Method for preparing a high-purity nickel sulfate solution

Abstract

The present invention provides a method for preparing a high purity nickel sulfate solution comprising the steps of: i. providing an aqueous feed solution comprising nickel, cobalt, calcium and magnesium; ii. extracting cobalt, calcium and partially magnesium from said aqueous feed solution using a first solvent comprising a first alkyl phosphorus based acidic extractant, thereby obtaining an aqueous raffinate comprising nickel and magnesium; iii. extracting magnesium from said aqueous raffinate comprising nickel and magnesium using a second solvent comprising a second alkyl phosphorus based acidic extractant, thereby obtaining a high purity aqueous nickel sulfate solution comprising nickel and magnesium; and iv. stripping the first entraining solvent comprising cobalt, calcium and magnesium with an aqueous solution comprising a mineral acid.

Description

Technical Field

[0001] The present invention relates to a novel method for producing an aqueous solution of high-purity nickel sulfate, which can be further processed in a crystallization unit to produce high-purity nickel sulfate crystals having a purity sufficient for use in electroless plating of nickel metal layers or production of battery materials.

Background Art

[0002] The development of lithium-ion batteries, particularly the use of cathode materials of nickel-manganese-cobalt and nickel-cobalt-aluminum, has increased the demand for high-purity nickel sulfate, either as a solid or in solution. In fact, impurities in the cathode material strongly affect the performance of the battery. Therefore, a great deal of effort has been devoted to the industrial-scale production of high-purity nickel sulfate in a reasonable way.

[0003] In this regard, US2014 / 322109 provides a method for obtaining high-purity nickel sulfate with low levels of impurities, specifically low levels of magnesium and chloride, by employing a selective nickel sulfide precipitation step and redissolution of nickel sulfide into a nickel sulfate solution. This solution is further purified by solvent extraction to remove cobalt and magnesium impurities, and during the treatment, the concentration and pH or acid concentration of the acidic organic extractant are adjusted. Since solvent extraction is required to remove impurity cobalt and magnesium following nickel bulk intermediate precipitation and redissolution, the described treatment strategy is complex for concentrated nickel sulfate solutions. In particular, the nickel sulfide step is dangerous due to the risk of hydrogen sulfide generation. In addition, the crude nickel raw material, which is typically much more impure, is only used to remove cobalt and magnesium by solvent extraction.

[0004] CN107162067 relates to the field of recycling solid waste, and specifically discloses a method for recycling high-purity nickel sulfate from nickel-containing waste batteries. The method includes the steps of disassembling nickel-containing waste batteries into battery powder, dissolving the battery powder with an acid to obtain a metal-containing solution, adding an alkali metal sulfate, removing iron by an oxidation precipitation method, further removing impurities by a solvent extraction method to obtain a magnesium-containing nickel liquid, passing the magnesium-containing nickel liquid through a chelating resin exchange column to selectively adsorb nickel ions and allowing a magnesium-rich solution to flow out for treatment, desorbing the nickel ions to obtain a nickel sulfate solution, evaporating the nickel sulfate solution, cooling, crystallizing, filtering, and finally drying to obtain a purified nickel sulfate product. By this long and complex method, the recycled nickel sulfate is a high-purity product with a nickel content of up to 99.5% or more, while the impurity, i.e., magnesium, is guaranteed to have a content of less than 0.005%. However, three different solvent extraction units are proposed to remove copper, manganese, and cobalt in separate steps. Apart from the high investment cost, other impurities such as calcium and magnesium are not even removed. Finally, nickel is recovered by adsorption onto the resin, and a fourth separation step and the consumption of a neutralizing agent equivalent to the amount of metal ions adsorbed are required. Overall, the described method is considered neither simple nor efficient.

[0005] EP1252345 describes a method for extracting cobalt from a cobalt-nickel solution with a nickel-added solvent to obtain a purified nickel sulfate stream. However, it does not teach a procedure for removing impurities such as calcium and magnesium to very low levels and thereby producing an electroless nickel or a purified nickel sulfate solution for battery applications. It seems that there are many attempts to develop a solvent extraction method that can avoid the formation of insoluble ammonium / nickel sulfate double salts.

[0006] EP2784166 describes a method for producing a pure nickel sulfate solution in a number of method steps including a sulfidation step, a redissolution step, a purification step by precipitation, and a solvent extraction step. In particular, the sulfidation and redissolution steps are costly operations that use a sulfiding agent to produce a nickel sulfide intermediate, both of which products are toxic and can result in high toxicity and the generation of gaseous hydrogen sulfide upon contact and reaction with mineral acids. At the final stage, the purified nickel sulfate solution still contains 50 mg / L of magnesium impurities which are excessive for battery-level nickel sulfate, indicating a lack of selectivity in the proposed method.

[0007] EP3733884 describes a solvent extraction method capable of selectively separating magnesium from an acidic aqueous solution of sulfuric acid. The solvent extraction method involves contacting an acidic aqueous solution of sulfuric acid containing nickel, cobalt, and magnesium with an organic solvent under very specific extraction conditions to selectively extract magnesium into the organic solvent, either at a relatively low pH = 1.5 - 2, i.e., using a concentrated solvent containing 40 - 60% alkylphosphonic acid as the extractant, or at a higher pH = 2.0 - 2.5 with a lower extractant concentration, i.e., using a solvent containing 20 - 50% alkylphosphonic acid. This method aims only at the removal of magnesium and does not separate cobalt from the nickel solution. Surprisingly, under the same extraction conditions, up to 46% of magnesium was removed from the nickel sulfate solution with already approximately 9% of co-extracted nickel. Under such conditions, only an 8 - 23 Mg / Ni separation factor was obtained. When the extractant concentration in the solvent used decreased below 40 vol.%, a higher Mg / Ni separation factor of up to 35 was obtained, but with a significantly lower, i.e., less than 28%, removal of magnesium.

[0008] EP3222735 discloses a method for separating cobalt and magnesium from a nickel-containing feed solution by liquid-liquid extraction, in which the organic solvent used contains an alkylphosphinic acid as an extractant. Both cobalt and magnesium are extracted together with some nickel. First, the nickel is washed out of the added solvent with an acidic solution. The resulting nickel solution may contain some cobalt and is thus returned to the feed solution. Thereafter, the magnesium is washed out of the solvent with an acidic solution. The resulting magnesium solution may contain some cobalt and is treated elsewhere. The cobalt is stripped from the solvent with a diluted aqueous solution of an acid to form a cobalt strip solution. In addition to cobalt and magnesium, this patent does not address the removal of other metal impurities such as calcium, zinc, cadmium, copper, manganese and iron in the nickel sulfate solution. The patent also does not detail the procedures for reaching the desired pH for the extraction of cobalt and magnesium from the nickel sulfate solution, which is considered in terms of the release of acidic protons during extraction with an acidic extractant.

