CA2949580A1

CA2949580A1 - Process for selective acid leaching nickel and cobalt from a mixed hydroxide intermediate

Info

Publication number: CA2949580A1
Application number: CA2949580A
Authority: CA
Inventors: Richard Clout; Scott Perry
Original assignee: BHP Billiton Nickel West Pty Ltd
Current assignee: BHP Billiton Nickel West Pty Ltd
Priority date: 2015-12-09
Filing date: 2016-11-24
Publication date: 2017-06-09
Also published as: AU2016256773A1

Abstract

A process for the selective leaching of nickel and cobalt from a mixed hydroxide intermediate that has been produced from the processing of a nickel ore or concentrate also containing manganese, the process including the steps of: a) providing a mixed hydroxide intermediate and forming a mixed hydroxide intermediate slurry; b) treating the mixed hydroxide intermediate slurry with an oxidizing agent to substantially oxidise the manganese present whilst minimising the oxidation of cobalt and nickel; and c) and either consecutively or simultaneously with the oxidation step, leaching the oxidised slurry in an acid sulphate medium, to produce a nickel and/or cobalt sulphate solution containing substantially all of the nickel and a major portion of the cobalt and a solid residue containing substantially all of the manganese in a resultant oxidised leach slurry.

Description

PROCESS FOR SELECTIVE ACID LEACHING NICKEL AND COBALT FROM A MIXED
HYDROXIDE INTERMEDIATE
BACKGROUND OF THE INVENTION
Field of the Invention This invention relates to a process for the sulphuric acid leaching of an impure nickel containing intermediate, to produce a solution containing substantially all of the nickel and a major portion of the cobalt and a solid residue containing substantially all of the manganese originally in the intermediate.
In particular, the process relates to the processing of a mixed hydroxide intermediate, preferably a nickel-cobalt-manganese-magnesium hydroxy-sulphate intermediate, which may also contain zinc and copper. Such intermediates are also known as Mixed Hydroxide Product (or Precipitate) or "MHP" or as referred to herein as a "mixed hydroxide intermediate".
Description of the Related Art Recovery of nickel as an intermediate product for subsequent refining to a metallic product is well established, with mixed sulphide mattes from smelting operations and mixed sulphide precipitates from leaching operations being common examples.
Precipitation of intermediates from sulphuric acid leaching liquors as hydroxides and hydroxy-sulphates has been under consideration over an extended time period, as discussed for example in U.S. Patents 1,091,545, USP 2,899,300 and USP
3,466,144 and Canadian Patent 618,826.
Nickel containing intermediates produced by addition of an alkali reagent are commonly referred to as mixed hydroxide precipitates (or products) or MHP, particularly when they contain significant quantities of cobalt and manganese and minor quantities of zinc and copper, as when they are derived from nickel laterite acid leach solutions or nickel sulphide acidic pressure oxidation leach solutions. In addition, if using magnesia as the precipitating agent, they typically contain some unreacted magnesium.
Such mixed hydroxide intermediates typically contain 3% to 5% sulphur in the form of sulphate (9 to 15% sulphate), so can more properly be termed a mixed hydroxy-sulphate or basic sulphate.

2 Patent Application AU 2013904693 in the name of BHP Billiton SSM Development Pty Ltd summarises a number of ammonia leached based refining processes for mixed hydroxide intermediates. These processes are generally selective for nickel and cobalt over manganese. However, it has been found that mixed hydroxide intermediates undergo a number of phenomena, collectively known as "ageing", which reduce the extraction of nickel and cobalt in ammonia leaching processes and leads to a leach residue that is difficult to filter.
Patent Application WO 2012100293 in the name of The University of Queensland describes a process for selectively leaching nickel from MHP, while retaining cobalt in the leach residue solids. The process described in this application seeks to leach nickel from MHP, whilst preventing substantial leaching of cobalt and incidentally manganese.
This process suffers from several disadvantages, including:
1. Cobalt, a valuable co-product of nickel refining, reports to the leach residue, so requiring separate re-leaching and separation from manganese.
2. Nickel-Cobalt separation is not perfect and there is significant cross contamination of these elements.
The present invention aims to overcome one or more of the difficulties or disadvantages identified in the prior art documents.
A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a process for the selective leaching of nickel and cobalt from a mixed hydroxide intermediate that has been produced from the processing of a nickel ore or concentrate also containing manganese, the process including the steps of:
a) providing a mixed hydroxide intermediate and forming a mixed hydroxide intermediate slurry;
b) treating the mixed hydroxide intermediate slurry with an oxidizing agent to substantially oxidise the manganese present whilst minimising the oxidation of cobalt and nickel; and

