RU2797855C2 - Method for producing high-pure hydrated nickel sulfate - Google Patents

Abstract

FIELD: chemicals.

SUBSTANCE: inventions relate to methods for producing high-purity hydrated nickel sulphate. NiSO₄⋅6H₂O crystals are recovered from the nickel-enriched organic phase. Nickel is extracted with a solvent to form a nickel-rich organic phase, then it is brought into contact with an aqueous separating solution with a concentration of H₂SO₄ sufficient to extract nickel from the organic phase, and with a concentration of Ni²⁺ sufficient to precipitate NiSO₄⋅6H₂O crystals and form a nickel-depleted organic phase. A method is also proposed for obtaining nickel sulphate, including previous stages of processing, such as low-temperature oxidation under pressure in an autoclave of nickel sulphide concentrate

EFFECT: obtaining a productive leaching solution, extraction of cobalt from a productive leaching solution.

15 cl, 9 dwg, 19 tbl, 10 ex

Description

Technical field

The present invention relates to a process for producing high-purity hydrated nickel sulfate and to a high-purity hydrated nickel sulfate obtained by this process.

State of the art

High purity nickel salts, for example in the form of high purity acid solutions of nickel sulfate and/or high purity solid hydrated nickel sulfate, are an important source of nickel metal as a component involved in the production of valuable products. In particular, nickel sulfate is an important industrial commodity with a wide range of uses. For example, acidic aqueous solutions of nickel sulfate are the main precursor of electrolytic nickel metal, and solid nickel sulfate hexahydrate is an important source of nickel for modern lithium-ion battery applications.

These subsequent applications require high purity nickel salts. Thus, nickel salts must be of sufficient purity to meet the required chemical and/or physical characteristics for use in these applications. For example, the electrowinning of nickel metal from an acidic nickel sulfate solution in the presence of certain soluble impurities results in excessive energy consumption, physical deformation, and unacceptable chemical characteristics. Critical impurities include, but are not limited to, calcium, sodium, magnesium, iron, copper, cobalt, manganese, and zinc.

Nickel reserves fall into two main categories: sulfide ore and oxide ore (laterite or laterite ore). According to WO2007/039663, conventional nickel sulfide ore mining is essentially a pyrometallurgical process in which the mined ore is finely ground and the minerals from the nickel sulfide ore are concentrated by froth flotation to produce a nickel concentrate. The concentrate is then further processed by melting and reducing to obtain an intermediate nickel-containing matte, which also contains copper, cobalt and iron. However, a disadvantage of the smelting process is the production of sulfur dioxide, which must be treated in an acid plant to produce sulfuric acid, a product that cannot always be easily disposed of at the smelter site. Losses of nickel and cobalt to the smelter slag are significant, and there may be problems with some by-products in the concentrates, such as magnesium and arsenic.

The intermediate matte requires further purification by hydrometallurgical processes. But these processes, including oxidative or pressure leaching followed by decontamination and hydrogen reduction or electrowinning, are subject to the same problems of generating sulfuric acid by-products as well as other wastes (eg, ammonium sulfate).

For some applications, a purified nickel sulfate solution can be used directly as a starting solution to recover the final high purity product. A typical, but non-limiting, example is the stock solution (pre-electrolyte) for a nickel electrowinning cycle. For other applications, a solid high purity nickel salt is the preferred starting material. Recovery of such solid, high purity nickel salts is typically energy intensive and may involve, for example, high temperature crystallization. Alternatively, recovery of such solid, high purity nickel salts by evaporative crystallization under normal or near ambient conditions is generally an undesirably time consuming process.

The main commercial sources of acidic aqueous nickel sulfate solutions are the result of pressure oxidation of base metal (copper/nickel/cobalt) sulfide concentrates (the so-called POX process) or high-temperature sulfuric acid leaching of nickel laterites (the so-called HPAL process). Hydrometallurgical steps used to produce nickel sulfate include, but are not limited to, roasting/leaching, atmospheric and high pressure leaching, heap leaching, and biohydrometallurgical technologies. Other possible sources of acidic nickel sulfate aqueous solutions are bacterial leaching of common ores and non-ferrous metal concentrates in both stirred tank and heap modes, and a by-product of a number of copper electrowinning processes.

These methods are generally non-selective as a number of other metal components of the feed material are simultaneously dissolved, in particular iron, manganese, copper, cobalt and zinc. The relative impurity metal concentrations compared to the target nickel concentration are a direct consequence of the original nickel source and the metallurgical methods involved in obtaining the initial productive leaching solution containing soluble nickel sulfate.

Regardless of the source of the acidic aqueous nickel sulfate solution (product leach solution), the removal of harmful soluble impurities is carried out using a sequence of bulk and/or selective steps using, but not limited to, solvent extraction and/or ion exchange and/or precipitation procedures. This sequence of purification steps is necessary because there is no commercially or technically viable method for recovering high purity nickel product from such contaminated acidic aqueous solutions.

Typically, such steps involve the use of one or more of solvent extraction and/or ion exchange and/or cementation and/or selective/non-selective precipitation. All of these concentration/purification steps are typically energy intensive and involve the use of one or more chemicals (consumables).

The actual choice and sequence of impurity removal steps depends on many factors, but in particular on the relative concentrations of nickel and impurity components. These steps should complement each other and take into account process water balance considerations while minimizing the types of reagents and their consumption. In particular, the use of non-standard reagents should be avoided, while method conditions should limit the degradation of method reagents.

Various methods have been proposed for crystallizing and/or precipitating nickel sulfate hexahydrate from a purified acidic aqueous nickel sulfate solution. The most commonly used standard thermal and vacuum methods. However, these processes are highly energy intensive processes and are subject to a number of operational and maintenance problems such as particle size distribution, scaling, excessive corrosion, etc.

An alternative approach, which, to the inventors' knowledge, has not yet been applied commercially, involves a solvent displacement process in which, for example, isopropanol is added to reduce the solubility limit of nickel sulfate and increase the crystallization of nickel sulfate hexahydrate. The problem with this approach is that, in addition to requiring an external reagent for the entire system, as much isopropanol as possible needs to be recovered and reused. This includes a distillation step which is energy intensive.

It is an object of the present invention to overcome one or more of the disadvantages of known processes for the recovery of nickel sulfate in the form of nickel sulfate hexahydrate.

Reference to any prior art in the description is not an acknowledgment or suggestion that this prior art forms part of the general knowledge in any jurisdiction or that this prior art can reasonably be expected to be understood, recognized as relevant to the subject matter. and/or combined with other elements of the prior art by a person skilled in the art.

The essence of the invention

The present invention relates to a process for the recovery of nickel sulfate hexahydrate (NiSO ₄ ⋅6H ₂ O). Nickel sulfate hexahydrate must be of high purity. By "high purity" is meant a nickel content in the nickel sulfate hexahydrate of at least 21%, preferably 21 to 24%, and most preferably about 22 to 23%. The skilled person will appreciate that this includes the nickel content in the nickel sulfate hexahydrate of 22.0%, 22.1%, 22.2%, 22.3%, 22.4%, 22.5%, 22.6% , 22.7%, 22.8%, 22.9% and 23%. This also means that high purity/battery grade nickel sulphate hexahydrate also has a very low content of trace metals, including no more than 350 ppm Co, no more than 10 ppm Cu, no more than 25 ppm Ca, no more than 15 ppm Cr, no more than 15 ppm Fe, not more than 35 ppm Mg, not more than 15 ppm Mn, not more than 15 ppm Pb and not more than 15 ppm Zn. Preferably, high purity/battery grade nickel sulfate hexahydrate contains no more than 250 ppm Co, no more than 5 ppm Cu, no more than 15 ppm Ca, no more than 10 ppm Cr, no more than 10 ppm Fe, no more than 25 ppm Mg, no more than 10 ppm Mn, not more than 10 ppm Pb and not more than 10 ppm Zn.

High purity nickel sulfate hexahydrate is an important source of nickel for modern lithium-ion battery applications. Therefore, it is also referred to herein as "battery grade" nickel sulfate, with battery grade nickel sulfate having the same nickel sulfate hexahydrate content as above for high purity nickel sulfate hexahydrate, and these terms are used interchangeably.

According to the first aspect of the present invention, there is provided a method for recovering NiSO ₄ ⋅6H ₂ O crystals from a nickel-rich organic phase, comprising:

bringing the nickel-rich organic phase into contact with an aqueous separating solution with a concentration of H ₂ SO ₄ sufficient to extract nickel from the organic phase and with a concentration of Ni ²⁺ sufficient to precipitate NiSO ₄ ⋅6H ₂ O crystals and form a nickel-depleted organic phase.

The skilled artisan will appreciate that the concentration of H ₂ SO ₄ and Ni ²⁺ in the separating solution will vary depending on the particular conditions under which the process is carried out (eg temperature, pressure, presence of other ions).

In one embodiment, the separating solution has a Ni ²⁺ concentration of 60 g/l or more. More preferably, the separating solution has a Ni ²⁺ concentration of 70 g/l or more. Most preferably, the separating solution has a Ni ²⁺ concentration of 80 g/l or more. Additionally or alternatively, the separating solution has a Ni ²⁺ concentration of up to 100 g/L.

In one embodiment, the separating solution has an H ₂ SO ₄ concentration of 300 g/L or more or 350 g/L or more, or the separating solution has an H ₂ SO ₄ concentration of about 350 to about 450 g/L.

According to an alternative implementation, the separating solution has a concentration of H ₂ SO ₄ 300 g/l or less. Preferably the separating solution has an H ₂ SO ₄ concentration of 10-300 g/l.

In one embodiment, the separating solution has SO ₄ ^2- and Ni ²⁺ concentrations, both of which are at or near the NiSO ₄ ⋅6H ₂ O solubility limit. The term "about the solubility limit" means that the concentration is such that at least 90 wt. % nickel extracted from the organic phase precipitates as NiSO ₄ ⋅6H ₂ O. Preferably 95 wt. % nickel extracted from the organic phase precipitates as NiSO ₄ ⋅6H ₂ O. More preferably 98 wt. % nickel extracted from the organic phase precipitates as NiSO ₄ ⋅6H ₂ O. Most preferably 99 wt. % nickel extracted from the organic phase is deposited as NiSO ₄ ⋅ 6H ₂ O.

In one embodiment, the nickel-rich organic phase is immiscible with water.

In one embodiment, the method further comprises separating the NiSO ₄ ⋅6H ₂ O crystals from the nickel-depleted organic phase.

In one embodiment, the nickel-rich organic phase includes at least nickel (eg, as Ni ²⁺ ), an organic extractant, and an organic diluent. Preferably, the nickel-rich organic phase includes a coordination complex of nickel and an organic extractant, wherein the organic extractant releases the nickel in the presence of a sufficient concentration of H ⁺ ions (eg, from the dissociation of H ₂ SO ₄ ). More preferably, H ⁺ ions are provided during ion exchange with NiSO ₄ .

According to the forms of the above embodiment, the organic extractant is selected from the group consisting of organophosphorus acids, chelating oximes or hydroxyoximes, carboxylic acids, and high molecular weight amines (e.g., n-octylaniline, trioctyl/decylamine, trioctylamine, triisooctylamine, N-n-octylaniline, and 2- ethylhexylaminomethylpyridine).

According to the forms of the above embodiment, the organic extractant is from about 10 wt. % to about 25 wt. % organic phase. Preferably, the organic extractant is from about 12 wt. % organic phase. More preferably, the organic extractant is from about 14 wt. % organic phase. Alternatively or in addition, the organic extractant is up to about 22 wt. % organic phase. More preferably, the organic extractant is up to about 20 wt. % organic phase. According to one example, the organic extractant is about 18 wt. % organic phase.

According to the forms of the above embodiment, the organic extractant is one or more branched carboxylic acids, such as a branched carboxylic acid having from 7 carbon atoms to 15 carbon atoms. Preferably the branched carboxylic acid has from 8 carbon atoms. Most preferably the branched carboxylic acid has from 9 carbon atoms. Alternatively or in addition, a branched carboxylic acid has up to 14 carbon atoms. Preferably the branched carboxylic acid has up to 13 carbon atoms. More preferably the branched carboxylic acid has up to 12 carbon atoms. Most preferably the branched carboxylic acid has up to 11 carbon atoms. In one form, a branched carboxylic acid has 10 carbon atoms.

According to the forms of the above embodiment, the organic extractant is a branched monocarboxylic acid.

According to the forms of the above embodiment, the organic extractant is a branched carboxylic acid with the structure:

where R ₁ and R ₂ are unsubstituted alkyl groups with a branched or straight chain, and R ₁ and R ₂ together contain from 5 to 13 carbon atoms.

Preferably the branched carboxylic acid is neodecanoic acid. Neodecanoic acid is a mixture of carboxylic acids with the general structural formula C ₁₀ H ₂₀ O ₂ . Thus, the term neodecanoic acid covers such compounds as: 2,2,3,5-tetramethylhexanoic acid, 2,4-dimethyl-2-isopropylpentanoic acid, 2,5-dimethyl-2-ethylhexanoic acid, 2,2 -dimethyloctanoic acid and/or 2,2-diethylhexanoic acid. According to preferred forms of the present invention, neodecanoic acid includes one or more compounds selected from the group consisting of the compounds listed above.

