countercurrent flows o~ aqueous and organic phases. The batch conversion of D2E acid to 30dlum D2E i~, however, o~ten carried out in a batch reactor.
Various forms of crystalliser may be used for the recrystallisation of the inorganic nickel salt, but it is important that all the water should not be removed during the crystallisation, because this would lead to impure inorganic nickel salt and to the absence of mother liquor for the preparation of nickel D2E.
The present invention is illustrated by the fol-lowing Examples.

The initial preparation of the or~anic solution of nickel D2E for recycling during the process was carried out as follows. [Once the recycling is established onl~
losses need be made up by this preparation].
A solution was prepared containing about 30~ by volume of D2E acid and about ~ by volume of tri-n-butyl phosphate dissolved in Shell Catenex Oil 11. The total amount of D2E acid was chosen 80 that the amount that will be in contact with the leach solution is about 1.3 times the stoichiometric amount required for the cobalt content [2 mols of D2E acid per mol of cobal~]. The dissolved D2E
acid was converted to its sodium salt by thoroughly mixing it with a 50% by weight aqueous solution of a substantially equivalent amount of sodium hydroxide. The sodium D2E was converted to nickel D2E at about 70~C by countercurrent contact in two mixer-settler~ between ~he or~anic solution containing the sodium D2E and an aqueous solution of an at least equivalent amount of nickel sulphate [2 mols of D2E

~759~7~

acid or sodiu~ salt per mol of nickel sulphate]. The organic solution of nickel D2E obtained contained 27.2 g/l of nickel, 0.44 g/l of sodium and 0.36 g/l of cobalt, the cobalt being derived from cobalt impurity in the nickel sulphate solution.
This Example hereinafter substantially follows the flowsheet of Fig. 1. As feed, an aqueous sulphate leach solu-tion was used containing 108.5 grams/litre (g/l) of nickel and 17.7 g/l of cobalt and having a pH of about 5Ø
The leach solution was contacted with the organic solution of nickel D2E in a five-stage countercurrent ex-; traction. The extraction was carried out in mixer-settlers of conventional design. The aqueous to organic volume ratio was about 1:1 and the temperature was about 80C.
The aqueous solution (raffinate) obtained from the extraction was sent to the nickel sulphate crystallisation.
The organic ~olution obtained from the extraction contained 20.3 g/l of cobalt as cobalt D2E and 9.3 g/l of nickel as nickel D2E and substantially no sodium. This organic solution was then scrubbed with aqueous sul~huric acid containing about 90 g/l of sulphuric acld. The scrub--- bing was a three-stage countercurrent scrub in conventional mixer-settlers and used an overall organic to aqueous volume ratio of about 5.2:1, with recycling of the aqueous pha e to produce an effective organic to aqueous volume ratio -of about 1:1. The scrubbing was carried out at about 70C.
The aqueous phase leaving the scrub contained about 53.5 g/l of nickel and about 4.8 g/l of cobalt.
The organic solution obtained from the scrub contained some D2E acid, 19.1 g/l of cobalt and 0.063 g/l of nickel. The cobalt and nickel were stripped from this organic solution by a three-stage countercurrent strip in 75~7~

