BACKGROUND OF THE INVENTION Pure nickel metal can be recovered by electrolysis of aqueous solutions of nickel salts, such as nickel chloride and/or nickel sulfate. In order to produce pure nickel metal, of at least 99.8 % purity, it is necessary to keep most transition metal impurities, e. g., copper, iron, manganese, and cobalt, at extremely low levels in the nickel electrolyte. In addition, other impurities, e. g., chromium, iron, aluminum and calcium, can cause significant deterioration of the physical properties of the nickel metal cathodes, rendering a nickel electrowinning process impractical. Thus, in commercial practice, it is usually necessary to use extremely pure nickel electrolyte. Other nickel processes, e. g. hydrogen reduction of nickel solution to form nickel powder, also require pure solutions.

Cobalt occurs in association with nickel in most of its ores, both laterite or oxide ores, and sulfide ores. The so-called limonitic ores (high iron oxide and hydroxide content, low magnesium silicates content) in particular often contain cobalt at ! 1/2 olh the nickel concentration. In certain ores, the cobalt content can even exceed the nickel content, which makes these ores more amenable to cobalt recovery only. This will still Sample Ni (%) Co (%) Fe (%) Mg (%) Sulfide ore A 0.5 0.02 5 25 Sulfide ore B 1.4 0.1 35 Sulfide concentrate A 9 0.3 17 Sulfide concentrate C 3 0.1 14 15 Sulfide concentrate D 10 0.2 25 8 Sulfide concentrate E 12 0.3 30 6 Limonite 1 1.6-1.9 0.15-0.2 15-18 Limonite 2 1.4 0.3 43 1 Limonite 3 0.9 0.05 29 4 Limonite 4 0.7 0.02 35 0.4 Saprolite 5 2.5-2.9 0.05-0.1 14-15 12-18 Saprolite 6 2.0 0.07 21 11 Saprolite 7 2.4 0.06-0.09 13-16 15 Limonite, typical 0.8-1.8 0.05-0.2 30-50 0-10 Saprolite, typical 1.8-3.5 0.01-0.05 10-30 10-25 Oxide ore # 0. 02-0.1 0.3-1.0 2-5 require the removal of nickel for the production of pure cobalt metal. Table 1 shows typical compositions for various sulfide and oxide ores and concentrates: Table 1 : Typical composition for various sulfide and oxide ores and concentrates Production of nickel that meets the London Metal Exchange contract specifications (Class I nickel), requires that the cobalt content of the nickel be less than 0.15%. This corresponds to a nickel to cobalt ratio of about 665, which is at least 33 times larger than the ratio in the limonitic ore. Successful nickel processing therefore requires an effective nickel/cobalt separation step. Unfortunately, the chemical similarity of nickel and cobalt makes their separation difficult.

Similarly, the production of high purity cobalt faces the same problems as the production of high purity nickel. Therefore, there is a continuing need for a process to produce both high purity nickel and high purity cobalt.

One commercial process for recovery of nickel and cobalt from limonite ores is described in M. E. Chalkiey and I. L. Toirac,"The acid pressure leach process for nickel and cobalt laterite. Part i: Review of operation at Moa"in Hydrometallurgy and Refining of Nickel and Cobalt, edited by W. C. Cooper and I Mihaylov, Proceedings of 27"annal Hydrometallurgical Meeting, The Metallurgical Society of CIM, Canada, 1997, pp. 341- 353. In this process, sulfuric acid pressure leaching (SAPL) is used to solubilize nickel and cobalt as sulfate salts, while precipitating most of the contained iron as hematite.

Other impurities, such as copper, manganese, magnesium, calcium, chromium, and aluminum, partially or completely dissolve. Thereafter, the nickel and cobalt must be separated from all of these impurities prior to recovery of the pure forms of nickel and cobalt. The first step in this purification process involves precipitation of the nickel and cobalt (plus copper and zinc impurities) as a mixed sulfide phase by the addition of hydrogen sulfide gas under pressure and at a slightly elevated temperature (about 120°C). This step is reasonably effective for separating nickel and cobalt from manganese, magnesium, calcium, chromium, aluminum, and iron, because the latter elements do not precipitate to any great extent. The purifie, solid (Ni, Co) S is separated from the barren solution by settling and filtration. Unfortunately, the mixed sulfide needs to be redissolved and further purifie prior to separation of the nickel and cobalt, and recovery of the pure metals. The redissolution and further purification is generally accomplished by releaching the mixed sulfide with water or aqueous solution of ammonia and ammonium sulfate and air or oxygen, under pressure and, in the case of water leaching, at elevated temperature (about 180-200°C). Thus, in this method, the production of a relatively pure nickel-cobalt solution from the ore requires three successive pressure metallurgy and solid/liquid separation steps that add to the complexity of the process. Moreover, the process uses hydrogen sulfide gas, a highly toxic and expensive compound, under pressure.

Because of the disadvantages of sulfide precipitation, it has been propose to directly recover nickel and cobalt as separate pure solutions from leach liquor.

