CA3236078A1

CA3236078A1 - Selective acid leaching of mixed hydroxide precipitate

Info

Publication number: CA3236078A1
Application number: CA3236078A
Authority: CA
Inventors: Maria Jose LACADENA; Alun Pryce James; Oscar VASQUEZ
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2021-11-12
Filing date: 2022-11-10
Publication date: 2023-05-19
Also published as: WO2023083953A1; AU2022387821A1

Abstract

The present invention relates to a process for selectively leaching nickel from a mixed hydroxide precipitate (MHP) by contacting the mixed hydroxide precipitate with an acidic leach solution and with peroxymonosulfuric acid to cause at least 75 wt.-% of the nickel to be dissolved in a leachate and at least 90 wt.-% of the cobalt to be recovered in a solid phase, based on the total amount of nickel and cobalt, respectively, present in the mixed hydroxide precipitate.

Description

Selective acid leaching of mixed hydroxide precipitate TECHNICAL FIELD
The invention relates to a process for recovering a metal from a source material. Particularly, to selectively recover nickel directly from a mixed hydroxide precipitate containing nickel, cobalt and optionally manganese.
TECHNICAL BACKGROUND
Nowadays, there is a growing number of electric vehicles (EV). The current predominant battery energy storage technology for EVs is the Li-ion battery (LIB). In a LIB lithium ions move from the negative electrode or anode (principally made from carbon e.g. graphite) through an electrolyte to the positive electrode (cathode) during discharge, and back when charging.
Chemistry, performance, cost and safety characteristics vary across LIB types.

Handheld electronics mostly use lithium polymer batteries (with a polymer gel as electrolyte) with lithium cobalt oxide (LiCo02) as cathode material, which offers high energy density but presents safety risks, especially when damaged.
Lithium iron phosphate (LiFePO4), lithium ion manganese oxide battery (LiMn204, Li2Mn03, or LMO), and lithium nickel manganese cobalt oxide (LiNiMnCo02 or NMC) offer lower energy density but longer lives and less likelihood of fire or explosion. NMC in particular is the leader for automotive applications i.e.
for EV. The cathode used in NMC batteries is a combination of nickel:manganese:cobalt for instance in a weight ratio of 8:1:1 hence called NMC 811.
Even though much more nickel will be needed in the near future to satisfy the demand for LIBs, most nickel in the global supply chain is not actually suited for battery production.
The source predominate for nickel is either sulphide or laterite mineral deposits. Large high grade sulphide deposits are increasingly rare and so the processing of laterite ores is predicted to become the dominant source of the metal.
A common method of treating laterite ores is to leach the solids in acid.
Acid leaching is generally followed by impurity precipitation, commonly achieved by adding limestone. Following impurity precipitation, nickel and cobalt are usually recovered from the aqueous solution together by either mixed

- 2 -sulphide precipitation (MSP), or mixed hydroxide precipitation (MHP). MEP is a relatively recent large scale industrial technology achieved by adding a basic chemical such as magnesia, lime, limestone or sodium hydroxide to the leach solution. The MHP consists of mostly nickel hydroxide but also contains 5 valuable cobalt hydroxides, possibly manganese, and various other impurities.
The MHP represents a more value concentrated product in that the approximately 1% nickel and 0.1% cobalt present in the original laterite ore are upgraded substantially in terms of their relative amounts in the MEP.
Since the MHP has such a high valuable metal content, the feasibility of 10 operating a centralized nickel and cobalt refinery increases. This is because the transportation costs for the upgraded intermediate product would be a fraction of that for the as-mined ore.
The MHP may be further processed in a number of ways. For example, it may be added to the melt of an iron smelter in order to alloy the contained nickel 15 with iron. This process is not suitable for MHP with significant cobalt content as the valuable cobalt is not recovered and hence, economically unfeasible.
Another major processing route for refining MHP, as described for example in US 2007/0166214, is by leaching the material in an ammonia/ammonium carbonate solution. The nickel and cobalt dissolve in the 20 ammonia solution to form ammonia complexes. This solution is further treated in a Caron type process to recover nickel and cobalt. By using this process, several process steps are necessary to recover nickel and/or cobalt.
WO 2010/118455 refers to a process, wherein MHP is treated with two acidic solutions to extract nickel and/or cobalt from MEP. In this process 25 additional solvent extraction steps necessary to remove impurities from the solution containing dissolved nickel and/or cobalt. Nickel and/or cobalt are subsequently recovered from the solution by an electrowinning or hydrogen reduction step.
Such prior art approaches are generally either relatively energy intensive, 30 do not return optimal nickel and/or cobalt recoveries, require an excessive number of processing stages or are sensitive to the presence of other impurities such as aluminium, iron and chromium. There is a need for an improved method of recovering nickel from nickel containing ores. It would be desirable to provide a process for a straightforward separation of nickel from cobalt in MEP and 35 which enables an efficient recovery of both commodities.