conventional mixer-settlers, using aqueous sulphuric acid containing about 90 g/l of sulphuric acid. The temperature used was about 85C and the organic to aqueous volume ratio was about 2.7:1.
The aqueous phase obtained from this strip con-tained as sulphates substantially all the cobalt and nickel from the organic phase and contains about ~5 g/l of cobalt sulphate and about 15 g/l of sulphuric acid. The cobalt sulphate was crystallised. The crystals produced had a cobalt/nickel weight ratio of about 250:1.
The stripped organic solution contained D2E acid and only 0.001 g/l of nickel and 0.0004 g/l of cobalt. This solution was vigorously stirred with an aqueou~ solution con-taining 50% by weight of sodium hydroxide to convert, by a batch method, the D2E acid to sodium D2E. The stirring was vigorous enough to prevent separation of the solutions and the amount of sodium hydroxide used was sufficient to con-vert substantially all the D2E acid to sodium salt.
sample of the organic solution produced was analysed to confirm that the conversion was substantially complete; it contained 20 g/l of sodium.
- Returning now to the aqueou3 solution obtained from the extraction [nickel/cobalt separation 2 in the accompanying drawings], this aqueous solution was sent, as already stated, to the nickel sulphate crystallisation.
This aqueous solution contained 120.6 g/1 of nickel, 0.44 g/l of cobalt and a little sodium, and was crystallised by concentrating the solution on a climbing film evaporator to about 105Tw (i.e. about 210 g/l of nickel) and crystal-lising the solution at a temperature in the range of from ~375~74 32 to 34C in a continuous crystalliser.
The nickel sulphate crystals obtained were dis-charged from the crystalliser from time to time and filtered from the mother liquor, washed and dried. The cyrstals had a nickel/cobalt weight ratio of about 250:1.
The mother liquor remaining from the crystalli-sation was used as aqueous feed in the conversion of sodium D2E to nickel D2E. The mother liquor contained 108 g/l of nickel and 0.85 g/l of cobalt. The conversion was carried out at about 80C using an organic to aqueous phase ratio of about 2.4:1 by two-~tage countercurrent contact in conventional mixer-settlers.
The organic solution produced contained 27.2 g/l of nickel, 0.36 g/l of cobalt and 0.44 g/1 of sodium. This organic solution was recycled to the nickel/cobalt separation (2 in the accompanying drawings).
The aqueous solution produced contained 46.7 gjl of nickel, 0.02 g/l of cobalt and 62 g/l of sodium. It was suitable for conversion of the nickel (and cobalt) to nickel hydroxide or carbonate.
The products of the process of this Example were thus cobalt and nickel sulphates as crystals and, if desired, nickel hydroxide or carbonate.
-~ EXAMPLE 2 A 30% by volume solution of D2E acid in Esso Mentor 28 but containing no tri butyl phosphate was con-verted to sodium salt and thence to nickel salt bv the method of Example 1, save that a synthetic mother liquor containing 120 g/l of nickel and 2 g/1 of sodium as chlorides was used as a source of nickel. The sodium/nickel exchange ~ 21 -7S47~

was carried out using an organic/aqueous phase ratio of about l:l.
The organic solution of nickel D2E obtained con-tained 26.5 g/l of nickel and only 0.15 g/l of sodium. ~his organic solution waQ used to separate cobalt from nickel in a synthetic nickel and cobalt chloride aqueous feed liquor containing about 100 g/l of nickel, 15 g/l of cobalt and no sodium. The separation was carried out in four counter-current stages in mixer-settlers using an aqueous to organic phase volume ratio of 1.5 to l and a temperature in the mixers of about 80C.
The organic cobalt-laden phase obtained may be treated by the method used in Example l (or the sulphuric acid in that Example may be replaced by hydrochloric acid) to obtain cobalt sulphate and reformed D2E acid which could be recycled to the beginning of this Example.
The aqueous raffinate obtained from the nickel/
`~ cobalt separation had the following analysis: ll9 g/l of nickel, 0.49 g/l of cobalt and 0.10 g/l of sodium, i.e.
a Ni/Co weight ratio of about 240:1 and a Ni/Na weight ratio of about 1200:1.
This raffinate on crystallisation gave a 67% yield of nickel as nickel chloride hexahydrate (NiCl2.6H2O) cry~tals having a Ni/Na weight ratio of about 2000:1, well within commercial requirements. The mother liquor from this crystallisation, mixed with washings from the crvstals, contained 150 g/l of nickel and 0.25 g/l of sodium and so has a higher Ni/Na weight ratio than the s~nthetic mother liquor used to start this ~xample; therefore the mother liquor and washings mixture is ~uitable, possibly diluted, . , .

`
.
, :~

~C3 7S47~

for stable recycling to the beginning of the Example and the process can be operated as a continuous cycle.
In comparison, if -the sodium D2E referred to above were used in the nickel/cobalt separation of the feed liquor used above the raffinate obtained would be expected to contain about lO0 g/l of nickel and lS g/l of sodium, i.e. a Ni/Na weight ratio of about 6.7:1. A
synthetic raffinate of this composition was crystallised but it was found that ~odium chloride crystalli~ed before nickel chloride and accordingly it is not possible to obtain nickel chloride crystals with a good Ni/Na weight ratio in a single step from such a raffinate because of the low solubility of sodium chloride.