[0009] When EHEHPA, which is also known as PC88A, is used as an extractant, the extraction behavior with respect to magnesium or calcium is similar to that with respect to nickel. JP10-310437 discloses an example of separating nickel and cobalt by extracting cobalt together with other impurities such as calcium, copper, zinc, iron and magnesium by solvent extraction using PC88A as an extractant. When a solution containing nickel at a high concentration is subjected to solvent extraction, there arises a problem that the extraction efficiency of magnesium or calcium decreases. Difficulties in removing magnesium from a nickel sulfate solution are mentioned. The final impurity output concentration in the purified nickel sulfate solution was still 3 to 26 mg / L of cobalt, 2 to 7 mg / L of calcium and 10 to 27 mg / L of magnesium when it contained 90 to 117 g / L of nickel. The present invention is advantageous for calcium extraction, but at the same time, solves the problem of insufficient calcium extraction by selecting operating conditions that reduce magnesium extraction. This is offset by the implementation of another solvent extraction of magnesium using a more preferred extractant and more preferred operating conditions.

[0010] JP2021 / 031729 shows the treatment of a crude nickel sulfate solution in a single solvent extraction process where an attempt is made to simultaneously remove all cobalt, magnesium, and calcium from the nickel sulfate solution. The ratio of the amount of nickel added to the solvent to the concentration of cobalt in the nickel sulfate solution must vary according to the desired removal of impurities. However, from the examples, it can be seen that the purified nickel sulfate solution still contains 1 - 60 mg / L of cobalt, 1 - 20 mg / L of magnesium, and 1 - 15 mg / L of calcium, indicating that it is impossible to remove all impurities. Furthermore, the input concentration of magnesium in the crude nickel sulfate solution is very low, only 19 - 31 mg / L, compared to a very high cobalt concentration of 8 - 12 g / L of cobalt, suggesting that the removal of magnesium seems minimal. This principle of co - extracting even a small amount of magnesium, albeit incompletely, along with a large amount of cobalt is evidence that a large amount of nickel is necessarily being used in the solvent. It is only claimed that increasing the amount of nickel added to the solvent, relative to the concentration of cobalt in the crude nickel sulfate solution, can better remove magnesium. In a similar patent, JP2021 / 031730, it is claimed that the amount of magnesium reported for the cobalt eluate by co - extraction into the solvent can be affected by the selected amount of nickel in the solvent. It is the same example as JP2021 / 031729. The purified nickel sulfate solution can still contain impurities as high as 1 - 60 mg / L of cobalt, 1 - 20 mg / L of magnesium, and 1 - 15 mg / L of calcium. Also, the amount of magnesium reported to be co - extracted into the cobalt eluate can clearly vary.

[0011] US 6,149,885 describes a method in which impurities such as cobalt, calcium, copper, and zinc are removed from a crude nickel sulfate solution by solvent extraction. A method is disclosed for adding nickel to a solvent in such a way that the nickel can be used later to remove impurities from the crude nickel sulfate solution. However, magnesium is only moderately removed. In one example, 34 mg / L of magnesium still remains in the purified nickel sulfate solution, which is generally considered too impure for battery-level nickel quality. In another example, 354 ppm of magnesium remains in the purified nickel sulfate solution relative to 100% nickel. The removal of other metals such as cadmium and manganese from the crude nickel sulfate solution is not even considered.

[0012] JP 2021 / 105206 discloses a solvent extraction method that can improve the separability between nickel and cobalt in the nickel recovery stage. The presented solvent extraction method includes a nickel recovery stage, in which an acidic extractant carrying nickel and cobalt and an acid are contacted to obtain a nickel recovery solution for the back-extraction of nickel. The extraction temperature in the nickel recovery stage is set at 47 to 60 °C. Since the extraction temperature in the nickel recovery stage is set at 47 °C or higher, the distribution ratio of cobalt to the organic solvent can increase while maintaining a low distribution ratio of nickel to the organic solvent, so the separability between nickel and cobalt can be improved. JP 2021 / 105206 shows that the amounts of magnesium and calcium in the nickel solution are affected by the extraction method for separating nickel from cobalt, but does not teach a means for optimally reducing the amounts of magnesium and calcium impurities in the nickel solution.

[0013] US2008 / 0003154 describes a two-stage solvent extraction circuit for the selective removal of zinc and cobalt metal impurities from the valuable metal nickel. For the selective extraction of zinc, in the Synex 272 system, there must be sufficient separation between zinc and cobalt. Similarly, for cobalt and nickel, the separation factor must be large enough to obtain a pure nickel product. The method for the solvent extraction of metal impurities is operated at a temperature of 80 °C to 100 °C. Thereby, it is recognized that cobalt can be selectively extracted from nickel, and any iron, copper, zinc, manganese, and magnesium are completely co-extracted with cobalt. Further removal of impurities from nickel is not advised, and thus, the impurities are considered to be presented at a very low level.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

Patent Document 12

Summary of the Invention

Problems to be Solved by the Invention

[0015] In conclusion, there is a need for a simple and practical method by which high-purity nickel sulfate having low levels of cobalt, calcium, magnesium and other impurities can be achieved, thereby resulting in nickel sulfate that can be used in applications where high purity is required, such as electroless plating of nickel metal layers or precursors for battery cathode materials. The object of the present invention is to provide a novel method for producing a high-purity nickel sulfate solution from an aqueous nickel solution containing cobalt, magnesium and calcium, and optionally impurities such as iron, zinc, copper, cadmium and manganese. Moreover, it is an object of the present invention that nickel sulfate having a stable quality can be easily produced. Finally, the object of the present invention is to provide a method capable of producing a cobalt-rich aqueous solution suitable for further treatment from nickel crude raw materials.

Means for Solving the Problems

[0016] The present invention at the present time provides a solution to at least one of the aforementioned problems by providing a method for preparing a high-purity nickel sulfate solution as described in claim 1.

[0017] The present invention has the advantage that the elements of cobalt, zinc, manganese, cadmium, aluminum, copper, calcium, and magnesium, if present, are all completely separated from nickel. The present invention consists of a two-stage solvent extraction method in which all of the impurities mentioned, except magnesium, are completely removed in the first step, and the remaining magnesium is removed in the second step.

[0018] The overall method described in the present invention provides a high-purity nickel solution, i.e., at least 99.8 at.% nickel with respect to the metal content of the solution, while avoiding material loss by minimizing co-extraction of the base metal nickel, and is thus efficient in the sense of avoiding the formation of complex nickel-containing mixtures. Therefore, the method described in the present invention is environmentally considerate. The treatment strategy is to avoid the presence of unwanted ions such as calcium from calcium bases, sodium from sodium bases, and chloride from hydrochloric acid, which are sourced from the reagents used during nickel purification in the final nickel sulfate solution. Thus, the nickel sulfate solution obtained from the presented method can be easily further processed by crystallization or spray drying to form nickel sulfate crystals or granules respectively, which can thereby be easily transported. Advantageously, the present invention can also produce a cobalt-rich eluate, which can be separately further processed to produce high-purity cobalt salts, such as cobalt chloride, cobalt sulfate, or others. The method of the present invention is simple, environmentally considerate, and provides high-purity nickel sulfate.