3 c) either consecutively or simultaneously to the oxidation step, leaching the oxidised slurry in an acid sulphate medium to produce a nickel and/or cobalt sulphate solution containing substantially all of the nickel and a major portion of the cobalt and a solid residue containing substantially all of the manganese in a resultant oxidised leach slurry.
Preferably, contacting the mixed hydroxide intermediate with the oxidising agent results in a substantial portion of the manganese being oxidised to thereby cause it to be stabilised in the solid phase while a substantial portion of the nickel and a major portion of the cobalt are subsequently dissolved in the following acidic leach step.
Preferably, the oxidising agent has sufficient oxidising potential to oxidise manganese(II) to manganese (IV), and is added only in sufficient quantity to minimise oxidation of cobalt(II) to cobalt(III).
Suitably, the oxidising agent is selected from the group consisting of persulphates, peroxides, peroxymonosulphuric acid (Caro's Acid), sulphur dioxide-air mixtures, sulphur dioxide-oxygen mixtures, permanganates, perchlorates, ozone, oxides, oxygen and chlorine.
Preferably, the oxidising agent is a persulphate.
In one embodiment, the oxidising agent is ammonium, sodium or potassium persulphate, hydrogen peroxide or Caro's acid. Ammonium, sodium or potassium persulphate are particularly preferred.
Preferably, the process includes the steps of:
(i) determining the stoichiometric amount of oxidising agent to be added to the mixed hydroxide intermediate slurry to cause the oxidation of a substantial proportion of the manganese; and (ii) adjusting the amount of oxidising agent determined in step (i) based on the amount of manganese, cobalt and nickel that dissolves in step c).
In a preferred form, the acid sulphate medium is sulphuric acid, preferably a concentrated sulphuric acid.
An advantage of the process is that the leach residue is easy to filter, regardless of the ageing history of the mixed hydroxide intermediate. In a preferred embodiment other metals

4 contained in the mixed hydroxide intermediate may also be leached, for example zinc and copper. The process has the advantage of stabilizing the manganese in a solid phase and rejecting manganese impurities from the liquor stream prior to the recovery of the metal values and producing a leach residue which is readily filtered.
The mixed hydroxide intermediate product may be produced as an intermediate product in the processing of both nickel laterite and nickel sulphide materials including concentrates. It is also commonly referred to as a mixed hydroxide precipitate (or product), or MHP, but herein is referred to as a "mixed hydroxide intermediate".
The mixed hydroxide intermediate may be recovered from a sulphuric acid leaching liquor during the processing of a nickel laterite ore. For example, such intermediate products are produced when an alkali reagent such as magnesia or lime is used to raise the pH of an acidic sulphate solution to precipitate a nickel product as a mixed hydroxide intermediate.
Such intermediates are also recovered from nickel sulphide acidic pressure oxidation leach solutions by the addition of a comparable alkali material.
Typically, a mixed hydroxide intermediate produced from processing a nickel laterite or nickel sulphide ore, contains the main elements of interest, namely nickel and cobalt, together with variable quantities of metals such as zinc and copper as well as sulphur in the form of sulphates, and impurities such as manganese, magnesium, iron and calcium.
Sodium and chlorine, in the form of chloride, may also be present.
In a preferred embodiment, the process further includes the steps of treating the resultant oxidised leach slurry with ammonia and/or ammonia containing liquors to progressively convert the nickel and/or cobalt sulphate to nickel and/or cobalt ammine sulphates in a neutralised ammine leach slurry.
The neutralised ammine leach slurry may then be subjected to a solid/liquid separation step to produce a neutralised ammine leach solution containing substantially all of the nickel and a major proportion of the cobalt, and a leach residue containing a major proportion of the manganese.
In a preferred embodiment, the neutralised ammine leach slurry is blended with a ground nickel matte and/ or mixed sulphide and subjected to an ammonia pressure leach step with the addition of air and ammonia to produce an ammonia leach slurry.

