Semi-batch process for oxidative leaching of nickel and cobalt

Abstract

The present invention provides a semi-batch process for the preparation of a nickel or cobalt sulphate solution, whereby sulphuric acid and hydrogen peroxide are peri- odically fed via a feed section to a reaction zone and whereby an acidic aqueous medium is circulated through the reactor until a predetermined concentration of nickel or cobalt, respectively, in said nickel or cobalt sulphate solution is achieved.

Description

[0001] SEMI-BATCH PROCESS FOR OXIDATIVE LEACHING OF NICKEL AND COBALT

[0002] TECHNICAL FIELD

[0003] The present invention relates to a process for manufacturing nickel sulphate and for cobalt sulphate.

[0004] INTRODUCTION

[0005] Secondary lithium-ion batteries (LIBs) have found wide-spread applications in portable devices and electric vehicles, as well as in specialized aerospace applications.

[0006] Important characteristics of reusable batteries include charge / discharge efficiency, cycle durability, energy density and safety. Many developments have focused on improving the performance of the cathode of LIBs.

[0007] Next to lithium cobalt oxide, lithium manganese oxide and lithium iron phosphate, lithium nickel manganese cobalt oxide ("NMC", LiNixMnyCozO2) and lithium nickel cobalt aluminium oxide ("NCA", LiNixCoyALOz) have received a lot of attention due to their superior performance. They can be easily obtained from mixing a suitable mixed metal precursor with a suitable lithium compound, and subsequent heat treatment of the mixture. Further processing steps are widely reported, e.g., for doping with further elements, providing a surface coating, improving crystallite size, etc.

[0008] The rising demand for electric vehicles (EVs) has led to an increased demand for high purity nickel and cobalt, especially for high purity nickel sulphate and high purity cobalt sulphate. Effectively, nickel refineries for preparing high purity nickel are considered of paramount importance for the supply of battery materials in the next decade.

[0009] Such nickel refineries will need to allow for high capacities and high efficiency of the processes to yield the desired nickel sulphate in a desired quantity and high purity. Therefore, novel processes need to be developed and optimized. Amongst other processes, the oxidative leaching of nickel (Ni) from a high purity nickel metal is considered one of the more promising routes. Processes for the leaching of Ni metal in sulphuric acid in the presence of hydrogen peroxide proceed according to the reaction:

[0010] Ni + H2O2 + H2SO4 -> NiSO4+ 2 H2O

[0011] This process is also known as oxidative leaching of Ni metal, a process which is highly exothermic (-423 kJ / mol). Similarly, processes for the leaching of Co metal in sulphuric acid in the presence of hydrogen peroxide proceed according to the reaction:

[0012] Co + H2O2 + H2SO4 -> CoSO4 + 2 H2O and are likewise highly exothermic.

[0013] WO 2021 / 105 365 describes a process for manufacturing nickel sulphate by leaching metal particles comprising nickel in an aqueous sulphuric acid solution, said process comprising the steps of introducing the metal particles in the aqueous sulphuric acid solution and introducing an aqueous hydrogen peroxide solution in the aqueous sulphuric acid solution containing the metal particles wherein the aqueous hydrogen peroxide solution is introduced progressively into the aqueous sulphuric acid solution containing the metal particles.

[0014] Yet, novel processes are in demand for ease of operation, high throughput, and optimized use of reactants as well as reduced consumption of hydrogen peroxide and reduced formation of H2.

[0015] JP 2011 / 126 757 describes a method for producing a nickel sulphate aqueous solution with a low content of free sulfuric acid. The method includes filling metal nickel masses in a metal dissolution column, feeding heated sulfuric acid from the upper part of the metal dissolution column and at the same time feeding air or oxygen from the lower part of the metal dissolution column.