One route is by using extractants developed by Cytec Ltd., as for example described in U. S. Pat. No. 5,378,262 and 5,447,552. These Cytec extractants are organic phosphinic and thiophosphinic compound and have high cobalt and nickel separation coefficients in sulfate systems, ranging from 5 for alkylated monothiophosphinic to >2500 for alkylated phosphinic acid. The separation coefficient (S) compares the distribution of the two metals between the aqueous and organic phase and is defined as: S = DA/DB where DA and DB are the distribution coefficients of the two metals at equilibrium. The distribution coefficient in turn is defined as : D = [Concentration of metal in organic phase]/ [Concentration of metal in the aqueous phase] One phosphinic compound is Cyanex 272, bis (2,4,4-trimethylpentyl) phosphinic acid. The extraction characteristics of Cyanex 272 as a function of solution pH are shown in Table 2 and FIG. 3. The pHso value in Table 2 represents the pH at which 50% of the metal is extracted from the aqueous into the organic phase at an organic to aqueous phase ratio of 1: 1.

Table 2: Comparison for metal extraction (0.001 M sulfate) from different Cyanex extractants (at 0.1M in xylene) Extractant pH50,Ni2+pH50,Mn2+pH50,Cu2+pH50,Zn2+pH50,Fe3+Co2+ Cyanex 272 5.2 7.05 3.5 4.6 3.0 1.6 Cyanex 302 4.0 5.8 4.8 <-1 1.8 1.0 Cyanex 301 0.85 1.55 N/A <-1 ~0 4 0 Obtained from K. C. Sole, J. B. Hiskey,"Solvent extraction characteristics of thiosubstituted organophosphinic acid extractants", Hydrometallurgy, 30, pp. 345-65 (1992) and Cytec Product Information FIG. 3 (which is derived from product information available from Cytec) shows the metal extraction as a function of solution pH for various metal sulfate solutions. The distance between the curves for any two metals increases as the separation coefficient increases. Thus, nickel and cobalt can be easily separated from each other with Cyanex 272, by extracting cobalt at a pH of about 5.5. At this pH, nickel extraction is negligible and cobalt extraction is more or less complete. Unfortunately, a substantial amount of copper and manganese is also extracted at this pH. Since manganese is always present in laterite leach liquors, the cobalt strip liquor would be contaminated if the leach liquor were treated directly by solvent extraction with Cyanex 272.

Magnesium and calcium may also cause problems in the solvent extraction process, if present in the feed solution, because these elements are extracted at pH values close to that at which cobalt is extracted (see FIG. 3).

The compound bis (2,4,4-trimethylpentyl) monothiophosphinic acid, commercially known as Cyanex 302, avoids the above problem, because manganese is extracted at higher pH values than cobalt, as shown in Table 2. Cyanex 302, however, may be unstable in the presence of certain impurities (such as iron) and its consumption would be uneconomically high to be practical for direct treatment of laterite leach liquors.

The compound bis (2,4,4- trimethylpentyl) dithiophosphinic acid, commercially known as Cyanex 301, also avoids the manganese problem, but this compound extracts some impurities, e. g. copper and ferric iron, almost irreversibly, resulting in poisoning of the extractant. Copper is almost always present in laterite leach liquors and can be removed by other means prior to treatment with Cyanex 301. Nevertheless, if there were an upset in the copper removal process, the subsequent Cyanex 301 processing circuit could be irreversibly contaminated with copper.

Another propose process for extracting nickel and cobalt from limonite ores uses the above-described sulfuric acid pressure leaching process (SAPL), followed by solvent extraction with Cyanex 301. This process is described in U. S. Pat. No.

5,378,262 and 5,447,552. In this process, hexavalent chromium, ferric iron and copper are first removed. The solution is then contacte with a water-immiscible organic phase containing an organic soluble dithiophosphinic acid to recover and separate nickel and/or cobalt. This patent has one important disadvantage, the extractant will not allow repeated use in the presence of iron. For example, U. S. Pat. No. 5,759,512 reports that small concentrations (20-50 mg/1) of ferric iron Fe (III) present in the aqueous feed caused significant oxidation of this extractant. Because the nickel in nickeliferous oxide ores is partially contained in iron oxides, the presence of small amounts of iron in the acid leach solution is inevitable even after precipitation of the ferric iron.

Another route for the recovery of metals from solution is through ion exchange (IX), which has been applied, for example, in the extraction of uranium. This technique is very useful for the recovery of ionic compound into a purifie and more concentrated eluate solution. One avantage of ion exchange is the ability to operate in the presence of solids, which can be flushed out of the resin with properly designed back wash steps. This is contrary to solvent extraction, where any suspende solids, such as fine clays or colloidal silica typically present in leach liquors, will cause'crud' formation. Crud may impair the organic/aqueous phase separation, leading to high organic losses and increased entrainment of organic in the aqueous phase and aqueous in the organic phase. This entrainment may cause operating problems in the downstream recovery processes and increased reagent consumption. Other avantages of ion exchange are the ease of handling solid resin beads and the chemical stability of resins at elevated temperatures. In solvent extraction, evaporation and flammability of the organic may limit the operating temperature to typically less than 50°C. Many ion exchange resins can easily handle higher temperatures up to normal solution boiling points, which enhances the resin kinetics and metals separation. The ability to operate at higher temperature also allows immediate treatment of the process solutions, as most leach solutions have temperatures over 50°C. For example, in the case of laterite pressure leaching, the prenant leach liquor is produced at a temperature close to the normal boiling point of the solution. Thus expensive cooling steps are not required and greater thermal efficiency is possible.

