WO2008128278A2

WO2008128278A2 - Treatment of nickel-containing solutions

Info

Publication number: WO2008128278A2
Application number: PCT/AU2008/000533
Authority: WO
Inventors: Andrew Langham Gillies; Patirck Anthony Treasure
Original assignee: Metallica Minerals Ltd
Priority date: 2007-04-19
Filing date: 2008-04-16
Publication date: 2008-10-30
Also published as: AU2008241353A1; WO2008128278A3

Abstract

A method for the separation of nickel and iron from an acidic iron-containing nickel solution containing at least some dissolved iron in the ferric [Fe(III)] state comprises conducting a crude precipitation to precipitate some of the iron present in the solution by increasing the pH of the solution, electrochemically reducing the remaining ferric [Fe(III)] content of the iron-containing nickel solution to the ferrous [Fe(II)] state; and selectively separating the soluble nickel and ferrous [Fe(II)] components of the liquor by contacting the liquor with an ion exchange resin to selectively capture nickel. The nickel-loaded resin may be stripped to form a nickel-rich solution and nickel or a nickel product recovered from the nickel rich solution. The substantially nickel-free liquor derived from the ion exchange step may be treated to remove soluble iron therefrom.

Description

TREATMENT OF NICKEL-CONTAINING SOLUTIONS

Field of the Invention

The present invention relates to the treatment of iron-containing leach liquors derived from nickel ores, concentrates and intermediate products.

The present invention relates more particularly but not exclusively to the treatment of iron-containing leach liquors derived from nickel ores, concentrates and intermediate products whereby all of the ferric [Fe(III)] iron content of the leach liquor is reduced to the ferrous [Fe(II)] state prior to the separation of the nickel and ferrous iron by suitable means.

In some embodiments, the present invention relates more particularly but not exclusively- to the treatment of iron-containing leach liquors derived from acid leached nickel ores, concentrates and intermediate products whereby all of the ferric [Fe(III)] iron content of the leach liquor is reduced to the ferrous [Fe(II)] state by electrochemical means prior to the separation of the nickel and ferrous iron by suitable means.

In some embodiments, the present invention relates more particularly but not exclusively to the treatment of iron-containing leach liquors derived from nickel ores, concentrates and intermediate products whereby all of the ferric [Fe(III)] iron content of the leach liquor is reduced to the ferrous [Fe(II)] state by electrochemical means prior to the separation of the nickel and ferrous by means of a suitable ion exchange resin.

In some embodiments, the_. present invention relates more particularly but not exclusively to the treatment of iron-containing leach liquors derived from nickel ores, concentrates and intermediate products whereby the co-dissolved cobalt is recovered with the soluble nickel.

In some embodiments, the present invention relates more particularly but not exclusively to the treatment of iron-containing leach liquors derived from the hydrometallurgical processing of one or more of any of the following nickel- containing feedstocks a) nickel laterites and oxide ores, b) nickel sulphide ores, c) nickel sulphide concentrates, d) nickel mattes, e) nickel hydroxide and related precipitates, f) nickel sulphide precipitates, and g) deep-sea manganese nodules in an acidic sulphate-based leachant at temperatures between ambient and about 275⁰C and an oxygen partial pressure equivalent to that at ambient temperature and up to about 1200 kPa.

In some embodiments, the present invention relates more particularly but not exclusively to the treatment of iron-containing leach liquors derived from a nickel- containing feedstock by any one of or a combination of two or more of any of the following acidic leaching technologies a) agitated tank leaching, b) vat leaching, c) column leaching, d) heap leaching, and e) autoclave leaching by means of an acidic sulphate-based leachant at temperatures between ambient and about 275⁰C and an oxygen partial pressure equivalent to that at ambient temperature and up to about 1200 kPa.

Background to the Invention

In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was, at the priority date: a) part of common knowledge; or b) known to be relevant to attempt to solve any problem with which this specification is concerned.

