AU2007200975A1 - Process for recovering nickel and cobalt from oversize ore particles - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Applicant: PROCESS FOR RECOVERING NICKEL AND COBALT FROM OVERSIZE ORE PARTICLES BHP Billiton SSM Development Pty Ltd The following statement is a full description of this invention, including the best method of performing it known to me: 1 0067 JAN PROCESS FOR RECOVERING NICKEL AND COBALT FROM OVERSIZE ORE PARTICLES FIELD OF THE INVENTION The present invention relates to the recovery of metal values from oversize ore particles using an atmospheric pressure leach process. The present invention particularly relates to the recovery of nickel and cobalt from oversize lateritic ore particles, without the need for a preliminary particle size reduction step. The present invention further relates to an integrated process for extracting nickel and cobalt from both oversize and undersize ore fractions of a lateritic ore.

BACKGROUND OF THE INVENTION Lateritic nickel and cobalt ore deposits are renowned for the variability in mineralisation that occurs through the depth of the ore body. However a typical lateritic nickel deposit can be divided into three main zones which occur at increasing depths from the surface and treatment processes are varied to suit the nature of the mineralisation.

For instance the uppermost or limonitic zone consists of goethite, FeOOH, and is low in magnesium content with nickel grades typically from 0.8 to This material is usually processed by the Caron reductive roast/ammonium carbonate leach process or alternatively by the high pressure acid leach (HPAL) process using autoclaves and sulfuric acid (H 2 S0 4 The garnierite zone, which is at the base of the ore body contains higher nickel grades, typically 1.8 to 2.5% Ni, and may be processed by electrical smelting techniques to produce a ferro-nickel end product. Typically it cannot be processed economically by hydrometallurgical processes.

The intermediate or serpentine zone, also known as the saprolite zone, consists of various magnesium silicates containing values typically in the range 1.5 to 1.8% Ni and may be processed by the HPAL process or a combination of HPAL and atmospheric leaching (AL) depending on the magnesium content of the ore solids.

The exploitation of many of the marginal nickel content ore bodies is made difficult because it is not possible to beneficiate a laterite ore body other than by selective mining techniques and particle size separation.

If an upgrading (beneficiation) or oversize rejection step is part of the ore slurrying and preparation process prior to HPAL or AL treatment, a reject ore consisting of oversize material (75 to 1000 microns) is produced. An economical method of processing this material to recover nickel and cobalt values followed by integration of this process stream with the HPAL discharge stream would be advantageous. This is so because mining, transport and ore preparation costs have been incurred prior to its rejection based on particle size.

The present invention accordingly aims to overcome or alleviate one or more of the problems associated with the prior art.

The above discussion of the background of the invention is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

SUMMARY OF THE INVENTION According to the present invention, there is provided a process for recovering nickel and cobalt from a lateritic ore comprising an oversize (as herein defined) ore fraction and an undersize (as herein defined) ore fraction, said process including the steps: subjecting the oversize ore fraction to atmospheric pressure acid leaching at elevated temperature to produce an oversize atmospheric leached (OAL) slurry; treating the OAL slurry in order to induce precipitation of dissolved iron from solution as jarosite with minimal coprecipitation of nickel and cobalt and thereby form a jarosite-containing atmospheric leached (JAL) slurry; subjecting the undersize ore fraction to high pressure acid leaching to produce a high pressure acid leached (HPAL) slurry; combining the JAL slurry with the HPAL slurry; and; treating the combined JAL and HPAL slurries to recover nickel and cobalt.

As used herein the term "oversize" refers to ore particles having a particle size greater than about 75 microns. Typically, the oversize particles have a particle size in the range 75 to 1000 microns. However, sizes larger than 1000 microns can be treated by the inventive process provided that the equipment used in the leaching process, such as agitation and pumping equipment, is designed to accommodate the larger particle sizes.

The term "undersize ore fraction" is intended to mean those ore particles having a particle size less than the oversize ore fraction. Typically, the undersize ore fraction includes particles having a particle size less than about 75 microns.

The inventive leaching process is able to successfully leach metal values into solution from the oversize ore particles without having to first grind the ore particles to a smaller particle size.

Ore particles having a size greater than 75 microns result from the treatment of run of the mine ore by crushing and scrubbing processes followed by screening and multistage cyclone classification at which stage the <75 micron ore solids are typically transported to the high pressure acid leach (HPAL) autoclaves.

