WO2001062989A1

WO2001062989A1 - Method for the recovery of nickel and/or cobalt

Info

Publication number: WO2001062989A1
Application number: PCT/AU2001/000179
Authority: WO
Inventors: Leslie Troman
Original assignee: ANACONDA NICKEL Ltd
Current assignee: ANACONDA NICKEL Ltd
Priority date: 2000-02-22
Filing date: 2001-02-22
Publication date: 2001-08-30
Anticipated expiration: 2002-08-22
Also published as: AUPQ578200A0

Abstract

A method for the recovery of nickel and/or cobalt from nickel and cobalt containing ores or concentrates, the method comprising the steps of:subjecting a nickel and cobalt containing ore or concentrate to acid pressure leaching thereby forming a process solution containing nickel ions, cobalt ions and residual ions of one or more impurity metals;treating the process solution containing nickel ions, cobalt ions and residual impurity metal ions with one or more alkaline agents to induce the precipitation of a mixed metal hydroxide of nickel, cobalt and some of the impurity metals;separating the mixed hydroxide from the supernatant solution;leaching the mixed metal hydroxide with an ammoniacal ammonium sulphate solution to produce a solution of nickel and cobalt amine complexes and thereby rejecting the majority of the impurity ions;substantially separating the cobalt ions from the nickel ions by solvent extraction in alkaline conditions; subjecting the predominantly nickel-containing aqueous phase to hydrogen reduction to produce metallic nickel and ammonium sulphate; andrecycling the ammonium sulphate so produced to the ammonium sulphate leaching step.

Description

"Method For The Recovery Of Nickel And/Or Cobalt"

Field of the Invention

The present invention relates to a method for the recovery of nickel and/or cobalt. More particularly, the method of the present invention relates to the recovery of nickel and/or cobalt from nickel laterite ores or concentrates.

Background Art

The occupational health and safety issues associated with the use of hydrogen sulphide render undesirable methods for the production of nickel and/or cobalt reliant on selective sulphide precipitation. Alternate methods reliant on selective solvent extraction typically consume considerable quantities of ammonia, and result in the production of considerable quantities of low-grade ammonium sulphate process streams. Whilst ammonium sulphate may be recovered and used as a fertiliser, current demand for such is low, consequently recovery, storage and disposal of ammonium sulphate is generally not economical and is problematic.

US Patent 5855858 describes a hydrometallurgical process for the extraction, and subsequent recovery of nickel and cobalt from ores or concentrates, that utilises an intermediate separation step to selectively precipitate nickel and cobalt as a mixed nickel/cobalt hydroxide. The nickel/cobalt hydroxide is then leached in a two stage, ammonium sulphate solution leach, with the two subsequent leach solutions being treated in separate solvent extraction circuits to separate and selectively recover cobalt, magnesium or nickel respectively. The nickel and cobalt is subsequently recovered from the solvent extraction solutions by electrowinning. An additional claim is that solvent extraction is conducted at up to about 60°C and is beneficially conducted with magnesium in the feed solution to solvent extraction to enhance the separation between cobalt and nickel. For the process described, the separation factor between cobalt and nickel is critical to ensure production of a commercially acceptable quality of nickel and cobalt cathodes. The requirement for two separate trains of leaching and solvent extraction, as well as the requirement to extract magnesium and nickel via solvent extraction, serves to increase the complexity and cost of the process. Additionally, the requirement for relatively low metal concentrations in the leach solution, which is subsequently advanced to solvent extraction, adds considerably to the size and cost of the equipment required.

It is one object of the present invention to provide a method for the production of nickel and/or cobalt that eliminates the use of hydrogen sulphide, reduces ammonia consumption, and consequently minimises ammonium sulphate production.

It is a further object of the present invention to provide a method for the recovery of nickel and/or cobalt that is relatively simple, and utilises chemistry that does not necessitate the use of 'exotic' materials in the construction of a plant based thereon.