It is, therefore, the object of the present invention to provide an economical process to recover substantially pure nickel and cobalt solutions from leach solutions by selective extraction with organic extractants, without degradation that would limit the repeated use of the organic extractant.

SUMMARY OF THE INVENTION The present invention provides a process for the selective recovery of pure nickel and cobalt solutions, suitable for electrolysis or other final recovery steps, from a feed solution. Preferably, the feed solution is obtained from sulfuric acid leaching of nickel and cobalt bearing laterite or oxide ore. The laterite ore may include the saprolite and/or limonite.

In general, the process inclues the steps of providing an aqueous feed solution containing nickel, cobalt, and at least one element selected from the group consisting of manganese, magnesium, calcium, iron (II), and chromium (lit), contacting the feed solution with a solid ion exchange resin to form a nickel and cobalt-loaded resin and an ion exchange raffinat, eluting the nickel and cobalt from the resin to form an eluate containing a soluble nickel salt and a soluble cobalt salt, contacting the eluate with a water-immiscible organic phase containing an extractant to load cobalt onto the extractant to form a cobalt-containing organic phase and a nickel-containing raffinat, and separating the cobalt-containing organic phase from the nickel-containing raffinat.

Each of the separated cobalt-containing organic phase and nickel-containing raffinat can be further treated to form a solution suitable for electrowinning or other process to recover substantially pure nickel and cobalt products. The nickel resulting from the electrowinning step meets the London Metal Exchange contract specification arid therefore, contains less than 0.15% by weight of cobalt. Similarly, the cobalt resulting from the electrowinning typically contains less than 0.1 % by weight of nickel.

By using ion exchange for the primary metals (nickel and cobalt) recovery, many disadvantages of solvent extraction are overcome. These include crud formation due to the presence of solids, extra purification steps for the removal of organics from the product stream, possible degradation of the organic thiophosphinic acids, and the ability to operate at elevated temperatures.

In one embodiment, any copper and chromium (VI) are removed from the feed solution prior to contact with the ion exchange resin. In another preferred embodiment, the raffinate from the ion exchange resin is contacte with at least a second ion exchange resin.

It is noted that, unless otherwise stated, all percentages given in this specification and the appende claims refer to percentages by weight.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow sheet for the process of the present invention.

FIG. 2 is a flow sheet showing one embodiment of the process of the present invention.

FIG. 3 is a graph of percentage of extraction of an element using Cyanex 272 in a sulfate solution at varying pHs.

DETAILED DESCRIPTION OF THE INVENTION Turning now to FIG. 1, a flow sheet for the process of the present invention is shown. In general, a feed solution 1 is contacte with an ion exchange resin in ion exchanger 10 to selectively load nickel and cobalt and to form a nickel and cobalt- loaded resin and a raffinate 2 that contains most of the impurities present in the feed solution. A strip solution 3 contacts the nickel and cobalt-loaded resin to elute the nickel and cobalt from the resin and to form an ion exchange eluate solution 4 that contains a soluble nickel salt and a soluble cobalt salt, substantially purifie of most of the impurity elements present in the feed solution. The eluate is then subjected to liquid/liquid extraction 20 by contacting the eluate 4 with an organic phase that contains an extractant to load cobalt onto the extractant to form a cobalt-containing organic phase and a nickel-containing raffinate. Thereafter, the cobalt-containing organic phase is separated from the nickel-containing raffinate (pure nickel solution) 6. A strip solution 5 contacts the cobalt-containing organic phase to recover a pure cobalt solution 7. Both the pure nickel solution and the pure cobalt solution may be subjected to further processes such as electrowinning to recover pure nickel and cobalt, respectively.

In the present process, the feed solution contains nickel and cobalt, as well as other elements such as aluminum, chromium, manganese, magnesium, calcium, iron, copper, and zinc. Preferably, the feed solution is derived from an ore that contains nickel and cobalt. This can be accomplished, for example, by leaching either oxide or sulfide ores with mineral acids or bio-leaching of sulfide ore. In addition, the feed solution may be derived from any of the processes described in PCT publication WO 97/04139, the relevant portions of which are incorporated herein by reference. The mineral acid may be selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof. The ore may be any laterite (oxide) or sulfide ore and the laterite ore may include the saprolite and limonite. Such ores generally contain about 0.5% to about 3% nickel and about 0.005% to about 0.5% cobalt.

The feed solution may be further treated after the acid leaching such as by neutralizing with a base (e. g., limestone) as is known and conventional in the art.

The feed solution is contacte with a solid ion exchange resin to selectively extract nickel and cobalt, while rejecting manganese, magnesium, calcium, iron (li), and chromium (lil), if present in the feed solution. The ion exchange resin is preferably a chelating resin that selectively absorbs nickel and cobalt. The simplifie chemical rection for the ion exchange is as follows: 2HR + M2+- MR2 + 2H+ In this equation, the underlined species represent the resin and M represents any metal, preferably Ni2+ or Cl2+.