[0019] As a further guide, figures are included to better understand the teachings of the present invention. The figures are intended to assist in the description of the present invention and are not intended to limit the invention disclosed herein. The figures and symbols contained herein have meanings generally understood by those skilled in the technical field to which the present invention pertains.

Brief Description of the Drawings

[0020]

Figure 1

Modes for Carrying Out the Invention

[0021] Unless otherwise defined, all terms used in the disclosure of the present invention, including technical and scientific terms, shall have the meanings commonly understood by those of ordinary skill in the technical field to which the present invention pertains. As a further guide, definitions of terms are included to facilitate a good understanding of the teachings of the present invention.

[0022] As used herein, the following terms have the following meanings.

[0023] As used herein, "a", "an", and "the" refer to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more than one compartment.

[0024] As used herein, "about" refers to measurable values such as parameters, amounts, lengths of time, and the like, and such variations are included as long as they are appropriate for the role they play in the disclosed invention, including variations of + / - 20% or less, preferably + / - 10% or less, more preferably + / - 5% or less, even more preferably + / - 1% or less, and still more preferably + / - 0.1% or less of a particular value, and variations from a particular value. However, the value to which the modifier "about" refers should also be understood to be specifically disclosed in itself.

[0025] As used herein, "comprise", "comprising", "comprises", and "comprised of" are synonymous with "include", "including", "includes", or "contain", "containing", "contains", and are inclusive or open-ended terms that at least identify the presence of what follows, and do not exclude or preclude the presence of additional recited components, features, elements, members, or steps known in the art or disclosed herein.

[0026] The citation of a numerical range by endpoints includes all numbers and fractions included within that range, as well as the cited endpoints. Unless otherwise defined, or unless a different meaning is not apparent to those skilled in the art from its use and the context in which it is used, all percentages are to be understood as mass percentages abbreviated as "wt.%", or volume percentages abbreviated as "vol.%", or atomic percentages abbreviated as "at.%".

[0027] Regarding the organic phase, the following terms are used to identify its components or the whole. i. The "extractant" or extraction agent is the active component in the organic phase that extracts metal species into the organic phase by chemically binding to the active component and forming a metal-extractant complex that is more soluble in the organic phase than in the aqueous phase. ii. The "diluent" is a mixture of different organic molecules that are usually added to the organic phase to dilute the extractant and to enable the dissolution of the metal complex, improving the physical properties of the organic phase (especially the phase separation phenomenon), and usually reducing its cost considering that the diluent is less expensive than the extractant. The diluent can often be a kerosene fraction and can be an aliphatic or aromatic hydrocarbon, naphthene, etc., or a mixture thereof. iii. The organic phase may contain a "modifier". The modifier is sometimes added to improve the solubility of the metal complex in the organic phase, to change the physical properties of the solvent, and to avoid these phenomena since the formation of a clad or a third phase is not desired during solvent extraction. The modifier can be added to prevent the chemical decomposition of the extractant or the diluent. However, since the modifier may sometimes participate in the complex formation of the metal with the extractant, it may impair the selectivity of the organic phase. iv. The "organic phase" is another term used to identify a "solvent" or "solvent mixture" and includes a mixture of the extractant, the diluent, and, if necessary, the modifier.

[0028] The "selectivity" S of an extractant of one metal with respect to another metal can be expressed as the ratio of the distribution coefficients D for both metals. SMg / Ni =D Mg / D Ni

[0029] The "distribution coefficient" of a metal is understood to be the ratio of the equilibrium concentrations of the metal in the organic phase and the same metal in the aqueous phase, D M =[M] O / [M] A where M is a metal such as nickel or magnesium, O refers to the organic phase, and A refers to the aqueous phase.

[0030] In the context of the present invention, a "solvent extraction circuit" should be understood as a synonym for the terms "solvent extraction", "solvent extraction process", "solvent circuit", "solvent loop", or "solvent extraction loop", and refers to a series of one or more solvent extraction sections, each consisting of one or more solvent extraction stages. Each extraction section can proceed with a different set of process parameters such as temperature, pH profile, and solvent-to-water ratio, but the solvent extraction circuit utilizes only one organic phase. The organic phase composition of the solvent extraction circuit is fixed as it is characterized by a single set of parameters such as the type of extractant, the type of diluent, and the extractant-diluent ratio.

[0031] In a first aspect, the present invention is a method for preparing a high-purity nickel sulfate solution, comprising: i. preparing a feed aqueous solution comprising nickel, cobalt, calcium, and magnesium, and zinc, manganese, cadmium, and / or copper if present; ii. using a first organic phase comprising a first alkylphosphorus-based extractant (I) and a first diluent to extract cobalt, calcium, and at least some magnesium from the feed aqueous solution, thereby obtaining a raffinate aqueous solution (A1) comprising nickel and residual magnesium, and a cobalt-rich organic phase (O1), wherein the organic phase typically comprises calcium, magnesium, and nickel, and zinc, copper, cadmium, and manganese if present; iii. Using a second organic phase (O2) comprising a second alkyl phosphorus extractant (II) and a second diluent, extracting magnesium from the raffinate aqueous solution (A1), thereby obtaining a magnesium-depleted high-purity nickel sulfate aqueous solution (A2) and a magnesium-enriched organic phase A method is provided which includes the above steps.

[0032] The present invention has the advantage that the elements of cobalt, magnesium, calcium, and, if present, further zinc, manganese, cadmium, iron, aluminum, and copper are completely separated from nickel in a single process. By this method, a high-purity nickel sulfate aqueous solution (A2) containing nickel having a concentration of 40 to 200 g / L and magnesium having a concentration of up to 10 mg / L, two added organic phases, namely a cobalt-rich organic phase (O1) containing calcium, magnesium, and nickel, and, if present, zinc, copper, cadmium, and manganese, and a magnesium-enriched organic phase (O2) containing nickel and magnesium are obtained. Preferably, the high-purity nickel sulfate aqueous solution contains up to 5 mg / L of magnesium, and more preferably up to 1 mg / L. The first and second organic phases may contain a modifier.

[0033] The raffinate aqueous solution A1 contains magnesium at a concentration of 20 mg / L to 20 g / L, preferably 20 mg / L to 2 g / L, more preferably 20 mg / L to 500 mg / L, together with nickel sulfate.

[0034] Overall, the residual magnesium content in the obtained raffinate aqueous solution (A1) is too high for high-purity applications and is thus subjected to a second solvent extraction step.