The rejects from cyclone classification, ie the 75 to 1000 micron solids, can be subjected to the inventive process described herein whereby the resulting acid leach slurry can be subsequently integrated with the discharge slurry from the HPAL treatment of the <75 micron fraction.

In step leaching process is conducted at elevated temperature and atmospheric pressure. Typically the leaching step is carried out at a temperature up to the boiling point of the leach reactants at atmospheric pressure. Preferably the reaction temperature is as high as possible to achieve rapid leaching at atmospheric pressure. The leaching temperature is at least 600C, preferably at least 750C. In an embodiment, leaching is carried out at around 800C or higher, such as at least 850C. In another, preferred embodiment, leaching is conducted at a temperature of at least 95 0

C.

Jarosite precipitation occurs during the process of the invention. The jarosite formed results in acid regeneration which is available for additional ore leaching.

In the atmospheric pressure acid leaching process of step the oversize ore particles are typically formed into an aqueous slurry and contacted with a concentrated sulfuric acid solution. The concentration of sulfuric acid is preferably greater than 90 wt and less than 100 wt The dose of sulfuric acid is preferably 100 to 140 of the stoichiometric amount required to dissolve approximately 90% of nickel, cobalt, and manganese, over 80 of the magnesium and about 30% of the iron and aluminium in the ore.

Leaching is conducted for a period of time sufficient to release at least a substantial portion of the nickel and cobalt from the laterite ore into solution.

Typically leaching is conducted for up to 20 hours. However, preferably leaching is conducted for up to 15 hours. In a preferred embodiment, leaching is conducted for between 8 to 10 hours.

Preferably, the leaching solution is a saline (particularly containing sodium chloride) or alkali (eg sodium (Na potassium and/or ammonium (NH 4 ions) containing acidic solution. The salinity of the leaching solution should be sufficient to provide enough alkali to form jarosites during the leaching and jarosite precipitation process. A suitable salinity is 1.5 times, or 150% that of seawater. A suitable solution is sea water or saline bore water to which acid is added. It may be advantageous to use such sources of water as they may be more readily available and/or less expensive to use than pure water, especially at remote mineral processing sites in arid areas.

The inventors have accordingly found that the 75 to around 1000 micron material requires no further grinding prior to atmospheric pressure leaching to achieve recoveries of 77% nickel and 80% cobalt. It has been found that the undersize fraction of the ore is relatively higher in nickel, and in associated iron and magnesium, than the oversize fraction which has higher levels of relatively inert silica. Accordingly, it has also been found that because the magnesium content of the oversize solids is low, typically as low as and the iron content also low, typically as low as acid consumption is modest and similar to HPAL systems. The equipment required is simple and the process chemistry relatively straightforward to operate and control.

In the preferred form of the invention, the leaching of oversize lateritic ore particles is incorporated into an integrated process for separately treating both oversize and undersize (as herein defined) ore fractions in order to extract metal values contained in each fraction.

In step the slurry produced by the atmospheric pressure leaching of the oversize fraction in step (hereafter "OAL slurry") is treated in order to effect precipitation of iron from solution as jarosite. Typically that treatment will include acid neutralisation of the OAL slurry. Acid neutralisation is typically effected by addition of a neutralising agent, preferably an alkaline material, more preferably an alkaline earth containing compound. Examples of suitable neutralising agents include limestone (CaC03), slaked lime (Ca(OH) 2 magnesite (MgCO 3 and/or caustic calcined magnesia (MgO). Conveniently, the neutralising agent may be naturally occurring limestone.

With further reference to step the iron containing precipitate is typically an alkali jarosite The amount of neutralising agent added to the slurry in step (b) is typically sufficient to result in a free acid concentration of less than 10 g/L

H

2 S0 4 preferably less than 7 g/L, more preferably between 2 and 5 g/L. The pH of the slurry after addition of the neutralising agent is typically greater than 1.0. It is an advantageous feature of the invention that the jarosite precipitates in acid solution and contains minimal or no co-precipitated nickel and cobalt.

Also, the precipitate that is formed typically settles readily and can be easily dewatered.

In step of the invention the undersize ore fraction is subjected to HPAL to produce a high pressure acid leached slurry (hereafter "HPAL slurry").