According to the forms of the above embodiment, the organic diluent is immiscible with water.

According to the forms of the above embodiment, the organic diluent is one or more C ₁₀₊ alkanes. Preferably the organic diluent is one or more C ₁₁₊ alkanes. Most preferably, the organic diluent is one or more C ₁₂₊ alkanes.

According to the forms of the above embodiment, the organic diluent includes one or more isoalkanes, one or more cycloalkanes, and mixtures thereof.

In one embodiment, the organic diluent includes, consists of, or consists essentially of one or more isoalkanes, one or more cycloalkanes, and mixtures thereof. According to one example, the organic diluent comprises, consists of, or consists essentially of one or more C ₁₀₊ isoalkanes and/or one or more C ₁₀₊ cycloalkanes. In preferred forms, the organic diluent comprises, consists of, or consists essentially of one or more C ₁₁₊ isoalkanes and/or one or more C ₁₁₊ cycloalkanes. More preferably, the organic diluent comprises, consists of, or consists essentially of one or more C ₁₂₊ isoalkanes and/or one or more C ₁₂₊ cycloalkanes.

According to one implementation variant, the method includes the extraction of nickel with a solvent, and the stage of extraction of nickel with a solvent includes:

contacting an acidic aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to selectively extract the nickel sulfate from the aqueous solution into the organic phase to form a nickel sulfate-depleted aqueous raffinate and a nickel-rich organic phase; And

separating the raffinate and the nickel-rich organic phase;

where the organic extractant is one or more branched carboxylic acids.

According to an alternative implementation, the method includes the extraction of nickel with a solvent, and the extraction of nickel with a solvent includes:

a solvent extraction step comprising contacting an aqueous solution containing nickel sulfate and one or more metal impurities with an organic phase, wherein the organic phase includes one or more branched carboxylic acid extractants to selectively promote the extraction of nickel sulfate from the aqueous solution into an organic phase and formation of a nickel-rich organic phase.

According to an alternative implementation, the method includes the extraction of nickel with a solvent, and the stage of extraction of nickel with a solvent includes:

contacting an aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to form a nickel-rich organic phase, wherein the aqueous solution containing nickel sulfate is a productive leach solution (PLS). This embodiment of the present invention is described in relation to PLS, which is a cobalt-depleted and nickel-rich raffinate.

According to the forms of the above embodiments, the nickel sulfate containing solution is a production leach solution obtained from high temperature pressure oxidation (HTPOX) of nickel sulfide concentrate. One skilled in the art will appreciate that "high temperature" in this context is typically about 200°C or more.

According to alternative forms of the above embodiments, which will be detailed below, the nickel sulfate containing solution is a production leach solution resulting from low temperature pressure oxidation (LTPOX) of nickel sulfide concentrate. One skilled in the art will appreciate that "low temperature" in this context is typically about 100-120°C or lower.

According to the forms of the above embodiments and alternative embodiments, the nickel sulfate containing solution is pre-extracted with cobalt prior to extracting the nickel with a solvent, wherein the cobalt extraction step uses an organic extractant that more selectively extracts cobalt compared to extracting nickel into the organic phase to form an enriched cobalt and nickel-depleted extractant stream and cobalt-depleted and nickel-enriched raffinate. Preferably, the organic phase of the cobalt-rich and nickel-depleted extractant stream is converted to a cobalt-depleted organic phase and the cobalt-depleted organic phase is reused as the organic phase or a component thereof.

According to the forms of the above embodiments and alternative embodiments, the solution containing nickel sulfate is pre-clarified before extraction of the nickel with a solvent. Preferably, the solution containing nickel sulfate is preclarified prior to the cobalt extraction step.

According to the forms of the above embodiments and alternative embodiments, the nickel sulfate containing solution is preliminarily subjected to a secondary neutralization step prior to solvent extraction of the nickel, wherein the secondary neutralization step is carried out using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide. Preferably, the solution containing nickel sulfate is first subjected to a secondary neutralization step prior to the cobalt extraction step. More preferably, the solution containing nickel sulfate is preliminarily subjected to a secondary neutralization step prior to clarification.

According to the forms of the above embodiments and alternate embodiments, the nickel sulfate containing solution is preliminarily subjected to a countercurrent decanting step prior to solvent extraction of the nickel. Preferably, the solution containing nickel sulfate is preliminarily subjected to a countercurrent decanting step prior to the cobalt extraction step. More preferably, the solution containing nickel sulfate is preliminarily subjected to a countercurrent decanting step prior to clarification. Even more preferably, the solution containing nickel sulfate is preliminarily subjected to a countercurrent decanting step prior to the secondary neutralization step.

According to the forms of the above embodiments and alternative embodiments, the nickel sulfate containing solution is preliminarily subjected to a primary neutralization step prior to solvent extraction of the nickel, wherein the primary neutralization step is carried out using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide. Preferably, the solution containing nickel sulfate is first subjected to a primary neutralization step prior to the cobalt extraction step. More preferably, the nickel sulfate containing solution is first subjected to a primary neutralization step prior to clarification. Even more preferably, the nickel sulfate containing solution is first subjected to a primary neutralization step before the secondary neutralization step is carried out. Even more preferably, the nickel sulfate containing solution is first subjected to a primary neutralization step prior to the countercurrent decanting step.

According to the forms of the above embodiments and alternate embodiments, the nickel sulfate containing solution is PLS obtained from a low temperature pressure oxidation (LTPOX) step in a nickel sulfide concentrate autoclave.

According to the forms of the above embodiments and alternative embodiments, the LTPOX step in the autoclave uses oxygen to oxidize nickel sulfide from the nickel sulfide concentrate to nickel sulfate.

According to the forms of the above embodiments and alternate embodiments, the nickel sulfide concentrate contains more than 10% nickel.

According to the forms of the above embodiments and alternate embodiments, the nickel sulfide concentrate is preliminarily subjected to a fine grinding step in which particles of the nickel sulfide concentrate are ground to a P ₈₀ of 10 microns.

According to the forms of the above embodiments and alternative embodiments, the nickel sulfide concentrate is preliminarily subjected to a repulp step prior to the autoclave LTPOX step. Preferably, the nickel sulfide concentrate is preliminarily subjected to a repulping step prior to the fine grinding step.

According to the forms of the above embodiments and alternative embodiments, the nickel-rich organic phase is converted to a nickel-depleted organic phase, and the nickel-depleted organic phase is reused as the organic phase or a component thereof.

According to the forms of the above embodiments and alternate embodiments, one or more bases selected from the group consisting of ammonium hydroxide, magnesia, and sodium hydroxide are used in the nickel solvent extraction step; preferably ammonium hydroxide.

According to the forms of the above embodiments and alternative embodiments, the nickel-depleted organic phase is reused as the organic phase or a component thereof.

According to the forms of the above embodiments and alternate embodiments, the organic phase comprises, consists of, or consists essentially of an organic diluent and an organic extractant.

In one embodiment, the nickel-rich organic phase comprises: 5 ppm or less Fe and/or 5 ppm or less Mn and/or 5 ppm or less Cu and/or 60 ppm or less Co and/or 10 ppm or less Zn.

According to one implementation variant, the NiSO ₄ ⋅6H ₂ O crystals include: 5 ppm or less Fe and/or 5 ppm or less Mn, and/or 5 ppm or less Cu, and/or 60 ppm or less Co, and/or 10 ppm or less Zn.

In one embodiment, the one or more metal impurities are selected from the group consisting of: Fe, Mn, Cu, Co, Zn, and combinations thereof.

In one embodiment, the nickel-depleted organic phase is substantially free of nickel sulfate. By "substantially free of nickel sulfate" is meant a content of less than 10 ppm.

In one embodiment, the acidic aqueous solution containing nickel sulfate is a production leach solution resulting from high temperature pressure oxidation of nickel sulfide concentrate.

In one embodiment, the acidic aqueous solution containing nickel sulfate is a product leach solution resulting from low temperature pressure oxidation of nickel sulfide concentrate.

According to one implementation variant, the method can be carried out in the temperature range, for example, at a temperature of from about 10 °C to about 50 °C. Preferably, the process can be carried out at a temperature of from about 10°C to about 40°C. However, the advantage is that the process can be carried out at ambient temperature.

According to the second aspect of the present invention, NiSO ₄ ⋅6H ₂ O crystals obtained according to the method of the first aspect of the present invention are provided.

The present application also provides a method for recovering nickel sulfate from an acidic aqueous solution containing nickel sulfate and one or more impurities, comprising:

contacting an acidic aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to selectively extract the nickel sulfate from the aqueous solution into the organic phase to form a nickel sulfate-depleted aqueous raffinate and a nickel-rich organic phase; And

separating the raffinate and the nickel sulfate-enriched organic phase;

where the organic extractant is one or more branched carboxylic acids.

In addition, the present application proposes a method for obtaining purified nickel sulfate, including:

a solvent extraction step comprising contacting an aqueous solution containing nickel sulfate with an organic phase, wherein the organic phase includes one or more branched carboxylic acid extractants to selectively promote the extraction of nickel sulfate from the aqueous solution into the organic phase and form a sulfate-rich nickel of the organic phase.

According to a third aspect of the present invention, there is provided a method for recovering nickel sulfate, comprising:

a low temperature pressure oxidation (LTPOX) stage in a nickel sulfide concentrate autoclave where the nickel sulfide concentrate contains more than 10% nickel.

In one embodiment of this aspect of the present invention, the nickel sulfide concentrate particles are finely ground to a P ₈₀ of 10 microns.

In another embodiment, the autoclave LTPOX step uses oxygen to oxidize the nickel sulfide from the nickel sulfide concentrate to nickel sulfate.

In another embodiment, the nickel sulfate recovery process further comprises a primary neutralization step using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite, and sodium hydroxide. Preferably, the method further comprises a secondary neutralization step using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide.

In a further embodiment, the method further comprises a countercurrent decanting step and preferably a secondary neutralization step. The PLS of the second neutralization step can be used in subsequent extraction steps. For example, in one embodiment, a cobalt solvent extraction step is provided that uses an organic extractant that more selectively extracts cobalt than extracting nickel into an organic phase to form a cobalt-rich, nickel-depleted extractant stream and a cobalt-depleted, nickel-rich raffinate. Preferably, the organic phase of the cobalt-rich and nickel-depleted extractant stream is converted to a cobalt-depleted organic phase and the cobalt-depleted organic phase is reused as the organic phase or a component thereof.

In an alternative implementation, either the PLS product of the secondary neutralization step or the cobalt-depleted and nickel-rich raffinate is subjected to the nickel solvent extraction and direct crystallization steps. This embodiment of the present invention is described in relation to the initial solution, which is depleted in cobalt and enriched in Nickel raffinate, and the stage of nickel extraction with a solvent includes:

contacting the cobalt-depleted and nickel-rich raffinate with an organic phase comprising an organic extractant to form a nickel-rich organic phase; And

direct crystallization stage includes:

bringing the nickel-rich organic phase into contact with an aqueous separating solution with a concentration of H ₂ SO ₄ sufficient to extract nickel from the organic phase and with a concentration of Ni ²⁺ sufficient to precipitate NiSO ₄ ⋅6H ₂ O crystals and form a nickel-depleted organic phase.

In an alternative implementation, the method further includes a nickel solvent extraction step in which the cobalt-depleted and nickel-rich raffinate is contacted with an organic phase comprising an organic extractant to selectively extract the nickel sulfate from the aqueous solution into the organic phase to form the nickel sulfate-depleted aqueous raffinate. and nickel-enriched organic phase; And

separating the raffinate and the nickel-rich organic phase;

where the organic extractant is one or more branched carboxylic acids.

According to an alternative implementation, the method further includes a nickel solvent extraction step comprising contacting the cobalt-depleted and nickel-rich raffinate and one or more metal impurities with an organic phase, wherein the organic phase includes one or more branched carboxylic acid extractants for selective facilitating the extraction of nickel sulfate from the aqueous solution into the organic phase; and forming a nickel-rich organic phase.

According to the above aspects and embodiments of the present invention, one or more bases selected from the group consisting of ammonium hydroxide, magnesia and sodium hydroxide are used in the nickel solvent extraction step; preferably ammonium hydroxide.

According to the forms of the above embodiments and alternative embodiments, the nickel-rich organic phase is converted to a nickel-depleted organic phase, and the nickel-depleted organic phase is reused as the organic phase or a component thereof.