3 US 2016/0355906 refers to a process for selective leaching nickel from MHP, while retaining cobalt in the leach residue solids by using sodium persulphate or potassium permanganate as oxidizing agent. However, also in the processes the nickel-cobalt separation is not perfect and there is a significant 5 cross contamination of these two metals.
The present invention aims to overcome one or more of the difficulties or disadvantages identified in the prior art documents.
SUMMARY OF THE INVENTION
10 The present invention relates to a process for selectively leaching nickel from a mixed hydroxide precipitate (MHP) by contacting the mixed hydroxide precipitate with an acidic leach solution and with peroxymonosulfuric acid to cause at least 75 wt.-% of the nickel to be dissolved in a leachate and at least 90 wt. -% of the cobalt to be recovered in a solid phase, based on the total amount of 15 nickel and cobalt, respectively, present in the mixed hydroxide precipitate.
The present invention also relates to a process for selectively leaching nickel from a mixed hydroxide precipitate by contacting mixed hydroxide precipitate (MEP) with a composition consisting essentially of an acidic leach solution and peroxymonosulfuric acid at a temperature of from 30 C to 80 C.
DETAILED DESCRIPTION OF THE INVENTION
Before the present formulations of the invention are described, it is to be understood that this invention is not limited to particular formulations described, since such formulations may, of course, vary. It is also to be understood that the 25 terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
The terms "comprising", "comprises" and "comprised of' as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, 30 elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of' as used herein comprise the terms "consisting of', "consists" and "consists of'.
Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being 35 employed to determine the value.

- 4 -As used herein, the terms "% by weight", "wt.- %", "weight percentage", or -percentage by weight" are used interchangeably.
The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range

5 (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed 10 therein.
All references cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references herein specifically referred to are incorporated by reference.
Unless otherwise defined, all terms used in disclosing the invention, 15 including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.
In the following passages, different alternatives, embodiments and variants 20 of the invention are defined in more detail. Each alternative and embodiment so defined may be combined with any other alternative and embodiment, and this for each variant unless clearly indicated to the contrary or clearly incompatible when the value range of a same parameter is disjoined. In particular, any feature indicated as being preferred or advantageous may be combined with any other 25 feature or features indicated as being preferred or advantageous.
Furthermore, the particular features, structures or characteristics described in present description may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include 30 some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.
The present invention relates to a process, wherein nickel can be directly 35 and selectively leached from mixed hydroxide precipitate (MHP).

The term "mixed hydroxide precipitate" or -MHP", as used herein, preferably refers to a solid mixed nickel-cobalt hydroxide precipitate. Such precipitate is generally known as an intermediate product in the commercial processing of nickel containing ores. This precipitate usually comprises a variety 5 of nickel, cobalt and possibly manganese compounds including oxides and hydroxides. It will be appreciated that references herein to "nickel", "cobalt" or "manganese- in relation to their separation may be taken as references to one or more of these compounds, including oxides and hydroxides of the metals. The nickel and cobalt are generally at a higher concentration within the MHP than in 10 the original mined ores representing the source material. Usually, the MHP used in the invention comprises 34 to 55 wt.-% of nickel, 1 to 4.5 wt.-% of cobalt, and optionally 1 to 7 wt -% of manganese based on the total amount of anhydrous MHP.
It has been surprisingly found that by treating MHP with an acidic leach 15 solution and peroxymonosulfuric acid according to the invention nickel dissolves in the acidic solution and cobalt, and manganese when present, can be nearly completely recovered in the solid phase as a precipitate. The recovering of the cobalt in the solid phase by using the process of the invention is stable, i.e.
following treatment of the MHP with an acidic leach solution and 20 peroxymonosulfuric acid does not result into a dissolving of the precipitated cobalt contrary to nickel. The solid phase generally contains as main components, Co304, Co203 and Co0OH. It can also contain unreacted Ni(OH)2 and Ni0OH. When manganese is present in the MHP, it can also be nearly completely recovered in the solid phase. The solid phase then contains as main 25 manganese component, manganese oxide Mn07.
According to the invention, the MHP is contacted with an acidic leach solution and with peroxymonosulfuric acid to cause at least 75% wt. -% of the nickel to be dissolved in a leachate and at least 90 wt-% of the cobalt to be recovered in a solid phase, based on the total amount of nickel and cobalt, 30 respectively, present in the MHP. It is preferred that the MHP is contacted with the acidic leach solution and with peroxymonosulfuric acid such that at least wt.-%, more preferably at least 85 wt.-%, and even more preferred at least 90 wt.-% of the nickel, based on the total amount of nickel present in the MHP, is dissolved in the acidic leach solution. Additionally, it is preferred that at least 95 35 wt.-%, at least 98 wt.-%, more preferably at 99 wt. -% of the cobalt, based on the total amount of cobalt present in the MHP, can be recovered in a solid phase.