The chemical specifications for nickel metal with respect to various impurities, particularly iron, copper, zinc and other base metals, are quite specific. Nickel metal is generally produced by either electro winning/electroreflning or by hydrogen reduction from a suitably concentrated and purified solution. Thus hydrometallurgical processing of nickel-containing feedstocks involves the selection and implementation of conditions that either limits or preferably excludes the co-dissolution of impurities and/or allows the separation of the nickel from solution by means such as solvent extraction, ion exchange or selective precipitation.

Iron is a common contaminant element present in virtually all nickel-containing ores and in many intermediate products derived from such ores. In some ores, such as nickel sulphide ores, a significant portion of the iron present in the as-mined ore will typically be present as the mixed iron-nickel sulphide mineral pentlandite (Fe₅Ni^Ss. In other ores, such as nickel laterites, there are few well-defined nickel-containing minerals present and the nickel present is generally directly associated by both physical and chemical means with various iron oxide and sheet silicate minerals.

Some ores, such as nickel sulphide ores, are amenable to concentration by physical means such as froth flotation whereby some but not all of the iron-containing phases present in the ore is rejected as the gangue. With such ores, the nickel grade may be increased from say about 1% in the ore to say about 8% or higher in the concentrate. Other ores, such as nickel laterites, are not readily concentrated by physical means apart from some relatively simple screening/washing techniques. With such ores, the nickel grade may be increased from say 1.1% to say 1.5%. Only a small percentage of the iron present in an as-mined nickel laterite is rejected in this minimal concentrating stage. The iron present in all of the nickel-containing feedstocks may be present in both the ferrous [Fe(II)] and the ferric [Fe(III)] states.

As a general rule, treatment of nickel -containing feedstocks such as nickel sulphide ores, nickel sulphide concentrates, nickel sulphide precipitates and nickel mattes involves oxidative conditions, whereby the metal sulphide sulphur is oxidised to the elemental state or right through to sulphate. _ι On the other hand, treatment of nickel laterites and nickel-containing intermediates such as nickel hydroxide precipitates does not necessarily involve an oxidation step.

Because of the direct chemical (mineralogical) association between nickel and iron in the run-of-mine ores (sulphide or laterile), sulphide concentrates or physically upgraded laterites, selective dissolution of the iron component of these feedstock is generally not achievable.

This fact of iron contamination introduces some considerable processing challenges with respect to nickel-iron separation as there is no simple direct method of recovering nickel from an iron-contaminated leach solution. In other words, it is necessary to remove the soluble iron, particularly the soluble ferric [Fe(III)] iron, before it is possible to recover and purify the final nickel-containing solution ahead of recovery of nickel metal.

In addition to the requirement for an efficient nickel-iron separation step, it is necessary to ensure that any soluble iron is ultimately converted into a stable iron- containing solid for discharge and storage in a well-managed tailings (residue) facility while an overall circuit water balance is established and maintained.

One way of limiting the amount of co-dissolved iron is to carry out the leach process at elevated temperatures, typically above 15O⁰C, whereby a significant portion of the dissolved ferric [Fe(III)] undergoes a hydrolysis reaction, precipitating for example, as hematite.

Fe₂(SO₄)₃ + 3H₂O → Fe₂O₃ + 3H₂SO₄

although other ferric iron solid products such as jarosites and basic iron sulphates may also be formed. It should be noted that not all the soluble ferric [FeIII] iron is precipitated under such conditions. In some nickel hydrometallurgical processes, such as heap leaching or atmospheric leaching of nickel laterites and bioleaching of nickel sulphide ores and concentrates, it is not possible to take advantage of this in-situ iron precipitation reaction as the leaching processes themselves are carried out at ambient temperatures or up to about 55⁰C in the case of the bioleaching processes. Thus the leach liquors derived from these processes generally have quite high soluble iron concentrations which may be several times greater than the respective nickel concentrations. Moreover, the iron may be present in both the ferrous [Fe(II)] and the ferric [Fe(III)] states.