According to a fourth aspect of the present invention, there is provided a process for producing nickel sulfate, which includes the steps of:

a) providing a source of nickel sulfide concentrate;

b) repulping the nickel sulfide concentrate;

c) finely grinding the nickel sulfide concentrate from step (b) to a P ₈₀ of 10 microns;

d) low temperature pressure oxidation (LTPOX) in an autoclave of the nickel sulfide concentrate from step (c) to produce a production leach solution (PLS) where the nickel sulfide concentrate contains more than 10% nickel;

e) neutralizing the PLS using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide;

f) countercurrent decanting the PLS from step (e) to separate the solids from the PLS slurry;

g) neutralizing the PLS from step (f) using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide;

h) optional PLS clarification from step (g);

i) extracting cobalt from the PLS, wherein the cobalt extraction uses an organic extractant that more selectively extracts cobalt than nickel into the organic phase to form a cobalt-rich and nickel-depleted extractant stream and a cobalt-depleted and nickel-rich raffinate;

j) extracting nickel from the cobalt-depleted and nickel-rich raffinate; the nickel extraction comprising contacting the cobalt-depleted and nickel-rich raffinate with an organic phase comprising an organic extractant to form a nickel-rich organic phase; And

k) direct crystallization of the nickel-rich organic phase, the direct crystallization comprising contacting the nickel-rich organic phase with an aqueous separating solution with sufficient H ₂ SO ₄ concentration to extract nickel from the organic phase and sufficient Ni ²⁺ concentration to precipitate crystals NiSO ₄ ⋅6H ₂ O and the formation of a nickel-depleted organic phase;

where nickel sulfate is contained in an amount of 21 to 24% nickel and exists as nickel sulfate hexahydrate (NiSO ₄ ⋅ 6H ₂ O).

As described in the description below and in Example 4, the H ₂ SO ₄ concentration "sufficient" for nickel extraction depends on the nickel concentration. Typically, the H ₂ SO ₄ separating solution contains 10-450 g/l H ₂ SO ₄ ; preferably 10-300 g/l and most preferably 10-20 g/l; and 80-100 g/l Ni ²⁺ .

According to an embodiment of the third or fourth aspects of the present invention, the nickel-rich organic phase comprises: 5 ppm or less Fe and/or 5 ppm or less Mn, and/or 5 ppm or less Cu, and/or 60 ppm or less Co, and/ or 10 ppm or less Zn.

According to a fifth aspect of the present invention, there is provided a method for producing a solution containing nickel sulfate, comprising:

contacting the nickel-rich organic phase with an aqueous separating solution having a concentration of H ₂ SO ₄ sufficient to extract the nickel from the organic phase to form a nickel-depleted organic phase.

According to the forms of any of the first, third, fourth or fifth aspects of the present invention, the by-product ammonium sulfate is recovered.

According to a sixth aspect of the present invention, there is provided nickel sulfate obtained in accordance with the method of any of the third, fourth or fifth aspects of the present invention.

Additional aspects of the present invention and additional embodiments of the aspects described in the preceding paragraphs will become apparent from the following description given by way of example and with reference to the accompanying drawings.

Definitions and meanings of special terms

In this application, except when the context otherwise requires, the terms "method" and "method" and variants of these terms are used interchangeably and in no case are used to indicate the difference between these terms.

P ₈₀ defines the particle size suspension product size at which 80% by weight of the particles is smaller than this particle size. Similarly, P _x defines the particle size slurry product size at which x % by particle weight is less than this particle size.

PLS stands for productive leach solution. Clarified PLS means a leach product from which slurry solids have been removed, for example by countercurrent decanting. In this application, when referring to PLS, which is located in the process flow after the removal of suspended solids in the method according to the present invention, except when the context requires otherwise, the reference to PLS is equivalent to clarified PLS.

In this application, the various streams and phases according to the present invention are referred to as either enriched or depleted in nickel and cobalt. When referring to streams and phases that form or are located in the process flow after the cobalt solvent extraction and nickel solvent extraction steps of the present invention, the mention of a stream or phase enriched in nickel or cobalt means that the stream or phase is depleted in another element, unless otherwise indicated. out of context. Similarly, when referring to streams and phases that form or are located in the process flow after the cobalt solvent extraction and nickel solvent extraction steps of the present invention, reference to a stream or phase depleted in nickel or cobalt means that the stream or phase is enriched in another element, unless otherwise does not follow from the context.

The specialist will understand that the terms "enrichment" and "enriched" in the context of the present invention mean that the relative concentration of nickel or cobalt becomes higher than before the treatment in the previous stage. For example, PLS raw materials include both cobalt and nickel. Applying the cobalt extraction process to the PLS feedstock results in a cobalt-depleted, nickel-rich raffinate and a cobalt-rich, nickel-depleted extractant. The relative concentration of nickel and cobalt in the raffinate and extractant, respectively, increases by at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least at least 80% and at least 90% relative to the feedstock PLS. Similarly, the nickel-enriched organic phase has a higher relative nickel content than the feedstock from which it was derived and is relatively increased by at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%.

The opposite is that "depleted" means that the nickel or cobalt content is reduced. Preferably, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least at least 97%, at least 98% and at least 99% nickel or cobalt. The lean phase preferably contains less than 20 ppm and more preferably less than 10 ppm nickel or cobalt.

The terms "nickel sulfide concentrate" and "nickel/cobalt sulfide concentrate" are used interchangeably unless the context dictates otherwise.

As described in the description below and in Example 4, the H ₂ SO ₄ concentration "sufficient" for nickel extraction depends on the nickel concentration itself. Typically, the H ₂ SO ₄ separating solution contains 10-450 g/l H ₂ SO ₄ ; most preferably 10-300 g/l. And the concentration of Ni ²⁺ sufficient for precipitation is 80-100 g/l.

In this application, except where the context otherwise requires, the term "comprise" and variants of this term such as "comprising" and "comprises" are not intended to exclude other additives, components, integers, or steps. The term "comprising", except where the context implies otherwise, is used interchangeably with the term "including".

Brief description of graphic materials

Figure 1: Process flow diagram illustrating an embodiment of the high temperature pressure oxidation (HTPOX) process of the present invention with a nickel recovery process of one embodiment of the present invention.

Figure 2: Photograph showing a portion of a 1.7 kg NiSO ₄ .6H ₂ O sample recovered from about 40 L of nickel-containing versatic acid extractant 10 according to one embodiment of the present invention.

Figure 3: Process flow diagram illustrating an embodiment of the Low Temperature Pressure Oxidation (LTPOX) process of the present invention for producing a solution containing nickel sulfate.

Figure 4: A process flow diagram illustrating the low pressure oxidation process of Figure 3, which includes a nickel recovery process according to one embodiment of the present invention.

Figure 5: An autoclave technology that has a significantly lower temperature and pressure required to leach the metal into solution compared to other processes in the nickel industry.

Figure 6: Plot of the equilibrium percentage extraction of nickel and selected co-extractable metals: Co, Ca, Mg and Cu as a function of pH in a nickel extraction pH profile trial on a large volume of cobalt raffinate to determine the optimal pH for extraction. The test was carried out at a temperature (50 °C) with a fixed contact aqueous phase:organic phase (B:O) in a ratio of 1:1 in the pH range (5.0, 5.5, 6.0, 6.5 and 7.0 ).

Figure 7: Quality comparison of nickel concentrates on ground and non-ground samples using 175 g/t TETA (triethylenetetramine) and 175 g/t CH (sodium sulfite). The release of pyrrhotite from pentlandite improved the removal of pyrrhotite. Figure 7a compares the S:Ni ratio for ground and non-ground samples. Figure 7b compares Eh (redox potential) for ground and non-ground samples. The activation of the pyrrhotite surface by TETA and CH is confirmed by the change in Eh.

Figure 8a: Comparison of sulfide oxidation kinetics in the LTPOX step for samples with different P ₈₀ values. The test was carried out at 105 °C and an overpressure of O ₂ 1000 kPa with 1 g/l Cl or 5 g/l Cl. Samples with P ₈₀ values less than 10 microns oxidized significantly faster than a sample with a P ₈₀ value of 18 microns.

Figure 8b: Comparison of nickel extraction rates in the LTPOX stage for samples with different P ₈₀ values. The test was carried out at 105 °C and an overpressure of O ₂ 1000 kPa with 1 g/l Cl or 5 g/l Cl. Nickel from samples with P ₈₀ values less than 10 microns was extracted significantly faster than nickel from a sample with a P ₈₀ value of 18 microns.

Figure 9: Relationship between total elemental sulfur (Total recovery S ₀ (%)) and flotation time (Total flotation time (min)) for various process slurries. These different slurries were made using different flotation reagents, where MIBK means methyl isobutyl carbinol, W24 means W24 Frother frother available from Huntsman, and Dowfroth 250a means Dowfroth 250 A frother available from Dow Chemical.

Utility

As the demand for lithium-ion batteries rises with the increase in sales of electric vehicles and energy storage systems, the demand for high-quality raw materials for batteries is also growing. Nickel sulfate is critical for some EV battery cathodes, especially for battery technologies using nickel-cobalt-manganese (NCM) and nickel-cobalt-aluminum (NCA) cathode chemistries. NCM and NCA technologies are becoming increasingly popular due to their high energy density, which, in the case of electric vehicles, leads to an increase in range. There has also been a shift towards an increase in the proportion of nickel in the cathode for both of these battery types.

As a rule, nickel sulfate is obtained from intermediate or refined nickel products that have been subjected to many complex metallurgical processes. These additional processes have resulted in nickel sulphate being sold at a higher price than the LME nickel metal price. The size of this difference in price is largely determined by market demand and supply, quality and origin.

The methods of the present invention optimize the production of nickel sulphate directly from nickel sulphide concentrates without the need to first prepare intermediate or refined nickel products. Nickel sulfate is in the form of hexahydrate (NiSO ₄ ⋅6H ₂ O) and is of high purity as defined above. This high purity nickel sulfate hexahydrate is also referred to herein as "battery grade" nickel sulfate.

In addition, the processes of the present invention are more environmentally friendly than conventional nickel sulphate production processes due to significantly lower emissions, energy consumption and waste generation. In addition, the methods for recovering nickel sulfate according to the present invention have an advantage over conventional evaporative crystallization methods conducted at or near normal ambient conditions, since the methods according to the present invention are significantly faster.

The methods and processes of the present invention also result in other commercially available by-products, including an elemental sulfur by-product and a cobalt-copper-containing mixed sulphide precipitate by-product.

Detailed description of implementation options

The processes of the present invention combine for the first time several technologies (both new and known) for use in the nickel industry for the commercial integrated production of nickel sulphate. The methods according to the present invention can be simplified to four successive steps, namely:

Stage 1, Leaching: Oxygen injection is used to partially oxidize the sulphide concentrate to soluble metal sulfates (nickel, cobalt, copper, iron, etc.), sulfuric acid and sulfur.

Stage 2, primary and secondary neutralization: A two-stage neutralization method to remove free acid, iron and other metals to obtain the required stock solution for subsequent solvent extraction.

Stage 3, solvent extraction and precipitation of cobalt and copper: Cobalt, copper, zinc, manganese and magnesium are removed from the solution. The cobalt, copper and zinc are then re-extracted with sulfuric acid from the resulting organic solution and recovered as a mixed sulfide precipitate (MSP).

Step 4, Nickel Solvent Extraction and Crystallization: Additional impurities are removed from the solution in a nickel solvent extraction cycle prior to crystallization using a new direct crystallization process.

According to one aspect of the present invention, there is a method for nickel solvent extraction and crystallization (step 4). This method can be incorporated directly into a general process for recovering cobalt and nickel from a nickel/cobalt sulfide concentrate, as described in the exemplary embodiment below.

Figure 1 is a process flow diagram 100 for treating nickel/cobalt sulfide concentrate using high temperature pressure oxidation (HTPOX) technology and associated separation and purification steps that incorporate a nickel recovery process in accordance with an embodiment of the present invention. The illustrated process includes initial milling and flotation techniques to produce a nickel/cobalt sulfide concentrate that can be stored in a concentrator 101. The concentrate can be used directly as feedstock to pressure oxidation process 104 or stored. In each case, the pulp density of the raw material can be controlled by repulping 102.

Once the feed is prepared, the process 100 includes conducting a high temperature pressure oxidation 104 of the nickel/cobalt sulfide concentrate prior to treating the oxidized nickel/cobalt sulfide concentrate in a countercurrent decanting process 108 to produce a nickel and cobalt containing leach solution and bottoms.

After the pressure oxidation 104 and prior to the countercurrent decanting process 108, the nickel/cobalt sulfide concentrate may be processed in a hot acid fix (HAC) cycle 106 to remove basic ferrous sulfate (BFS), which may otherwise release iron during waste treatment processes or storage.

Waste undergoes neutralization 110 and thickening 112 prior to disposal, process water 114 is regenerated during thickening to return to pressure oxidation 104. The nickel and cobalt containing leach solution is then subjected to neutralization process 116 and gypsum treatment 118. Filter cake 120 after gypsum treatment 118 is combined with the waste from the countercurrent decanting process 108 and subjected to the same neutralization 110 and thickening 112 processes. The result of the cobalt extraction process is an extractant stream rich in Co and depleted in Ni, and depleted in Co and enriched in Ni raffinate. The Co-rich and Ni-depleted extractant stream is subjected to precipitation 128 and thickening/filtering 130 to recover cobalt as cobalt product 131. can subsequently be processed to produce solid, high purity nickel sulfate hexahydrate.