The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention

In accordance with the present invention there is provided a method for the recovery of nickel and/or cobalt from nickel and cobalt containing ores or concentrates, the method comprising the steps of: subjecting a nickel and cobalt containing ore or concentrate to acid pressure leaching thereby forming a process solution containing nickel ions, cobalt ions and residual ions of one or more impurity metals;

treating the process solution containing nickel ions, cobalt ions and residual impurity metal ions with one or more alkaline agents to induce the precipitation of a mixed metal hydroxide of nickel, cobalt and some of the impurity metals;

separating the mixed metal hydroxide from the supernatant solution;

leaching the mixed metal hydroxide with an ammoniacal ammonium sulphate solution to produce a solution of nickel and cobalt amine complexes and thereby rejecting the majority of the impurity ions;

substantially separating the cobalt ions from the nickel ions by solvent extraction in alkaline conditions;

subjecting the predominantly nickel-containing aqueous phase to hydrogen reduction to produce metallic nickel and ammonium sulphate; and

recycling the ammonium sulphate so produced to the ammonium sulphate leaching step.

Preferably, the step of treating the process solution containing nickel ions, cobalt ions and undesired metal ions with one or more alkaline agents to induce the precipitation of a mixed metal hydroxide of nickel and cobalt and the impurity metals comprises the following sub-steps:

partially neutralising the process solution containing nickel ions, cobalt ions and undesired metal ions by the addition of a first alkaline agent such that the pH of the process solution is about 5, and thereby causing the majority of the residual undesired metal ions, such as iron, aluminium and chromium, to precipitate as hydroxides, thereby forming a slurry; subjecting the slurry so formed to filtration to remove the precipitated hydroxides of the impurity metal ions, leaving a process solution containing nickel ions, cobalt ions and impurity metal ions; and

treating the process solution containing nickel ions, cobalt ions and other impurity metal ions, such as copper and zinc, with a second alkaline agent such that the pH of the process solution is between about 7 and 7.5, thereby causing the precipitation of the majority of the nickel, cobalt and some of the impurity metal ions as a mixed hydroxide.

In one form of the invention, having subjected the ore to acid pressure leaching, the resulting mixture is part neutralised to pH 3 with calcrete or limestone, then subjected to counter current decantation to produce the process solution containing nickel ions, cobalt ions and ions of one or more undesired metals.

Preferably, after the step of treating the process solution containing nickel ions, cobalt ions and undesired metal ions with one or more alkaline agents to induce the precipitation of a mixed metal hydroxide of nickel, cobalt and some of the undesired metals, the method of the present invention comprises the additional steps of:

treating the supernatant solution with a third alkaline agent to raise the pH of such to about 8 to cause precipitation of residual nickel and cobalt as a contaminated mixed nickel cobalt hydroxide; and

leaching the contaminated nickel cobalt hydroxide so produced by returning such prior to or at the counter-current decantation step.

Preferably, after the step of treating the supernatant solution with a third alkaline agent to raise the pH of such to about 8 to cause precipitation of residual nickel and cobalt as a contaminated mixed nickel cobalt hydroxide, the method of the present invention comprises the additional step of: adding a fourth alkaline agent to the supernatant solution to raise the pH of such to about 8.5 to cause undesired metal ions, such as manganese ions, to precipitate as manganese hydroxide.

The first alkaline agent may be a metal oxide or hydroxide or carbonate. Preferably, the first alkaline agent is calcrete, or limestone.

The second alkaline agent may be a metal oxide or hydroxide. Preferably, the second alkaline agent is magnesium hydroxide or oxide.

The third alkaline agent may be a metal oxide or hydroxide. Preferably, the third alkaline agent is calcium hydroxide.

The fourth alkaline agent may be a metal oxide or hydroxide. Preferably, the fourth alkaline agent is calcium hydroxide.

Preferably, after the step of leaching the mixed metal hydroxide with an ammoniacal ammonium sulphate solution to produce a solution of nickel and cobalt amine complexes, the method of the present invention comprises the step of:

evaporating excess water generated by the leaching step to maintain nickel tenor.

Preferably, an organic extractant is used in the step of substantially separating the cobalt ions from the nickel ions by solvent extraction in an alkaline medium. A suitable extractant is an organic phosphorous acid, more specifically an organic phosphinic acid extractant. In a highly specific form of the invention, the extractant is bis (2,4,4-trimethylpentyl) phosphinic acid, known commercially as CYANEX 272.