[0035] The solvent extraction steps ii and iii can be carried out in any suitable apparatus and are not particularly limited. Solvent extraction equipment generally includes at least one or a plurality of devices consisting of a mixer-settler, a column contactor, a centrifugal contactor, or any other type of contactor. Preferably, the extraction is carried out in a countercurrent configuration.

[0036] Preferably, the present invention further provides the method according to the first aspect of the present invention, which further includes step iv in which the cobalt-rich organic phase (O1) containing calcium, magnesium and nickel, and zinc, copper, cadmium and manganese when present, is stripped with an aqueous solution containing a mineral acid. Thereby, the elution of cobalt, calcium, magnesium, and zinc, copper, cadmium and manganese when present, is effectively achieved from the first solvent. Preferably, the mineral acid is one or more selected from the group consisting of hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, phosphoric acid, sulfuric acid, boric acid and perchloric acid. More preferably, the mineral acid is one or more selected from the group consisting of hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid and perchloric acid. In another embodiment, the mineral acid is sulfuric acid. Most preferably, the mineral acid is hydrochloric acid. Thereby, a concentrated eluate containing cobalt, calcium, magnesium, and zinc, copper, cadmium and manganese when present, can be obtained from the first solvent.

[0037] The stripping step can be carried out in any suitable apparatus and is not particularly limited. Stripping equipment generally includes at least one or more devices consisting of a mixer settler, a column contactor, a centrifugal contactor, or any other type of contactor. Preferably, the stripping step is carried out in a countercurrent configuration.

[0038] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the aqueous feed solution containing nickel, cobalt, magnesium, and iron and / or aluminum, and optionally calcium, zinc, copper, cadmium, and manganese is obtained by a step of removing iron and / or aluminum from a leach pregnant solution containing nickel, cobalt, magnesium, and iron and / or aluminum, and optionally calcium, zinc, copper, cadmium, and manganese. The iron and / or aluminum can preferably be removed by adding a basic reagent such as a hydroxide or other salt to the aqueous solution, thereby forming an iron and / or aluminum hydroxide precipitate. Potentially, the addition of an oxidizing agent such as oxygen or hydrogen peroxide may be included in the iron and / or aluminum removal step.

[0039] In a preferred embodiment, the iron and / or aluminum is removed by precipitation using a calcium base such as calcium hydroxide, calcium oxide, calcium carbonate, calcium bicarbonate, or any other calcium-containing basic reagent. The use of a calcium base is advantageous because calcium forms calcium sulfate, also known as gypsum, which has low water solubility in this step of the process. Thus, the use of an excess amount of calcium base is not detrimental to the purity of the resulting nickel sulfate solution. Only a limited amount of calcium will remain in the nickel solution sent to the solvent extraction step ii. The latter part of the process is designed to enable complete removal of calcium from the nickel solution. The formation of calcium sulfate during the precipitation of iron and / or aluminum enhances the filterability of the iron and / or aluminum precipitate. Thus, it may be preferred that the calcium base is used in a stoichiometric excess relative to the amount of iron and / or aluminum impurities present in the aqueous feed solution containing nickel, cobalt, magnesium, and iron and / or aluminum.

[0040] In another preferred embodiment, the base used may be nickel hydroxide or carbonate or any other nickel-containing basic reagent, thereby introducing beneficial nickel ions into the nickel sulfate solution. Other preferred nickel bases are nickel bicarbonate and nickel hydroxysulfate.

[0041] In yet another preferred embodiment, since magnesium is efficiently and effectively removed in subsequent steps of the method of the present invention, the base used may be magnesium hydroxide or carbonate or any other magnesium-containing basic reagent. Other preferred magnesium bases are magnesium bicarbonate and magnesium hydroxysulfate.

[0042] In yet another preferred embodiment, impurities such as iron and / or aluminum can be separated by precipitation using a combination of two or more precipitating agents selected from calcium bases, magnesium bases, and nickel bases.

[0043] Moreover, impurities such as iron and / or aluminum can be removed by precipitation in two or more precipitation steps, where different precipitating agents can be used in each precipitation step. In a preferred embodiment, a nickel base is used in the first precipitation step and a calcium base is used in subsequent precipitation steps.

[0044] Alternatively, impurities such as iron and / or aluminum can be separated by other methods such as neutralization. However, the use of an alkali base such as sodium hydroxide or potassium hydroxide introduces metal impurities into the feed aqueous solution that cannot be extracted by subsequent solvent extraction methods, and thus, at the final stage of the flowsheet, the potential crystallization or granulation process can become complicated.

[0045] In another embodiment, due to the raw materials preceding or by using calcium-containing reagents such as calcium base, calcium hydroxide, calcium oxide, calcium carbonate, calcium bicarbonate, or another Ca-containing basic reagent, calcium already exists in the nickel feed solution involved in the solvent extraction step ii before being introduced into the solvent extraction step ii.

[0046] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the feed aqueous solution prepared in step i contains nickel in an amount of at least 60 at.% based on the total metal content of the feed aqueous solution and cobalt in an amount of at most 40 at.% based on the total metal content of the feed aqueous solution. Preferably, the feed aqueous solution contains nickel in an amount of at least 70 at.% and cobalt in an amount of at most 30 at.%, more preferably, the feed aqueous solution contains nickel in an amount of at least 80 at.% and cobalt in an amount of at most 20 at.%, and most preferably the feed aqueous solution contains nickel in an amount of at least 90 at.% and cobalt in an amount of at most 10 at.%.

[0047] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the feed aqueous solution prepared in step i further contains calcium, magnesium, zinc, copper, cadmium, and manganese in a total amount of at most 25 at.% based on the total metal content of the feed aqueous solution. Preferably, the feed aqueous solution further contains calcium, magnesium, zinc, copper, cadmium, and manganese in a total amount of at most 10 at.%, and even more preferably in an amount of at most 5 at.%.

[0048] Accordingly, the feed aqueous solution can be derived from all kinds of resources such as the mixed hydroxide precipitate, crude nickel sulfate or any other suitable kind of resource, and is itself suitable or, if necessary, is processed into a suitable feed solution. This treatment can include filtration, selective filtration, dissolution, precipitation steps and / or any other kind of pretreatment steps. Combinations of these are also possible. For example, if at least filtration and finally prior lithium removal are included in the pretreatment, the pretreated battery recycling material containing nickel, cobalt, manganese and lithium can be treated in this flow sheet to produce a pure nickel sulfate solution. Alternatively, lithium is removed, for example, at the final stage of step iii using a lithium ion exchange column.

[0049] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the extractant used in steps ii and iii contains an alkylphosphoric acid. Suitable alkylphosphoric acids include bis(2-ethylhexyl)phosphoric acid (D2EHPA), mono(2-ethylhexyl)ester of (2-ethylhexyl)phosphonic acid (EHEHPA, PC88A), bis-(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272 or Ionquest 290), and diisooctylphosphinic acid (DOPA). Alkylphosphoric acids function as chelating extractants due to the presence of coordinated phosphorus and oxygen atoms in these molecules. Among the elements in the aqueous solution, elements that form corresponding chelate compounds with higher stability compared to elements with a lower possibility of forming chelate compounds promote the extraction efficiency more.