In more detail, as shown in Example 3, the Co-depleted and Ni-rich raffinate 133 includes a number of impurities such as Fe, Mn, Cu, Co, and Zn. The inventors have found that this stream 133 can be subjected to a solvent extraction process 132 to selectively extract nickel from the nickel sulfate containing stream and thereby produce a Ni-depleted raffinate that contains substantially all impurities and a Ni-rich extractant stream that is substantially does not contain impurities. This solvent extraction process 132 uses an organic phase that includes an organic acid extractant. According to this exemplary embodiment, the organic phase comprises versatic acid 10 (neodecanoic acid) as an extractant dissolved in a suitable diluent such as Escaid110 (paraffin diluent containing a mixture of C ₁₂₊ iso- and cycloalkanes). Versatic acid 10 is a cation exchange extractant that extracts metals from aqueous solution through an ion exchange process to release the H ⁺ ion. This H ⁺ ion is returned to versatic acid 10 in a separation step using acid to remove the metal from the organic phase. The advantage is that this solvent extraction process does not involve the use of any extraneous reagents. However, the skilled person will appreciate that other extractants and/or diluents may be used. Suitable extractants include: organophosphorus acids, chelating oximes (or hydroxyoximes), carboxylic acids and high molecular weight amines (HMWAs). The diluents used are matched to the extractants selected for the particular extraction steps.

Nickel sulfate hexahydrate can then be recovered in the crystallization process 134. Crystallization of nickel sulfate hexahydrate 140 is accomplished by separating the nickel-containing organic phase with a separating solution of sulfuric acid 136. The concentration of sulfuric acid used to remove nickel from the nickel-containing organic phase with versatic acid 10, not particularly important, but it is related to the concentration of nickel itself, as shown in Example 4. The concentration of sulfuric acid used must be high enough to shift the separation reaction to the right (for example, the formation of NiSO ₄ ⋅6H ₂ O in this case) and to provide so that the value of the solubility product of nickel sulfate hexahydrate 140 under process conditions (eg at operating temperature) is exceeded and maintained during the separation step. Typically, the separating solution of sulfuric acid 136 contains 300-450 g/l H ₂ SO ₄ . However, according to an alternative implementation, separating the solution of sulfuric acid contains 10-300 g/l H ₂ SO ₄ . According to preferred forms, the process comprises recirculating a separating solution 138 which is depleted in sulfuric acid but contains a high concentration of Ni ²⁺ , typically 80-100 g/l Ni ²⁺ , present to ensure that the saturation level of the nickel sulfate hexahydrate solution 140 is exceeded upon addition fresh nickel-containing organic phase from the extraction process 132. As shown in Table 10, more than 99% of the introduced nickel content in the phase with versatic acid 10 after extraction can be removed in one step. The contained nickel is removed as a denser solid at the bottom of the solvent extraction mixer by the addition of sulfuric acid, from where it can be recovered by appropriate gravity filtration/centrifugation and washing techniques. After removal of the nickel sulfate hexahydrate solid 140, the substantially nickel-free aqueous and organic phases are separated by conventional methods, with the organic phase recycled back to the solvent extraction process 132 and the aqueous stream recycled to upstream processes as part of the overall process water balance. The amount of sulfuric acid in the separating solution depends on the nickel concentration in the organic phase of the extractant.

To ensure that the target purity of the final nickel sulfate hexahydrate 140 is achieved, the nickel-containing phase with versatic acid 10 may be subjected to a final wash step after extraction and purification. This diluent wash step is designed to minimize possible metal carryover and minimize decomposition of the extractant. By "target purity" is meant that the nickel sulfate hexahydrate is of high purity/battery grade and contains at least 21% nickel, preferably 21 to 24% and most preferably about 22 to 23% nickel. The skilled person will appreciate that this includes the nickel content in the nickel sulfate hexahydrate of 22.0%, 22.1%, 22.2%, 22.3%, 22.4%, 22.5%, 22.6% , 22.7%, 22.8%, 22.9% and 23%. This also means that high purity/battery grade nickel sulphate hexahydrate also has a very low content of trace metals, including no more than 350 ppm Co, no more than 10 ppm Cu, no more than 25 ppm Ca, no more than 15 ppm Cr, no more than 15 ppm Fe, not more than 35 ppm Mg, not more than 15 ppm Mn, not more than 15 ppm Pb and not more than 15 ppm Zn. Preferably, high purity/battery grade nickel sulfate hexahydrate contains no more than 250 ppm Co, no more than 5 ppm Cu, no more than 15 ppm Ca, no more than 10 ppm Cr, no more than 10 ppm Fe, no more than 25 ppm Mg, no more than 10 ppm Mn, not more than 10 ppm Pb and not more than 10 ppm Zn.

The extraction and removal of nickel in the solvent extraction process 132 and the crystallization process 134 may be carried out at ambient temperature or at a slightly higher temperature. For example, the temperature may be from room temperature to 50°C. Usually, however, no thermal energy supply is required.

The inventors believe that the solvent extraction and crystallization process of nickel according to the present invention is the first development and implementation of such a technology for producing a highly pure (special purpose chemical) product. As far as the authors of the invention know, the development of the stage of purification and crystallization (metal recovery) within the framework of one technological process in the metallurgical industry, and even more so in the nickel industry, has not been carried out before.

The inventors have also developed a process that allows the production of high purity nickel sulfate crystals in an integrated process that aims to produce a low cost and high purity nickel sulfate product and overcome one or more of the drawbacks of the existing methods. It is important to note that the methods of the present invention differ significantly from the known “whole ore” high pressure acid leaching (PAL) and high pressure acid leaching (HPAL) methods, both of which are designed to treat nickel and cobalt rich lateritic ore. Specific differences include:

⋅ Nickel sulfide concentrates typically contain 8-10% nickel and 40% iron. Direct roasting of such nickel sulfide concentrates followed by refining directly to battery grade materials is not considered technically feasible due to nickel losses occurring in the iron residues that must be leached. In contrast, the process of the present invention is designed to treat high grade nickel sulfide concentrate (greater than 10% nickel) as opposed to low grade "whole ore" lateritic feedstock. The method according to the present invention is preferably designed to treat high grade nickel sulfide concentrate containing 18-20% nickel.

The significantly lower temperatures and pressures used in the autoclave are less risky and capital intensive than the temperatures and pressures used in the PAL and HPAL processes (see Figure 5 and below for further explanation).

The autoclave leaching cycle uses oxygen to oxidize sulfide minerals, allowing metals to be selectively leached into solution. In contrast, the sulfuric acid in the PAL and HPAL processes dissolves many of the other gangue minerals present in the lateritic ore feed.

A more efficient option for switching from nickel sulphide concentrate to battery grade nickel sulphate is direct leaching of the concentrate by bioleaching or pressure leaching to form either a mixed hydroxide precipitate (MHP) or a mixed sulphide precipitate (MSP), which can then be further refined. Pressure leaching of sulfide concentrates was used by Sherrit in Fort Saskatchewan to treat nickel concentrates from Lynn Lake, Prov. Manitoba, Canada from 1953 until closing in 1976

Figure 1 illustrates one such embodiment of the nickel recovery aspect of the present invention as part of a pressure oxidation process. But the use of embodiments of the present invention is not limited to these raw materials or the combination of separation and purification steps.

By modifying steps 102-124 in Figure 1, the inventors have developed an alternative implementation (method 300 - Figure 3) that also results in a high quality and concentrated solution containing nickel sulfate that can be subjected to the crystallization step of the present invention and importantly also does not require the preparation of intermediate products.

Accordingly, according to one aspect of the present invention, there is provided a process for recovering nickel sulfate, comprising:

a low temperature pressure oxidation (LTPOX) stage in a nickel sulfide concentrate autoclave where the nickel sulfide concentrate contains more than 10% nickel.

This method is described in more detail below.

1. Enrichment (302)

Flotation of mined nickel sulfide ore to form nickel sulfide concentrate; preferably the concentrate has a nickel content of more than 10%, preferably more than 12% nickel and more preferably more than 15% nickel. The post-flotation process step increases the nickel content and improves the removal of some of the iron sulfides, which allows for a smaller process equipment size (lower volumetric capacity), which in turn allows the refinery to be built at a lower capital cost and still achieve the required specific nickel throughput ( see below).

2. Repulping (304)

Repulping the milled nickel sulfide concentrate with process water to produce a slurry with a weight percent solids content of preferably 10 to 20 percent.

3. Regrinding and storage of suspension (306)

Fine grinding of nickel sulfide concentrate particles to a P ₈₀ of 10 microns is the preferred step for low temperature pressure oxidation (see Example 5). Fine grinding improves the sulfide oxidation kinetics and the nickel extraction rate, which reduces the time and energy consumption of the LTPOX stage.

4. LTPOX (308)

Low temperature pressure oxidation (LTPOX) of the slurry from step 3 to produce a productive leach solution (PLS). LTPOX, as opposed to the POX stage in a medium (approximately 150 °C - 170 °C) or high (typically above 200 °C) temperature autoclave (HTPOX) autoclave (according to the application in the alternative implementation shown in Figure 1 ), allows the autoclave to be tapped at a lower concentration of free sulfuric acid (>10 g/l sulfuric acid), resulting in less base consumption and lower reagent costs, as shown in Example 6. When limestone or lime is used, the advantage is also consists in less deposition of gypsum in the waste. Ammonia (ammonium hydroxide) is the preferred base, resulting in even less solid waste because no calcium is added to the cycle other than the calcium that is introduced with the nickel feedstock source. The autoclave LTPOX step is carried out at a temperature of 100 to 120°C with the addition of oxygen to the autoclave to achieve an oxygen overpressure of about 800-1200 kPa, preferably about 1000 kPa, while the residence time of the concentrate in the autoclave is less than 3 hours.

Previously, LTPOX was used only for processing low grade nickel concentrates. As far as the inventors know, it has not been adapted to a process for producing high grade nickel sulphate products from high grade nickel sulphide concentrate. The person skilled in the art will appreciate that a high grade nickel sulfide concentrate contains more than 10% nickel, preferably more than 12% nickel, and even more preferably 15% nickel.

As shown in Figure 5, this autoclave technology has significantly lower temperatures and pressures required to leach the metal into solution than other processes in the nickel industry. This method according to the present invention is indicated in this figure as "IGO". Despite the lower temperature and pressure, the other two methods presented in the figure are not comparable to the claimed method. Corefco's process uses a different feed material (MSP - mixed sulphide sludge) and process type (POX ammonia leach); in Quinan's process, the starting material is nickel matte and is also based on the ammonia leaching of POX. The use of LTPOX in the context of the method described in this application according to the present invention to obtain a solution containing nickel sulfate, is considered unique.

It should also be noted here that the development of the process of the present invention, including LTPOX, eliminates the need for hot acid fixing (HAC), resulting in the advantage of better nickel recovery and less waste. The function of the HAC cycle is to process BFS generated in the autoclave, which may otherwise decompose during waste neutralization or release iron into solution from the Waste Storage Facility (TSF). The HAC cycle consumes some of the free acid in the autoclave effluent. This is not required in the LTPOX process because BFS is not the thermodynamically dominant or stable form of iron under the conditions used and the free acid levels are much lower and thus not sufficient to dissolve any solids formed.

5. PN (310)

Primary neutralization (PN) - any amount of free acid resulting from the oxidation of sulfides and soluble impurities such as iron and aluminum is neutralized from PLS and precipitates as hydroxides at pH 3 and 90 °C, as shown in Example 7. Raising the pH can be accomplished by adding a variety of neutralizing agents, which include, but are not limited to, limestone, lime, calcrete, magnesia, magnesite, ammonium hydroxide, and sodium hydroxide.

By eliminating the need for HAC, the PN step can be carried out before the countercurrent decantation (CCD) step. This is an advantage as it minimizes the risk of nickel loss.

6.CCD (312)

The PLS slurry is thickened and solid-liquid separation is performed by countercurrent decantation (CCD) to feed the clarified PLS further.

7. Sulfur flotation (314-320)

It is possible to optionally recover the salable elemental sulfur by-product by flotation of the thickened solids obtained from the PLS slurry and the remaining solids collected in the waste storage after the solid waste has been neutralized to pH > 8 with lime. Extraction of elemental sulfur is described in Example 8.

8. SN (322) and clarification PLS, storage and filtration (324, 326, 328)

Secondary Neutralization (SN) - This optional but preferred step is used to remove the remaining impurities from the leach solution (PLS) at pH 4 and 70°C using the same possible neutralizing agents listed in step 5. This additional neutralization step serves to obtaining an acceptable feedstock (which is the product of step 328) for the next solvent extraction steps and to prevent the loss of nickel and cobalt due to the fact that only a small amount of solids is deposited and purified from the PLS.