Almost without exception, commercially viable processes for treating iron-containing nickel leach liquors involve the precipitation of the soluble iron before proceeding to the separation and purification of the iron-free or significantly-removed iron containing nickel liquor. This step involves the addition of a suitable basic reagent, typically limestone and/or lime, to raise the nickel-iron bearing liquor pH to a value of above about 3.5-4.0 to induce the precipitation of iron. Where appropriate, the reaction system is aerated to ensure that all ferrous [Fe(II)] iron is oxidised to the ferric [Fe(III)] state.

Other suitable basic reagents include magnesite, magnesia and calcrete, but for convenience, the present invention is described in terms of using limestone and/or lime for pH control and precipitation of ferric [Fe(III)] iron. This does not preclude the use of one or more of other suitable basic reagents.

The resultant iron-containing precipitate, which for convenience can be termed hydrated goethite or ferric hydroxide with a nominal chemical composition of

Fe(OH)₃. nH₂0, tends to be quite gelatinous and difficult to settle and wash free of entrained liquor. Typically separation of the iron-containing precipitate is earned out in a series of quite large counter-current decantation (CCD) thickeners. In addition, many soluble components in the original liquor, including nickel, tend to be quite strongly adsorbed onto the gelatinous precipitate. This loss of nickel can be quite significant in terms of overall recovery of the nickel from the initial feedstock. Settling and washing characteristics can be improved by operating at an elevated temperature, say about 45⁰C to about 65⁰C, and by ensuring that there is sufficient inert material present to act as a seed, for example, by means of recycling CCD thickener underflow. Both of these techniques incur increased capital and operating costs.

Neutralisation of the excess acid present in the iron-containing nickel liquor and precipitation of the iron as hydrated goethile using limestone and/or lime is further complicated by the fact that the system becomes saturated in calcium, leading to the precipitation of gypsum, CaSO₄.2H₂O. This has a great tendency to form a scale on reaction vessel surfaces resulting in a loss of equipment efficiency and increased maintenance costs, as well as interference with downstream nickel recovery steps such as solvent extraction.

The present invention involves an alternative method of treating iron- containing nickel leach liquors that incorporates a nickel-iron separation stage.

Summary of the Invention

According to one aspect of the present invention there is provided a method for the separation of nickel and iron from an acidic iron-containing nickel solution containing at least some dissolved iron in the ferric [Fe(III)] state, the method comprising the steps of: a) precipitating some of the iron present in the solution by increasing the pH of the solution; b) electrochemically reducing the ferric [Fe(III)] content of the iron- containing nickel solution to the ferrous [Fe(II)] state; and c) selectively separating the soluble nickel and ferrous [Fe(II)] components of the liquor derived from step (b) by contacting the liquor from step (b) with an ion exchange resin to selectively capture nickel.

Step (a), of the present invention involves treating the liquor to increase its pH to a level where precipitation of some of the iron in the solution takes place. This step may be considered to be a crude precipitation step in that it removes some but not all of the dissolved iron. In some embodiments, this step may involve raising the pH of the solution to above 2, such as between 2 and 4, for example, to about 2.5. The pH may be raised by adding lime to the solution. The lime may be in the form of CaO or hydrated lime. In one embodiment, this step may remove up to about 70 to 95% of the dissolved iron, more preferably 75 to 95% of the dissolved iron, even more preferably 80 to 90% of the dissolved iron in solution.

By limiting the amount of ferric [Fe(III)] precipitated in step (a) the amount of nickel coprecipitated with the ferric [Fe(III)] precipitated will be significantly reduced thereby assisting in maximizing the amount of nickel in solution that is forwarded to step (c).

The method may include the further steps of:

d) stripping the nickel from the nickel-loaded resin derived from step (c) into a nickel-rich solution; and

e) processing the substantially nickel-free liquor derived from step (c) using, for example, nanofiltration, to remove soluble iron therefrom.