[0050] When EHEHPA (PC88A) is used as an extractant, the extraction behaviors of magnesium and calcium are similar to those of nickel. Therefore, when a solution containing nickel at a high concentration is subjected to solvent extraction, there arises a problem that the extraction efficiencies of magnesium and calcium decrease. The present invention solves the problem of insufficient calcium extraction by selecting operating conditions that are advantageous for calcium extraction while simultaneously reducing magnesium extraction. The latter is offset by performing another solvent extraction of magnesium under more preferable operating conditions for the more preferable second extractant and extraction of magnesium.

[0051] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the second extractant (II) has a higher selectivity for magnesium than the first extractant (I). In other words, the second extractant (II) has a higher affinity for magnesium than the affinity of the first extractant (I). In addition, the second extractant (II) has a higher selectivity for magnesium than for nickel. Most preferably, the second extractant (II) contains an alkylphosphinic acid such as IONQUEST 290.

[0052] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the first extractant (I) has a higher selectivity for calcium over nickel than the second extractant (II). In other words, the first extractant (I) has a higher affinity for calcium with respect to nickel than the affinity of the second extractant (II) for calcium with respect to nickel. In addition, the first extractant (I) has a higher selectivity for calcium than for nickel. Most preferably, the first extractant (I) contains an alkylphosphonic acid such as PC88A. Preferably, the first alkylphosphorus-based extractant (I) contains an alkylphosphonic acid and / or its nickel salt, and the second alkylphosphorus-based extractant (II) contains an alkylphosphinic acid and / or its nickel salt.

[0053] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the first and second diluents are hydrocarbons. More generally, any water-immiscible organic solvent capable of dissolving the extractant can be used. Thus, the diluent is not particularly limited. As an example of the diluent, kerosene-based compounds can be used, which can be aliphatic, naphthenic, aromatic or even a mixture thereof.

[0054] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the first organic phase used in step ii contains the first extractant (I) in an amount of 5 to 50 vol.% based on the total volume of the first organic phase, and the first diluent in an amount of 50 to 95 vol.% based on the total volume of the first organic phase. More preferably, the first organic phase contains the first extractant (I) in an amount of 30 to 40 vol.% and the first diluent in an amount of 60 to 70 vol.%.

[0055] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the second organic phase used in step iii contains the second extractant (II) in an amount of 5 to 50 vol.% based on the total volume of the second organic phase, and the second diluent in an amount of 50 to 95 vol.% based on the total volume of the second organic phase. More preferably, the second organic phase contains the second extractant (II) in an amount of 10 to 25 vol.% and the diluent in an amount of 75 to 90 vol.%. It has been found that the optimum extraction of magnesium can be achieved without losing the processing suitability of the solvent depending on the extractant concentration in the organic phase.

[0056] In a preferred embodiment, the extractant used in steps ii and iii is neutralized with an alkali metal hydroxide, nickel is pre-added at a high pH, and then used for extraction in steps ii and iii, and the organic phase pre-added with nickel is brought into contact with a feed aqueous solution containing impurities. In such a case, on the one hand, an exchange reaction occurs in which elements that are more likely to be extracted than nickel are transferred to the solvent, and on the other hand, nickel in the organic phase is transferred to the aqueous phase. As a result, impurities are removed from the feed aqueous solution while increasing the nickel concentration in the resulting raffinate solution, thus greatly avoiding the introduction of alkali metals from the neutralizing agent into the main process (raffinate) stream. As the alkali metal hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide or the like may be used. Further, preferably, sodium hydroxide is used as the alkali metal hydroxide.

[0057] It has been found that by pre-adding nickel to the extractant used in steps ii and iii, optimal and improved extraction can be achieved without losing the processing suitability of the extractant. During this pre-adding process, the partially neutralized extractant, that is, in a form in which the alkali metal has been converted, exchanges the alkali metal of the extractant, typically sodium, with nickel from an aqueous nickel sulfate solution. Preferably, when extracting impurities from this solution, the residual amount of alkali metal in the pre-added solvent is as low as possible to limit the transfer of residual alkali metal from the pre-added solvent to the feed aqueous solution.

[0058] A portion of the nickel can be replaced by another harmless metal that will exchange with the impurities to be extracted from the aqueous nickel sulfate solution to be purified. This may be an alkali metal such as sodium or potassium, or a similar species such as ammonium. However, these other metals may be able to extract such metals present in the aqueous nickel sulfate solution to be purified, or may even contaminate the nickel sulfate solution by exchange with the impurities to be extracted.

[0059] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein prior to extraction, the extractant is converted into those nickel salts corresponding to the appropriate conversion of the extractant, and thus in an amount of 20 to 70% of the available extractant capacity of nickel, and containing residual sodium up to a maximum of 2 g / L, preferably up to a maximum of 0.5 g / L, more preferably up to a maximum of 0.1 g / L. Preferably, nickel is pre-added in an amount of residual sodium that occupies up to 25 to 60% of the available extractant capacity, preferably more than 30% of the available extractant capacity, and up to a concentration of 0.5 g / L. More preferably, nickel is pre-added in an amount of residual sodium that occupies up to 30 to 50% of the available extractant capacity and up to a concentration of 0.1 g / L.

[0060] The preferred nickel concentration of the pre-added solvent is thus based on the extractant concentration and the degree of conversion. Since both are determined by the target pH of the feed aqueous solution, they are a function of the total amount of impurities to be removed. On the one hand, the higher the degree of conversion of the extractant, the higher the pH during extraction, and more extraction of impurities (and nickel) from the nickel-containing feed solution can be achieved. On the other hand, the lower the degree of conversion of the extractant, the lower the pH during extraction, and good selectivity for impurities over nickel can be realized.

[0061] In a preferred embodiment, a pre-added solvent containing nickel and optionally some other metals such as sodium, potassium or other metals, or other cations such as ammonium, may be contacted again with a pure nickel-containing solution such as a nickel sulfate or nickel chloride solution, whereby the metal sodium, potassium, ammonium or other metal of the solvent is further exchanged with nickel from the pure nickel-containing solution. The pre-addition operation of nickel is preferably carried out in at least two stages, preferably in a countercurrent operation, using at least a pure nickel sulfate solution, so as to scrub the alkali metal co-extracted from the used base derived from the solvent in some cases. As a result, a nickel pre-added solvent containing significantly less other metals is obtained, and this solvent can be used in extraction steps ii and iii, and by this means, contamination of the nickel aqueous solution with undesired metals is maximally avoided.