Generally, the undersize ore fraction is formed into a slurry, advantageously, by mixing with a saline or alkali containing solution. A concentrated mineral acid, typically sulfuric acid, is then added as the leaching reagent, typically after heating the slurry to the leaching temperature.

The HPAL in step is typically conducted in an autoclave at a temperature in the range of 2000C to 2700C, preferably around 250 0

C.

The duration of the HPAL in step is sufficiently long to effect substantial leaching of metal values from the ore. For example, leaching is advantageously conducted until greater than approximately 90%, preferably greater than extraction of nickel and cobalt occur. Typically, leaching is conducted for up to 120 minutes and for a minimum of 30 minutes. Preferably, leaching is conducted for between 45 and 90 minutes such as around 60 minutes.

Preferably the resulting HPAL slurry has a relatively low final free acid value at the end of the leaching step consistent with achieving high extractions of nickel and cobalt. It is also typically the case that the HPAL slurry has relatively low dissolved iron and aluminium therein at the end of the leaching step Those skilled in the art would be aware that this is an artefact of HPAL. This is particularly so with aluminium in the presence of an alkali compound such as sodium chloride in solution during leaching.

If necessary, the HPAL slurry is treated at the end of the leaching step to reduce the amount of free acid present in the slurry. Preferably, the free acid concentration is reduced to less than 10 g/L. Free acid reduction is typically effected by addition of a neutralising agent as previously described, which may conveniently be CaCO 3 In step of the invention, the JAL slurry from step and the HPAL slurry from step are combined to form a common process stream.

In step of the invention, the combined slurries are subjected to various treatments in order to eventually recover nickel and cobalt. Such treatments are typically those conventionally used in the field and may include one or more of solid-liquid separation, neutralisation step(s), further iron precipitation and nickel and cobalt precipitation. It is convenient and cost reducing to combine the JAL slurry from step and the HPAL slurry from step to form a common process stream, in order to be able to utilise common processing equipment.

In step the slurries are preferably first subjected to a primary neutralisation step. In this step, a neutralising agent is preferably added to the slurries to effect an increase in pH to a value preferably greater than 2, more preferably at least 2.5 Simultaneously, it is preferred that the temperature of the slurries is maintained above 80 0 C, preferably to at least 90 0 C. This is to ensure some aluminium precipitation has occurred to prevent a build up in downstream circuits that would be detrimental to hydroxide refining. The primary neutralisation step is preferably conducted for at least 15 minutes, more preferably for 60 minutes or longer.

The neutralised combined slurries then typically undergo solid-liquid separation to produce a supernatant leach liquor and a leached solid residue. The supernatant liquor is preferably subjected to a secondary neutralisation step in which a neutralising agent, conveniently CaCO 3 is added to the liquor in order to increase pH to a value greater than 4.0. Increasing solution pH causes iron O (111), aluminium, chromium and silica to precipitate. Preferably, the pH is increased to a value in the range of 4.5 to 5.5. If necessary, an oxidising agent, typically air or oxygen, is also introduced into solution in order to oxidise any ferrous iron in solution to ferric ion and thereby effect precipitation. The Ssecondary neutralisation slurry undergoes a solid-liquid separation, leaving a substantially iron-free supernatant liquor.

N 10 The substantially iron-free liquor is then typically treated in order to recover dissolved nickel and cobalt. Nickel and cobalt recovery may be by known processes and may typically be by either a mixed nickel/cobalt hydroxide route or a mixed nickel/cobalt sulfide route, or a direct solvent extraction route.

Where the mixed nickel/cobalt hydroxide route is taken, a precipitation agent is added to the substantially iron-free liquor to cause precipitation of the mixed nickel/cobalt hydroxides. Typically, this will require a solution pH around 7.0 to The precipitation agent is preferably magnesia, more preferably caustic calcined magnesia. The magnesia may also be produced from magnesium salts recovered from downstream barren solution. The precipitation is conducted at a temperature typically around 50 0 C, although higher or lower temperatures are also suitable. The duration of precipitation is up to 4 hours, preferably for up to 3 hours.

Where the mixed nickel/cobalt sulfide route is taken, the substantially iron-free liquor is treated with a sulfiding reagent in order to cause precipitation of a mixed nickel/cobalt sulfide. Examples of suitable sulfiding reagents include hydrogen sulfide (H 2 sodium hydrosulfide (NaHS), sodium sulfide (Na 2 S) and ammonium sulfide (NH 4 2

S.