Suitable chelating ion exchange resins include those derived from aminopyridine compound such as the 2-picolylamines described in U. S. Pat. No. 4,098,867 and 5,141,965, the relevant portions of each are incorporated herein by reference. A preferred chelating resin contains a functional group selected from the group consisting of 2-picolylamine, bis- (2-picolyl) amine, N-methyl-2-picoylamine, N- (2-hydroxyethyl)-2- pocolylamine, and N- (2-hydroxypropyl)-2-picoylamine, and mixtures thereof. Suitable resins inclue Rohm and Haas IR 904, Amberlite XE 318, Dow XFS-43084, Dow XFS- 4195, and Dow XFS-4196. The Dow XFS-4196 contains N- (2-hydroxyethyl)-2- picolylamine and the XFS-43084 contains N- (2-hydroxypropyl)-2-picolylamine. A preferred chelating resin is Dow XFS-4195, manufactured by The Dow Chemical Company. It contains bis- (2-picolyl) amine as the primary chelating group.

The distribution coefficients for a variety of elements using XFS 4195 are shown in Table 3 (the values are obtained from K. C. Jones and R. R. Grinstead,"Properties and hydrometallurgical applications of two new chelating ion exchange reins", Chemistry and Industry, 6 August 1977, pp. 637-41).

Table 3-Absorption constants for XFS 4195 in sulfate solution at pH=2 Fe3+CdZnCoFe2+CaMgAlMnCuNi 807060303<2<1<1<1700190 Nickel and cobalt can be extracted at relatively low pH (1-4), leaving all of the above-mentioned impurities in the raffinate solution. If necessary or desirable, the pH of the feed solution may be adjusted to provide for optimum selective loading of the nickel and cobalt onto the resin. Generally, the pH of the feed solution is between about 1.0 and about 5.0, preferably between about 2 and about 3.

It is also sometimes desirable to adjust the temperature of the feed solution prior to contact with the ion exchange resin to improve the kinetics of selective nickel and cobalt ion exchange. Generally, the temperature of the feed solution is between about 20°C and about 95°C, preferably between about 60°C and about 70°C.

The ion exchange process may inclue, but is not limited to, a single fixed bed of resin, two or more fixed beds in parallel or in series, or a plurality of resin columns that move countercurrently to the flow of the feed solution. For example, an ISEP continuous contactor manufactured by Advanced Separation Technologies, Inc. of Lakeland, Florida or a Recoflo ion exchange system made by Eco-Tec of Pickering, Ontario, Canada may be used.

It is to be understood that any arrangement of ion exchange resin suitable to selectively absorb substantially all the nickel and cobalt in the feed solution can be used. The term"substantially all"means that greater than 90% of the nickel and cobalt in the feed solution is absorbe.

In a preferred embodiment, the ion exchange resin is provided in two steps in series. As shown in FIG. 2, the feed solution is passed through two ion exchange steps such that the raffinate of the first stage, after neutralization, forms the feed of the second stage. By using two stages, the absorption of nickel and cobalt onto the resin is enhanced, resulting in substantially complete removal of nickel and cobalt from the feed solution. It is understood that more than two steps could be used for complete nickel and cobalt removal from the feed solution.

In the preferred embodiment shown in FIG. 2, the feed solution 101 is contacte with a first ion exchanger 110, which absorbs most of the nickel and only a small portion of the cobalt. This is because the resin is selective for nickel over cobalt while the low pH generated by the replacement of the H+ ions on the resin with the nickel prevents cobalt from loading.

The raffinate 102 from the first ion exchange step contains a small portion of the original nickel from the feed solution but most of the cobalt from the feed solution. The ion exchange raffinate 102 is treated with a base 111, such as limestone, in a neutralization process 112 to neutralize the acid generated by the first ion exchange step. Of course, it is to be understood that the acid may be completely or only partially neutralized. The degree of neutralization is generally determined based on the absorption constant (s) of the material (s) sought to be removed at a particular pH.

Generally, the pH is adjusted to provide a neutralized raffinate pH of about 2.0 to about 4, preferably from about 3 to about 3.5.

If necessary, the neutralized raffinate is subjected to a solid-liquid separation 114 to form a neutralized raffinate solution 115 (a feed solution to the second ion exchanger). The neutralized raffinate is then subjected to a second ion exchange step 116 to recover virtually all of the remaining cobalt and nickel.

To allow repeated use of the ion exchange resin, the feed solution desirably has low levels of chromium (VI) and copper because the chelating resins containing the 2- picolylamines as functional groups have a high affinity for copper and for chromium (VI) (but do not load or absorb chromium (lil)). These elements can be removed by well- known techniques, such as chemical reduction or ion exchange. For example, the copper and chromium (VI) may be removed by a metal cementation step using iron, zinc or even nickel to reduce chromium (VI) to chromium (III) and to cement copper.

Therefore, the process of the present invention contemplates the additional step of removing copper and/or chromium prior to contacting the feed solution with the ion exchange resin.