In a further embodiment, the neutralised ammine leach slurry may be blended with the ammonia leach slurry after the ground nickel matte and/or mixed sulphide has been subjected to the ammonia pressure leach step. This blended leach slurry may then be subjected to a solid/liquid separation step to produce an ammonia leach solution that contains substantially all of the nickel and a major proportion of the cobalt together with a leach residue containing a major proportion of the manganese.
The ammonia leach slurry from the ammonia pressure leach step may be combined with either the leach residue and/or the neutralised ammine leach solution and then subjected to a solid/liquid separation step to produce an ammonia leach solution and a further residue containing a major proportion of the manganese. This neutralised ammine leach solution may be combined with the ammonia leach solution to form a blended leach solution containing substantially all the nickel and a major proportion of the cobalt for further processing.
Copper may be removed from the blended leach solution with the addition of steam and/or sulphuric acid and/or sulphur to remove copper as a copper sulphide product.
The blended leach solution may then undergo oxydrolysis where it is oxidised with air and heated with steam to remove any remaining thiosulphates and convert sulphamates to sulphates.
Nickel may then be recovered from the blended leach solution by hydrogen pressure reduction, or other suitable means leaving a nickel depleted reduction end solution. Cobalt may be recovered from the nickel depleted reduction end solution by adding a sulphiding agent to recover cobalt, residual nickel and/or zinc as a mixed nickel/cobalt sulfide or nickel/cobalt/zinc sulphide product. Suitable sulfiding agents include hydrogen sulphide, sodium hydrosulphide, sodium sulphide or ammonium sulphide.
In a further embodiment of the invention, a mixed sulphide slurry may be subjected to a pressure oxidation step with the addition of oxygen to form a pressure oxidation leach slurry.
The resultant oxidised leach slurry from the mixed hydroxide intermediate oxidation step may be either directly blended into the pressure oxidation step or blended with the pressure oxidation leach slurry to produce a blended leach slurry. The resultant oxidised leach slurry from the mixed hydroxide intermediate oxidation step may have undergone a solid/liquid separation step prior to the addition with the mixed sulfide slurry so as to first form a nickel/cobalt sulphate solution and a leach residue. The nickel/cobalt sulphate solution may alternatively be added to the pressure oxidation leach slurry to produce the blended leach slurry which may then optionally undergo a solid/liquid separation step to produce a blended leach solution and a leach residue prior to further impurity removal and nickel recovery.
The blended leach solution may be subjected to an iron and copper removal step with the addition of an ammonia solution to raise the pH to precipitate the iron as an iron oxide, and the addition of a sulphide product or sulphiding agent to precipitate copper as a copper sulphide. The iron oxide and copper sulphide may be removed as a residue following a solid/liquid separation step.
Zinc may be removed from the blended leach solution by an ion exchange or solvent extraction process.
Nickel may be recovered from the blended leach solution by adding an ammonia solution to form a nickel ammine solution and subjecting the nickel ammine solution to a hydrogen pressure reduction step to produce a metallic nickel product and a nickel reduction end solution.
Cobalt may be recovered by first separating the cobalt from the nickel in the blended leach solution by solvent extraction or ion exchange and then subjected to a hydrogen pressure reduction step or other suitable means to produce a metallic cobalt product and a cobalt reduction end solution.
Excess ammonium sulphate is formed through the process and may be recovered by crystallisation of ammonium sulphate to form ammonium sulphate crystals. The ammonium sulphate crystals and/or any ammonium sulphate solution may be recycled to the step of neutralising the resultant leach slurry, the ammonia pressure leach step or the hydrogen pressure reduction step.
The nickel reduction end solution and the cobalt reduction end solution may be combined and treated with a sulphiding reagent in a mixed sulphide precipitation step to produce a cobalt/nickel sulphide which may then be recycled to either the pressure oxidation step or the iron and copper removal step.
Preferably, both the nickel and cobalt product are metallic nickel and metallic cobalt powders.

A 'major portion' as used herein may refer to greater than 50%, preferably greater than 60%, more preferably greater than 70%, even more preferably greater than 80% in relation, independently, to both stabilisation of the manganese in the solid phase and to dissolution of the nickel and cobalt.
"Substantially all" as used herein, may refer to greater than 90%, preferably greater than 95% in relation, independently, to both stabilisation of the manganese in the solid phase and to dissolution of the nickel and cobalt.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flowsheet of the oxidising, leaching, neutralisation and solid-liquid separation phases of the preferred embodiment of the invention.
Figure 2 is a schematic flowsheet where the oxidising and leaching steps have been combined into a simultaneous step.
Figure 3 is a schematic flowsheet of a preferred embodiment of the invention involving integration into a Nickel Sulphide Matte or Mixed Sulphide Ammonia Pressure Leach.
Figure 4 is a schematic flowsheet of the product recovery phase of the process described in Figure 3.
Figure 5 is a schematic flowsheet of a preferred embodiment of the invention involving integration into a Mixed Sulphide Acid Sulphate Pressure Oxidation Leach.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described with reference to the accompanying figures. It is to be understood that the figures or illustrations of the preferred processes of the invention should not be taken as limited to particular features described herein.
First Embodiment: Integration into Nickel Sulphide Ammonia Pressure Leach As illustrated in Figure 1, mixed hydroxide intermediate 100 is water washed 110 using desalinated water 120, to remove or partially remove contaminants. These include magnesium, calcium, sulphate, chloride, and sodium components. The water wash can consist of the washing of a filter cake on a filter, re-pulping of the mixed hydroxide intermediate in water to give a "water leach", a combination of these, or other techniques such as continuous counter-current decantation. Multiple stages of water washing have been found to be beneficial as has extended leaching times of up to several days. Multiple contacts are especially advantageous for calcium removal, as calcium will continue to leach out of the mixed hydroxide intermediate, constrained only by its solubility limit. An additional benefit of the water wash has been found to be the "fixing" of most of the remaining magnesium in the mixed hydroxide intermediate, so that it does not substantially dissolve in downstream ammonia leaching operations. The waste wash liquor 130 must be disposed of separately to other refinery liquors, so the water washing step is preferably carried out at the location where the mixed hydroxide intermediate is produced.
The washed mixed hydroxide intermediate 140 is initially repulped 150 with repulp liquor 160.
This repulp liquor 160 typically contains 0 to 20 g/L of titratable ammonia and 0 to 200 g/L of ammonium sulphate. It may also contain minor amounts of nickel (0 to 5 g/L) and cobalt (0 to 0.5 g/L). The mixed hydroxide intermediate slurry 170, is oxidised 180 typically using ammonium persulphate 190. The oxidised repulp slurry 200 is then leached 210 with sulphuric acid 220. Leaching is carried out preferably at 50 to 60 C for 3 to 4 hours, with a target terminal pH of 2. Relevant metal extractions are: Nickel: > 95%, Cobalt: > 80% and Manganese: < 0.5%. The resultant oxidised leach slurry 230 is neutralised 240, using ammonia 250, and ammonia leach liquor 260 to form an ammine leach slurry.
Ammonium sulphate 270 is also added to stabilise the resulting metal ammines in solution. The neutralised ammine leach slurry 280 is subjected to solid-liquid separation 290, to produce a neutralised ammine leach solution 300 containing substantially all of the nickel and a major portion of the cobalt originally in the washed mixed hydroxide intermediate and a Leach residue 310 containing a substantial portion of the manganese originally in the washed mixed hydroxide intermediate. The solid-liquid separation step may be thickening, filtration, or a combination of both and preferably includes a washing step to remove soluble nickel and cobalt from the manganese containing leach residue.
An alternative embodiment to this is shown in Figure 2 where the oxidation step 180 (of Figure 1) and the leaching step 210 (of Figure 1) are conducted simultaneously in combined oxidation and leaching step 210.
Figure 3 shows a further embodiment where the neutralised ammine leach solution 300 is forwarded to Leach Liquor Blending 510 where it is blended with nickel matte or mixed sulphide ammonia leach liquor 480. Alternatively the neutralised ammine leach slurry 320 may be sent directly to solid liquid separation 470, or at any suitable point within the Ammonia Pressure Leach 430.