BRIEF DESCRIPTION OF THE DRAWING The features of the invention are further illustrated in the accompanying drawings, in which: Figure 1 is a flowsheet illustrating the process steps of an embodiment of the invention; Referring to Figure 1, there is shown a flowsheet for the processing of a lateritic ore comprising an oversize ore fraction and an undersize ore fraction. The oversize ore particles having a particle size of between 75 and 1000 microns are formed into a slurry by mixing in a 50% weight ratio with saline slurrying solution. The saline slurrying solution has a dissolved solids content 1.5 times (150%) that of sea water. Concentrated sulfuric acid is added as the leaching reagent. The oversize ore slurry is subjected to an atmospheric leach conducted at atmospheric pressure and a temperature greater than 950C for hours thereby producing an OAL slurry At the completion of the atmospheric leaching, limestone is added to the OAL slurry, whilst maintaining a temperature of above 950C, thereby inducing precipitation of jarosite This process is maintained for about 4 hours until the free acid concentration in the slurry is reduced to 2 to 5 g/L of H 2 S0 4 The OAL slurry containing precipitated jarosite ("JAL slurry") can then be fed to downstream processing (discussed below).

An undersize ore fraction, in which the ore solids have a particle size less than microns, is combined with a saline slurrying solution and acid leached at a temperature of 2500C. The resulting HPAL slurry is then subjected to acid neutralisation by addition of limestone (10) until the free acid content is 2 to g/L.

The pH adjusted HPAL slurry (11) is then combined with the JAL slurry to form a combined slurry Limestone (13) is fed to the combined slurry in a primary neutralisation step (14) to adjust pH to 2.5 at a temperature of 950C.

The neutralised slurry is then subjected to a solid/liquid separation and the supernatant liquor (16) undergoes a secondary neutralisation step (17) at 600C.

During secondary neutralisation, limestone (18) is added in order to increase solution pH to between 4.5 and 5.5 and air (19) is introduced to cause oxidation of ferrous ions to ferric ions. These precipitate out and are subsequently separated from solution (20) and may be recycled back to the OAL and/or 1 HPAL slurries prior to limestone addition to recover any nickel or cobalt precipitates therein.

The supernatant liquor (21) resulting from the secondary neutralisation is then treated with MgO (22) to cause precipitation of mixed cobalt and nickel hydroxides which are then separated giving a mixed hydroxide product The raffinate solution (25) may then undergo nickel scavenging and manganese removal (26).

Further features and advantages will become more readily apparent from a consideration of the following Examples.

Example 1 was designed to determine the amenability of the oversize ore solids to atmospheric pressure acid leaching in accordance with step of the invention in saline water to measure optimum acid consumption, reaction time, metal dissolution and impurity deportment.

The atmospheric pressure leaching parameters of 95 0 C, 50% w/w solids in saline water with a dissolved solids content 1.5 times that of seawater, 250 kg/t of H 2 S0 4 acid addition and a leaching time of 10 hours were tested. Leach times of 8 to 10 hours were found to be suitable, producing an OAL slurry. The leaching results are given in Table 1.

Table 1 Time Element Concentration (Mins) Phase Ni Co Mg Mn Fe Al 0 Solid 0.53 0.026 2.87 0.12 8.2 0.42 600 Solid 0.15 0.007 0.94 0.02 5.0 0.35 dissolution 77 80 76 86 38 Example 2 exemplifies the conditions required to remove iron from solution by jarosite precipitation in accordance with step of the inventive process. The OAL slurry resulting from Example 1 was the feed material for the induced jarosite precipitation. Limestone was added to the feed material in an amount equivalent to the measured free sulfuric acid in the slurry to maintain a target range of 2 to 5 g/L free acid in the final mixture and final pH of 1.5. This jarosite containing OAL slurry (JAL slurry) was then carried forward for combination with a HPAL slurry also at pH 1.5. Details of the iron removal values obtained at 950C are given in Table 2.

Table 2 Time Element Concentrations mg/L (Mins) Test Ni Co Mg Mn Fe Al Free acid g/L 0 Lig A 3670 196 20800 941 17400 681 39 360 Li A 3350 182 19600 925 68 455 3 The results show that iron in solution can be reduced limestone addition to reduce free acid to 2 to 5 g/L.

precipitation is also apparent.

to very low levels by Significant aluminium The JAL slurry was then carried forward for combination with a HPAL slurry described in Example 5 below.