As noted above, PLS obtained by pressure oxidation of nickel sulfide concentrate represents a significant improvement over prior art methods. In turn, the LTPOX process provides advantages over the HTPOX processes in terms of lower emissions, lower energy consumption, less waste, higher efficiency, and elimination of the need to pre-finish intermediates or refined nickel products.

For example, LTPOX is a process for the partial oxidation of sulfide compounds in a concentrate that oxidizes some of the sulfur to a less oxidized form, elemental sulphur. This is different from what happens in the HTPOX process, where all the sulfide in the concentrate is oxidized to sulfate. All sulfate not associated with metal products will consume the base (lime, limestone and/or other hydroxides) and these materials will become waste products that will be sent to waste and placed in a waste repository. Because LTPOX converts some of the sulfide to elemental sulfur (a marketable by-product) via flotation, this not only results in additional product, but also greatly reduces the amount of waste and reagents required for the process.

HTPOX also produces an increased concentration of sulfuric acid (free acid), which consumes more base and generates additional solid waste. The lower acid levels in LTPOX (compared to HTPOX) also provide less gangue dissolution and, along with the use of high grade concentrates, result in significantly less waste to be handled and stored compared to the conventional prior art methods discussed previously. for the production of nickel sulfate.

By eliminating the pyrometallurgical roasting steps, significantly fewer greenhouse gases are generated. Lower greenhouse gas emissions are an advantage as the products of these methods are ultimately intended for use in renewable or "green" energy technologies such as electric vehicles or solar energy storage.

Additional process steps

After this new method, the clarified PLS is subjected (with reference to Figures 1 and 4):

9. CoSX (430, 432, 434)

Cobalt Solvent Extraction (CoSX) - Co, Cu, Zn, Mn and Mg are removed from clarified PLS in a CoSX cycle using an organophosphinic acid such as Cyanex 272 in an organic diluent such as VivaSol 2046 as shown in Example 9. Ammonium hydroxide , magnesia or sodium hydroxide can be used to neutralize H ⁺ ions substituted by metals during the extraction of metals into the organic phase from the aqueous phase. Optionally, a mixed sulfide precipitate containing cobalt and copper can be recovered from the CoSX cycle.

10NiSX (132)

Nickel Solvent Extraction (NiSX) - Ni and minor residual impurities in the clarified PLS, such as Co, Na, Ca and Mg, are removed in the NiSX step using an organic phase with versatic acid 10. Similarly, ammonium hydroxide can be used as a neutralizing base , magnesium or sodium hydroxide. When using ammonium hydroxide as the base for adjusting the pH, the process of the present invention includes an ammonium sulfate crystallization cycle.

11. NI DXTL (134)

Direct Crystallization (DXTL) - The nickel recovery/crystallization step is described above as a novel process according to the present invention for recovering NiSO ₄ ⋅6H ₂ O crystals from a nickel-rich organic phase. The new recovery/crystallization step according to the present invention is shown in the context of a new process for producing a solution containing nickel sulfate in Figure 4.

As detailed above, the contained nickel is removed using solubility as a parameter resulting in immediate crystallization of the metal sulfate hexahydrate as it separates into an acidic aqueous nickel sulfate separating solution with a nickel sulfate solution. According to one implementation variant, the separating solution contains more than 300 g/l of sulfuric acid. However, in a preferred embodiment, the separating solution contains 10 to 300 g/l sulfuric acid. The organic phase may optionally be recovered for additional nickel extraction in the NiSX step.

The nickel sulfate crystals are then washed, centrifuged and dried before being packaged for commercial sale to consumers to make a precursor material for use in lithium ion batteries.

The advantage of the process for preparing a solution containing nickel sulfate according to the present invention is that no intermediate products are formed. Starting with processes using lateritic ore or prior art processes using sulfide ore, mixed hydroxide and mixed sulfide precipitates form in the intermediate precipitation steps, which must be subjected to additional purification steps. These additional refining steps lead to waste, efficiency and nickel recovery problems already discussed above. Even in the case of the process in which the raw material is sulfide ore, matte is formed during the smelting process, which requires the most additional processing and refining to remove the iron present.

The preferred base for the PN, SN, CoSX and NiSX steps is ammonium hydroxide. When using ammonium hydroxide, a valuable by-product, ammonium sulfate, crystallizes from the cycle. This by-product is valuable in the fertilizer market and is a unique by-product of the nickel sulfide concentrate process of the present invention. This means that no other integrated processes using nickel sulphide to produce nickel sulphate without an intermediate precipitation step produce this by-product.

The method for producing a solution containing nickel sulfate according to the present invention also results in the formation of a co-product of a high-grade mixed sulfide precipitate containing cobalt and copper, in accordance with Table 1 below:

Table 1: Cu/Co mixed sulphide precipitate (MSP product) Element Units Average* Range* Cu % 32.8 31.8-33.8 co % 28.7 27.7-29.7 Ni % 0.3 0.1-0.5 S % 32.8 30.5-34.5 Zn md 1537 500-3000 Ag md 25 0-50 Al md 650 400-900 As md <15 NGOs Ca md <200 NGOs CD md 35 15-90 Fe md 240 50-430 TO md 140 50-270 mg md 220 50-480 Mn md 470 100-600 Na md 3000 1000-5000 P md 1220 1100-1300 Pb md 90 75-105 Sb md 20 10-20 V md 10 2-20 Cr md 120 105-150 Si md <0.2 NGOs

NPO - below detection limit

*Based on dry matter

This recovers the value of any residual amounts of copper and cobalt that are introduced into the process from the nickel sulfide concentrate. Table 5 lists the copper and cobalt contents of the feedstock used to make the Cu/Co MSP mixed sulfide product shown in the table above. The inclusion of a cobalt/copper product step in this process is unique.

An additional advantage of the process of the present invention is the ability to process nickel concentrates with a high arsenic content (up to 5000 ppm As) to battery grade nickel sulfate products as described in Example 10 and to quantitatively recover cost-effective PGM levels after extraction of nickel and cobalt while quantitatively recovering a stream of valuable leftovers. The process of the present invention can be used to process nickel concentrates containing more than 100 ppm arsenic, preferably more than 1000 ppm arsenic, to battery grade nickel sulfate products.

The methods of the present invention also serve to reduce the content of impurities:

• The calcium content decreases and the calcium is removed in the NiSX stages.

• Copper is removed in the CoSX stages and precipitated in the mixed sulphide precipitation stage.

• Iron precipitates as oxides in autoclaves and neutralization stages (PN and SN); most of the iron is then sent to waste after solid-liquid separation in the CCD cycle. Some iron is removed in the final filtration after the SN step.

Examples

The following examples show the results of the nickel solvent extraction and crystallization steps, that is, the nickel recovery steps of the present invention. Unless otherwise stated, element levels were measured using ICP-OES.

Example 1 Versatic Acid as an Extractant Using a Cobalt-Depleted Nickel Feed Solution

Table 2 shows the composition (ppm) of fresh and recycled versatic acid 10 at 15% v/v. Escaid 110 after extraction using a cobalt-depleted nickel stock solution (note: laboratory tests up to 25% v/v have also been successful). Despite very slight differences in impurity levels, the results show no significant effect on the overall extractability in nickel extraction.

Table 2: Composition of fresh and recycled organic phases after extraction Element Fresh organic phase after extraction
(md) Reusable organic phase after extraction
(md) Al <1 <1 Ca 46 44 co 4.4 12 Cr <0.1 <0.1 Cu 0.46 <0.05 Fe 10 <1 mg 8 10 Mn <0.1 <0.1 Na 6.8 14.6 Ni 18320 18320 Zn 1.46 0.38

An additional series of tests was carried out to confirm that the separation of nickel-containing versatic acid 10 with concentrated sulfuric acid did not lead to decomposition of the versatic acid extractant 10 after numerous stages of reuse. Table 3 shows the extraction capacity for nickel extraction before and after the versatic acid 10 phase at 15% v/v. Escaid 110 was contacted with 430 g/l H ₂ SO ₄ for 1 week.

Table 3: Composition of versatic acid 10 after extraction Sample Ni content
(g/l) Fresh organic phase 12.84 Organic phase treated with acid 13.56

The data in Table 2 confirms that prolonged treatment with excess sulfuric acid had no effect on the extractive power of Versatic Acid Reagent 10.

Example 2 Crystallization of Nickel Sulfate Hexahydrate

The steps of extracting the nickel with a solvent and crystallizing the nickel sulfate hexahydrate were repeated several times to obtain the bulk sample shown in Figure 2. Figure 2 shows a portion of a 1.7 kg NiSO ₄ ⋅6H ₂ O sample extracted from about 40 L of nickel-containing versatic acid extractant. 10 using the Ni DXTL approach.

The average chemical composition of a number of sample samples from the bulk sample depicted in Figure 2 was analyzed and the results are shown in Table 4.

Table 4: Product Composition of Crystallized Nickel Sulfate Hexahydrate Element Unit Meaning Ni min. wt. % 23.4 co md 53 Cu md 2 Fe md <1 Zn md 8 Mn md <1 mg md <1 Pb md <1 Cr md <1 Ca md 7.6

The product whose composition is shown in Table 4 was obtained from a feedstock (concentrate from the Nova deposit) whose composition is shown in Table 5.

Table 5: Composition of raw materials used to obtain the crystallized product of Table 4 Element Unit Concentrate from the Nova deposit Ni % 19.3 co % 0.64 Fe % 35.2 Na md 823 As md 8 Al % 0.59 Cu % 1.17 Ca % 0.34 Mn md 255 mg % 0.86 Zn md 82 Ti md 801 K % 0.15 Sb md below detection limit Si % 2.0 S % 31.0 S:Ni ratio 1.61

Example 3 Selective Extraction of Nickel from Co-Depleted and Ni-Enriched Raffinate

Table 6 shows the results of nickel extraction pH profile trials on a large volume of cobalt-depleted and nickel-rich raffinate to determine the optimum pH for extraction. The test was carried out at a temperature (50 °C) with a fixed contact aqueous phase:organic phase (B:O) in a ratio of 1:1 in the pH range (5.0, 5.5, 6.0, 6.5 and 7.0 ).

The results in Table 6 demonstrate that the maximum achievable nickel extraction obtained from a single batch contact with a 1:1 B:O ratio at an equilibrium pH of 7.0 was 94%. Metal extraction in the case of Co, Ca, Mg and Cu was 81.1%, 7.58%, 1.4% and 80.8%, respectively.

A graph of the equilibrium percentage extraction of nickel and selected co-extractable metals (Co, Ca, Mg and Cu) as a function of pH is shown in Figure 6.

Table 6: Results of trial tests of the nickel extraction isotherm with a change in pH at 50 °C, V:O 1:1 Results of Trial Tests of the Nickel Extraction Isotherm with Changes in pH Contact Extraction of metals (%) pH B:O Ni co Ca mg Cu 5.00 1:1 3.23 1.23 6.80 0.27 65.4 5.50 1:1 29.03 8.85 7.33 0.32 80.8 6.00 1:1 58.77 33.91 8.12 0.57 80.8 6.50 1:1 83.18 60.20 8.41 0.92 80.8 6.99 1:1 94.05 81.08 7.58 1.44 80.8

Table 7 shows the results of trial tests of the nickel extraction isotherm at 50 °C using different ratios of contacting aqueous and organic phases (W:O) on cobalt-depleted and nickel-rich raffinates. Based on previous results, tests were carried out around an equilibrium pH of 7.0.

Table 7: Trial results of nickel extraction isotherm with B:O change at 50 °C, pH approx. 7 Contact Extraction (%) pH IN Ni co Ca mg 6.98 10:1 20.9 23.0 0.7 0.1 6.95 5:1 26.2 20.5 1.6 0.1 6.98 1:1 86.4 75.0 7.4 1.4 6.98 1:1.5 98.2 96.5 32.3 10.7 6.97 1:5 99.8 99.0 93.4 54.6 7.00 1:10 99.8 98.9 96.5 65.2

Table 8 shows the results of nickel extraction on a large volume of cobalt-depleted and nickel-enriched raffinate. Based on the pilot test results shown in Table 7, a B:O phase contact ratio of 1:1 was used around an equilibrium pH of 7.0. A total of three series of nickel extractions were performed on a large volume of cobalt-depleted and nickel-rich raffinate to obtain an organic phase with a maximum metal content for testing separation and crystallization processes. Consistent nickel extraction results were obtained in all three batches from 85.8% (batch 1) to 88.4% (batch 2) with high cobalt extraction in all three batches ranging from 60.7% (batch 1 ) to 79.7% (batch 3). However, the co-extraction of the main impurities (Ca, Mg and Na) was relatively low and was <8%, <2% and <0.1% for Ca, Mg and Na, respectively.

Other minor impurities (Cu, Fe and Zn) found in the cobalt raffinate (water feed from the Ni SX stage) were at trace levels (all <1 ppm).