[0016] Such batch processes may, however, suffer from entrainment of non-reacted metal fines in the resulting process output and the equipment must withstand harsh chemical reaction conditions, as high initial H2SO4 acid concentrations are required WO 2022 / 053448 describes a process for preparing battery grade metal sulphate solutions. Battery grade metal sulphate solutions are prepared directly from electro- lytically produced metal objects, such as cathode plates, that are subjected to an aqueous leaching solution comprising at least one acid leaching agent and a liquid oxidizing agent in a continuous process at elevated temperature in a column with vigorous mixing. Such a continuous process is, however, operated at low acid contents, because typically only a low residual acid content is tolerated in the product stream. This limits the leaching rate and the overall production capacity. Further such continuous processes are not flexible toward changes of reactivity or composition of the reagents, and there is a risk of H2 formation when loading the metal feed into the column during operation.

[0017] SUMMARY

[0018] It is therefore an object of the present invention to provide novel, non-continuous processes for preparing metal sulphate solutions under safe conditions with high productivity. The current invention provides a solution for at least one of the above- mentioned problems by providing a process for the oxidative leaching of nickel or cobalt, respectively, in the presence of an acid and an oxidizing agent according to claim 1. Since the inventive process and system can be applied to the oxidative leaching of nickel as well as to the oxidative leaching of cobalt, the process and system is described for both nickel and cobalt. Where reference is made in the description below to "nickel or cobalt," it is to be understood that the skilled person will know from the context of the description whether nickel or whether cobalt is indicated.

[0019] The process is performed at controlled temperature, and controlled hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) injection rates.

[0020] The inventors have found that under such conditions, the conversion rate of nickel to nickel sulphate (NiSC ) and cobalt to cobalt sulphate (COSO4), respectively, is optimized and the formation of H2 is very limited. This optimizes the process control and increases process safety. The inventors further found that the use of a column reactor helps increasing the batch size compared to a stirred tank. Moreover, recirculation helps preserving the heat balance at the start of a new cycle and during the entire process.

[0021] The inventors further observed no peak in cooling and heating occurs through the process of the present invention.

[0022] The inventive process is schematically shown in Figure 1.

[0023] In a first aspect, the present invention provides a semi-batch process for the preparation of a nickel or cobalt sulphate solution in a column reactor (100) comprising a reaction zone (10), said process comprising the steps of: i. feeding metal particles containing nickel or cobalt, respectively, to a reaction zone (10) of said column reactor (100); ii. feeding an aqueous medium to said reaction zone (10); iii. feeding sulphuric acid and hydrogen peroxide via a feed section to the reaction zone (10), thereby contacting hydrogen peroxide with said metal particles containing nickel or cobalt in an acidic aqueous medium; iv. simultaneously with step iii., circulating said acidic aqueous medium by evacuating a fraction of said acidic aqueous medium from said column reactor (100) and by recirculating the evacuated fraction to said column reactor (100) until a concentration of nickel or cobalt of at least 80 g / L, respectively, and a residual acid concentration below 20 g / L in said nickel or cobalt sulphate solution is achieved; and v. after step iv. evacuating said nickel or cobalt sulphate solution from said column reactor (100).

[0024] In this semi-batch batch process, the reagents sulphuric acid and hydrogen peroxide are periodically or continuously added during step iii., but the process is interrupted to evacuate the nickel and cobalt sulphate solution when the desired batch volume, nickel or cobalt concentration and residual acid concentration is reached.

[0025] The inventors found that extremely high acidic conditions, such as those used in batch processes whereby all sulphuric acid is already present in the starting solution, are preferably avoided for reasons of avoiding demanding conditions to the processing equipment and for reasons of safety in case of leakage or spilling. In a preferred embodiment according to the first aspect of the invention, feeding of sulphuric acid and hydrogen peroxide in step iii. comprises the subsequent steps of: a) feeding sulphuric acid and hydrogen peroxide in a molar ratio of sulphuric acid to hydrogen peroxide of 0.9: 1.0 to 1.1 : 1.0; b) feeding hydrogen peroxide to further reduce the residual acid concentration of said nickel or cobalt sulphate solution.

[0026] The inventors found that a semi-batch process with this dosing strategy of sulphuric acid and hydrogen peroxide enables fast leaching at relatively high acid concentrations, in combination with low residual acid amounts in the product solution, high hydrogen peroxide efficiency, as well as simple temperature control.