Step (d) above may suitably comprise an elution step to strip the nickel from the nickel loaded resin. Step (d) may result in the formation of a highly concentrated nickel rich solution.

The nickel containing solution obtained from step (d) may be treated to recover nickel or a nickel product. The solution may be treated to recover nickel or a nickel product using any process known to be suitable to a person skilled in the art, such as precipitation, electrowinning or indeed any other suitable method.

The treatment in step (e) of the substantially nickel free liquor to remove soluble iron therefrom suitably allows for ultimate disposal of the iron under conditions that allow the establishment and maintenance of an overall circuit water balance.

The relatively simple soluble nickel-iron separation technique of the present invention has several advantages when compared with existing technologies. For example, it avoids losses of nickel that is chemically and/or physically adsorbed to the iron- containing precipitates in conventional technology while at the same time reducing the amount of soluble nickel that is circulating throughout the entire circuit. A further significant advantage of the present invention is that the final nickel recovery circuit is not affected by the undesirable formation of gypsum scale. As noted previously, the chemical specifications for the final nickel products are quite strict with respect to the presence of a range of impurities.

Electrochemical reduction of a metal to a lower valence state or to the metallic state itself is a relatively common step in many electroplating and metal recovery industries. . Surprisingly, however, it is rarely used where the soluble metal is iron. There are many reasons for this, including the relative ease of alternative methods of producing metallic iron while most iron removal technologies used in the hydrometallurgical industry involve an oxidation step rather than a reduction step.

Electrochemical reduction of an acidic ferric-containing solution can be carried out in a relatively simple membrane cell, the actual cell voltage and maximum current density obtainable without the evolution of hydrogen as a competing cathodic reaction being dependent upon the cell configuration itself. Typically the maximum cell voltage will be of the order of about 2.5 volts.

As with all electrochemical processes there has to be a balance between the extent of the electrochemical reduction reaction and the current efficiency. As the electrochemical reduction reaction approaches completion there . is a decrease in current efficiency and hence the cost-effectiveness of the whole process is affected.

In order to maintain a cost competitive current efficiency, the present invention may incorporate where appropriate a secondary ferric [Fe(III)] reduction stage [step (bl)] between the primary electrochemical reduction [step (b)] and the nickel-ferrous iron separation stage using ion exchange resins [step (c)]. This step acts to further lower the concentration of ferric ions in the solution prior to step (c). The inventors have discovered that an efficient method of reducing the last traces of ferric [Fe(III)] is by passing the liquor exiting the electrochemical reduction cell through a column packed with steel wool or by adding iron filings to the liquor to bring about the following reaction:

Fe³⁺ + Fe → 2Fe²⁺

However, it is to be noted that other methods of completing the final stage of ferric [Fe(III)] iron reduction are possible. These include sparging the liquor with sulphur dioxide gas or by the addition of sodium metabisulphite. These additional options are included in the overall claims of this invention.

Detailed Description of the Invention

The following detailed description of a presently preferred but non-limiting embodiment of the invention refers to the overall flowsheet outlined in Figure 1.

In the embodiment shown in Figure 1, the clarified iron-containing nickel solution or liquor [1] derived from leaching of an iron-containing nickel feedstock is directed via a series of surge tanks to a crude iron precipitation step IA. In step IA, the solution is treated so that the pH increases to a level where from 70 to 95%, suitably greater than 80% of the iron in solution, is removed by precipitation. This may be achieved by adding lime to the solution to increase the pH to greater than 2, such as about 2.5. This results in the formation of iron-containing precipitates that can be removed from the solution using known solid/liquid separation techniques. Such techniques include, but are not limited to settling, clarification, thickening, filtration and the like.

In step (a) of the present invention, some, but not all of the ferric iron is precipitated.