- 6 -According to another embodiment of the invention, nickel is selectively leached from MHP by contacting the MHP with a composition consisting essentially of an acidic leach solution and peroxymonosulfuric acid at a temperature of from 30 C to 80 C.
5 The acidic leach solution used in the process of the invention is an aqueous acidic leach solution. Preferably, the acid of the acidic leach solution is sulfuric acid (H2SO4) or any suitable strong acid which can achieve adequate dissolution of the nickel. Further examples of acids which may be suitable include nitric acid, hydrochloric acid and other strong mineral acids. Alternatively, the acid of 10 the acidic leach solution can be peroxymonosulfuric acid. The best results are obtained when the acid is sulfuric acid or peroxymonosulfuric acid.
In the process of the invention, the mixed hydroxide precipitate contains nickel, cobalt and optionally manganese. Usually, nickel is dissolved and cobalt is recovered in a solid phase, and when manganese is present in the MHP, the 15 manganese is also recovered in the solid phase.
It is further preferred that the acidic leach solution has an initial acid concentration in the process (preferably an initial sulphuric acid concentration) of about 0.5 wt.-%, of about 1.0 or more, preferably of about 5.0 wt.-% or more, more preferably of about 10 wt.-% or more. The acidic leach solution generally 20 has an initial acid concentration (preferably an initial sulphuric acid concentration) of about 30 wt.-% or less, preferably of about 20 wt. -% or less.
Preferably, the acidic leach solution used in the process of the invention has an initial acidic concentration (preferably an initial sulphuric acid concentration) between 1.0 wt.-% and 20 wt.-%, between 2.0 to 15.0 wt.-%, more preferably 25 between 3.0 and 10.0 wt.-% or even more preferred between 5.5 and 7.0 wt.-%.
According to the invention, the MHP may be brought in contact with a pre-prepared acidic leach solution as defined above, or in a first step water is added to MHP and afterwards the acid to form the acidic leach solution is added to the mixture of MHP and water in an amount to obtain an acidic leach solution 30 having the initial concentration in the process of the invention as defined above.
The acid, which is added to the mixture of MHP and water, may be a high concentrated acid, i.e. the acid is an aqueous acidic solution having an acid concentration of 93 to 98 %, preferably of 95 to 98 %, or may be an aqueous acidic solution having an acid concentration, which is high enough to obtain an 35 acidic leach solution having the initial concentration in the process of the invention as defined above.