[0062] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the feed aqueous solution involved in step ii has a pH of 1.0 to 6.0, more preferably a pH of 2.0 to 5.5, and most preferably a pH of 3.0 to 5.0, before contacting with the solvent containing extractant I, so as to generate a chemical equilibrium between the nickel aqueous solution and the solvent.

[0063] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the extraction in step ii is carried out at a temperature of 25 to 70 °C, preferably 30 to 60 °C, more preferably 30 to 55 °C, or even more preferably 30 to 50 °C. More preferably, the extraction in step ii is carried out at a temperature of 35 to 45 °C. The inventors have found that the extraction of calcium from the nickel solution is improved at lower temperatures. Therefore, the extraction temperature in step ii is preferably less than 50 °C, preferably less than 45 °C. However, at lower temperatures, the efficiency of cobalt extraction is reduced. Therefore, it is preferable to use an extraction temperature above 25 °C, preferably above 30 °C, more preferably above 35 °C. Therefore, most preferably, the extraction temperature in step ii is higher than 25 °C and lower than 45 °C, preferably higher than 30 °C and lower than 45 °C, more preferably higher than 35 °C and lower than 45 °C. Specifically, the extraction temperature is 36 °C, 38 °C, 40 °C, 42 °C or 44 °C, or any temperature therebetween.

[0064] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the raffinate aqueous solution obtained from step ii and involved in step iii has a pH of 2.0 to 7.0, more preferably 3.0 to 6.5, and most preferably 4.0 to 6.0, before contacting with the second solvent containing the extractant II, to generate a chemical equilibrium between the nickel aqueous solution and the second solvent.

[0065] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the extraction in step iii is carried out at a temperature of at least 25°C, at least 30°C, preferably at least 35°C and at most 80°C. Preferably, the extraction in step iii is carried out at a temperature of 40 to 70°C, or even more preferably 45 to 65°C. More preferably, the extraction in step iii is carried out at a temperature of 50 to 60°C. The inventors have found that the extraction of magnesium from the nickel solution is improved by a higher extraction temperature. Nevertheless, the extraction temperature is preferably limited to less than 80°C, less than 70°C or less than 65°C for the processing suitability of the organic solvent and the safety of the organic solvent.

[0066] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the extraction in step iii is carried out at a temperature higher than the temperature of the extraction in step ii. Preferably, the temperature in step iii is at least 5°C higher than the temperature in step ii, more preferably at least 10°C higher, more preferably 10 to 20°C higher, and most preferably about 15°C higher.

[0067] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the high-purity nickel sulfate aqueous solution obtained after step iii is subjected to crystallization or granulation. Preferably, the nickel sulfate in the nickel sulfate solution is crystallized, whereby an additional purification step can be carried out. In the case of granulation, any granulation technique known to those skilled in the art, such as spray drying, is suitable.

[0068] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein nickel is scrubbed from the cobalt-rich organic phase and / or the magnesium-enriched organic phase. Before the impurities proceed to the stripping step, in order to recover this co-extracted nickel from the added organic phase, by washing with an acidic solution such as an aqueous sulfuric acid solution, nickel is first selectively scrubbed from these solvents. By applying the optimal pH conditions, particularly the acidity of the final scrubbing solution, nickel is selectively scrubbed, and the amount of acid added is adapted to reach the required pH.

[0069] In a preferred embodiment, the present invention provides the method according to the first aspect of the present invention, wherein the stripping step in step iv is carried out with hydrochloric acid. By the stripping step, nickel can be eluted from the first added solvent (O1) together with cobalt, calcium, magnesium, and zinc, copper, cadmium, and manganese if present. Therefore, the extractant is regenerated to produce a solvent free of metals that can be reused for extraction or pre-addition. Considering the presence of calcium in the obtained stripping solution, the use of hydrochloric acid is preferred. By the step of stripping with hydrochloric acid, calcium chloride, which is readily soluble in water, is formed. Thus, the metal content can be concentrated from the solvent to the aqueous solution. Considering the low solubility of calcium sulfate, the use of sulfuric acid may induce the formation of solid precipitates that interfere with the solvent extraction process.

[0070] In a preferred embodiment, the hydrochloric acid solution has a concentration of at least 50 g / L, more preferably a concentration of 100 g / L to 300 g / L.

[0071] In a preferred embodiment, the stripping step in step iv is carried out at a temperature of 40°C to 55°C, preferably 40°C to 50°C, more preferably at a temperature of about 45°C.

[0072] In a preferred embodiment, the present invention provides the post-treatment process according to the first aspect of the present invention, wherein the magnesium-depleted high-purity nickel sulfate aqueous solution contains nickel at a concentration of 40 to 180 g / L and magnesium at a maximum concentration of 5 mg / L, preferably at a maximum concentration of 1 mg / L. Preferably, the high-purity nickel sulfate aqueous solution has a content of calcium, cobalt, iron, aluminum, zinc, manganese, and / or cadmium, each individually, at a maximum amount of 15 mg / L, preferably at a maximum amount of 10 mg / L, or even more preferably at a maximum amount of 5 mg / L.

[0073] In a preferred embodiment, the present invention provides the post-treatment process according to the first aspect of the present invention, wherein after the step of stripping the cobalt-enriched organic phase with hydrochloric acid in step iv, it is additionally washed with sulfuric acid. Preferably, the solvent is washed with sulfuric acid contained in an aqueous solution having a concentration of 10 to 200 g / L. Washing with sulfuric acid can remove chloride ions and, in some cases, residual metals such as iron or aluminum from the solvent. Therefore, the solvent can be pre-added and then regenerated and reused for extraction.

[0074] In a preferred embodiment, the present invention provides a step of stripping a second solvent containing magnesium and nickel with sulfuric acid. Preferably, the solvent is washed with sulfuric acid contained in an aqueous solution having a concentration of 10 to 200 g / L. Washing with sulfuric acid can also remove residual metals such as iron or aluminum from the solvent in some cases. Therefore, the solvent can be pre-added and then regenerated and reused for extraction.

Examples

[0075] Examples are shown below to further clarify the present invention for each treatment step. These examples are based on experimentally derived data and are not intended to limit the scope of the present invention.

[0076] Preparation of the feed aqueous solution The leach aqueous solution is obtained from the filtration of the NiSO4 crude raw material. This leach solution is subjected to an iron removal operation by neutralization using Ca(OH)2 following Ni(OH)2 in subsequent steps. A solid iron cake is formed that is filtered and separated from the aqueous solution. The composition of the nickel sulfate aqueous solution before and after this two-stage iron removal operation is presented in the table below. The resulting feed aqueous solution, containing nickel, cobalt, calcium, magnesium, copper, zinc, and manganese, is free of iron and aluminum and proceeds to a solvent extraction unit.