Complete precipitation of all ferric iron in this step would require a pH of greater than 4. Under these conditions nickel hydroxide will start to precipitate. In other words, the pH-precipitation curves of ferric and nickel overlap. In embodiments where the pH in step (a) is raised to a value of greater than 2 but less than 4, such as to about 2.5

^• virtually no nickel will be precipitated. The solution leaving step IA contains nickel and some dissolved iron, although the dissolved iron content is lower than the solution [1] fed to the flowsheet shown in Figure 1. The solution leaving step IA is supplied to the electrochemical ferric [Fe(III)] reduction circuit [2] where in excess of about 90% of the soluble ferric [Fe(III)] iron is electrochemically reduced to the ferrous [Fe(II)] state.

Typically the ferric [Fe(III)] reduction circuit [2] consists of a series of electrochemical membrane cells consisting of uncoated titanium cathodes and iridium-coated dimensionally stable anodes. The design and operation of the cells allows efficient separation of the anolyte and catholyte flows. It will be understood that other arrangements of cells may be used in this operation.

The treated liquor [3] exiting the ferric Fe(III) reduction circuit [2] is passed to a secondary ferric [Fe(III)] reduction- circuit [4] where the remaining ferric [Fe(III)] iron content is chemically reduced to the ferrous [Fe(II)] state by interaction with metallic iron such as steel, wool. Typically the secondary ferric [Fe(III)] reduction circuit [4] will consist of two or more interchangeable column reactors with bypass facilities, each column reactor containing a mass of high surface area steel wool. The bypass system allows for fresh steel wool to be added to the column reactors without any interruption to the continuous operation of the overall circuit. Other forms of metallic iron such as iron filings and suitably treated scrap may be used in place of steel wool.

Other treatment steps that reduce the ferric content of the solution may be incorporated into step [4], such as treatment with sulphur dioxide, or sodium metabisulphite or contacting the solution with a ferric-specific ion exchange resin.

The ferric [Fe(III)] -free nickel liquor [5] exiting the secondary reduction circuit [4] is forwarded to the nickel-iron separation circuit [6] which typically consists of a series of ion exchange columns arranged on a carousel. This facilitates the continuous loading, stripping, scrubbing and regeneration stages of the overall nickel-iron separation circuit. Other modes of operating the ion exchange circuit may be used. A range of ion exchange resins is available to carry out this nickel-iron separation, with the proviso that the iron is present in the ferrous [Fe(II)] state since any ferric [Fe(III)] present in the feed liquor will be strongly bound to the resins and will be co-eluted with the nickel. Resins that can be effectively used for the nickel- iron separation include those based upon bis-picolylamine. A suitable resin for use in the present invention may be a bis-picolylamine resin sold by Dow Chemical Company under the trade designation XUS-43578. It will be appreciated that the present invention encompasses the use of all ion exchange resins that enable the selective extraction of nickel from the liquor and the invention should not be considered to be limited solely to the particular resins mentioned herein. Separation selectivity of nickel over ferrous [Fe(II)] and other minor "impurity" elements such as copper and cobalt that may be present in the leach liquors derived from a range of nickel-containing feedstocks is achieved by careful pH control. pH cpntrol of an ion exchange circuit used in metal separation is well understood by the person skilled in the art and the skilled person would be readily able to determine the necessary pH operating conditions required to obtain the selective extraction of nickel. Thus, it is not necessary to describe those parameters further. The skilled person will also understand that the operating parameters may vary according to the particular resin being used. The nickel-loaded resins are readily stripped by elution with moderately concentrated sulphuric acid.

Loading, scrubbing and elution operating design criteria are determined by the characteristics of the resin itself, in conjunction with consideration of the nickel/iron ratio of the feedstock and that required for the final product liquor.