Brief Description of the Drawings

The method of the present invention will subsequently be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:-

Figure 1 is a schematic representation of a precipitation phase and a leaching phase of a production plant for the production of nickel according to the method of the embodiment;

Figure 2 is a schematic representation of a solvent extraction phase of the production plant of Figure 1 ;

Figure 3 is a schematic representation of a cobalt removal phase of the production plant of Figure 1 ; and

Figure 4 is a schematic representation of a hydrogen reduction phase of the production plant of Figure 1.

Best Mode(s) for Carrying Out the Invention

Ore containing nickel and cobalt is crushed, optionally upgraded to a concentrate, and subjected to acid leaching. The solution from the acid leach is partially neutralised to approximately pH 2.8 to 3.0 by the addition of calcrete or limestone, thereby rejecting the majority of iron, chromium and aluminium from the solution. A counter current decantation circuit is then used to produce a process solution containing nickel ions, cobalt ions with some residual undesirable metal ions, such as iron, aluminium, chromium, zinc, copper and manganese. The solution from the counter-current decantation circuit is partially neutralised to a pH of about 5 using a limestone or calcrete slurry. This causes the residual iron, aluminium and chromium to precipitate as hydroxides. The hydroxides, along with some nickel and cobalt, may then be removed along with the gypsum from the neutralised slurry by thickening prior to leaching and return prior to or at the counter current decantation circuit.

After thickening, the clarified liquor is reacted with magnesium hydroxide or oxide at a pH of about 7 to 7.5 to precipitate approximately 90% of the nickel, cobalt and some other impurity metals, such as zinc and copper, as a mixed hydroxide.

After the primary precipitation, residual nickel and cobalt are precipitated with calcium hydroxide at pH 8 to produce a mixed metal hydroxide that is typically heavily contaminated by gypsum. This product is then thickened and the slurry leached upon return prior to the counter current decantation circuit. The pH of the clarified liquor from the thickener overflow is raised to about 8.5 using calcium hydroxide, thereby causing manganese to precipitate as manganese hydroxide. The liquor and the manganese hydroxide slurry are then utilised in the counter current decantation circuit as wash water, with the solids being disposed to tails.

The mixed metal hydroxide is transferred to a vacuum belt filter for washing, prior to being leached using ammonium sulphate solution from the nickel hydrogen reduction process, which will be discussed subsequently. In the leach step, residual iron and manganese are reduced to acceptable levels. Excess water generated by the leaching process is removed by evaporation from the process stream to maintain a high nickel tenor.

Having been filtered, the process liquor is then contacted with an extractant, such as Cyanex 272, to extract sufficient cobalt and impurity metals such as zinc and copper to allow hydrogen reduction to be used to selectively precipitate nickel, whilst retaining any residual cobalt in solution. That is, the nickel to cobalt ratio is increased from about 12 to 1 to at least 50 to 1. The organic phase is then stripped of the extracted metals, leaving a sulphate solution rich in cobalt and impurity metals such as copper, zinc and iron.

The nickel is then recovered by hydrogen reduction, before being processed into briquettes or being sold as a powder.

The ammonium sulphate leaching solution quality is maintained by taking a bleed stream of the solution remaining after nickel reduction to an ammonia recovery process in which an alkaline agent, preferably calcium hydroxide, is reacted with the ammonium sulphate to regenerate ammonia, and reject the sulphate as gypsum, with the slurry so produced being returned to the counter current decantation circuit to recover any residual nickel and cobalt values.

The method of the present invention may be further understood with reference to the following example, although such is not to be understood as limiting the generality of the forgoing description.

Example

In Figures 1 to 4 there is shown a production plant for the production of nickel according to the method of the embodiment comprising a precipitation phase 10, a leaching phase 12, a solvent extraction phase 14, a cobalt removal phase 16 and a hydrogen reduction phase 18.

Ore containing nickel and cobalt is crushed, optionally upgraded to a concentrate, and subjected to acid leaching.