In a preferred embodiment of the invention, copper is removed from the feed solution prior to contact with the ion exchange resin. It is also recognized that if the copper concentration is very low, this removal step may not be required. Copper removal can be carried out with a number of ion exchange resins or by selective sulfide precipitation at low pH, or by any other method apparent to those skilled in the art. For example, the copper can be precipitated from the feed solution by adding to the feed solution a sulfide-containing compound selected from the group consisting of H2S, NaHS, and mixtures thereof.

It has also been found convenient to use a resin with iminodiacetate functionality, for example, the resin IRC 718 manufactured by Rohm and Haas. This resin extracts copper in preference to nickel and cobalt as shown in Table 4 (the values are obtained from W. H. Waitz, Jr., "lon exchange in heavy metals removal and recovery", Amber-hi-lites #162, Rohm and Haas Company, Philadelphia, PA, Fall 1979) Table 4-Absorption constants for IRC-718 relative to calcium at pH=4 Hg Cu Pb Ni Zn Cd Co FeZ+ Mn Ca 2800 2300 1200 57 17 15 6. 7 4.0 1.2 1 1.0 | In another preferred embodiment of the invention, chromium (VI) is removed from the feed solution prior to contact with the ion exchange resin. It is also recognized that if the chromium (VI) concentration is very low, this removal step may not be required.

The chromium (VI) can be removed by a variety of techniques. For example, chromium (VI) can be converted to chromium (vil) by reduction, for example, with gaseous suifur dioxide.

Zinc may also be present in the feed solution and the ion exchange resin will extract the zinc with the cobalt. Because the zinc is generally carried with the cobalt, it does not unduly contaminate the resulting nickel solution. If, however, it is desired to produce cobalt substantially free of zinc, it can be removed from the ion exchange eluate by solvent extraction or ion exchange, in any manner understood by those skilled in the art. For example, solvent extraction using di-2, ethyl hexyl phosphoric acid can be used. The cobalt can then be extracted from the resulting pure solution using Cyanex 272.

To recover the nickel and cobalt from the nickel and cobalt loaded resin, it is eluted with a strip solution 3 (103) to form an ion exchange eluate solution 4 (104a, 104b, 104) containing a soluble nickel salt and a soluble cobalt salt. Before eluting the nickel and cobalt, the resin may be washed with water to remove entrained raffinate solution. Where more than one ion exchanger is used, the eluate from each (104a, 104b) may be combine (104) before the solvent extraction process 20 (120).

The strip solution may be any protonated material that will selectively replace the nickel and cobalt with H+ ions. The strip solution 3 (103), therefore, may be a mineral acid selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, or other suitable acid. The choice of suitable acid depends on the subsequent nickel- cobalt separation process. Because the present invention contemplates the use of solvent extraction to separate the nickel from the cobalt, the choice of mineral acid will, in large part, be dictated by the choice of extractant. For example, where the extractant exhibits favorable nickel-cobalt separation coefficients in a chloride solution, the selected mineral acid will be hydrochloric acid. Preferably, sulfuric acid is used because the preferred extractant, Cyanex 272, exhibits large nickel-cobalt separation coefficients in the sulfate system.

In a preferred embodiment of the invention, shown in FIG. 2, the stripping solution inclues at least a portion of spent electrolyte 131 from a subsequent nickel electrowinning step. If feasible, the spent electrolyte can form all or a portion of the stripping solution 131 (3). The electrowinning rection generates one mole of sulfuric acid for each mole of nickel electrowon. Each mole of acid so generated can theoretically strip one mole of nickel and cobalt from the loaded ion exchange resin.

Thus, the ion exchange process can operate in a closed circuit with the electrowinning step, allowing the spent electrolyte to contain a high concentration of nickel. This nickel is recycle to the ion exchange step and not lost.

As shown in FIG. 2, the ion exchange eluate is treated with a base 105 in a neutralization process 108 and subsequently, if necessary, separated in a solid-liquid separation 109 to leave an ion exchange eluate suitable for separation of the cobalt from the nickel.

The neutralized ion exchange eluate 4 (104) is contacte with a water-immiscible organic phase containing an extractant for the selective extraction of cobalt, leaving nickel in the raffinate 6 (106) as a substantially pure nickel solution.

One method for the separation of cobalt from nickel in chloride solutions is by solvent extraction with tri-butyl phosphate (TBP) and tri-iso-octyl amine (TIOA).

Impurities such as iron, copper and manganese, however, need to be removed prior to cobalt extraction. Another method is by solvent extraction with Cyanex 301, such as described in U. S. Pat. No. 5,378,262 and 5,447,552.

If the ion exchange resin is stripped with sulfuric acid, the extractant for the cobalt and nickel separation can be selected from phosphoric, phosphinic and thiophosphinic compound. Preferably, the extractant is selected from the group consisting of bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), bis (2,4,4- trimethylpentyl) monothiophosphinic acid (Cyanex 302), and bis (2,4,4- trimethylpentyl) dithiophosphinic acid (Cyanex 301). More preferably, the extractant is bis (2,4,4- trimethylpentyl) phosphinic acid (Cyanex 272).