[0077]

Table 1

[0078] Preparation of Extractant I with Pre-added Nickel (2-Ethylhexyl)phosphonic acid mono(2-ethylhexyl)ester (PC88A) and a hydrocarbon diluent, Escaid 110 (ExxonMobil), are combined to prepare a first solvent. The first solvent is composed of 36 vol% PC88A and 64 vol% hydrocarbon diluent. In two consecutive steps, a high-purity nickel sulfate aqueous solution containing 125 g / L of nickel and 1.0 g / L of sodium is contacted with the solvent. A 125 g / L NaOH solution is added to the mixer settler in a volume such that a pre-added solvent containing 11 g / L of nickel is targeted. This corresponds to a conversion degree of 36% of the total extractant volume. After one pre-adding step, the solvent contains 10.4 g / L of nickel and 0.82 g / L of sodium. After the second pre-adding step, a solvent is obtained that contains 10.8 g / L of nickel and a residual sodium concentration of 0.12 g / L.

[0079] Extraction of Cobalt, Calcium, and Other Impurities The feed aqueous solution is mixed in multiple stages with a first solvent containing PC88A and pre-added to 9.1 g / L of nickel to extract cobalt, calcium, zinc, copper, manganese, and some magnesium at a temperature of 40 °C. The extraction section consists of four consecutive mixer settlers. A first added solvent (O1) containing nickel, cobalt, calcium, magnesium, copper, zinc, manganese, and cadmium, as well as a raffinate aqueous solution (A1) containing a significant residual amount of magnesium together with nickel sulfate, is obtained by adding to sodium having a concentration of less than 1 g / L. The compositions of the feed solution and the raffinate are presented in the table below. The increase in the nickel concentration in the aqueous raffinate compared to the nickel concentration in the feed aqueous solution is because the nickel in the pre-added solvent was stoichiometrically exchanged with impurities from the feed solution during extraction.

[0080]

Table 2

[0081] Stripping of the extractant I with hydrochloric acid After extraction, the first added solvent containing sodium, nickel, cobalt, calcium, magnesium, zinc, cadmium, and manganese is treated at a temperature of 43 °C with an aqueous solution composed of hydrochloric acid having a concentration of 200 g / L. The elution section consists of a multi-stage mixer settler setup. The solvent is regenerated to produce an aqueous eluate having 35 g / L of residual hydrochloric acid. The compositions of the added and stripped solvents are presented in the table below.

[0082]

Table 3

[0083] Washing of the first solvent with sulfuric acid After the stripping section, the first solvent may be washed with an aqueous solution composed of sulfuric acid. The most important goal of this post-treatment of the stripped solvent is to remove the hydrochloric acid entrained from the previous stripping section. To that end, the stripped solvent is brought into contact with a sulfuric acid (33 g / L) solution. As a result, all residual impurities are removed from the stripped solvent, and Ni, Co, Ca, Mg, Zn, Mn, Cd, Na, and Cl are all <1 mg / L. Therefore, this solvent can be recycled for the next cycle.

[0084] Scrubbing of Extractant I with Sulfuric Acid After extraction, prior to the stripping step, an additional scrubbing step may be determined to avoid the loss of nickel to the eluate. A first added solvent containing sodium, nickel, cobalt, calcium, magnesium, zinc, and manganese is combined with an aqueous solution composed of sulfuric acid having a concentration of 500 g / L. The experiment is carried out at a temperature of 40 °C. The scrubbing section consists of three consecutive mixer settlers. The composition of the solvent before and after scrubbing is presented in the table below. High selectivity is obtained, with nickel being scrubbed at a yield of 91% and Mg being scrubbed at 13%, while all other impurities remain in the solvent.

[0085]

Table 4

[0086] Preparation of Extractant II with Pre-Added Nickel A second solvent is prepared by combining bis-(2,4,4-trimethylpentyl) phosphinic acid (IONQUEST 290) and Escaid 110 (ExxonMobil), a hydrocarbon diluent. The second solvent consists of 15 vol% IONQUEST 290 and 85 vol% Escaid 110. In two consecutive steps in a countercurrent configuration, the solvent is contacted with an aqueous nickel sulfate solution of high purity containing 130 g / L nickel and 0.90 g / L sodium. A 125 g / L NaOH solution is used, thereby obtaining a pre-loaded solvent containing approximately 5.0 g / L nickel. This corresponds to a conversion degree of 38% of the total extractant volume. After one pre-loading step, the solvent contains 2.2 g / L nickel and 79 mg / L sodium. After a second pre-loading step, a solvent is obtained containing 4.6 g / L nickel and a residual sodium concentration of 67 mg / L. In fact, the nickel or residual sodium in the pre-loaded solvent can depend on the exact conditions.

[0087] In another example, a higher extractant concentration was applied. A second solvent containing IONQUEST 290 and Escaid 110 was contacted in one step at a temperature of 55 °C with an aqueous nickel sulfate solution of high purity containing 97 g / L nickel, 40 mg / L magnesium and 27 mg / L sodium. The pH was kept constant at a value of 6.0 with a 125 g / L NaOH solution. The amount of nickel added to the solvent is shown in the table below as a function of the extractant concentration.

[0088]

Table 5

[0089] Extraction of magnesium to form a high-purity nickel sulfate solution The aqueous raffinate (A1) obtained after the first solvent extraction contains 127 g / L of nickel and 690 mg / L of magnesium, is mixed with a second solvent containing IONQUEST 290, pre-added with 6.0 g / L of nickel, and the remaining magnesium is extracted at a temperature of 55 °C. The extraction section consists of five mixer settlers in a countercurrent configuration. What remains in the solvent extraction apparatus is (i) a second added solvent (O2) containing nickel and magnesium, and (II) an aqueous nickel sulfate solution (A2) containing only 1.0 mg / L of magnesium, and thus, it can proceed to a crystallization or granulation operation to obtain a high-purity nickel sulfate product. The nickel concentration in the aqueous raffinate increased to 138 g / L because the nickel in the pre-added solvent was stoichiometrically exchanged with impurities from the feed solution during extraction.

[0090] Scrubbing of Extractant II with Sulfuric Acid After extraction and prior to elution, an additional scrubbing step may be determined to avoid loss of nickel to the eluate. A second added solvent containing 1.10 g / L of nickel and 1.30 g / L of magnesium is combined with an aqueous solution composed of sulfuric acid having a concentration of 70 g / L. The experiment is carried out at a temperature of 40 °C. The scrubbing section consists of three consecutive mixer settlers. A 99.7% scrubbing yield is obtained with a decrease in nickel concentration of the solvent after scrubbing to 0.003 g / L of nickel. During this scrubbing operation, magnesium is not co-scrubbed, producing a solvent after scrubbing having 1.30 g / L of magnesium.