A 30~ by volume solution of D2E acid in Esso Mentor 28 was converted to sodium salt and then to nickel salt by the method of Example l, save that a synthetic mother liquor containing 150 g/l of nickel and 5 g/l o~
sodium as nitrates was used as the source of nickel. The sodium/nickel exchange was carried out at about 70C using an organic to aqueous phase volume ratio of about 2:1.
-~ The organic solution of nickel ~2E obtained contained 20.2 g/l of nickel and l.0 g/l of sodium.
This organic solution was used to separate cobalt from nickel in a synthetic nickel and cobalt nitrate aqueous feed liquor containing about 126 g/l of nickel, 18.1 g/l of cobalt and 0.4 g/l of sodium, i.e. a Ni/Co weight ratio of 7:1. The sepaxation was carried out in four countercurrent stages in mixer-settlers using an aqueous to organic phase volume ratio of about 1.5:1 and a temperature in the mixers of about 80C.

.

~7547~

The organic cobalt-laden phase obtained had an analysis of 7.58 y/l of nickel, 18.9 g/l of cobalt and 0.54 g/l of sodium. This organic phase may be treated b~ the method used in Example 1 (or the sulphuric acid in that method may be replaced by nitric acid) to obtain cobalt sulphate and reformed D2E acid, which could be re-cycled to the beginning of this Example.
The aqueous raffinate obtained from the nickel/
cobalt separation had the following analysis: 145 g/1 of nickel, 0.27 g/] of cobalt and 0.71 g/l of sodium, i.e.
a Ni/Co weight ratio of 537:1 and Ni/Na weight ratio of 204:1.
This raffinate on crystallisation gave a 60%
yield of nickel as nickel nitrate hexahydrate (Ni(NO3)2.
6H2O) crystals having a Ni/Na weight ratio of more than 500:1, well within the commercial requirements.
The mother liquor from this crystallisation, mixed with washings from the crystals, contained 174 g/l of nickel and 1.62 g/l of sodium and so has a higher Ni/Na weight ratio than the synthetic mother li~uor used to start this Example; therefore the mother liquor and washings mix-ture is suitable, possibly diluted, for stable recycling to the beginning of the Example and so the process could be operated as a continuous cycle.

This Example shows the formation of an organic solution of the nickel salt of D2E acid by the single step conversion and the use of the resulting nickel D2E solution, ; either as freshly prepared or as recycled, to extract cobalt from a synthetic leach feed liquor.

~75~7~

A stream of a 30% by volume solution of D2E acid in Esso Mentor 28 was mixed in a conventional mixer-settler with a stream of a synthetic nickel sulphate mother liquor containing 140 g/l of nickel as nickel sulphate and about 5 g/l of sodium at an organic to aqueous phase volume ratio of 4:1. A stream of a 10~ by weight aqueous sodium hydroxide solution was simultaneously added at a rate about equal to that of the synthetic nickel sulphate mother liquor, ~o as to give an overall organic to aqueous volume ratio of about 2-1. The solutions were heated before mixing so that the temperature in the mixer compartment of the mixer-settler was about 70 to 80C. The pH of the mixed phases was ad-justed at about 5.9, a~ measured by a glass hydrogen electrode with a calomel reference electrode, by control-ling the flow of the stream of sodium hydroxide solution.
: When steady condition~ had been established in the mixer compartment for an hour or so, the organic solu-tion of the nickel salt of D2E acid overflowing from the settler compartment was collected and contained 23.0 g/l of nickel and 1.1 g/l of sodium and so had a nickel to sodium weight ratio of about 21:1.
The collected NiD2E solution was used to extract cobalt from a synthetic feed liquor containing lO0 g/l of nickel, 14.1 g/l of cobalt and 3.0 g/l of sodium and having a pH of about 5. The extraction was carried out in four countercurrent stages using an aqueous to organic phase volume ratio of l.S:l and a temperature of from 80 to 85C.
The loadPd organic phase obtained from this ~, extraction contained 2.72 g/l of nickel, 19.9 g/l of cobalt and 0.03 g/l of sodium, and was suitable for :

1~7547~1 scrubbing to remove substantially all the nickel and sodium and for strippinc3 to obtain the cobalt, and reform D2E acid for recycle to the beginning of this Example.
The aqueous raffinate obtained from the extraction contained 113.6 g/l of nickel, 1.04 g/l of cobalt and 4.1 g/l of sodium and so had a nickel to cobalt weight ratio of 109.2:1 and a nickel to sodium weight ratio of 27.7:1.
This rafEinate was crystallised to give a 45~ yield of washed NiSo4.6H2O crystals having a nickel to sodium weight ratio of more than 400:1.
; The mother liquor and washings from the crystals together contained 130 g/l of nickel and 4.6 g/l of sodium, and were suitable for preparing organic solution of nickel D2E by recycling to the beginning of this Example.