The pH may be controlled at about 5 to 5.5 by addition of a base, such as NaOH solution, during the extraction to neutralize free acid liberated by cobalt extraction.

Virtually all of the cobalt can be extracted in this manner. The term"virtually all" means that greater than 99%, preferably greater than 99.8% of the cobalt can be extracted. A small portion of the nickel is also extracted, but this can be"scrubbed"off the loaded organic by contact with a strong cobalt solution, such as the product strip liquor.

Interference by manganese, magnesium, and calcium, as well as other trace impurities is virtually eliminated because of the excellent purification against these impurities afforded by the previous ion exchange process.

As shown in FIG. 1, the extraction process 20 (120) separates the nickel and cobalt into a resulting pure nickel solution 6 (106) and a cobalt-containing organic phase. The nickel containing raffinate may be further processed such as by electrowinning.

The cobalt-loaded organic solution is stripped with a strip solution 5 to recover substantially pure cobalt solution. The strip solution may be a mineral acid and can be selected from the group consisting of sulfuric acid and hydrochloric acid. The resulting pure cobalt solution 7 (107) can be further processed such as by electrowinning.

In a preferred embodiment of the above solvent extraction process, best seen in FIG. 2, the cobalt-loaded organic solution is stripped with spent electrolyte 141 from a subsequent cobalt electrowinning step 140. This spent electrolyte contains one mole of sulfuric acid for each mole of cobalt electrowon. This is the quantity of sulfuric acid required by the organic stripping rection, thus allowing the electrowinning circuit to operate in closed circuit with the cobalt solvent extraction circuit.

As also shown in FIG. 2, the resulting pure nickel solution 106 is further processed by electrowinning 130. The spent electrolyte 131, with some concentrated sulfuric acid added as make-up, is used as the ion exchange strip solution 131.

The following examples illustrate, but do not limit, the present invention. Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLE 1 This example illustrates the problem of contacting the feed solution (resulting from acid leach) with an organic phase containing the extractant, Cyanex 272.

Typically, after sulfuric acid pressure leaching and limestone neutralization for ferric iron removal, a laterite leach solution would contain metal sulfates, as 5-8 g/l Ni, 3-20 g/l Mg, 1-4 g/l Mn, 0.5-2.0 g/l Co and 0.2-4.0 g/l Al. Figure 3 shows that co-loading of Mn and Co will occur, because the Mn and Co extraction curves are very close to each other. Because of the high Mn to Co ratio (3: 1) in laterite leach liquor, Mn will load in preference to cobalt. Therefore, Cyanex 272 is not suitable for the direct treatment of the laterite leach liquor (feed solution) to separate cobalt from other impurities in the leach liquor.

EXAMPLE 2 This example shows the co-loading of impurities with cobalt in an organic phase containing the extractant, Cyanex 272. Using an acid leach liquor, iron was oxidized with hydrogen peroxide, neutralized to pH of 5.8 to precipitate all iron, and filtered prior to the experiment. The feed solution was mixed for 5 minutes with different volumes of 15% v/v Cyanex 302 in kerosene (Philips Orfom SX12) in a baffled beaker at a total volume of 120 ml. The phases were allowed to separate after mixing and then an aqueous sample was taken. The expriment was done at room temperature, controlling the pH by the addition of 0.5N NaOH to obtain a final pH of 5.0. The composition of the feed solution and raffinate is shown in Table 5.

Table 5-Aqueous concentration for Cyanex 272 shake-out test Solution O: A Ca Co Mg Ni Fe Mn Zn Co/Ni ratio g/i g/I g/I g/l g/l g/l g/l sep. Feed 0.60 7.45 0.17 9.23 0.001 0.086 0.400 n. a. Raffinate 1 0.55 1.67 0.16 9.08 <. 001 0.006 <. 001 210 5 0.21 0.11 0.06 8.45 <. 001 <. 001 0.001 723 10 0.09 0.04 0.03 7.88 0.002 <. 001 <. 001 1081 The expriment shows a good separation between cobalt and nickel, but a poor separation between manganese and cobalt. It also shows the co-loading of other impurities, such as calcium and magnesium, with the cobalt. This shows that Cyanex 272 is not suitable for the direct treatment of the laterite leach liquor to separate cobalt from other impurities in solution.

EXAMPLE 3 This example illustrates the degradation of thiophosphinic acid in the presence of iron sulfate. An aqueous cobalt/iron sulfate solution was mixed for 5 minutes with an equal volume of 10% v/v Cyanex 302 in kerosene (Philips Orfom SX12) in a baffled beaker. The phases were allowed to separate and then the organic was contacte with a fresh aliquot of the feed solution. The expriment was done at room temperature, maintaining the pH at 3.5 by the addition of 0.9N NaOH. This was repeated eight times, so that the organic was contacte nine times with the same concentration feed solution. The composition of the feed solution and raffinate is shown in Table 6.