The steps from Copper Boil 530 through to ammonium sulphate crystallisation 720 as shown in Figure 3 and 4 are carried out in a conventional manner. The blended leach solution 520 is forwarded to Copper Boil 530. Here copper is precipitated from solution as copper sulphide product 560, and titratable ammonia levels are adjusted, by the addition of steam 540 and sulphuric acid 550, to a ratio of around 2 moles of ammonia per mole of nickel, in preparation for nickel reduction. The blended leach solution 570 is forwarded to Oxydrolysis 580 where it is oxidised with air 590 and heated with steam 600 to remove any remaining thiosulphate, polythionate and sulphamate compounds which would otherwise cause product contamination. The blended leach solution 610 then flows into Nickel Pressure Reduction 620, where hydrogen 630 is added in a batchwise manner to an agitated Autoclave to produce nickel metal powder. Nickel depleted reduction end solution 640 undergoes powder ¨ solution separation 650. Metallic nickel powder product 660 may be transformed into other forms such as briquettes by drying and compacting in a conventional manner.
The nickel depleted reduction end solution 670 is then treated with a sulphiding reagent such as hydrogen sulphide 690 in a mixed sulphide precipitation step 680 to produce a mixed cobalt-nickel-zinc sulphide product 700. The barren ammonium sulphate solution 710 passes to ammonium sulphate crystallisation 720. Steam 730 is used to evaporate the water for crystallisation. Crystalliser configurations can include multiple effect evaporators, vapour recompression or a combination of both. Ammonium sulphate crystal slurry 740 undergoes crystal ¨ liquor separation 750 and drying 780. The liquor 760 may be returned to crystallisation as shown in Figure 4. Ammonium sulphate crystal is directed to both product 800 and Ammonium Sulphate Crystal Dosing 790 of Leach liquor.
Further Embodiment: Integration into Mixed Sulphide Acid Sulphate Pressure Oxidation Leach With reference to Figure 5, after repulping 150, oxidation 180 and leaching 210, the leached slurry 230 is subjected to solid-liquid separation 295, to produce a nickel/cobalt sulphate solution 305 containing substantially all of the nickel and a major portion of the cobalt originally in the washed mixed hydroxide intermediate and a Leach residue 315 containing a substantial portion of the manganese originally in the washed mixed hydroxide intermediate.
The nickel/cobalt sulphate solution 305 is forwarded to Leach Liquor Blending 515 where it is blended with pressure oxidation leach slurry 465 to create a blended leach slurry 525.
Alternatively the resultant oxidised leach slurry 325 from the mixed hydroxide intermediate oxidation step may be sent to the pressure oxidation leach 435, or directly to Leach Liquor Blending 515. An optional solid/liquid separation step may occur here to create a blended leach solution.