[0027] In another aspect, the concentration of nickel in said nickel sulphate product solution is between 80 and 200 g Ni / L, preferably between 90 and 175 g Ni / L and more preferably between 100 and 150 g Ni / L.

[0028] In another aspect, the concentration of cobalt in said cobalt sulphate product solution is between 80 and 200 g Co / L, preferably between 90 and 175 g Co / L and more preferably between 100 and 150 g Co / L.

[0029] Another aspect of the present invention is a system for producing nickel or cobalt sulphate, comprising:

[0030] ■ one or more reactors (100), preferably column reactors (100), operating a process for preparing a nickel or cobalt sulphate solution, respectively, according to the invention; and

[0031] ■ one or more buffer tanks configured to receive a nickel or cobalt sulphate solution, respectively, from said reactors (100).

[0032] DESCRIPTION OF THE FIGURES

[0033] By means of further guidance, figures are included to better appreciate the teaching of the present invention.

[0034] Said figures are intended to assist the description of the invention and are nowhere intended as a limitation of the presently disclosed invention. The figures and symbols contained therein have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0035] Figure 1 shows schematically a process according to the invention in a circulation reactor (100).

[0036] Figure 2 shows the cross section of a circulation reactor (100) of the present invention.

[0037] Figure 3 shows schematically a process according to Example 4 and Example 5 of the present invention.

[0038] DETAILED DESCRIPTION OF THE INVENTION

[0039] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0040] By means of further guidance, term definitions are included to better appreciate the teaching of the present invention. As used herein, the following terms have the following meanings:

[0041] "A", "an", and "the" as used herein refers 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.

[0042] "About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass 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 and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed. "Comprise," "comprising," and "comprises" and "comprised of" as used herein are synonymous with "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open-ended terms that specifies the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, element, members, steps, known in the art or disclosed therein.

[0043] The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints.

[0044] All percentages are to be understood as percentage by weight, abbreviated as "wt.%" or as volume per cent, abbreviated as "vol.%", unless otherwise defined or unless a different meaning is obvious to the person skilled in the art from its use and in the context wherein it is used.

[0045] In a first aspect, the present invention provides a semi-batch process for the preparation of a nickel or cobalt sulphate solution in a column reactor (100) comprising a reaction zone (10), said process comprising the steps of: i. feeding metal particles containing nickel or cobalt, respectively, to a reaction zone (10) of said column reactor (100); ii. feeding an aqueous medium to said reaction zone (10); iii. feeding sulphuric acid and hydrogen peroxide via a feed section to the reaction zone (10), thereby contacting hydrogen peroxide with said metal particles containing nickel or cobalt in an acidic aqueous medium; iv. simultaneously with step iii., circulating said acidic aqueous medium by evacuating a fraction of said acidic aqueous medium from said column reactor (100) and by recirculating the evacuated fraction to said column reactor (100) until a concentration of nickel or cobalt of at least 80 g / L, respectively, and a residual acid concentration below 20 g / L in said nickel or cobalt sulphate solution is achieved; and v. after step iv. evacuating said nickel or cobalt sulphate solution from said column reactor (100).

[0046] In this semi-batch batch process, the reagents sulphuric acid and hydrogen peroxide are periodically or continuously added during step iii., but the process is interrupted to evacuate the nickel and cobalt sulphate solution when the desired batch volume, nickel or cobalt concentration and residual acid concentration is reached.

[0047] The inventors found that very high acidic conditions, such as those used in batch processes whereby all sulphuric acid is already present in the starting solution, are preferably avoided for reasons of avoiding demanding conditions to the processing equipment and for reasons of safety in case of leakage or spilling. Additionally, it was found that high concentrations of acid, although affording a fast-leaching reaction, also result in the formation of relatively high amounts of heat which are more difficult to control. In addition, higher leaching kinetics as a result of higher acid concentrations may lead to higher temperatures, which promotes decomposition of the hydrogen peroxide. Therefore, the inventors contemplated a process according to the first aspect, whereby a substantially continuous feed of hydrogen peroxide is provided to the reaction zone while periodically sulphuric acid is fed to the reaction zone, and whereby sulphuric acid is allowed to be consumed in the oxidative leaching of the metal before a new feed of sulphuric acid is introduced in the reaction zone.