Example 3 was conducted in accordance with step of the inventive process to produce a HPAL slurry by autoclaving the undersize (<75 micron) ore solids at 35% w/w at 250°C for 60 minutes in saline water having salinity 150% that of seawater with a sulfuric acid addition rate of 430 kg/t. The results are presented in Table 3.

Table 3 Time Element Concentrations (Mins) Phase Ni Co Mg Mn Fe AI Free acid g/L 0 Solid 1.76 0.065 6.78 0.33 20.6 1.92 Solid 0.10 0.005 0.56 0.01 28.1 2.54 18 Dissolution 96 94 94 98 2.3 0.7 13 It is to be noted that a low final dissolution rate for iron of 2.3% was achieved with a low free acid value of 18 g/L.

IND

Example 4 was carried out to observe the effect of acid neutralisation of the S 5 HPAL slurry with limestone. The test was conducted at 950C. It was found there was no measurable precipitation of most elements during this test with the exception of iron and silicon. The former gave consistently 8% iron precipitation possibly due to jarosite precipitation.

In Example 5, the JAL slurry from Example 2 was combined with the acid neutralised HPAL slurry from Example 4 to form a common process stream in accordance with step of the process of the invention. It was found that there was precipitation of approximately 50% of the aluminium upon mixing of the two slurries.

In accordance with step of the inventive process, primary neutralisation tests were then conducted on the combined process stream by maintaining the temperature at 900C and adjusting the pH to 2.5 over a period of two hours. A further 30% of the aluminium precipitated during the primary neutralisation and iron precipitation ranged from 14% to 28%. There was, however, no measurable precipitation of nickel, cobalt, or manganese during primary neutralisation.

Examples 6 and 7 exemplify further treatments of the combined process stream in accordance with step of the inventive process, after primary neutralisation.

Example 6. The primary neutralised combined slurry from Example 5 was then subjected to liquid solid separation and settling tests and the supernatant liquor was then used in a secondary neutralisation study. The aim of this study was to add limestone to the clear combined liquors to increase the pH from to 4.5 while sparging the solution with oxygen gas to oxidise any ferrous iron to the ferric state to facilitate precipitation. Table 4 lists the quantitative results.

Table 4 Time Element Concentration mg/L (Mins) Phase Ni Co Mg Mn Fe Al pH 0 1Liquor 4000 135 19700 880 1510 3 440 Liquor 3750 125 19500 850 26 0.1 Precipitation 2 3 0.4 1 98 97 Example 7. The liquor recovered from the above secondary neutralisation step in Example 6 was treated with caustic calcined magnesia, thereby precipitating nickel and cobalt as mixed hydroxides. Results after 3 hours reaction time at using approximately 0.8 g MgO gram of nickel in solution are given in Table Table Time Element Concentration mg/L (Mins) Phase Ni Co Mg Mn Fe Al pH 0 Liq F 4200 167 16900 1040 14 10 4.6 180 Lig F 151 2 19100 505 2 1 Precipitation 97 99 4 42 90 86 Those skilled in the art would be aware that the clarified liquor recovered following the secondary neutralisation step, analyses shown in Table 4 above, could be subjected to treatment with a sulfiding reagent to produce a mixed nickel/cobalt sulfide product as an alternative to the mixed nickel/cobalt hydroxide product described in Example 7 above.

The above Examples clearly demonstrate that the oversize ore solids (75-1000 microns) that would otherwise be discarded as reject material for the HPAL process can be successfully digested at atmospheric pressure and elevated temperature, particularly in a saline medium, and the resultant discharge slurry after in situ jarosite precipitation could be effectively combined with the discharge from a high pressure acid leach. The combined streams can then be subjected to conventional settling and pH adjustment steps to result in the production of a mixed nickel/cobalt hydroxide or sulfide product.

SThose skilled in the art would be aware that during the secondary neutralisation of the supernatant liquor as described above (eg in Example 6) some nickel and cobalt losses to the precipitate are unavoidable. These losses can be substantially reversed by recycling the precipitate to the OAL or HPAL slurry before neutralisation.