The steps from Iron and Copper Removal 535 through to ammonium sulphate crystallisation 725 Figure 5 are carried out in a conventional manner. The blended leach solution or blended leach slurry 525 is forwarded to Iron and Copper Removal 535 where anhydrous ammonia 545 is added to raise the pH and precipitate iron. Copper is precipitated as a sulphide by the addition of nickel-cobalt sulphide 555, or hydrogen sulphide 995. The nickel-cobalt sulphide may be sourced from the "strip" mixed sulphide precipitation step 685 carried out on the pressure reduction end solutions. Discharge from Iron and Copper Removal 575 undergoes solid / liquid separation 585. The iron oxide / copper sulphide residue 565 is typically recycled to recover the contained nickel and cobalt values. The iron and copper free blended leach solution 595 undergoes a zinc solvent extraction step 815, typically using a phosphorous based extractant such as a phosphoric acid, phosphonic acid or phosphinic acid dissolved in a hydrocarbon diluent. Most commonly used extractants are Di-ethylhexylphosphoric acid, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, and bis-(2,4,4-trimethylpentyl) phosphinic acid. Ammonia 825 is typically added for pH
control in extraction and sulphuric acid 835 is used to strip the zinc from the loaded organic extractant, to produce a zinc sulphate solution 845. A loaded organic wash step is typically used between the extraction and stripping steps to remove co-loaded cobalt and nickel from the organic.
The zinc free blended leach solution 855 undergoes a cobalt solvent extraction step 865, typically using one of the aforementioned phosphorous based extractants dissolved in a hydrocarbon diluent. Ammonia 875 is typically added for pH control in extraction and sulphuric acid 885 is used to strip the cobalt from the loaded organic extractant, to produce a cobalt sulphate solution 1895. A loaded organic wash step is typically used between the extraction and stripping steps to remove co-loaded nickel from the organic.
The purified nickel blended leach solution 895 proceeds to nickel reduction solution preparation 905, where anhydrous ammonia 915 and ammonium sulphate 925 are added to form a nickel annmine solution 615, which is pumped into Nickel Pressure Reduction 625.
Hydrogen 635 is added in a batchwise manner to an agitated Autoclave to produce nickel metal powder. Nickel reduction discharge undergoes powder ¨ solution separation to produce a metallic nickel powder product 665 that may be transformed into other forms such as briquettes by drying and compacting in a conventional manner. Cobalt sulphate solution 1895 is treated in a similar manner to the nickel sulphate solution, to produce cobalt powder 1665 and a cobalt reduction end solution 1675. The nickel reduction end solution 675 and cobalt reduction end solution 1675 are combined and treated with a sulphiding reagent such as hydrogen sulphide 695 in a mixed sulphide precipitation step 685 to produce a cobalt-nickel sulphide 705. The cobalt-nickel sulphide 705 is typically recycled to the pressure oxidation leach 435 or iron and copper removal 535. The barren ammonium sulphate solution 715 passes to ammonium sulphate crystallisation 725. Steam 735 is used to evaporate the water for crystallisation. Crystalliser configurations can include multiple effect evaporators, vapour recompression or a combination of both. Ammonium sulphate crystal is directed to both product 805 and Ammonium Sulphate Crystal Dosing 795 of nickel and cobalt reduction feed solutions.
Examples Example 1 Typical assays of mixed hydroxide intermediate feeds are shown in the table below. In addition, a typical nickel matte refinery feed and precipitated mixed sulphide analyses are provided as leach solutions from these sources will often be blended with the leach liquor from the invented process.

Refinery Feeds Analysis, wt% dry basis Ni Co Mn Mg Fe Al Ca S Zn Cu Typical Mixed 47 1.7 2.0 1.5 0.13 0.04 0.09 4.4 0.31 0.03 Hydroxide Intermediate Aged Mixed Hydroxide 45 1.6 1.7 1.5 0.5 0.07 0.1 3.7 0.27 0.03 Intermediate Typical Nickel Matte 70.5 0.72 - 3.75 20 -3.1 = _________________________________________________________________________ Typical Precipitated 55 5 1 35 1 0.1 Mixed Sulphide Those skilled in the art would understand that the compositions of the feeds can vary over a significant range from those presented above.
Mixed hydroxide intermediates can be highly variable in composition. Iron, aluminium and silicon levels vary depending on the efficiency of upstream impurity removal processes.
Manganese and cobalt levels vary depending on their concentration relative to nickel in the feed solution to the hydroxide precipitation step, which ultimately reflects on the ore or concentrate feed composition to the leaching process upstream of the mixed hydroxide precipitation step.