[0048] The aforementioned aqueous medium in step ii. may be water, preferably demineralised water, or most preferably is a diluted sulphuric acid solution. Using a nickel or cobalt sulphate solution results in a lower capacity of the process but allows for using a smaller reactor or obtaining a higher nickel or cobalt concentration. In a preferred embodiment, the aqueous medium is circulated through the reactor zone in step ii.

[0049] In a preferred embodiment according to the first aspect of the invention, feeding of sulphuric acid and hydrogen peroxide in step iii. comprises the subsequent steps of: a. feeding sulphuric acid and hydrogen peroxide in a molar ratio of sulphuric acid to hydrogen peroxide of 0.9: 1.0 to 1.1 : 1.0; preferably 0.95: 1.0 to 1.05: 1.0, more preferably 0.97: 1.0 to 1.03: 1.0, most preferably about 1 : 1; b. feeding hydrogen peroxide to further reduce the residual acid concentration of said nickel or cobalt sulphate solution.

[0050] In step a., sulphuric acid and hydrogen peroxide may be fed periodically or continuously. Preferably, in step a. sulphuric acid and hydrogen peroxide are fed with a constant supply rate. The required total amount of sulphuric acid is calculated upfront based on the batch volume, the desired metal content and residual acid content. When the desired volume and metal content in the nickel or cobalt solution is reached, only hydrogen peroxide is fed in step b. In step b. hydrogen peroxide may be fed periodically or continuously. Preferably, in step b. hydrogen peroxide is fed with a constant supply rate. In a preferred embodiment, the constant supply rate of hydrogen peroxide in step b. is lower than in step a., more preferably the supply rate of hydrogen peroxide in step b. is 10 to 60% of the supply rate of hydrogen peroxide in step a., even more preferably 20 to 50%, most preferably 20 to 30%.

[0051] The inventors found that a semi-batch process with this dosing strategy of sulphuric acid and hydrogen peroxide enables fast leaching at relatively high acid concentrations versus a corresponding continuous process, in combination with low residual acid amounts in the product solution, high hydrogen peroxide efficiency, as well as simple temperature control.

[0052] In a preferred embodiment according to the first aspect of the invention, the sulphuric acid content of the acidic aqueous medium in step iii. a. entering the bottom of the reaction zone (10) is between 10 and 60 g / L, preferably between 15 and 60 g / L, preferably from 20 g / L to 55 g / L, even more preferably from 30 g / L to 50 g / L, more preferably around 40 g / L.

[0053] Preferably, the present invention provides a process according to the first aspect of the invention, whereby during step iii. a., while circulating of the aqueous sulphuric acid solution as described in step iv., the reaction zone has a sulphuric acid solution at the top having a concentration from 10 g / L to 30 g / L, preferably from 15 g / L to 25 g / L.

[0054] In a preferred embodiment according to the first aspect of the invention, the hydrogen peroxide content of the acidic aqueous medium in step iii. a. entering the bottom of the reaction zone (10) is between 3 and 15 g / L, preferably between 5 and 10 g / L, more preferably between 7.5 and 9 g / L.

[0055] In a preferred embodiment according to the first aspect of the invention, the hydrogen peroxide content of the acidic aqueous medium in step iii. b. entering the bottom of the reaction zone (10) is between 0.5 and 10 g / L, preferably between 1 and 5 g / L, more preferably between 1.5 and 4 g / L.

[0056] In a preferred embodiment, the entire volume of the aqueous medium or acidic aqueous medium is circulated in counter-current mode in step ii., step iii. and step iv, whereby nickel or cobalt are loaded upfront from the top of the reactor into the reactor, and whereby said aqueous medium or acidic aqueous medium is fed to the bottom section of the reactor. In a preferred embodiment, the cumulative H2O2 efficiency for the full semi-batch process is at least 80%, more preferably at least 85%, most preferably at least 92%, most preferably at least 97%, whereby the cumulative hydrogen peroxide efficiency is determined as total moles of nickel or cobalt consumed per total moles of hydrogen peroxide added during the full batch process.