Locked cycle atmospheric pressure leach tests were conducted to assess the 0effect of recycling the nickel and cobalt bearing precipitate from the secondary neutralisation stage to the OAL slurry prior to jarosite precipitation thereby utilizing the free acid in the slurry to re-dissolve the precipitate and release the trapped metal values into solution. It was found that high dissolution of nickel, cobalt and aluminium occurred while iron appeared to re-dissolve and then reprecipitate as jarosite.

It is also apparent from the results in Table 5 that addition of caustic calcined magnesium oxide to the supernatant liquor from the secondary neutralisation step some nickel remains in solution.

Most of this nickel could be recovered from the liquor by a scavenger precipitation using slaked lime. In a locked cycle test program, the recovered precipitate was recycled back to an acidic leach discharge stream.

The above description of the invention is illustrative of the preferred embodiments of the invention. Variations without departing from the spirit or ambit of the invention described herein are considered to form part of the invention.

Claims (16)

1. A process for recovering nickel and cobalt from a lateritic ore comprising an oversize (as herein defined) ore fraction and an undersize (as herein defined) ore fraction, said process including the steps: subjecting the oversize ore fraction to atmospheric pressure acid leaching at elevated temperature to produce an oversize atmospheric leached slurry (OAL slurry); treating the OAL slurry in order to induce precipitation of dissolved iron from solution, with minimal co-precipitation of nickel and cobalt, as jarosite and thereby form a jarosite-containing atmospheric leached (JAL) slurry; subjecting the undersize ore fraction to high pressure acid leaching to produce a high pressure acid leached (HPAL) slurry; combining the JAL slurry with the HPAL slurry; and treating the combined JAL and HPAL slurries to recover nickel and cobalt.

2. The process of claim 1, wherein said atmospheric pressure acid leaching is conducted at a temperature of at least 800C, preferably at least 950C.

3. The process of any preceding claim, wherein said acid leaching in each of steps and is conducted using a leaching solution including a concentrated mineral acid, preferably concentrated sulfuric acid.

4. The process of claim 3, wherein said leaching solution is saline or alkali containing. The process of claim 4, wherein said saline leaching solution contains NaCI.

6. The process of claim 4, wherein said alkali containing leaching solution contains one or more of Na', K' and NH 4

7. The process of claim 4 or 5, wherein, the salinity of the leaching solution is 1.5 times that of seawater.

8. The process of claim 4 or 5, wherein the leaching solution contains seawater or saline bore water.

9. The process of any preceding claim, wherein the treatment in step (b) includes reducing the amount of free acid in the OAL slurry, preferably by addition of a neutralising agent. The process of claim 9, wherein said neutralising agent is selected from CaCO 3 Ca(OH) 2 MgCO 3 and MgO, and is preferably naturally occurring limestone.

11. The process of claim 9 or 10, wherein the amount of neutralising agent added to the OAL slurry in step is sufficient to result in a free acid concentration of less than 10 g/L.

12. The process of any one of claims 1 to 11, wherein in step the undersize ore fraction is subjected to high pressure acid leaching in an autoclave at a temperature in the range of 200 to 270 0 C.

13. The process of any one of claims 1 to 12, wherein in step the JAL and HPAL slurries are combined into a single process stream.

14. The process of any one of claims 1 to 13, wherein in step the slurries are subjected to a primary neutralisation step to effect an increase in pH to a value greater than 2, more preferably at least The process of claim 14, wherein the temperature of the slurries is maintained at a value no lower than 80 0 C, preferably at least 90 0 C.

16. The process of claim 14 or 15, wherein the primary neutralised combined slurries then undergo solid-liquid separation to produce a supernatant leach liquor and a leached solid residue, wherein the supernatant liquor is subjected to a secondary neutralisation step in order to increase pH to a value greater than 4.0, preferably, in the range of 4.5 to 5.5, to thereby cause precipitation of iron from solution, leaving a substantially iron-free liquor.

17. The process of claim 16, wherein a precipitation reagent is added to the substantially iron-free liquor in a sufficient quantity to cause precipitation of mixed nickel/cobalt hydroxides.

18. The process of claim 17, wherein said precipitation reagent is caustic calcined magnesia.

19. The process of claim 16, wherein a sulfide containing reagent is added to the substantially iron-free liquor in a sufficient quantity to cause precipitation of mixed nickel/cobalt sulfides. The process of claim 19, wherein said sulfide containing reagent is selected from H 2 S, NaHS, Na 2 S and (NH 4 2 S, and is preferably H 2 S.