Nickel matte may have differing levels of iron content, depending on the extent to which iron is removed in the smelter converting process. Copper and cobalt levels can also vary significantly, depending on the concentrate feed to the smelter and the converting process used.
Mixed sulphide precipitates will have varying levels of cobalt, also depending on the on the ore or concentrate feed composition to the leaching process upstream of the mixed sulphide precipitation step.
Example 2 - First example of leaching MHP
A bench scale test using the process of the invention was carried out as follows:
1366 grams of "as received" aged mixed hydroxide intermediate, containing 698 grams of dry solids, of the composition shown in example 1 above was slurried in 802 mL
of deionised water. The slurry was agitated while 37 grams of ammonium persulphate was added, calculated to be the stoichiometric quantity required to oxidise the contained manganese from the 2+ to the 4+ oxidation state. Under continued agitation, 503 grams of 98%
sulphuric acid was added to the oxidised slurry to give a terminal pH target of 2. Leaching was continued for 8 hours, with the temperature controlled at 60 C. Solid-liquid separation was carried out using a laboratory pressure filter, of 0.005 m2 filtration area, with a feed pressure of 600 kPag, using a Machery-Nagel MN1672 filter paper as the filtering medium.
The compositions of the final solution and washed solids were as shown in the following Table:

Ni, g/L Co, g/L Mn, mg/L
Leach Solution 191 5.0 0.5 Ni, % Co, % Mn, %
Washed Solids 5.1 7.4 23.6 A mass balance around the test showed that the nickel extraction was 99%, the cobalt extraction was 63% and the manganese extraction was 0.02%
Example 3 Second example of leaching MHP
A bench scale test using the process of the invention was carried out as follows:
830 grams of "as received" aged mixed hydroxide intermediate, containing 462 grams of dry solids, of the composition shown in example 1 above was slurried in 1617 mL of deionised water. The slurry was agitated while 12.1 grams of ammonium persulphate was added, calculated to be the stoichiometric quantity required to oxidise the contained manganese from the 2+ to the 4+ oxidation state. Under continued agitation, 476 grams of 98%
sulphuric acid was added to the oxidised slurry to give a terminal pH target of 1. Under continued agitation, leaching was continued for 4 hours, with the temperature controlled at 80 C. Solid-liquid separation was carried out using a laboratory pressure filter, of 0.005 m2 filtration area, with a feed pressure of 600 kPag, using a Machery-Nagel MN1672 filter paper as the filtering medium. The compositions of the final solution and washed solids were as shown in the following Table:

Ni, g/L Co, g/L Mn, mg/L
Leach Solution 89 3.0 123 Ni, (Y0 Co, % Mn, %
Washed Solids 3.6 3.47 35.4 A mass balance around the test showed that the nickel extraction was 99.7%, the cobalt extraction was 92.5% and the manganese extraction was 4.8%.
Example 4 - Combined oxidation and acid leaching of MHP
A bench scale using the process of the invention with a combined oxidation-acid leach of aged mixed hydroxide intermediate of the composition shown in TABLE 1 was carried out as follows:
830 grams of "as received" aged mixed hydroxide intermediate, containing 462 grams of dry solids, of the composition shown in example 1 above was slurried in 1617 mL of deionised water. The slurry was agitated while 427 grams of 98% sulphuric acid was added to give a terminal pH target of 1. After 1 hour, 12.1 grams of ammonium persulphate was added, calculated to be the stoichiometric quantity required to oxidise the contained manganese from the 2+ to the 4+ oxidation state. Under continued agitation, leaching was continued for 4 hours, with the temperature controlled at 80 C. Solid-liquid separation was carried out using a laboratory pressure filter, of 0.005 m2 filtration area, with a feed pressure of 600 kPag, using a Machery-Nagel MN1672 filter paper as the filtering medium.
The compositions of the final solution and washed solids were as shown in the following Table:

Ni, g/L Co, g/L Mn, mg/L
_Leach Solution 88 3.0 215 Ni, % Co, % Mn, %
Washed Solids 5.45 2.11 32.4 A mass balance around the test showed that the nickel extraction was 99.6%, the cobalt extraction was 95.3% and the manganese extraction was 8.7%.
Comparative Example - Ammonia Leach of Aged MHP
A bench scale ammonia leach of aged mixed hydroxide intermediate of the composition shown in TABLE 1 was carried out as follows:
Aged mixed hydroxide intermediate, of the composition shown in Example 1 above was leached in an ammonia ammonium sulphate liquor of composition 42 g/L free ammonia, and 440 g/L ammonium sulphate. Aged mixed hydroxide intermediate addition rate to the liquor was 27.5% solids (360 g of dry solids per litre of leach solution). Leaching was continued for 2 hours, with the temperature controlled at 60 C.
Solid-liquid separation was carried out using a laboratory pressure filter, of 0.005 m2 filtration area, with a feed pressure of 600 kPag, using a Machery-Nagel MN1672 filter paper as the filtering medium. The compositions of the final solution and washed solids were as shown in the following Table:

Ni, g/L Co, g/L Mn, g/L
Leach Solution 63.6 3.0 0.16 Ni, % = Co, % Mn, cYo Washed Solids 23.2 0.71 3.2 A mass balance around the test showed that the nickel extraction was 76%, the cobalt extraction was 83% and the manganese extraction was 5%.
This test illustrates that aged mixed hydroxide intermediate leached in ammonia solutions has relatively poor extraction characteristics, compared to the invention.

FIGURE 6 is a graphical representation of the manganese and nickel leach extractions measured over the range of cobalt extractions referred to in the invention.