The acid leach of the ore is conducted in pressurised vessels at a temperature of between 240°C and 290°C, but more generally between 255°C and 275°C and at a pressure of between 4500 kPa and 6500 kPa. The residence time in the autoclave is nominally 60 minutes. The leach is conducted so as to have excess acid to result in an acid concentration of approximately 20 to 50 gL^"1 at the completion of the leach. The precise quantity of acid added is dependent on the chemistry of the feed. The slurry feed density is generally in the range of 30-45 wt% generally dependent on slurry rheology.

A quantity of limestone or calcrete is added to the leach residue slurry prior to the counter-current decantation circuit to raise the pH to about 3 that will precipitate the majority of the iron and other impurity metals prior to the feed to counter- current decantation

A counter current decantation circuit (not shown) is then used to produce a process solution containing nickel ions, cobalt ions and ions of other impurity metal ions. Referring now to Figure 1 , a quantity of calcrete 20 or limestone is added to the solution to increase the pH to approximately 5, causing the precipitation of iron, aluminium and chromium as hydroxides thereof.

The slurry so produced is subjected to thickening 22, the thickener overflow 23 in turn being subjected to filtration 24. The thickener underflow 25 is passed to a recycle leach 27, then back to the counter current decantation circuit (not shown). A quantity of magnesium oxide hydroxide 26 sufficient to precipitate about 90% of the nickel and cobalt, is added to the filtrate in the primary precipitation stage 28 causing the precipitation of the nickel and cobalt as a mixed metal hydroxide. The mixed metal hydroxide is passed to a thickener 30, with the thickener underflow 32 being subjected to filtration 34.

The thickener overflow 36 is subjected to a secondary precipitation 39 with calcium hydroxide 37 being added to raise the pH to approximately 8.0 and thereby cause precipitation of the remaining nickel and cobalt as hydroxides. The mixed metal hydroxide slurry 41 is advanced to a thickener 40. The thickener overflow 44 is subjected to a tertiary precipitation 45, calcium hydroxide 42 being added to raise the pH to approximately 8.5 and thereby cause the precipitation of manganese as manganese hydroxide. The resultant slurry 47 is returned to the counter-current decantation circuit.

The solution 50 from the filtration 34 is returned to the primary precipitation 28, whilst the solids 52 are advanced to the leaching phase 12. ln the leaching phase 12, the solids 52 are mixed with ammoniacal ammonium sulphate solution 54 of concentration approximately 500 to 650 gL^"1, the leached slurry 55 being subjected to evaporation 56 and thickening 58. The thickener underflow is subjected to filtration 59, with the filtrate being returned to the thickener 58, and the filter cake being transferred to recycle leach 27. The thickener overflow 60 is subjected to filtration 62, the filtrate 64 being passed on to the solvent extraction phase 14, and the filter cake being transferred to recycle leach 27.

Referring now to Figure 2, the filtrate 64, containing both nickel and cobalt diamine sulphates is mixed with an organic phase 66 containing an organic extractant 68, such as bis(2,4,4-trimethylypentyl) phosphinic acid. Organics are removed from the raffinate, leaving nickel as nickel diamine sulphate 70. The organic phase is subjected to scrubbing 71 with aqueous cobalt sulphate solution 73, and stripping 72. Organics are removed from the stripping liquid to leave cobalt sulphate 74, which is passed to the cobalt removal phase 16, as can be seen in Figure 3. The organic phase is then recycled back to extraction.

Referring now to Figure 4, the nickel diamine sulphate 70 is then pre-heated 74 before being subjected to hydrogen reduction 76. The ammonium sulphate solution 54 generated in the hydrogen reduction phase 18 is recycled to the leaching phase 12. After cooling by flashing 78, the slurry containing the metallic nickel is filtered 80, and the metallic nickel so collected dried 82, briquetted 84, sintered 86 in an atmosphere of nitrogen and hydrogen and, finally, packaged 88.

Although the method of the present invention may be conducted as a series of batch processes, it is envisaged that the method of the present invention will be conducted as a continuous process.