Table 8: Nickel Extraction - Result of a test on a large volume of raffinate Batch number Feed organic phase Contact Metal extraction (%) pH IN Ni co Ca mg Na 1 Fresh 6.98 1:1 85.8 60.7 7.7 1.02 0.04 2 Fresh 6.99 1:1 88.4 73.7 7.4 1.43 0.05 3 Reusable 6.98 1:1 87.4 79.7 7.2 1.15 0.08

Table 9 shows the results of nickel cleaning trials using a nickel-rich organic phase as the organic feed and a 10 g/L nickel solution as the aqueous wash feed. The test used a B:O phase ratio of 1:1 over the target pH range of the cleaning process (6.0, 6.50 and 7.0) using a 50 g/l sulfuric acid solution as pH adjuster.

The results of the cleaning process test showed that with a single contact at an equilibrium cleaning process pH of 6.50, more than 75% Co, 89% Mg and 34% Ca were removed from the nickel-containing organic phase. It has also been shown that nickel from a dilute wash solution containing nickel passes into the organic phase (~4.8% Ni) at an equilibrium cleaning process pH of 6.50 as a replacement for the removed metals and compounds, and this is a key step. purification in the process for producing battery-grade nickel sulfate.

Table 9: Nickel Cleaning Test Results cleaning % Metal Removed (%) IN pH Ni co Ca mg Na 1:1 6.00 13.9 88.7 28.5 86.1 78.0 1:1 6.50 -4.8 75.2 34.5 89.9 78.0 1:1 7.00 -23.5 59.6 26.8 86.1 75.6

Table 10 lists the amount of each metal removed from the nickel-rich organic phase (consisting of versatic acid 10) in each step. The conditions used to create Table 10 are shown in Table 11. More than 99% of the introduced nickel content in the versatic acid 10 phase after extraction can be removed in a single step.

Table 10 - Analysis of the organic solution after separation Analysis of the organic solution after separation (mg/l) Ni Al Ca CD co Cr Cu Fe TO Feed organic phase 20733 14 10 0.032 9.6 <0.2 0.51 <2 <10 Cycle 1 after separation 1 <2 8.2 <0.004 <0.1 <0.2 <0.1 <2 <10 Cycle 2 2 <2 9 <0.004 <0.1 <0.2 <0.1 <2 <10 Cycle 3 2 <2 13 <0.004 <0.1 <0.2 <0.1 <2 <10

mg Mn Na S P Pb Si Zn Feed organic phase 4.1 <0.2 10 120592 22.4 <0.04 <10 0.9 Cycle 1 after separation 1.6 <0.2 4.8 108674 <0.6 <0.04 <10 0.2 Cycle 2 2 <0.2 5.8 109234 <0.6 <0.04 <10 0.1 Cycle 3 3 <0.2 4.6 107738 <0.6 <0.04 <10 0.2

Table 11 - Conditions used to create Table 10 Target test temperature (°C): 45 Stirring speed (rpm): 400 Ratio of contacting B:O phases 1:1 Number of cycles: 26 Target residual concentration of separating acid (g/l): 10 Contact time (min): 5

Example 4 Nickel Separation and Crystallization

The nickel-enriched organic phase (unwashed and unpurified) was subjected to separation and crystallization in a crystallizer to obtain nickel sulfate crystals at a temperature of 40°C. Each batch containing Nickel organic phase (3 l) was separated with sulfuric acid with a concentration of 480 g/l at a ratio of aqueous separating solution to the organic phase (W:O) 1:1. After each separation step, the separated organic phase was removed from the mold and another batch of nickel-containing organic phase was added to the mold. This process was repeated 12 times to concentrate the aqueous separating solution to obtain nickel sulfate crystals. Summarized test results are shown in Table 12a.

The concentration of the free acid depends on the concentration of nickel itself. Nickel sulfate crystals began to crystallize after the 7th cycle (7th contact). The nickel concentration in the separated aqueous product began to change less significantly after the seventh contact. After the 12th contact, nickel sulfate crystals were collected by vacuum filtration, washed with analytical grade acetone, dried at 40°C, and sent for analysis. The results of crystal analysis are shown in Table 4.

Table 12a: Nickel separation and crystallization test results cycle number Ratio of separating solution to organic phase (W:O) Free acid (g/l) Separation solution analysis (mg/l) Ni Ca co Fe mg Na Zn 1 1:1 488 18300 8 10.2 <1 9 5 1.5 2 1:1 488 34946 16 18.4 20 15 16 2.9 3 1:1 488 53556 25 29.7 thirty 24 25 4.3 4 1:1 488 67927 31 37 thirty thirty 37 5.5 5 1:1 483 82402 54 44.5 40 46 51 7.1 6 1:1 454 89122 59 50 50 52 58 7.4 7* 1:1 410 101839 73 58.7 60 63 64 9 8 1:1 377 93200 57 61.1 60 59 66 7.8 9 1:1 352 108000 64 70.2 60 69 81 8.4 10 1:1 340 112000 68 74.2 50 72 92 7.8 eleven 1:1 340 109000 76 74.1 50 75 103 7.4 12 1:1 352 101000 85 75.8 60 79 144 7.4 • *Note that nickel sulfate begins to crystallize from the separated aqueous phase

The nickel-rich organic phase was also subjected to separation and crystallization in a crystallizer with a target free acid concentration of 10 g/l to obtain nickel sulfate crystals. The conditions are shown in Table 12b. The results are shown in Table 12c.

Table 12b: Nickel Separation - Direct Crystallization Conditions (DXTL) Target test temperature (°C): 45 Stirring speed (rpm): 400 Ratio of contacting B:O phases 1:1 Total number of cycles: 26 Cumulative cycles for obtaining the first batch of crystals eleven Cumulative cycles to obtain the second batch of crystals 14 Cumulative cycles for obtaining the third batch of crystals 18 Cumulative cycles to obtain the fourth batch of crystals 22 Cumulative cycles to get the fifth batch of crystals 26 Target residual concentration of separating acid (g/l): 10 (10-20 supported) Contact time (min): 5

Table 12c: Test results of the direct nickel separation and crystallization process under the conditions indicated in Table 12b cycle number Batch number Free acid (g/l) Separation phase ratio Analysis of the organic phase after separation (mg/l) Analysis of the aqueous phase after separation (mg/l) Metal removal (%) Ni co Ni co Ni co raw material - 46.2 - 20733 10 0 <0.05 - - 1 1 12.5 1:1 1 <0.1 20200 11.1 100.0 99.0 2 13.2 1:1 2 <0.1 41000 23.8 100.0 99.0 3 21.2 1:1 2 <0.1 59500 34 100.0 99.0 4 0.3 1:1 798 0 78700 46.8 96.2 97.7 4A 17.5 1:1 8 <0.1 79300 46.6 100.0 99.0 5 18.4 1:1 2 <0.1 98300 55.5 100.0 99.0 6 18.9 1:1 2 <0.1 124000 63.2 100.0 99.0 7 17.3 1:1 4 <0.1 142000 79.7 100.0 99.0 8 15.7 1:1 6 <0.1 157000 90.1 100.0 99.0 9 19.6 1:1 3 <0.1 175000 89 100.0 99.0 10 14.0 1:1 5 <0.1 123000 64.4 100.0 99.0 eleven 12.8 1:1 10 <0.1 140000 71.9 100.0 99.0 12 2 12.5 1:1 4 <0.1 142814 64 100.0 99.0 13 9.3 1:1 3 <0.1 143392 72 100.0 99.0 14 7.7 1:1 9 <0.1 195688 104 100.0 99.0 15 3 5.8 1:1 3 <0.1 190982 113 100.0 99.0 16 4.0 1:1 5 <0.1 198197 109 100.0 99.0 17 9.1 1:1 5 <0.1 193454 104 100.0 99.0 18 7.9 1:1 eleven <0.1 195422 102 99.9 99.0 19 4 10.1 1:1 9 <0.1 198902 114 100.0 99.0 20 10.7 1:1 6 <0.1 183348 114 100.0 99.0 21 11.9 1:1 3 <0.1 198780 137 100.0 99.0 22 10.7 1:1 10 <0.1 186019 137 100.0 99.0 23 5 18.9 1:1 4 <0.1 188495 128 100.0 99.0 24 15.2 1:1 10 <0.1 191767 130 99.9 99.0 25 16.2 1:1 7 <0.1 189506 128 100.0 99.0 26 14.9 1:1 5 <0.1 190088 121 100.0 99.0

Example 5 Fine Grinding for a High Grade Concentrate

Fine grinding of the nickel sulfide concentrate to a P ₈₀ of 10 microns is the preferred step for low temperature pressure oxidation. Fine grinding improves the sulfide oxidation kinetics and the nickel extraction rate, which reduces the time and energy consumption of the LTPOX stage.

Figure 7 compares the quality of the results obtained for nickel sulfide concentrates in which the slurry solids were ground to a P ₈₀ of 38 microns and unground samples. In both cases, 175 g/t TETA (triethylenetetramine) and 175 g/t CH (sodium sulfite) were used. The release of pyrrhotite from pentlandite improved the removal of pyrrhotite. Figure 7a compares the S:Ni ratio for ground and non-ground samples. Figure 7b compares Eh (redox potential) for ground and non-ground samples. The activation of the pyrrhotite surface by TETA and CH is confirmed by the change in Eh.

Figure 8a compares the kinetics of sulfide oxidation in the LTPOX step for samples with different P ₈₀ values. The test was carried out at 105 °C and an overpressure of O ₂ 1000 kPa with 1 g/l Cl or 5 g/l Cl. Samples with P ₈₀ values less than 10 microns oxidized significantly faster than a sample with a P ₈₀ value of 18 microns.

Figure 8b compares the nickel extraction rate in the LTPOX step for samples with different P ₈₀ values. The test was carried out at 105 °C and an overpressure of O ₂ 1000 kPa with 1 g/l Cl or 5 g/l Cl. Nickel from samples with P ₈₀ values less than 10 microns was extracted significantly faster than nickel from a sample with a P ₈₀ value of 18 microns.

Table 13 shows the main results shown in Figure 8 and Figure 8b: LTPOX Trial - Summarizing Key Findings Test number P ₈₀ raw material um Cl in solution g/l Time min SOx ¹
% Extraction, % Solution analysis, mg/l End balance %S° Ni co Cu Fe Fe(II) St. to-ta thirty 88 81 83 51 1.39 0.75 2.1 19.1 60 93 94 94 56 0.43 0.19 3.4 23.7 14 6.6 5.0 90 94 96 97 58 0.31 0.10 5.7 20.6 120 95 97 97 58 0.27 0.06 6.3 17.8 thirty 91 90 91 62 1.76 1.23 2.9 18.7 60 95 97 97 70 0.89 0.34 3.8 19.8 15 6.6 1.0 90 95 97 97 71 0.85 0.28 4.2 21.7 120 96 97 97 70 0.91 0.28 5.5 27.8 thirty 89 80 81 45 1.11 0.95 1.7 19.3 60 95 94 93 48 0.54 0.35 2.9 23.4 16 6.6 5.0 90 93 96 96 47 0.41 0.15 3.4 24.4 120 95 97 97 48 0.36 0.09 3.4 19.4 thirty 52 31 29 4 3.84 0.00 2.1 15.1 60 70 48 45 23 3.29 0.00 2.6 18.8 17 18 5.0 90 80 64 61 44 2.05 0.00 3.4 21.8 120 85 76 74 56 1.52 0.00 3.4 21.2 1. SOx means % oxidation of sulfide sulfur

Example 6 Comparison of LTPOX and HTPOX Processes

Suitable conditions for both the HTPOX process and the LTPOX process using the nickel sulfide concentrate slurry after regrinding were evaluated and compared, and the results are presented in Table 14 (HTPOX) and Table 15 (LTPOX).

HTPOX - High leach recovery rates have been demonstrated at 210°C where feed solids were obtained by grinding to a P ₈₀ of 48 µm and diluted to 20% (w/w) with a solution containing 1 g/l Cl . The resulting PLS contained 62 g/l free acid, 16 g/l iron (predominantly as Fe(III)), 36.4 g/l nickel, 1.08 g/l cobalt and 0.8 g/l aluminum.

Tests on the LTPOX process have shown that extractions of 97% nickel, 97% cobalt and 70% copper can be achieved. The partial oxidation process led to the formation of a residue containing up to 26% S ⁰ (elemental sulfur). PLS contained 5.5 g/l free acid, 0.9 g/l iron (0.3 g/l Fe(II)), 32.9 g/l nickel, 0.98 g/l cobalt and 0.14 g/l aluminum, which is a significant advantage of this method compared to POX leaching, which is much less selective.

Leaching of nickel concentrate at a temperature of 210-225 °C can be considered as an effective and standard technological way, since all sulfide from the raw material is completely oxidized to sulfates. However, consideration should be given to the need for high oxygen pressure, pressure vessel ratings, and the potential for formation of basic iron(III) sulfate. In addition, PLS post-treatment will require significantly more limestone to neutralize acid and remove iron compared to PLS from the LTPOX process and atmospheric leaching. This results in lower reagent costs when using the LTPOX process.