The concentrated iron-free nickel liquor [7] exiting the ion exchange circuit [6] is forwarded to the final nickel recovery circuit [8]. Depending upon the scale of the overall operation and a range of economic factors, this may take the form of a relatively simple crystallisation process to recover hydrated nickel sulphate, or may involve electro winning nickel in either powder or conventional cathode sheet formats, or may involve precipitation of a very clean hydroxide or carbonate with low levels of contaminants such as iron and other metals. The iron-containing liquor [9] exiting the ion exchange circuit [6] is forwarded to an iron precipitation/removal circuit [10] and associated residue disposal and water balance facilities using, for example, nanofiltration. The design and operation of the iron precipitation/removal circuit [10] is outside the claims of this specification but the skilled person would readily appreciate that there are a number of processes that could be used to separate iron from the liquor to enable liquor of low iron content to be returned to the process or to be disposed of.

In the preceding description of the invention and in the claims which follow, except where the context requires otherwise due to express language or necessary implication, the words "comprise" or variation such as "comprises" or "comprising" are used in an inclusive sense, i.e., specify the presence of the stated features, but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that this invention and the preferred embodiments are not limited to the particular materials described, as these may vary. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention in any way.

It is also to be noted that, as used herein, the singular forms of "a", "an" and

"the" include the plural unless the context requires otherwise. Unless defined otherwise, all technical and scientific terms herein have the same meanings as commonly understood by one of ordinary skill in the art to which the invention belongs.

Claims

Claims.

1 . A method for the separation of nickel and iron from an acidic iron-containing nickel solution containing at least some dissolved iron in the ferric [Fe(III)] state, the method comprising the steps of: a) precipitating some of the iron present in the solution by increasing the pH of the solution; b) electrochemically reducing the ferric [Fe(III)] content of the iron- containing nickel solution to the ferrous [Fe(II)] state; and c) selectively separating the soluble nickel and ferrous [Fe(II)] components of the liquor derived from step (b) by contacting the liquor from step (b) with an ion exchange resin to selectively capture nickel.

2. A method as claimed in claim 1 wherein step (a) comprises raising the pH of the solution to above 2 to cause precipitation of some of the iron present in the solution.

3. A method as claimed in claim 2 wherein the pH is raised to about 2.5.

4. A method as claimed in any one of the preceding claims wherein the pH is raised by adding one or more of limestone, lime, magnesite, magnesia or calcrete to the solution.

5. A method as claimed in any one of the preceding claims wherein up to about 70 to 95% of the dissolved iron is removed from the solution in step (a).

6. A method as claimed in claim 5 wherein up to about 75 to 95% of the dissolved iron is removed from the solution in step (a).

7. A method as claimed in claim 5 wherein up to about 80 to 90% of the dissolved iron is removed from the solution in step (a).

8. A method as claimed in any one of the preceding claims further comprising the steps of: d) stripping the nickel from the nickel-loaded resin derived from step (c) into a nickel-rich solution; and ej processing the substantially nickel-free liquor derived from step (c) to ^■ 5 remove soluble iron therefrom.

9. A method as claimed in claim 8 wherein the nickel rich solution is treated to recover nickel or a nickel product.

10 10. A method as claimed in any one of the preceding claims wherein step (b) is carried out in a membrane cell.

11. A method as claimed in any one of the preceding claims wherein step (b) is carried out with a maximum cell voltage of about 2.5 volts.

15

12. A method as claimed in any one of the preceding claims further comprising treating the solution between step (b) and step (c) to further reduce a concentration of

■ ferric ions in solution. 0 13. A method as claimed in claim 12 wherein the step of treating the solution between step (b) and step (c) to further reduce a concentration of ferric ions in solution comprises passing the liquor exiting step (b) through a column packed with steel wool or by adding iron filings to the liquor to bring about the following reaction:

5 Fe³⁺ + Fe → 2Fe²⁺

14. A method as claimed in claim 12 wherein the step of treating the solution between step (b) and step (c) to further reduce a concentration of ferric ions in solution comprises sparging the liquor with sulphur dioxide gas or the addition of 0 sodium metabisulphite.

15. A method as claimed in claim 1 wherein the pH is raised to between 2 and 4 in step (a).

16. A method as claimed in claim 15 wherein the pH is raised to 2.5.