= = = = % = =
= =
9 - = 99 =

=

u 6 - 96 o i7:7) w 5 - 95 = r<
c 4 - 94 a) cis 3 - 93 2 - = Mn Extraction =
Ni Extraction =

=
= = = =
=
=
0 == = _________________________________________________ 90 Cobalt Extraction, %

Referring to FIGURE 6, this shows that manganese extraction is less than 10%, even as cobalt extraction is increased from 55% to over 90%, while nickel extraction at all times is in excess of 97%.
Limitations to Addition of Mixed Hydroxide Intermediate The limits of mixed hydroxide intermediate addition to an ammonia pressure leach process depend primarily on economic drivers. As the level of cobalt in refinery feed increases, an equivalent mass of nickel is typically not reduced and reports to mixed sulphide. As a saleable product, the revenue received for the contained nickel in this stream is less than if sold as nickel metal. One variant to overcome this limitation is to add the cobalt hexamine precipitation process, as discussed for instance in U.S. Patent 5,468,281, into the flowsheet.
Zinc may reach an economic limit, as refiners of cobalt-nickel-zinc mixed sulphide typically have limits on zinc levels and/or apply penalties for high zinc feeds. This limitation may be overcome by producing separate zinc sulphide and mixed sulphide products by a two stage sulphiding process.

As the relative quantity of mixed hydroxide intermediate increases, the ability of the leach process to produce a nickel leach solution of high nickel tenor may become a limitation. This again is an economic rather than a technical limitation, with a wide range of nickel concentrations contemplated, for instance, US Patent 6,949,232 stating, "The leach solution produced will typically contain from 40 to 110 g/L nickel..."
Thus, within the constraints described above, there is no particular limitation to the relative quantity of mixed hydroxide that may be processed.
Advantages of processing the mixed hydroxide intermediate in this manner are:
1. Nickel and cobalt recovery are maximised whilst minimising manganese leach extraction, to give leach solutions compatible with existing sulphide matte and mixed sulphide refineries.
2. A way of dealing with a mixed hydroxide intermediate that has aged, giving improved nickel and cobalt recovery, and a leach residue that is readily filterable.
3. Nickel pressure reduction capacity is not compromised because the nickel concentration is maintained, due to the co-processing of leach solutions.
4. Copper & zinc do not have to be removed from the mixed hydroxide intermediate feedstock.
The invention described herein is susceptible to variations, modification and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.
Further patent applications may be filed in Australia or overseas on the basis of, or claiming priority from the present application. It is to be understood that the following provisional claims are provided by way of example only and are not intended to limit the scope of what may be claimed in any such future application.
Features may be added to or omitted from the provisional claims at a later date so as to further define or re-define the invention or inventions.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A process for the selective leaching of nickel and cobalt from a mixed hydroxide intermediate that has been produced from the processing of a nickel ore or concentrate also containing manganese, the process including the steps of:
a) providing a mixed hydroxide intermediate and forming a mixed hydroxide intermediate slurry;
b) treating the mixed hydroxide intermediate slurry with an oxidizing agent to substantially oxidise the manganese present whilst minimising the oxidation of cobalt and nickel; and c) and either consecutively or simultaneously with the oxidation step, leaching the oxidised slurry in an acid sulphate medium, to produce a nickel and/or cobalt sulphate solution containing substantially all of the nickel and a major portion of the cobalt and a solid residue containing substantially all of the manganese in a resultant oxidised leach slurry.

2. A process as claimed in claim 1 wherein step b) includes the steps of:
determining the stoichiometric amount of oxidising agent to be added to the mixed hydroxide intermediate slurry to cause the oxidation of a substantial proportion of the manganese; and (ii) adjusting the amount of oxidising agent determined in step (i) based on the amount of manganese, cobalt and nickel that dissolves in step c).

3. A process according to claim 1 or 2 wherein the acid sulphate medium is sulphuric acid.

4. A process according to any one of claims 1 to 3 wherein the oxidising agent is selected from the group consisting of persulphates, peroxides, peroxymonosulphuric acid (Caro's Acid), sulphur dioxide-air mixtures, sulphur dioxide-oxygen mixtures, permanganates, perchlorates, ozone, oxides, oxygen and chlorine.

5. A process according to any one of claims 1 to 4 further including the step of treating the resultant oxidised leach slurry with ammonia and/or ammonia containing liquors to progressively convert the nickel and/or cobalt sulphate to nickel and/or cobalt ammine sulphates in a neutralised ammine leach slurry.

6. A process according to any one of claims 1 to 5 wherein the neutralised ammine leach slurry is subjected to a solid/liquid separation step to produce a neutralised ammine leach solution containing substantially all of the nickel and a major proportion of the cobalt, and a leach residue containing a major proportion of the manganese.

7. A process according to claim 5 wherein the neutralised ammine leach slurry is blended with a ground nickel matte and/ or mixed sulphide and subjected to an ammonia pressure leach step with the addition of air and ammonia to produce an ammonia leach slurry.