Table 14 - Summary of HTPOX Comparative Test Results Summary of Comparative POX Results Influence of particle size and temperature (overpressure O ₂ 350 kPa) POX test P ₈₀ raw material um POX temperature °C Time min SOX % Extraction, % Solution analysis, g/l Ni co Cu Fe Fe(II) St, acid 60 99 95 99 99 14.6 0.15 78.0 Trial 8 62 225 90 99 96 99 100 14.1 0.11 76.7 60 99 95 98 99 15.5 0.11 62.9 Trial 9 62 210 90 99 96 99 99 16.2 0.09 68.5 120 99 96 99 99 16.5 0.09 65.4 60 99 97 99 99 8.6 0.39 73.6 Trial 10 48 225 90 99 98 99 99 7.9 0.34 72.9 60 99 98 99 99 14.4 0.15 62.9 Trial 11 48 210 90 99 98 99 99 11.5 0.09 70.4 thirty 99 98 99 98 18.6 1.76 56.0 45 99 98 99 99 14.2 0.13 66.0 Trial 12 18 225 60 99 98 100 99 22.0 0.15 60.4 90 99 98 99 99 20.6 0.08 64.8

Table 15 - Summarized results of comparative tests of the LTPOX process LTPOX Trial - Summarizing Key Findings Test number P ₈₀ raw material um Cl in solution g/l Time min SOx ¹ % Extraction, % Solution analysis, mg/l End balance %S° Ni co Cu Fe Fe(II) St. to-ta thirty 88 81 83 51 1.39 0.75 2.1 19.1 60 93 94 94 56 0.43 0.19 3.4 23.7 14 6 6 50 90 94 96 97 58 0.31 0.10 5.7 20.6 120 95 97 97 58 0.27 0.06 6.3 17.8 thirty 91 90 91 62 1.76 1.23 2.9 18.7 60 95 97 97 70 0.89 0.34 3.8 19.8 15 6.6 1.0 90 95 97 97 71 0.85 0.28 4.2 21.7 120 96 97 97 70 0.91 0.28 5.5 27.8 thirty 89 80 81 45 1.11 0.95 1.7 19.3 60 95 94 93 48 0.54 0.35 2.9 23.4 16 6.6 5.0 90 93 96 96 47 0.41 0.15 3.4 24.4 120 95 97 97 48 0.36 0.09 3.4 19.4 thirty 52 31 29 4 3.84 0.00 2.1 15.1 60 70 48 45 23 3.29 0.00 2.6 18.8 17 18 50 90 80 64 61 44 2.05 0.00 3.4 21.8 120 85 76 74 56 1.52 0.00 3.4 21.2 1. SOx means % oxidation of sulfide sulfur

Example 7 Primary Neutralization

Table 16 shows the composition of tested PLS after primary neutralization as a function of pH change over time (t in minutes). Any amount of free acid resulting from the oxidation of sulfides and soluble impurities such as iron and aluminum is neutralized and precipitates as hydroxides at a pH of approximately 3.

Table 16 - Primary neutralization at various pH values and times Test results Solution analysis The resulting solution Solution g Density kg/l pH ORP mV H ₂ SO ₄ g/l Ni mg/l Co mg/l Fe mg/l Na mg/l As mg/l Al mg/l Cu mg/l Ca mg/l Mn mg/l Stock solution 1208 1.141 5.7 21900 724 738 22500 0.31 38 931.00 122 13.2 Test sample t=0 26 1.141 1.81 460 5.7 22500 736 743 22900 0.30 45 961.00 130 13.5 pH=2.0, t=11 37 1.144 2.02 458 3.5 22400 739 730 23000 0.31 43 945 926 13.6 pH=2.25, t=21 49 1.144 2.29 424 2.3 22900 753 344 23300 0.36 38 971 995 13.9 pH=2.5, t=30 51 1.142 2.52 382 1.5 22600 743 189 22800 0.34 35 954 822 13.8 pH=2.75, t=44 57 1.142 2.83 358 0.8 22700 741 174 22800 0.26 26 958 1050 13.8 pH=3.0, t=59 56 1.141 3.20 313 0.7 22800 757 109 22900 0.31 8 946 910 14.0 pH=3.25, t=90 3 1.141 3.90 313 0.5 22700 747 19 23000 0.26 NGOs 923 1090 13.9 pH=3.5, t=115 35 1.140 4.83 297 0.7 22500 758 NGOs 22900 0.41 NGOs 694 913 14.1 Final PN,
large volume 852 1.149 4.99 260 0.5 23400 761 NGOs 23200 0.32 NGOs 730 1050 14.2 (LLL means below detection limit)

Example 8 Recovery of Elemental Sulfur By-Product

Figure 9 depicts the relationship between total elemental sulfur (Total recovery S ⁰ (%)) and flotation time (Total flotation time (min)) for various PLS process slurries. These different slurries were made using different flotation reagents, where MIBK means methyl isobutyl carbinol, W24 means W24 Frother frother available from Huntsman, and Dowfroth 250a means Dowfroth 250 A frother available from Dow Chemical.

At 20 t/h and with a content of 9% S ⁰ in the raw material, the total amount of elemental sulfur in the flotation raw material was 14191 t/year. It is expected that up to 60% of the elemental sulfur can be recovered, minimizing the release of sulfur to the waste.

Example 9 Solvent Extraction of Cobalt

Table 17 shows the percentage extraction of metals from clarified PLS in the CoSX run. Volumetric extraction of cobalt was carried out at an equilibrium pH of 5.70 at a ratio of the contacting phases B:O 3:1 using 10% v/v. Cyanex 272 (with 5% v/v TBP). In two stages, more than 99% of the metals (Co, Al, Cu and Mn) were extracted from the aqueous phase. Nickel co-extraction was relatively low (<0.6%). Purification of the metal-containing organic phase at a phase ratio B:O of 1:1 at an equilibrium pH of 5.50 made it possible to achieve the removal of more than 94% Ni, 76% Mg and 32% Ca from the metal-containing organic phase.

Table 17 - Percentage extraction of metals from clarified PLS in the CoSX cycle Stage number The ratio of the contacting phases B:O Extraction (%) (based on analysis of organic and feed aqueous phases) Al As Ca CD co Cr Cu Fe mg 1 2:1 33.2 - 2.1 - 85.4 - 96.9 - 15.3 2 2:1 32.9 - 2.3 - 99.8 - 86.3 - 22.9 Total - 99.9 - 4.3 - 99.9 - 98.2 - 33.7

Stage number The ratio of the contacting phases B:O Extraction (%) (based on analysis of organic and feed aqueous phases) Mn Na Ni P Pb S Si Zn 1 2:1 93.0 0.02 0.06 8.7 - - - 99.4 2 2:1 94.0 0.01 0.06 8.2 - - - - Total - 99.3 0.03 0.11 15.0 - - - -

Example 10 Production of Battery Grade Nickel Products from High Arsenic Concentrates

This method makes it possible to process nickel concentrates with a high content of arsenic (up to 5000 ppm As) to battery-grade nickel sulfate products.

Table 18 lists the composition of an alternative high arsenic concentrate. Table 19 shows the crystal composition of the product obtained from the high arsenic concentrate of Table 18. The higher arsenic content in the feed did not result in high levels of arsenic in the product.

The method according to the present invention is effective and suitable for use with various concentrates, since there is no systematic negative or positive effect on the quality of the product due to the use of an alternative raw concentrate.

Table 18 - Alternative composition of high arsenic nickel concentrate Element Unit Alternative concentrate Ni % 15.0 co % 0.27 Fe % 31.6 Na md NGOs As md 3052 Al % 0.60 Cu % 0.71 Ca % 0.87 Mn md 777 mg % 1.27 Zn md 90 Ti md 200 K % 0.17 Sb md NGOs Si % 4.85 S % 32.5 S:Ni ratio 2.17

Table 19 - Composition of crystals obtained from the high arsenic concentrate of Table 18 Element
(ppm except Ni) Product Ni (%) 22.3 co 45 Cu 3 Al 6 As 1 Ca 10 CD 1 Cr 1 Fe 4 K 1 mg 20 Mn 1 Na 1 P 1 Pb 1 Sb 1 Si 1 Zn 2

It should be understood that the invention disclosed and defined in the present description, extends to all alternative combinations of two or more individual features mentioned or explicit from the text or drawings. All of these various combinations constitute various alternative aspects of the present invention.

Statement of the Invention

Statement 1. A method for extracting NiSO ₄ ⋅6H ₂ O crystals from an organic phase enriched with nickel, including:

bringing the nickel-rich organic phase into contact with an aqueous separating solution with a concentration of H ₂ SO ₄ sufficient to extract nickel from the organic phase and with a concentration of Ni ²⁺ sufficient to precipitate NiSO ₄ ⋅6H ₂ O crystals and form a nickel-depleted organic phase.

Claim 2 The method of Claim 1 further comprising separating NiSO ₄ ⋅6H ₂ O crystals from the nickel-depleted organic phase.

Statement 3. The method according to Statement 1 or 2, characterized in that the separating solution has a concentration of H ₂ SO ₄ 10-300 g/l.

Statement 4. The method according to any of the previous statements, characterized in that the nickel-rich organic phase includes a coordination complex of nickel and an organic extractant, and the organic extractant releases nickel in the presence of a sufficient concentration of H ⁺ ions.

Statement 5. The method according to Statement 4, characterized in that the H ⁺ ions are provided in the process of ion exchange with NiSO ₄ .

Statement 6. The method according to Statement 4 or 5, characterized in that the organic extractant is selected from the group consisting of organophosphorus acids, chelating oximes or hydroxyoximes, carboxylic acids and high molecular weight amines.

Statement 7. The method according to any of the Statements 3-6, characterized in that the organic extractant is from about 10 wt. % to about 25 wt. % organic phase.

Statement 8. The method according to any of Statements 4-7, characterized in that the organic extractant is a branched carboxylic acid having the structure:

where R ₁ and R ₂ are unsubstituted alkyl groups with a branched or straight chain, and R ₁ and R ₂ together contain from 5 to 13 carbon atoms.

Claim 9. The method of Claim 8, wherein the branched carboxylic acid is neodecanoic acid.

Statement 10. The method according to any of the previous Statements, characterized in that the organic phase comprises an organic diluent and the organic diluent is one or more C ₁₀₊ alkanes.

Claim 11. The method of Claim 10, wherein the organic diluent comprises one or more isoalkanes, one or more cycloalkanes, and mixtures thereof.

Statement 12. The method according to any of the Statements 1-11, characterized in that the method includes:

contacting an acidic aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to selectively extract the nickel sulfate from the aqueous solution into the organic phase to form a nickel sulfate-depleted aqueous raffinate and a nickel-rich organic phase; And

separating the raffinate and the nickel-rich organic phase;

where the organic extractant is one or more branched carboxylic acids.

Statement 13. The method according to any of the Statements 1-11, characterized in that the method includes:

a solvent extraction step comprising contacting an aqueous solution containing nickel sulfate and one or more metal impurities with an organic phase, wherein the organic phase includes one or more branched carboxylic acid extractants to selectively promote the extraction of nickel sulfate from the aqueous solution into an organic phase and formation of a nickel-rich organic phase.

Statement 14. The method according to Statement 12 or 13, characterized in that the solution containing nickel sulfate is a productive leaching solution obtained as a result of high temperature pressure oxidation of nickel sulfide concentrate.

Statement 15. The method according to Statement 12 or 13, characterized in that the solution containing nickel sulfate is a productive leaching solution obtained as a result of low-temperature pressure oxidation of nickel sulfide concentrate.

Statement 16. The method according to any one of Statements 12-14, characterized in that the nickel-depleted organic phase is reused as the organic phase or its component.

Statement 17. The method according to any of the previous Statements, characterized in that the nickel-rich organic phase comprises: 5 ppm or less Fe and/or 5 ppm or less Mn, and/or 5 ppm or less Cu, and/or 60 ppm or less Co, and/or 10 ppm or less Zn.

Statement 18. The method according to any of the previous Statements, characterized in that the NiSO ₄ ⋅6H ₂ O crystals include: 5 ppm or less Fe and/or 5 ppm or less Mn, and/or 5 ppm or less Cu, and/or 60 ppm or less Co, and/or 10 ppm or less Zn.

Statement 19. The method according to any of the previous statements, characterized in that one or more metal impurities are selected from the group consisting of: Fe, Mn, Cu, Co, Zn and combinations thereof.

Statement 20. The method according to any of the previous statements, characterized in that the separating solution has a Ni ²⁺ concentration of 60 g/l or more.

Statement 21. Crystals of NiSO ₄ ⋅6H ₂ O obtained according to the method according to any of the previous Statements.

Statement 22. A method for extracting nickel sulfate, including:

a low temperature pressure oxidation (LTPOX) stage in a nickel sulfide concentrate autoclave where the nickel sulfide concentrate contains more than 10% nickel.

Statement 23. The method according to Statement 22, characterized in that the nickel sulfide concentrate is subjected to fine grinding to a P ₈₀ equal to 10 microns.