[0091] Effect of Temperature on Extraction Rates of Different Impurities In this example, the effect of temperature on the extraction rates of calcium, cobalt, and magnesium is shown. A first solvent containing 35 vol% PC88A and 65 vol% Escaid 110 with 17 g / L nickel pre-added is contacted with a feed aqueous solution containing 118 g / L nickel, 9 mg / L calcium, 68 mg / L cobalt, and 124 mg / L magnesium in two consecutive steps. For different impurities, the extraction rate percentages at 25°C and 65°C are shown in the table below. On the one hand, a low temperature is favorable for the extraction of calcium, and on the other hand, a high temperature is favorable for the extraction of cobalt and magnesium.

[0092]

Table 6

[0093] Therefore, the experimental results show that the extraction rate of calcium from the nickel solution is improved at a lower extraction temperature. Therefore, the extraction temperature in this step is preferably less than 50°C, preferably less than 45°C. However, at a lower extraction temperature, the efficiency of cobalt extraction also decreases. Therefore, an extraction temperature above 25°C, preferably above 30°C, more preferably above 35°C is preferably used. Most preferably, the extraction temperature is higher than 25°C and less than 45°C, preferably higher than 30°C and less than 45°C, more preferably higher than 35°C and less than 45°C.

[0094] In another example, the effect of temperature on the extraction rate of magnesium is shown. A second solvent containing 15 vol% IONQUEST 290 and 85 vol% Escaid 110 is contacted with a feed aqueous solution containing 127 g / L nickel and 180 mg / L magnesium in one step. The pH is controlled at pH = 5.0. In the table below, on the one hand, the extraction rate percentage of magnesium increases from 25°C to above 44°C up to 65°C, and on the other hand, it is shown that the extraction rate of nickel remains low. As a result, the selectivity of magnesium with respect to nickel increases at a higher temperature.

[0095]

Table 7

[0096] From the experimental results in the above table, it is clear that the extraction of magnesium from the nickel solution is improved by a higher extraction temperature, i.e., an extraction temperature of at least 25°C, preferably at least 30°C, or even more preferably at least 35°C. More preferably, the extraction temperature is higher than 40°C, higher than 50°C, higher than 55°C, or even more preferably higher than 60°C. Nevertheless, in order to avoid the processing suitability of the organic solvent, the safety aspect of the organic solvent, and the need for high energy input, the extraction temperature is preferably limited to less than 80°C, less than 70°C, or less than 65°C.

Claims

1. A method for preparing a high-purity nickel sulfate solution, comprising: i. preparing a feed aqueous solution containing nickel, cobalt, calcium and magnesium; ii. in a first solvent extraction circuit, using a first organic phase containing a first alkyl phosphorous extractant (I) and a first diluent to extract cobalt, calcium, and at least a certain amount of magnesium, as well as zinc, copper, cadmium and manganese if present, from the feed aqueous solution, thereby obtaining a raffinate aqueous solution containing nickel and residual magnesium, and a cobalt-rich calcium-containing organic phase; iii. in a second solvent extraction circuit, using a second organic phase containing a second alkyl phosphorous extractant (II) and a second diluent to extract magnesium from the raffinate aqueous solution, thereby obtaining a magnesium-depleted high-purity nickel sulfate aqueous solution and a magnesium-enriched organic phase; iv. stripping the cobalt-rich organic phase obtained in step ii with an aqueous solution containing a mineral acid; and the first solvent extraction circuit and the second solvent extraction circuit are operated at different temperatures and / or with different extractants.

2. The method according to claim 1, wherein the mineral acid is hydrochloric acid.

3. The method according to claim 1, wherein the feed aqueous solution further contains zinc, copper, cadmium, and / or manganese.

4. The method according to claim 1, wherein nickel is scrubbed from the cobalt-rich organic phase and / or from the magnesium-enriched organic phase.

5. The method according to claim 1, wherein the feed aqueous solution containing nickel, cobalt, calcium, magnesium, and zinc, copper, cadmium and / or manganese if present, and further containing iron and / or aluminum is obtained by removing iron and / or aluminum therefrom by a precipitation step using a precipitant.

6. The method according to claim 5, wherein the iron and / or aluminum is removed by precipitation using a precipitant containing a calcium base.

7. The method according to claim 5, wherein the iron and / or aluminum is removed by precipitation using a precipitant containing a magnesium base.

8. The method according to claim 5, wherein the iron and / or aluminum is removed by precipitation using a precipitant containing a nickel base.

9. The method according to claim 5, wherein the iron and / or aluminum is removed by precipitation in two or more precipitation steps, and different precipitating agents or combinations of precipitating agents can be used in each precipitation step.

10. The method according to claim 1, wherein the first and second alkylphosphorus extractants contain an alkylphosphorus acid and / or a nickel salt thereof.

11. The method according to claim 1, wherein the second extractant (II) has a higher selectivity for magnesium than the first extractant (I).

12. The method according to claim 1, wherein the first alkylphosphorus extractant (I) contains an alkylphosphonic acid and / or a nickel salt thereof, and the second alkylphosphorus extractant (II) contains an alkylphosphinic acid and / or a nickel salt thereof.

13. The method according to claim 1, wherein the first and second extractants are converted to their nickel salts and contain nickel having an available extractant capacity at a concentration of at least 20%.

14. The method according to claim 13, wherein the first and second extractants are converted to nickel salts, and the first and second organic phases contain less than 2 g / L of sodium.

15. The method according to claim 1, wherein the first and second organic phases prepared in steps ii and iii each contain the first and second extractants in an amount of 5 to 50 vol.% based on the total volume of the solvent, and the diluent in an amount of 50 to 95 vol.% based on the total volume of the solvent.

16. The method according to claim 1, wherein the extraction in step ii is carried out at a temperature of 25 to 55 °C.

17. The method according to claim 1, wherein the extraction in step iii is carried out at a temperature of 40 to 70 °C.

18. The method according to claim 1, wherein the stripping step iv is carried out at a temperature of 40 °C to 50 °C.

19. The method according to claim 1, wherein the magnesium-depleted high-purity nickel sulfate aqueous solution contains nickel at a concentration of 40 to 180 g / L and magnesium at a maximum concentration of 5 mg / L.

20. The supply aqueous solution prepared in step i contains nickel in an amount of at least 60 at.% with respect to the total metal content of the supply aqueous solution, and the supply aqueous solution prepared in step i contains cobalt, calcium, magnesium, and, optionally, zinc, copper, cadmium, and manganese in a maximum amount of 40 at.% with respect to the total metal content of the supply aqueous solution. The method according to claim 1.

21. The method according to claim 1, wherein the high-purity nickel sulfate aqueous solution obtained after removal of residual magnesium in step iii is subjected to crystallization or granulation.

22. The method according to claim 1, wherein the first organic phase is washed with sulfuric acid after the step of stripping with the mineral acid.

23. The method according to claim 1, wherein nickel is added to the first and / or second organic phase using an alkali hydroxide and a nickel salt-containing solution after the step of washing or stripping with sulfuric acid, and is subsequently recycled in step ii and / or step iii to terminate the loop of the method by this means.

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