[0057] Steering the semi-batch process to obtain a residual amount of sulphuric acid in the target solution ensures that all peroxide is fully consumed.

[0058] In a preferred embodiment according to the first aspect of the invention, the residual amount of sulphuric acid of said nickel or cobalt sulphate solution evacuated in step v. is between 1 g / L and 20 g / L, preferably between 2 g / L and 15 g / L, more preferably between 2 g / L and 10 g / L.

[0059] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the concentration of nickel or cobalt in said nickel or cobalt sulphate solution, respectively, is between 80 g / L and 200 g / L, preferably between 90 g / L and 175 g / L and more preferably between 100 g / L and 150 g / L. Further, it may be advisable to dilute the target solution to obtain a predetermined concentration of the metal in the target solution. Such processes are advantageous in that they allow processing in a high-capacity reactor.

[0060] Furthermore, it is undesired that hydrogen peroxide is still present in the nickel or cobalt sulphate product. Therefore, the remaining hydrogen peroxide after step iii. may be removed by heating and / or circulation of the nickel or cobalt sulphate solution.

[0061] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby circulating in step iv. is continued, after step iii. has ended, until hydrogen peroxide in the nickel or cobalt sulphate solution is substantially exhausted. Preferably, circulation is continued until the hydrogen peroxide concentration is below 1 g / L, more preferably below 0.1 g / L, most preferably approximately 0 g / L.

[0062] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the molar ratio of the total amount of hydrogen peroxide fed in step iii. to the total amount of sulphuric acid fed in step ii. and iii. is more than 0.9 and less than 1.1, preferably more than 0.95 and less than 1.05, and most preferably between 0.95 and 0.99. In a preferred embodiment, according to the first aspect of the invention, the semibatch process is interrupted and the nickel or cobalt sulphate solution is evacuated before the particles containing nickel or cobalt have fully reacted with the sulphuric acid and hydrogen peroxide. Preferably, at least 1 wt.% of the initial amount of particles containing nickel or cobalt introduced in the reactor have not reacted with the sulphuric acid and hydrogen peroxide when the semi-batch process is interrupted and the nickel or cobalt sulphate solution is evacuated, more preferably at least 2 wt.%, at least 5 wt.%, at least 10 wt.%, or at least 15 wt.% and even more preferably at least 20 wt.%. More preferably, at least 25 wt.% of the initial amount of particles containing nickel or cobalt introduced in the reactor have not reacted with the sulphuric acid and hydrogen peroxide when the semi-batch process is interrupted and the nickel or cobalt sulphate solution is evacuated, more preferably at least 30 wt.%, 40 wt.%, 50 wt.% or even 60 wt.%. This is important, amongst others because the inventors found that leaching kinetics are more favourable when an amount of starting materials is allowed to remain in the reactor. In an especially preferred embodiment, at least 80 wt.% of the initial amount of particles containing nickel or cobalt introduced in the reactor have not reacted with the sulphuric acid and hydrogen peroxide when the semi-batch process is interrupted and the nickel or cobalt sulphate solution is evacuated, more preferably at least 90 wt.%, 92 wt.%, 94 wt.% or even 96 wt.%.

[0063] An aqueous medium is fed in step ii. to said reaction section (10) of the reactor (100), upfront of leaching with peroxide in step iii. The aqueous medium preferably is water, preferably demineralised water, most preferably a diluted sulphuric acid solution.

[0064] In a preferred embodiment according to first aspect of the present invention, said aqueous medium fed in step ii. comprises sulphuric acid in a concentration of 0 to 30 g / L, preferably 5 to 30 g / L, more preferably 10 to 20 g / L, most preferably about 15 g / L. Feeding a diluted sulphuric acid solution in step ii. ensures a sufficient reactivity when initiating the leaching with hydrogen peroxide in step iii., thereby facilitating a gradual temperature rise during start-up.