From the preceding description, it can generally be seen that the method of the present invention is adapted to recovery of nickel and/or cobalt from ores or concentrates thereof without the use of hydrogen sulphide, without the production of significant ammonium sulphate by-product and with greatly reduced ammonia consumption. Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

The Claims Defining the Invention are as Follows

1. A method for the recovery of nickel and/or cobalt from nickel and cobalt containing ores or concentrates, the method characterised by the steps of:

subjecting a nickel and cobalt containing ore or concentrate to acid pressure leaching thereby forming a process solution containing nickel ions, cobalt ions and residual ions of one or more impurity metals;

separating the mixed metal hydroxide from the supernatant solution;

2. A method according to claim 1 characterised in that the step of treating the process solution containing nickel ions, cobalt ions and undesired metal ions with one or more alkaline agents to induce the precipitation of a mixed metal hydroxide of nickel and cobalt and the impurity metals comprises the following sub-steps:

partially neutralising the process solution containing nickel ions, cobalt ions and undesired metal ions by the addition of a first alkaline agent such that the pH of the process solution is about 5, and thereby causing the majority of the residual undesired metal ions, such as iron, aluminium and chromium, to precipitate as hydroxides, thereby forming a slurry;

subjecting the slurry so formed to filtration to remove the precipitated hydroxides of the impurity metal ions, leaving a process solution containing nickel ions, cobalt ions and impurity metal ions; and

3. A method according to claim 1 or claim 2 characterised in that having subjected the ore to acid pressure leaching, the resulting mixture is part neutralised to pH 3 with calcrete or limestone, then subjected to counter current decantation to produce the process solution containing nickel ions, cobalt ions and ions of one or more undesired metals.

4. A method according to any one of the preceding claims characterised in that after the step of treating the process solution containing nickel ions, cobalt ions and undesired metal ions with one or more alkaline agents to induce the precipitation of a mixed metal hydroxide of nickel, cobalt and some of the undesired metals, the method of the present invention comprises the additional steps of: treating the supernatant solution with a third alkaline agent to raise the pH of such to about 8 to cause precipitation of residual nickel and cobalt as a contaminated mixed nickel cobalt hydroxide; and

5. A method according to claim 4 characterised in that after the step of treating the supernatant solution with a third alkaline agent to raise the pH of such to about 8 to cause precipitation of residual nickel and cobalt as a contaminated mixed nickel cobalt hydroxide, the method of the present invention comprises the additional step of:

adding a fourth alkaline agent to the supernatant solution to raise the pH of such to about 8.5 to cause undesired metal ions, such as manganese ions, to precipitate as manganese hydroxide.

6. A method according to any one of claims 2 to 5 characterised in that the first alkaline agent may is a metal oxide or hydroxide or carbonate.

7. A method according to claim 6 characterised in that the first alkaline agent is calcrete, or limestone.

8. A method according to any one of claims 2 to 7 characterised in that the second alkaline agent is a metal oxide or hydroxide.

9. A method according to claim 8 characterised in that the second alkaline agent is magnesium hydroxide or oxide.

10. A method according to any one of claims 4 to 9 characterised in that the third alkaline agent is a metal oxide or hydroxide.

11. A method according to claim 10 characterised in that the third alkaline agent is calcium hydroxide.

12. A method according to any one of claims 5 to 11 characterised in that the fourth alkaline agent is a metal oxide or hydroxide.

13. A method according to claim 12 characterised in that the fourth alkaline agent is calcium hydroxide.

14. A method according to any one of the preceding claims characterised by, after the step of leaching the mixed metal hydroxide with an ammoniacal ammonium sulphate solution to produce a solution of nickel and cobalt amine complexes, the step of:

15. A method according to any one of the preceding claims characterised in that an organic extractant is used in the step of substantially separating the cobalt ions from the nickel ions by solvent extraction in an alkaline medium.

16. A method according to claim 15 characterised in that the organic extractant is an organic phosphorous acid.

17. A method according to claim 16 characterised in that the organic extractant is an organic phosphinic acid extractant.

18. A method according to claim 17 characterised in that the organic extractant is bis (2,4,4-trimethylpentyl) phosphinic acid.

19. A method for the recovery of nickel and/or cobalt from nickel and cobalt containing ores or concentrates substantially as hereinbefore described with reference to Figures 1 to 4.