This Example shows the formation of an organic solution of the nickel salt of D2E from a s~nthetic chloride mother liquor containing about 200 g/l of nickel and 2 g/l of sodium. This mother liquor was fed as a stream to the mixer compartment of a conventional mixer-settler simultaneousl~
- with a 30~ by volume solution of D2E acid in Mentor 28 and a 10% by weight aqueous solution of sodium hydroxide. The phase volume ratio o~ the nickel chloride aqueous solution ` to the organic D2E acid solution was about 1:1, which with the sodium hydroxide solution gave an overall aqueous to organic volume ratio of about 1.25:1. The solutions were preheated so that the temperature in the mixer compartment was from 70 to 80C. When steady conditions were achieved at a pH of about 5.6 the organic solution of nickel D2E
overflowing from the settler compartment contained 25.4 ~7S~

g/l of nickel and 0.4 g/l of sodium, and so had a nickel to sodium weight ratio of about 63:1. This organic solution was suitable Eor extracting cob~lt from a feed liquor con-taining nickel and cobalt.

This Example was carried out as described in Example 5 except that the nickel solution was a synthetlc nickel nitrate mother liquor containing about 200 g/l of nickel and substantially no sodium. At a steady pH of about 5.9 in the mixer compartment, the organic solution of nickel D2E overflowing from the settler contained 26.9 g/l of nickel and only 0.2 g/l of sodium. This organic ~olution was suitable for extracting cobalt from a feed liquor con-taining nickel and cobalt.

- ~7 -

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for separating cobalt values from nickel values in an aqueous acid sulphate, chloride or nitrate leach solution, which comprises contacting the aqueous leach solu-tion with a solution, in an inert substantially water-immiscible organic liquid, of the nickel salt of an organophosphoric acid of formula (RO)2PO(OH), wherein each R, which may be the same or different, is hydrogen or substituted or un-substituted alkyl, aryl or aralkyl, with the provisos that not more than one R is hydrogen, each R group other than hydrogen contains at least 8 carbon atoms and the phosphoric acid molecule contains at least 12 carbon atoms, so as to transfer cobalt values from the aqueous leach solution to the organic solution; separating the organic solution con-taining transferred cobalt values from the aqueous raffinate solution thus obtained; and crystallising some or all of the aqueous raffinate solution so as to produce crystals of nickel sulphate, chloride or nitrate.

2. A process according to claim 1 in which the aqueous leach solution has a pH of from about 4.0 to about 6Ø

3. A process according to claim 1 or 2 in which the organophosphoric acid is di-(2-ethylhexyl) phosphoric acid.

4. A process according to claim 1 or 2 in which the organic liquid is a kerosene or a naphtha.

5. A process according to claim 1 or-2 in which the organic solution containing transferred cobalt values is scrubbed to increase the cobalt to nickel ratio therein.

6. A process according to claim 1 in which the organic solution containing transferred cobalt values is stripped to remove substantially all the cobalt values and form an organic solution containing the organo-phosphoric acid itself.

7. A process according to claim 6 in which the organophosphoric acid is reconverted to its nickel salt, and the solution of nickel salt produced is recycled for contact with the aqueous leach solution.

8. A process according to claim 7 in which the organophosphoric acid is reconverted to its nickel salt by first converting the acid to its alkali metal or am-monium salt and then contacting the organic solution of this salt with mother liquor from the crystallisation of the aqueous raffinate containing nickel sulphate, chloride or nitrate.

9. A process according to claim 1 or 2 in which the aqueous leach solution is a sulphate solution.

10. A process according to claim 7, in which the organo-phosphoric acid is reconverted to its nickel salt by thoroughly mixing the organic solution of the organophosphoric acid, an aqueous solution of nickel sulphate, chloride or nitrate, and an aqueous alkaline solution, to cause transfer of nickel values from the aqueous nickel solution to the organic solu-tion.

11. A process according to claim 10 in which the aqueous solution of nickel sulphate, chloride or nitrate is mother liquor from the crystallisation of the aqueous raffinate containing nickel sulphate, chloride or nitrate.

12. A process according to claim 10 or 11 in which the reconversion is carried out substantially continuously, the mixed aqueous phase is substantially continuous and the pH of this phase is maintained in the range of from 5.0 to 6Ø

13. A process according to claim 10 in which the aqueous alkaline solution is of ammonium hydroxide or of an hydroxide of an alkali metal.

14. A process according to claim 1 in which the or-ganic solution of the organophosphoric acid or salt thereof in the organic liquid is substantially free of added emulsion inhibitor.