[0065] In a preferred embodiment according to first aspect of the present invention, said aqueous medium fed in step ii. comprises sulphuric acid in a concentration of 0 to 30 g / L, preferably 5 to 30 g / L, more preferably 10 to 20 g / L, most preferably about 15 g / L. Preferably, said aqueous medium is pre-heated prior to its use in step ii. Preferably, the reaction heat of a previous semi-batch reaction is used to pre-heat said aqueous medium.

[0066] Preferably, said aqueous medium in step ii. is fed to said reaction zone at a temperature from 50 °C to 80 °C, preferably at a temperature from 70 °C to 80 °C, even more preferably at a temperature from 75 °C to 80 °C.

[0067] Preferably, whereby the aqueous medium entering the reaction zone (10) in step ii. , step iii. and step iv. has a temperature from 50 °C to 80 °C, preferably from 70 °C to 80 °C, even more preferably from 75 °C to 80 °C.

[0068] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the reaction temperature at the top of the reaction zone (10) is from 80 °C to the boiling point of the leaching solution, preferably from 85 °C to 99 °C, even more preferably from 92 °C to 99 °C.

[0069] The term leaching solution means the aqueous solution comprising sulphuric acid and hydrogen peroxide in the reaction zone (10) of the circulation reactor (100).

[0070] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the metal particles containing nickel or cobalt are electrolytically produced, and preferably are cut cathodes. The inventors showed that the electrolytically produced nickel or cobalt cathodes can be successfully leached using the process of the present invention.

[0071] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said metal particles containing nickel or cobalt comprise nickel or cobalt, respectively, in an amount of at least 96 wt.%, preferably at least 99 wt.%, even more preferably at least 99.9 wt.% relative to the total weight of said metal particles.

[0072] In a preferred embodiment, the height h of the reaction zone (10) is at least 1 m, preferably from 1 m to 12 m, even more preferably from 3 m to 10 m. Alternatively, the height h of the reaction zone (10) is at least 1 m, preferably from 1 m to 3 m, even more preferably from 1.5 m to 2.5 m. In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the column reactor (100) comprises an insulation and / or heating jacket (50).

[0073] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the pressure in the headspace above the reaction zone (10) is atmospheric pressure or an under-pressure of less than 0.2 atm.

[0074] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said column reactor (100) further comprises an H2 detector (40).

[0075] In a preferred embodiment, the process of the present invention is a semi-batch process. This means that the reaction is stopped and the nickel or cobalt sulphate solution is evacuated when the target nickel concentration, cobalt concentration, respectively, or density is reached. Reactants are continuously added to the system over a certain period of time, yet harvesting of the solution is done in a discrete manner. A semi-batch process has several advantages versus a continuous process, including handling feed or reagents variability (e.g. Ni metal reactivity, or H2O2 quality), suppressing l-hformation during leaching and metal loading, increasing throughput by leaching at higher acid content, enabling low residual acid content, and more flexibility in general.

[0076] In one embodiment, the process of the present invention is a semi-batch, i.e. a discontinuous process. The term "semi-batch process" is to be considered as a process adapted to add reactants periodically and / or to remove products periodically, and thus in which the process does not have any continuous outflow conditions. Specifically, in the context of the current invention refers the term "semi-batch process" refers to a process whereby a batch of solids is processed and whereby liquid or liquified reagents are periodically introduced into the reactor. Consequently, the bed volume of metal particles containing nickel or cobalt decreases over the reaction time in the reaction zone (10) of the semi-batch reactor (100) until at least a part of the particles containing nickel or cobalt have reacted with the sulphuric acid and hydrogen peroxide. In one embodiment, the semi-batch process is stopped and the nickel or cobalt sulphate solution is evacuated when the particles containing nickel or cobalt have fully reacted with the sulphuric acid and hydrogen peroxide.

[0077] In a preferred embodiment, the semi-batch process is interrupted and the nickel or cobalt sulphate solution is evacuated when the nickel or cobalt sulphate solution has the desired, i.e. a predetermined nickel or cobalt content, respectively.