- 7 -The term "acidic leach solution" as used herein refers to a prepared acidic leach solution or to a solution obtained by adding water to MHP and subsequently adding an acid to the mixture of water and MHP. It usually is an aqueous acidic leach solution.
5 The term leachate", as used herein, refers to the solution obtained after contacting the MHP with the acidic leach solution and with peroxymonosulfuric acid. This leachate solution contains the dissolved nickel, the non-consumed acid if any, the non-consumed peroxymonosulfuric acid if any, and most often water.
Peroxymonosulfuric acid (H2S05) is also known as persulfuric acid, 10 peroxysulfuric acid, or Caro's acid. The 1UPAC name of peroxymonosulfuric acid is (dioxidanido)hydroxidioxidosulfur.
Peroxymonosulfuric acid, preferably the peroxymonosulfuric acid solution used in the process of the invention, is obtained by adding hydrogen peroxide (H202) to sulfuric acid (H2S05) achieving the following equation:
15 H202 + H2SO4 411-10' H2S05 H20 Equitation 1 According to the invention, it is preferred that the peroxymonosulfuric acid (solution) used in the process contains not more than 1 mole of hydrogen peroxide per 8 moles of peroxymonosulfuric acid. Preferably, the molar ratio of peroxymonosulfuric acid to hydrogen peroxide is greater than 8:1, more 20 preferably 10:1, and even more preferred 12:1.
It is further preferred that the molar ratio of sulfuric acid (H2SO4) to hydrogen (H202) for generating the peroxymonosulfuric acid is between 3:1 to

8:1, more preferably between 4:1 and 6:1. Preferably the peroxymonosulfuric acid solution used in the process of the invention has concentration of between 5 25 and 20 wt. -% preferably between 8 and 12 wt.-%, based on the total amount of the peroxymonosulfuric acid solution used in the process.
Peroxymonosulfuric acid works as an oxidizing agent in the process, i.e. it is a reagent, which is capable of causing a substrate to increase its oxidation state, e.g. to lose an electron, whereby the reagent itself being reduced in the 30 process. The divalent ions of nickel (Ni2+) and cobalt (Co2+) and optionally manganese (Mn2+), present in the acidic leach solution of the invention have different ability to be oxidised. According to the invention, peroxymonosulfuric acid oxidizes dissolved divalent cobalt (Co (II)) to trivalent cobalt (Co (III)), which precipitates (see Equation 2):
35 H2S05 + 2Co2+ + 5 H20 2 Co(OH)3 + H2SO4 + 41-1' Equation 2 112S05 mn2I + H20 MnO2 + H2SO4 + 2H' Equation 3 The process of the invention may be carried out such that the MEP is first contacted with the acidic leach solution and subsequently with the peroxymonosulfuric acid to cause nickel to be at least partially dissolved, cobalt to be at least partially dissolved and then precipitated, and manganese, when 5 present, to be at least partially oxidised and precipitated to a solid phase. The term -subsequently" used in this regard means after the total amount of the acidic leach solution is contacted with the MHP or after a portion of the total amount of acidic leach solution used in the process of the invention is added to MHP.
10 Alternatively, the MHP is contacted simultaneously with the acidic leach solution and with peroxymonosulfuric acid to cause nickel to be at least partially dissolved, cobalt to be at least partially oxidized and precipitated, for instance in the form of Co304, Co203 or Co0OH, and manganese, when present, to be at least partially oxidized and precipitated, for instance in the form of Mn02.
In a 15 first embodiment of this alternative, the acidic leach solution is different from the peroxymonosulfuric acid solution. In a second embodiment, the acidic leach solution is identical to the perxoymonosulfuric acid solution. In this case, all of the acid is present in the perxoymonosulfuric acid solution as sulfuric acid, and there is no separate addition of the acid.
20 In yet another alternative, the MHP is first contacted with the peroxymonosulfuric acid and subsequently with the acidic leach solution to cause nickel to be at least partially dissolved, and cobalt and manganese, when present, to remain in solid phase.
It is further preferred that the amounts of acidic leach solution and/or the 25 peroxymonosulfuric acid used in the process of the invention are progressively added to MHP. The progressive addition of acidic leach solution may be carried out such that in a first step water is added to the MEP and afterwards the acid to form the acidic leach solution is added to the mixture to obtain the acidic leach solution as defined above. In another embodiment a pre-prepared acidic leach 30 solution as defined above is progressively added to MHP. In a further preferred embodiment, the peroxymonosulfuric acid is progressively added to a mixture of MEP and the acidic leach solution.
The term "progressively" or -progressive" as used herein means that the total amount of acidic leach solution and/or the peroxymonosulfuric acid is 35 added to MHP either in small increments (preferably of at most 1 wt. -%
or less than 1 wt. -% of the total amount of acidic leach solution and/or