8. A process according to claim 7 wherein the ammonia leach slurry is subjected to a solid/liquid separation step to provide an ammonia leach solution containing substantially all of the nickel and a major proportion of the cobalt, and a leach residue containing a major proportion of the manganese.

9. A process according to claim 7 wherein the neutralized ammine leach slurry is blended directly with the ammonia leach slurry after the ground nickel matte and/or mixed sulphide has been subjected to the ammonia pressure leach step, and subjected to a solid/liquid separation step, to produce an ammonia leach solution containing substantially all of the nickel and a major proportion of the cobalt, and a leach residue containing a major proportion of the manganese.

10. A process according to claim 6 including the additional steps of:
(i) subjecting a ground nickel matte and /or mixed sulphide product to an ammonia pressure leach step with the addition of air and ammonia to produce an ammonia leach slurry;
(ii) subjecting the ammonia leach slurry and optionally together with the leach residue of claim 5, to a solid/liquid separation step to produce an ammonia leach solution and a further leach residue; and (iii) combining the neutralised ammine leach solution with the ammonia leach solution to form a blended leach solution.

11. A process according to claim 10 wherein steam and/or sulphuric acid and/or sulphur is added to the blended leach solution to remove copper as a copper sulphide product.

12. A process according to claim 11 wherein the blended leach solution is subjected to oxydrolysis.

13. A process according to claim 11 or 12 wherein nickel is recovered as a metallic nickel product from the blended leach solution by hydrogen pressure reduction, electrowinning or other suitable means leaving a nickel depleted reduction end solution.

14. A process according to claim 13 wherein a sulphiding agent is added to the nickel depleted reduction end solution to recover cobalt, residual nickel and/or zinc as a mixed nickel/cobalt sulphide or nickel/cobalt/zinc sulphide product.

15. A process according to claim 14 wherein the sulphiding agent is hydrogen sulphide, sodium hydrosulphide, sodium sulphide or ammonium sulphide.

16. A process according to any one of claims 1 to 4 including the additional steps of:
(i) subjecting a mixed sulphide slurry to a pressure oxidation step with the addition of oxygen to form a pressure oxidation leach slurry; and (ii) adding the resultant oxidised leach slurry either directly to the pressure oxidation step or the pressure oxidation leach slurry to produce a blended leach slurry.

17. A process according to any one of claims 1 to 4 wherein the resultant oxidised leach slurry undergoes a solid/liquid separation step to produce a nickel/cobalt sulphate solution and a leach residue.

18. A process according to claim 17 wherein the nickel/cobalt sulphate solution is added to the pressure oxidation leach slurry to produce a blended leach slurry and optionally undergoing a solid/liquid separation step to produce a blended leach solution and a leach residue prior to further impurity removal and nickel recovery.

19. A process according to claim 18 wherein the blended leach slurry or blended leach solution is subjected to an iron and copper removal step with the addition of an ammonia solution to raise the pH to precipitate the iron and the addition of a sulphide product or sulphiding agent to precipitate copper as a copper sulphide.

20. A process according to claim 19 wherein the blended leach slurry or blended leach solution is subjected to a solid/ liquid separation step to remove the iron oxide and copper sulphide as a residue and leave a blended leach solution for further impurity removal and nickel recovery.

21. A process according to any one of claims 16 to 20 wherein zinc is removed from the blended leach solution by an ion exchange or a solvent extraction process.

22. A process according to any one of claims 16 to 21 wherein nickel is removed from the blended leach solution by adding an ammonia solution to form a nickel ammine solution and subjecting the nickel ammine solution to a hydrogen pressure reduction step to produce a metallic nickel product and a nickel reduction end solution.

23. A process according to any one of claims 16 to 22 wherein cobalt is recovered by first separating the cobalt from the nickel in the blended leach solution by solvent extraction or ion exchange, then subjected to a hydrogen pressure reduction step or other suitable means to produce a metallic cobalt product and a cobalt reduction end solution.

24. A process according to any one of the preceding claims wherein excess ammonium sulphate is formed through the process, and is recovered by crystallization of ammonium sulphate to form ammonium sulphate crystals.

25. A process according to claim 22 or 23 wherein the nickel reduction end solution and the cobalt reduction end solution are combined and treated with a sulphiding reagent in a mixed sulphide precipitation step to produce a cobalt-nickel sulphide.

26. A process according to claim 25 wherein the cobalt-nickel sulphide is recycled to either the pressure oxidation step or the iron and copper removal step

27. A process according to claim 24 wherein the ammonium sulphate crystals and/or ammonium sulphate solution are recycled to the step of neutralising the resultant leach slurry, the ammonia pressure leach step, or the hydrogen pressure reduction step.

28. A process according to claim 13 or 22 wherein the metallic nickel product is a metallic nickel powder.

29. A process according to claim 23 wherein the metallic cobalt product is a metallic cobalt powder.