Table 6-Aqueous concentration for Cyanex 302 shake-out test Solution Contact Co Fe Fie2+ g/l g/l g/l Feed 2.25 4.22 3.89 Raffinate 1 1. 98 3.82 3.85 2 1.83 3.75 3.64 3 1.66 3.73 3.61 4 1.47 3.49 3.48 5 1.32 3.28 3.24 6 1.16 3.06 3.00 7 1.15 2.57 2.54 8 1.06 2.17 2.28 9 0.95 1.88 1.89 The data show how the iron content gradually decreased to 3.06 g/l after six contacts. In the next three contacts, there was substantial precipitate formation, while decreasing the iron content to 1.88 g/l. The precipitate, thoroughly washed to remove any entrained organic, was analyzed to find elemental sulfur and phosphorous, indicating the chemical degradation of the extractant.

EXAMPLE 4 This example illustrates the instability of monothiophosphinic acid and the conversion to dithiophosphinic acid in the presence of iron sulfate in continuous multi- stage counter-current solvent extraction operation. An aqueous sulfate solution containing, 0.74 g/l iron (II), 0.08 g/l iron (lit), 3.65 g/l nickel (II), 0.38 g/l cobalt (II), 1.65 magnesium (II) and 1.54 g/l manganese (II), and having a pH of 5.0 at a temperature of 23°C, was contacte in a counter-current fashion in two consecutive extraction stages at a flow-rate of 78 ml/min with a 10 vol % solution of Cyanex 302 extractant in kerosene (Philips Orfom SX12). The organic flow rate was 33 ml/min, which gives an A/O ratio of 2.4. Sodium hydroxide at 0.2 N was added to maintain the pH at 4.5. The loaded organic solution was contacte in a counter-current fashion in two consecutive scrubbing stages with a bleed stream from the cobalt eluate. The cobalt eluate flow rate was 1.5 ml/min with an aqueous recycle of 15 ml/min, to maintain an A/O ratio of 0.5. The scrubbed organic was contacte in a counter-current fashion in three consecutive stripping stages. The strip solution contained 22.5 g/l cobalt (II), 0.03 g/l iron (II), 0.04 g/l nickel (II), and 10 g/l sulfuric acid and was fed to the stripping stages at a flow-rate of 12 ml/min. After five hours, the continuous operation was stopped because of the formation of crud and poor metal loading. The composite eluate contained 27.8 g/l cobalt (II), 0.16 g/l iron (III), 2.85 g/l manganese (il), and 0.22 g/l nickel (II) at pH of 3.23. Elemental sulfur crystals were recovered from the organic storage container and the mixers/settlers. Chemical analysis by the manufacturer showed that over 90% of the original extractant, Cyanex 302, had converted to Cyanex 272. This would explain the manganese loading, because Cyanex 272 has greater affinity for manganese than cobalt.

EXAMPLE 5 This example illustrates the scavenging of copper with a chelating resin. As shown in Table 3, copper has higher affinity to XFS 4195 than nickel and cobalt. After SAPL leaching, there is copper in the leachate, though typically less than 100 mg/l. To prevent loading of this trace amount of copper on the XFS 4195 and contamination of pH Cu (mg/1) SAPL Leachate 1 Feed solution 1.9 106 Raffinat (45 BV) n. a. 0.8 SAPL Leachate 2 Feed solution 1.5 45 Raffinat (10 BV) n. a. 0.0 the ion exchange eluate with copper, an ion exchange scavenging step for copper is used ahead of Ni and Co ion exchange. SAPL leachate was passed through a 200 ml IRC718 column at 60-70° C at a flow rate of 12-30 bed volumes (BV) per hour. The feed and raffinate composition is shown in Table 7.

Table 7-Results for single column tests for copper scavenging with IRC718 EXAMPLE 6 This example describes the results from single column XFS 4195 extraction of nickel and cobalt with rejection of manganese, magnesium, calcium, aluminum, chromium, and iron (II). A synthetic laterite leach solution was prepared. The composition of this solution is typical for sulfuric acid pressure leaching, followed by limestone neutralization for iron removal and scavenging of copper with the ion exchange resin IRC718. In this experiment, the nickel and some cobalt were extracted from solution in preference to other impurities, especially manganese. A single column with 200 ml XFS 4195 resin (1 Bed Volume) was used at ambient temperature, passing the feed solution at 15 BV/hr. A total of 2.4 liters (12 Bed Volumes) of feed solution were passed through the column. A 100 g/l sulfuric acid solution was used for stripping at 6 BV/hr. A total of 1.6 liters (8 Bed Volumes) of sulfuric acid solution were used to strip the column. After collection of each bed volume, a small liquid sample was taken.

At the end, all individual samples were combine for the overall raffinate or eluate bulk sample. After loading and stripping, the resin was washed with DI water. Table 8 shows the composition of feed solution, raffinate and eluate for this single-column test.

The selectivity of the resin for nickel and cobalt over chromium (III), aluminum, magnesium and manganese (ll) is clearly demonstrated.