- 9 -peroxymonosulfuric acid, respectively, to be used in the process), preferably evenly timed over a given period, or in a continuous stream. Usually, the period for adding progressively the acidic leach solution and/or the peroxymonosulfuric acid to MHP is at least 30 minutes, in particular at least lh. This period is 5 usually at most 8 hours, in particular at most 6 hours, more particularly at most 4 hours, sometimes at most 3 hours, possibly at most 2 hours. The preferred period is from 30 minutes to 4 hours.
In case the component(s), i.e. acidic leach solution and/or peroxymonosulfuric acid, are added to the MHP in small increments evenly

10 timed over a given period, the component(s) are preferably added in about 5 to about 12 portions, in about 6 to about 10 portions, or more preferably in about 6 to about 8 portions, to the MHP in intervals of preferably every about 5 to about every 40 minutes, more preferably of every about 10 to about every 30 minutes.
In a further preferred embodiment of the invention, the component(s) are 15 added to the MHP in a continuous dosage, preferably in a continuous dosage of from 0.1 to 1.0 ml/min at lab scale, from 0.2 to 0.9 ml/min at lab scale or from 0.3 to 0.8 ml/min at lab scale, more preferably from 0.4 to 0.6 ml/min at lab scale. For industrial scale, as known in the art, this dosage must be adjusted accordingly.
20 In a more preferred embodiment, the total amount of peroxymonosulfuric acid used in the process is added to a mixture of MHP and acidic leach solution in a continuous dosage of from 0.7 to 0.9 ml/min at lab scale. Additionally, it is preferred that peroxymonosulfuric acid is added to the mixture of MHP and acidic leach solution for a duration of 1.0 to 2.5 hours, more preferably of 1.5 to 25 2.0 hours.
It has been found that in most cases, cobalt is leached initially by the acid of the acidic leach solution and once peroxymonosulfuric acid is dosed starts to precipitate. On the other hand nickel progressively dissolves with the dose of peroxymonosulfuric acid.
30 The total amount of acidic leach solution and peroxymonosulfuric acid used in the process depends on the amount of nickel, cobalt, and optionally manganese, present in the MLIP. In other words, the amount of metal dissolution and precipitation can be controlled by the amount of acidic leaching solution and of peroxymonosulfuric acid, respectively, used in the process.
35 It is preferred that the molar ratio of the acid, i.e. the acid of the acidic leach solution in combination with the sulfuric acid that is generated during the process, in particular by the reaction of cobalt ions, and of manganese ions when present, with peroxymonosulfuric acid (see Equation 2 and 3), to nickel, which should be dissolved, is from 0.6 to 0.9, more preferably from 0.7 to 0.85.
By using the acid in lower stoichiometric amounts in the process, the 5 nickel hydroxide (Ni(OH)')) present in MHP works as neutralizing agent.
In that case, there is no need to use an additional neutralizing agent in the process to control the pH of the contacting step of the process.
In the invention, it is preferred that the molar ratio of peroxymonosulfuric acid to cobalt, which should be recovered, is at least 0.7, in particular at least 1.0, 10 more particularly at least 1.5. This molar ratio is usually at most 6.0, often at most 5.0, in particular at most 4.0, more particularly at most 3Ø Good results are obtained with a ratio of from 0.7 to 3Ø
Furthermore, in order to ensure that nickel is dissolved in the acidic leach solution, and that cobalt and optionally manganese, is(are) recovered in the solid 15 phase in the desired amounts, the process of invention should be carried out at an appropriate pH. Preferably, according to the invention, the pH during the contacting step is from 2 to 7, in particular from 3 to 6, more particularly from 3.5 to 5. The pH value of the liquid present during the contacting step is determined by methods generally used in the art. One possible method is to use a 20 pH probe from VWR, pHenomenalk 111 pH electrode, 3 in 1, with a sensor for the pH and the ORP.
The process according to the invention is conducted preferably at a temperature of from 30 to 80 'V, in particular from 35 C to 65 'V, and more particularly from 40 to 55 'C. Depending on the reaction conditions, the heat of 25 reaction may be enough to reach the required temperature range without additional heating.
It is further preferred that the MHP is present in a stoichiometric % amount of between 100 % and about 40 % compared to the amount of acid of the acidic acid solution, about 90% and about 50 %, more preferably about 85 to about 60 30 %.
Preferably, the solution, i.e. the acidic acid solution and the solution of acidic acid solution and peroxymonosulfuric acid that contacts the MHP, is stirred during the process of the invention or otherwise agitated under mechanical conditions in a vessel/reactor usually used in metal leaching 35 processes. One advantage of doing so is to minimise, as far as possible, local variations of temperature from the introduction of the acidic leach solution and