Statement 24. The method of Statement 22 or 23, wherein the LTPOX step in the autoclave uses oxygen to oxidize nickel sulfide from the nickel sulfide concentrate to nickel sulfate.

Statement 25 The method of any of Statements 22-24 further comprising the step of primary neutralization using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite, and sodium hydroxide.

Statement 26. The method according to Statement 25, further comprising the step of countercurrent decanting.

Claim 27 The method of Claim 26 further comprising the step of secondary neutralization using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite, and sodium hydroxide.

Statement 28. The method of Claim 27, further comprising the step of extracting cobalt with a solvent, which uses an organic extractant that more selectively extracts cobalt compared to extracting nickel into an organic phase to form a cobalt-rich and nickel-depleted extractant stream and a cobalt-depleted and nickel-rich raffinate .

Statement 29. The method of Statement 28, wherein the organic phase of the cobalt-rich and nickel-depleted extractant stream is converted to a cobalt-depleted organic phase, and the cobalt-depleted organic phase is reused as the organic phase or a component thereof.

Statement 30. The method according to Statement 28 or 29, further comprising the steps of nickel extraction with a solvent and direct crystallization;

where the nickel solvent extraction step comprises:

contacting the cobalt-depleted and nickel-rich raffinate with an organic phase comprising an organic extractant to form a nickel-rich organic phase; And

direct crystallization stage includes:

bringing the nickel-rich organic phase into contact with an aqueous separating solution with a concentration of H ₂ SO ₄ sufficient to extract nickel from the organic phase and with a concentration of Ni ²⁺ sufficient to precipitate NiSO ₄ ⋅6H ₂ O crystals and form a nickel-depleted organic phase.

Statement 31. The method of Statement 28 or 29, further comprising a nickel solvent extraction step in which the cobalt-depleted and nickel-rich raffinate is contacted with an organic phase comprising an organic extractant to selectively extract nickel sulfate from an aqueous solution into an organic phase to form a depleted nickel sulfate aqueous raffinate and nickel-rich organic phase; And

separating the raffinate and the nickel-rich organic phase;

where the organic extractant is one or more branched carboxylic acids.

Statement 32. The method of Statement 28 or 29, further comprising a nickel solvent extraction step comprising contacting the cobalt-depleted and nickel-rich raffinate and one or more metal impurities with an organic phase, wherein the organic phase includes one or more branched carboxylic acids - extractants for selectively promoting the extraction of nickel sulfate from an aqueous solution into the organic phase and the formation of a nickel-rich organic phase.

Statement 33. The method of any one of Statements 31-33, wherein one or more bases selected from the group consisting of ammonium hydroxide, magnesia and sodium hydroxide are used in the nickel solvent extraction step.

Statement 34. The method of any one of Statements 31-33, wherein the nickel-rich organic phase is converted to a nickel-depleted organic phase, and the nickel-depleted organic phase is reused as the organic phase or a component thereof.

Statement 35. The method according to any of Statements 25-34, characterized in that the by-product ammonium sulfate is recovered.

Statement 36. A method for producing nickel sulfate, which includes the steps:

a) providing a source of nickel sulfide concentrate;

b) repulping the nickel sulfide from the concentrate of step (a);

c) finely grinding the nickel sulfide concentrate from step (b) to a P ₈₀ of 10 microns;

d) low temperature pressure oxidation (LTPOX) in an autoclave of the nickel sulfide concentrate from step (c) to produce a production leach solution (PLS) where the nickel sulfide concentrate contains more than 10% nickel;

e) neutralizing the PLS from step (d) using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide;

f) countercurrent decanting the PLS from step (e) to separate the solids from the PLS slurry;

g) neutralizing the PLS from step (f) using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide;

h) optional PLS clarification from step (g);

i) extracting cobalt from the PLS from step (g) or step (h), wherein the cobalt extraction uses an organic extractant that more selectively extracts cobalt than nickel into the organic phase to form a cobalt-rich and nickel-depleted and cobalt-depleted extractant stream and nickel-enriched raffinate;

j) extracting nickel from the cobalt-depleted and nickel-rich raffinate from step (i); the nickel extraction comprising contacting the cobalt-depleted and nickel-rich raffinate with an organic phase comprising an organic extractant to form a nickel-rich organic phase; And

k) direct crystallization of the nickel-rich organic phase from step (j), the direct crystallization comprising contacting the nickel-rich organic phase with an aqueous separating solution with a concentration of H ₂ SO ₄ sufficient to extract the nickel from the organic phase and with a concentration of Ni ²⁺ sufficient to precipitate NiSO ₄ ⋅6H ₂ O crystals and form a nickel-depleted organic phase;

where nickel sulfate is contained in an amount of 21 to 24% nickel and exists as nickel sulfate hexahydrate (NiSO ₄ ⋅ 6H ₂ O).

Statement 37. The method according to any of Statements 30-36, characterized in that the nickel-rich organic phase comprises: 5 ppm or less Fe and/or 5 ppm or less Mn, and/or 5 ppm or less Cu, and/or 60 ppm or less Co, and/or 10 ppm or less Zn.

Statement 38. Nickel sulfate obtained according to the method according to any of the Statements 22-37.

Statement 39. The method according to any of the Statements 1-6, characterized in that the method includes:

a nickel solvent extraction step comprising contacting an acidic aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to selectively extract the nickel sulfate from the aqueous solution into the organic phase to form a nickel sulfate-depleted aqueous raffinate and a nickel-rich organic phase; And

separating the raffinate and the nickel-rich organic phase;

where the organic extractant is one or more branched carboxylic acids.

Statement 40. The method according to any of the Statements 1-6, characterized in that the method includes:

a nickel solvent extraction step comprising contacting an aqueous solution containing nickel sulfate and one or more metal impurities with an organic phase, wherein the organic phase includes one or more branched carboxylic acid extractants to selectively promote the extraction of nickel sulfate from the aqueous solution into the organic phase and form a nickel-rich organic phase.

Statement 41. The method according to any of the Statements 1-6, characterized in that the method includes:

a nickel solvent extraction step comprising contacting an aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to form a nickel-rich organic phase, wherein the aqueous solution containing nickel sulfate is a production leach solution (PLS) which is cobalt-depleted and nickel-enriched raffinate.

Statement 42. The method according to any of the Statements 39-41, characterized in that the method includes:

extraction of cobalt from a solution containing nickel sulfate, prior to extraction of nickel with a solvent, and at the stage of extraction of cobalt an organic extractant is used, which more selectively extracts cobalt compared to the extraction of nickel into the organic phase with the formation of a cobalt-rich and nickel-depleted extractant stream and a cobalt-depleted and enriched nickel raffinate.

Statement 43. The method according to any one of Statements 39-42, wherein the solution containing nickel sulfate is a productive leach solution obtained from low temperature pressure oxidation of nickel sulfide concentrate.

Statement 44. The method according to Statement 43, characterized in that the nickel sulfide concentrate contains more than 10% nickel.

Statement 45. The method according to any of Statements 36, 39-44, characterized in that the NiSO ₄ ⋅6H ₂ O crystals comprise: 5 ppm or less Fe and/or 5 ppm or less Mn, and/or 5 ppm or less Cu, and/or 60 ppm or less Co, and/or 10 ppm or less Zn.

Statement 46. The method according to any of Statements 36, 39-45, characterized in that the separating solution has a Ni ²⁺ concentration of 60 g/l or more.

Claims (36)

1. A method for extracting NiSO ₄ ⋅ 6H ₂ O crystals from an organic phase enriched with nickel, including: a step of extracting the nickel with a solvent to form a nickel-rich organic phase, and bringing said nickel-rich organic phase into contact with an aqueous separating solution with a concentration of H ₂ SO ₄ sufficient to extract nickel from the organic phase and with a concentration of Ni ²⁺ sufficient to precipitate crystals of NiSO ₄ ⋅6H ₂ O and form a nickel-depleted organic phase . 2. The method of claim 1 further comprising separating the NiSO ₄ ⋅6H ₂ O crystals from the nickel-depleted organic phase. 3. The method according to p. 1 or 2, characterized in that the separating solution has a concentration of H ₂ SO ₄ 10-300 g/l. 4. A process according to any one of the preceding claims, characterized in that the nickel-rich organic phase comprises a coordination complex of nickel and an organic extractant, wherein the organic extractant releases the nickel in the presence of a sufficient concentration of H ⁺ ions. 5. The method according to claim 4, characterized in that the organic extractant is selected from the group consisting of organophosphorus acids, chelating oximes or hydroxyoximes, carboxylic acids and high molecular weight amines. 6. The method according to claim 4 or 5, characterized in that the organic extractant is a branched carboxylic acid having the structure:

where R ₁ and R ₂ are unsubstituted alkyl groups with a branched or straight chain, and R ₁ and R ₂ together contain from 5 to 13 carbon atoms. 7. The method according to any one of paragraphs. 1-6, characterized in that the method includes: said nickel solvent extraction step to form a nickel-rich organic phase comprising contacting an acidic aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to selectively extract the nickel sulfate from the aqueous solution into the organic phase to form a nickel sulfate-depleted aqueous raffinate and a nickel-rich organic phase, and separation of the raffinate and nickel-rich organic phase, where the organic extractant is one or more branched carboxylic acids. 8. The method according to any one of paragraphs. 1-6, characterized in that the method includes: said nickel solvent extraction step to form a nickel-rich organic phase, comprising contacting an aqueous solution containing nickel sulfate and one or more metal impurities with the organic phase, wherein the organic phase includes one or more branched carboxylic acid extractants for selective facilitating the extraction of nickel sulfate from the aqueous solution into the organic phase; and forming a nickel-rich organic phase. 9. The method according to any one of paragraphs. 1-6, characterized in that the method includes: said step of extracting nickel with a solvent to form a nickel-rich organic phase, comprising contacting an aqueous solution containing nickel sulfate with an organic phase comprising an organic extractant to form a nickel-rich organic phase, wherein the aqueous solution containing nickel sulfate is a productive solution leaching (PLS), which is a cobalt-depleted and nickel-rich raffinate. 10. The method according to any one of paragraphs. 7-9, characterized in that before nickel extraction with a solvent, cobalt is extracted from a solution containing nickel sulfate, and an organic extractant is used at the cobalt extraction stage, which more selectively extracts cobalt compared to nickel extraction into the organic phase with the formation of cobalt-enriched and depleted nickel extractant stream and cobalt-depleted and nickel-enriched raffinate. 11. The method according to any one of paragraphs. 7-10, characterized in that the solution containing nickel sulfate is a productive leaching solution obtained as a result of low-temperature oxidation under pressure of nickel sulfide concentrate. 12. The method according to p. 11, characterized in that the nickel sulfide concentrate contains more than 10% nickel. 13. A method for producing nickel sulfate, which includes the steps: a) providing a source of nickel sulfide concentrate, b) repulping the nickel sulfide from the concentrate of step (a), c) finely grinding the nickel sulfide concentrate from step (b) to a P ₈₀ of 10 µm, d) low temperature pressure oxidation (LTPOX) in an autoclave of the nickel sulfide concentrate from step (c) to produce a production leach solution (PLS) where the nickel sulfide concentrate contains more than 10% nickel, e) neutralizing the PLS from step (d) using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide, f) countercurrent decanting the PLS from step (e) to separate the solids from the PLS slurry, g) neutralizing the PLS from step (f) using one or more bases selected from the group consisting of ammonium hydroxide, limestone, lime, calcrete, magnesia, magnesite and sodium hydroxide, h) optional PLS clarification from step (g), i) extracting cobalt from the PLS from step (g) or step (h), wherein the cobalt extraction uses an organic extractant that is more selective in extracting cobalt compared to extracting nickel into the organic phase to form a cobalt-rich and nickel-depleted and cobalt-depleted extractant stream and nickel-enriched raffinate, j) extracting the nickel from the cobalt-depleted and nickel-rich raffinate from step (i), wherein the nickel extraction comprises contacting the cobalt-depleted and nickel-rich raffinate with an organic phase comprising an organic extractant to form a nickel-rich organic phase, and k) direct crystallization of the nickel-rich organic phase from step (j), wherein the direct crystallization comprises contacting the nickel-rich organic phase with an aqueous separating solution with a concentration of H ₂ SO ₄ sufficient to extract the nickel from the organic phase and with a concentration of Ni ²⁺ , sufficient for the precipitation of NiSO ₄ ⋅ 6H ₂ O crystals and the formation of an organic phase depleted in nickel, where nickel sulfate is contained in an amount of from 21 to 24% nickel and exists as nickel sulfate hexahydrate (NiSO ₄ ⋅6H ₂ O). 14. The method according to any one of the preceding claims, characterized in that the NiSO ₄ ⋅6H ₂ O crystals comprise: 5 ppm or less Fe, and/or 5 ppm or less Mn, and/or 5 ppm or less Cu, and/or 60 ppm or less Co, and/or 10 ppm or less Zn. 15. The method according to any one of the preceding claims, characterized in that the separating solution has a Ni ²⁺ concentration of 60 g/l or more.

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