Table 8-Concentration profile for single-column test Solution Bed Al Co Cr Fe Mg Mn Ni Volume mg/l mg/i mg/l Mg/I mg/l Mg/l mg/l Feed 253 585 114 6 5087 1742 6532 Al Co Cr Fe Mg Mn Ni Raffinat 1 0 0 0 0 11 3 16 2 23 0 11 0 1893 555 0 3 245 0 57 0 4771 1672 0 4 274 0 97 1 5108 1840 0 5 281 40 120 9 5034 1789 1 6 285 777 130 7 5141 1841 6 7 273 1010 114 4 5038 1801 32 8 272 839 ill 4 5013 1752 177 9 266 728 108 3 4943 1730 406 10 259 733 114 4 5132 1779 1000 11 274 721 112 4 5128 1798 1940 12 268 723 113 4 5164 1820 3318 Al Co Cr Fe Mg Mn Ni Overall Raffinate 227 464 91 3 4365 1532 575 Al Co Cr Fe Mg Mn Ni Eluate 1 0 10 2 0 1 0 142 2 0 34 2 0 0 0 5802 3 0 65 3 4 0 0 26850 4 0 14 1 0 0 0 15260 5 0 0 0 0 0 0 3460 6 0 0 0 0 0 0 1192 7 0 0 0 0 0 0 429 8 0 0 0 0 0 0 214 CrFeMgMnNiAlCo Overall Eluate 0 15 1 1 0 0 6669 EXAMPLE 7 This example describes the continuous processing of neutralized laterite leach solution for the recovery and electrolytic production of cobalt and nickel. In continuous pilot plant operation, limonitic laterite was pressure leached with sulfuric acid at a throughput of 1.1 tpd, at 270°C and 0.27 ton of sulfuric acid per ton of ore, yielding about 93% nickel extraction. The autoclave discharge leach solution was neutralized with limestone, followed by liquid/solid separation in a six-stage CCD circuit. Sodium metabisulfite was added to reduce hexavalent chromium to Cr (III). The solution was subsequently passed through an ion exchange fixed bed circuit with IRC 718 resin for copper removal. This solution was used for the extraction of nickel and cobalt in two ion exchange steps in a continuous pilot plant operation for ten days. The average composition of the feed solution and raffinate for the first ion exchange step with XFS 4195 is tabulated below: Table 9-Average feed and raffinate composition for Ni IX in mg/l CoCrCuFeMgMnNiSiAlCa Feed 1214 577 514 140 2. 6 41 2949 1955 5085 90 Raffinate 3621160.019419 2364 71940 The raffinate from the nickel ion exchange step was neutralized with limestone to a pH of 3.5 and the resulting gypsum residue was removed by filtration. The filtrate solution was subsequently passed through a second ion exchange stage with XFS 4195 to recover cobalt and remaining nickel, while rejecting the major impurities. The composition of the feed (neutralized nickel ion exchange raffinate) and final raffinate for the second ion exchange step with XFS 4195 is tabulated below: Table 10-Average feed and raffinate composition for Co IX in mg/l AI Ca Co Cr Cu Fe Mg Mn Ni Si Feed 9 495 359 110 19 13 2392 1466 975 78 Raffinat 785 411 7 82 0 11 1906 1149 0 61 The nickel and cobalt recoveries calculated from the composition of the final raffinate were 100% and 97.5%, respectively. Nickel electrolyte was used to strip the loaded resin from the first ion exchanger. A dilute sulfuric acid solution was used to strip the loaded resin from the second ion exchanger. The compositions are tabulated below: Table 11-Average feed and eluate composition for Ni and CL SIX in mg/i- CoCrCuFeMgMnNiAlCa Si Ni strip feed (Ni electrolyte) 0.8 249 1. 9 15 3.0 28 32 0.4 46604 48 Ni IX eluate (first exchanger) 42 240 231 52 52 64 30 0.6 60540 47 Co IX eluate (second exchanger) 12 3 1096 26 54 1 4 7 4138 7 Both eluate streams were combine and neutralized with soda ash to a pH of about 5.5. The resulting residue with hydrolyzed impurities was removed by filtration, prior to feeding to the solvent extraction circuit. The solvent extraction (SX) circuit was operated at 40°C with 10% Cyanex 272 in Philips Orfom SX11. Sodium hydroxide at 0.5 N was used for neutralization in the extraction stages. The composition of the neutralized ion exchange eluate (SX feed) and SX raffinate is tabulated below: Table 12-Average Co SX feed and raffinate composition in mg/i Al Ca Co Cr Cu Fe Mg Mn Ni Feed 1. 6 128112570 3.9 1.0 11.0 53 12 69500 Raffinate 2.50.00.12.0350.165580273 After the SX with Cyanex 272, a very pure nickel sulfate raffinate was produced, suitable for the production of Class I electrolytic nickel. The loaded organic was stripped with acid-fortified cobalt anolyte to obtain a substantially pure cobalt solution.

Table 13-Average Co SX strip feed and eluate composition in mg/i CoCrCuFeMgMnNiAlCa Strip feed 7.0 351.0240497384640543 Eluate 10. 8 93 72182 49 4. 1 120 48 79 1073 Although the present invention has been described in conjunction with preferred embodiments and examples, it is to be understood that modifications and variations may be made without departing from the spirit and scope of the invention. Such modifications and variations are considered to be within the scope of the invention and followingclaims.