- 11 -peroxymonosulfuric to MHP, because such variations end to lead to an impaired performance, which manifests itself by way of increased peroxymonosulfuric acid, or higher residual level of undissolved nickel.
The process is preferably carried out at atmospheric pressure.
5 The MHP used in the process of the invention may contain in addition to nickel and cobalt also manganese compounds. The process of the invention may have the same effects as described with respect to cobalt on manganese.
According to the invention, the nickel dissolved in the acidic leach solution can be directly recovered from said solution. Alternatively, after the contacting 10 step, in a first further step the leachate including dissolved nickel in high concentration is separated from the solid phase including precipitated cobalt, and optionally manganese, and in a second further step the cobalt and/or the manganese when present is (are) separated from the solid phase, and in a third further step the nickel is recovered from the leachate by various suitable means 15 known in the art. In particular, the nickel can be recovered from the leachate by means including electrowinning of nickel metal, hydrogen reduction to nickel metal or crystallisation to nickel sulphate hydrate. The process may further include the step of separating the cobalt and, if present in MHP, manganese solids, by selective dissolution of either cobalt or manganese in either acidic 20 solution or alkaline ammonia containing solution as for example described in US
2016/0355906.
In the process according to the invention, the solid phase recovered at the end of the process, may be subjected to at least one further contact with a leaching fluid to recover the nickel remaining in the solid phase. The leaching 25 fluid used in the further contact steps can be identical to the acidic leach solution and peroxymonosulfuric acid used in the first contact step. It can also be different and be any kind of known leaching fluid. The operating conditions of the further contact step can be identical to or different from the ones of the first contact step.
30 By using the process of the invention the separation of nickel from cobalt and optionally manganese in the MHP is surprisingly effective and provides distinct advantages over certain prior art approaches which instead attempt to selectively precipitate cobalt and optionally manganese out of a solution containing both nickel and cobalt, and optionally manganese, and/or by using 35 another oxidant agent than peroxymonosulfuric acid.

- 12 -The present invention is further illustrated by the following examples. It should be understood that the following examples are for illustration purposes only, and are not used to limit the present invention thereto.
EXAMPLES
Example 1 (according to the invention) In Example 1 peroxymonosulfuric acid was progressively dosed to the reactor containing Ni(OH)2, Co(OH)2 and sulfuric acid in a continuous stream at a dosing rate of 0.8 ml/min at lab scale.
Ni(OH)2 was present in the reactor in an amount of 38 g and the molar ratio of nickel to cobalt (Ni:Co) was 1:0.05. The slurry concentration present in the reactor was 10 wt. -%. The molar ratio of sulfuric acid to hydrogen peroxide (H2SO4:H202) for generating peroxymonosulfuric acid was 5:1 and the peroxymonosulfuric acid concentration of the solution used in the reaction was 10%. The molar ratio of peroxymonosulfuric acid to cobalt was 3 and the molar ratio of sulfuric acid to nickel was 0.85, taking into account that sulfuric acid was additionally generated during the reaction according to Equation 2.
The mixture present in the reactor was stirred at 300 rpm, the reaction temperature was 45 C and the pH was above 4. No neutralizing agent to control the pH of the solution during the reaction was used. A pH measurement probe was utilised, from VWR, pHenomenal 111 pH electrode, 3 in 1, with a sensor for the pH and the ORP.
Example 2 (comparative) In Example 2 at first persulphate (Na7S708) was dosed to MHP. After 30 minutes of the reaction sulfuric acidic solution was then dosed.
Ni(OH)2 was present in the reactor in an amount of 38 g and the molar ratio of nickel to cobalt (Ni:Co) was 1:0.05. The slurry concentration present in the reactor was 10 wt.-% . The molar ratio of sodium persulfate to cobalt (Na2S208:Co) was 1.87 and the molar ratio of sulfuric acid to nickel (H2SO4:Ni) was 0.83, taking into account that during the reaction of sodium persulfate and cobalt sulfuric acid was additionally generated.
The mixture present in the reactor was stirred at 300 rpm, the reaction temperature was 60 'C.

- 13 -Results As can be seen from Figure 1, in Example 1 cobalt is leached initially by the sulfuric acid and once the peroxymonosulfuric acid (Caro's acid, CA) is dosed starts to precipitate. Nickel progressively dissolves with the dose of Caro's acid.
5 In Example 2 the sulfuric acid leaches the nickel while keeps the cobalt remains in the precipitate (see Figure 1).
The graph of Figure 2 shows that when peroxymonosulfuric acid (CA) is used as oxidizing agent (see Example 1), less cobalt is recovered in the acidic leach solution, i.e. more cobalt is recovered in the solid phase, compared to the 10 use of persulphate as oxidizing agent (see Example 2).
Sodiumpersulphate Result wt. -%]
Nickel dissolved 92.13 Cobalt dissolved 2.25 Caro's Acid Nickel dissolved 92.01 Cobalt dissolved 0.14 Hence, the use of peroxymonosulfuric acid results into a selective acid leaching of MHP to produce nickel sulphate solution free of cobalt, without the 15 addition of a neutralizing agent.
Examples 3 and 4 (Nickel/Cobalt/Manganese) In Example 3 peroxymonosulfuric acid was progressively dosed, in a continuous stream at a dosing rate of 0.8 ml/min, to a reactor containing 20 Ni(OH)2, Co(OH)2 and MnSO4 suspended in water.
Ni(OH),, was present in the reactor in an amount of 38 g, the molar ratio of nickel to cobalt (Ni:Co) was 1:0.05 and the molar ratio of nickel to manganese (Ni:Mn) was 1:0.05. The slurry concentration present in the reactor was 10 wt.-%. The molar ratio of sulfuric acid to hydrogen peroxide (H2SO4:H202) for 25 generating peroxymonosulfuric acid was 5:1, the peroxymonosulfuric acid concentration of the solution used in the reaction was 10 wt.-%, and the sulfuric acid concentration of the solution used in the reaction was 42 wt.-%. The molar ratio of peroxymonosulfuric acid to cobalt and manganese (H2S05:Co+Mn) was 3 and no addition of sulphuric acid was carried out.

- 14 -The mixture present in the reactor was stirred at 300 rpm, the reaction temperature was 70 C and the pH was above 4. No neutralizing agent to control the pH of the solution during the reaction was used. A pH measurement probe was utilised, from VWR, pHenomenalk 111 pH electrode, 3 in 1, with a sensor 5 for the pH and the ORP.
Example 4 was exactly as example 3 with a dropwise addition of sulphuric acid starting 30 minutes after the last drop of peroxymonosulfuric acid was added, keeping the pH above 4.
The results of examples 3 and 4 are presented in Figure 3. As can be seen 10 from Figure 3, in Example 3, manganese was dissolved in water and with the addition of peroxymonosulfuric acid it precipitated. Cobalt was partially dissolved and then it precipitated with the addition of peroxymonosulfuric acid.
Nickel was progressively dissolved with the dose of peroxymonosulfuric acid.
In Example 4, a dropwise addition of sulphuric acid keeping the pH above 4 (Figure

15 4), allowed an additional dissolution of nickel while keeping the cobalt and manganese in the solid phase.
Caro's Acid Example 3 [wt.-%I Example 4 [wt.-%I
Nickel dissolved 77,7 92.8 Cobalt dissolved 0.13 0.16 Manganese dissolved 0.02 0.02 Example 5 (MHP sample) 20 In Example 5 peroxymonosulfuric acid was progressively dosed, in a continuous stream at a dosing rate of 0.8 ml/min, to a reactor containing an MHP
sample suspended in water.
The MHP sample contained 47% wt. -% moisture and the following composition (wt. -%):
MHP Ni Co Mn Mg Al 25.9 1.0 2.4 1 0.2 The MHP sample was present in the reactor in an amount of 60 g and the slurry concentration present in the reactor was 10% wt. The molar ratio of sulfuric acid to hydrogen peroxide (H2SO4:H202) for generating peroxymonosulfuric acid was 5:1, the peroxymonosulfuric acid concentration of 5 the solution used in the reaction was 10% wt, and the sulphuric acid concentration of the solution used in the reaction was 42 wt.-%.
The mixture present in the reactor was stirred at 300 rpm, the reaction temperature was 70 C and the peroxymonosulfuric acid was progressively dosed until the pH was 2 (Figure 6). No neutralizing agent to control the pH
of 10 the solution during the reaction was used. A pH measurement probe was utilised, from VWR, pHenomenalk 111 pH electrode, 3 in 1, with a sensor for the pH
and the ORP.
The results of Example 5 are presented in Figure 5. The figure highlights the dissolution of nickel from the MHP into the solution as time progressed and 15 peroxymonosulfuric acid was added.
Caro's Acid Example 5 [wt.-%1 Nickel dissolved 96 Cobalt dissolved 0.5 Manganese dissolved 1.6

Claims

- 16 -

1. A process for selectively leaching nickel from a mixed hydroxide precipitate by contacting the mixed hydroxide precipitate with an acidic leach 5 solution and with peroxymonosulfuric acid to cause at least 75 wt.-% of the nickel to be dissolved in a leachate and at least 90 wt.-% of the cobalt to be recovered in a solid phase, based on the total amount of nickel and cobalt, respectively, present in the mixed hydroxide precipitate.

10 2. A process for selectively leaching nickel from a mixed hydroxide precipitate by contacting the mixed hydroxide precipitate with a composition consisting essentially of an acidic leach solution and peroxymonosulfuric acid at a temperature of from 30 C to 80 C.

15 3. The process according to claim 1 or 2, wherein the mixed hydroxide precipitate contains nickel, cobalt and optionally manganese, and wherein nickel is dissolved and cobalt is recovered in a solid phase, and when manganese is present in the mixed hydroxide precipitate, manganese is also recovered in the solid phase.

20 4. The process according to any one of preceding claims, wherein the mixed hydroxide precipitate is first contacted with the acidic leach solution and subsequently with the peroxymonosulfuric acid to cause nickel to be at least partially dissolved, cobalt to be at least partially dissolved and then precipitated, and manganese, when present, to be at least partially oxidised and precipitated, 25 or wherein the mixed hydroxide precipitate is contacted simultaneously with the acidic leach solution and with peroxymonosulfuric acid, to cause nickel to be at least partially dissolved, cobalt to be at least partially oxidised and precipitated, and manganese, when present, to be at least partially oxidized and precipitated, or wherein the mixed hydroxide precipitate is first contacted with the 30 peroxymonosulfuric acid and subsequently with the acidic leach solution, to cause nickel to be at least partially dissolved, and cobalt and manganese, when present, to remain in solid phase.

5. The process according to any of the preceding claims, wherein the solid phase recovered at the end of the process, is subjected to at least one further 35 contact with a leaching fluid to recover the nickel remaining in the solid phase.

6. The process according to any of the preceding claims, wherein the acid in the acidic leach solution is peroxymonosulfuric acid or sulfuric acid.

7. The process according to any one of the preceding claims, wherein the acidic leach solution and/or the peroxymonosulfuric acid are added to the mixed 5 hydroxide precipitate during a period of from 30 minutes to 4 hours.

8. The process according to any one of the preceding claims, wherein the contacting step of the process is carried out at a pH of from 2 to 7, preferably from 3.5 to 5.

9. The process according to any one of the preceding claims, wherein no 10 additional neutralising agent is used to control the pH of the contacting step of the process.

10. Process according to any one of the preceding claims, wherein the peroxymonosulfuric acid contains not more than 1 mole hydrogen peroxide per 8 moles peroxymonosulfuric acid.

15 11. Process according to the proceedings claims, wherein sulfuric acid is generated during the process by reaction of peroxymonosulfuric acid with cobalt ions, and wherein the molar ratio of the total amount of acid of the acidic leach solution and the additional sulfuric acid generated during the process, to nickel to be dissolved, is from 0.6 to 0.9.

20 12. Process according to any one of the preceding claims, wherein the molar ratio of peroxymonosulfuric acid to cobalt to be recovered is from 0.7 to 3.

13. The process according to any one of the preceding claims, wherein the process is carried out at temperature of from 30 to 80 C.

14. The process according to any one of the preceding claims, wherein, 25 after the contacting step, in a first further step the solid phase is separated from the leachate containing dissolved nickel, in a second further step the cobalt and/or the manganese when present is(are) separated from the solid phase, and in a third further step the nickel is recovered from the leachate.

15. The process according to any one of the preceding claims, wherein the nickel is recovered from the leachate by electrowinning, hydrogen reduction, or crystal 1 i sati on.