[0078] In a preferred embodiment, the semi-batch process is interrupted and the nickel or cobalt sulphate solution is evacuated when the nickel or cobalt sulphate solution has the desired, i.e. a predetermined, nickel or cobalt content, respectively, and the desired, i.e. a predetermined, residual acid content.

[0079] In a preferred embodiment, the semi-batch process is interrupted and the nickel or cobalt sulphate solution is evacuated when the nickel or cobalt sulphate solution has the desired, i.e. a predetermined, nickel or cobalt content, respectively, and the desired, i.e. a predetermined, residual sulphuric acid content and no more remaining H2O2.

[0080] In a preferred embodiment, the reaction is stopped, and the circulation reactor is evacuated, when the leach rate is low.

[0081] In one embodiment, the process is not a continuous process. The term "continuous" means that the particles containing nickel or cobalt, the sulphuric acid and the hydrogen peroxide can be added and resulting in a metal sulphate solution which is withdrawn without interrupting the process.

[0082] Nickel or cobalt metal may be fed to the semi-batch process upfront. Preferably, the nickel or cobalt is fed upfront to the reaction zone (10) of the reactor (100).

[0083] In a preferred embodiment, Ni and Co are reloaded after evacuating the leach solution of the first semi-batch process, before starting the next semi-batch process. By avoiding the contact between the leach solution and fresh Ni metal, occupational and process safety is maximized because there is no hot acid solution present when the reactor is opened. Further this limits the risk of reaction between fresh metal feed and leaching solution and thus limits the risk of H2 formation when opening the reactor.

[0084] In an alternative embodiment, the Ni and Co particles are reloaded before evacuating the leaching solution, but after stopping the hydrogen peroxide and sulphuric acid addition. In this way, Ni and Co are loaded into a reactor that is filled with leaching solution. This will reduce the downward velocity of particles loaded from the top and hence limit the impact of particle loading onto the reactor walls, reducing the risk that particles damage the surface.

[0085] The process may be started from a cold bed of metal particles or a preheated bed of metal particles. In a preferred embodiment, preheating the bed of metal particles is achieved by heating the aqueous medium while circulating it over the bed, until said aqueous medium fed to said reaction zone is at a temperature from 50 °C to 80 °C, preferably at a temperature from 70 °C to 80 °C, even more preferably at a temperature from 75 °C to 80 °C, and has a similar temperature at the reactor outlet.

[0086] In another preferred embodiment, the bed of metal particles is not preheated and the aqueous medium is heated to about 75°C in the circulation or buffer tank (200), before circulation of said aqueous medium to the reactor bed is started.

[0087] In a preferred embodiment, the aqueous medium is pre-heated. In a preferred embodiment, pre-heated water is circulated until the circulation reactor and the reaction zone (10) of the circulation reactor (100) have the desired temperature. This avoids the pre-heating of the circulation reactor (100) and increases the reaction efficiency. In a preferred embodiment, the aqueous medium is pre-heated for the first cycle but not for the subsequent cycles. For subsequent cycles, the temperature of the aqueous medium may be in the range of 50 °C to 70 °C. In a preferred embodiment, during the subsequent cycles, i.e. after evacuating the nickel or cobalt sulphate solution and subsequent feeding of particles containing nickel or cobalt to the reaction zone (10), the aqueous medium is not pre-heated.

[0088] The inventors found that the residual heat of the preceding cycle can be sufficient to start the leaching process in the subsequent cycle. In a preferred embodiment, the time between two consecutive cycles is sufficiently short to avoid the cooling of the reaction zone (10) below a threshold temperature for the nickel or cobalt metal leaching reaction. The process of the present invention allows to produce a "concentrated nickel sulphate solution". This is to be considered as synonymous to the term "nickel sulphate solution having a nickel content of at least 60 g Ni / L," optionally comprising further contents, such as sulphuric acid in an amount of less than 30 g / L H2SO4, preferably less than 20 g / L and more preferably less than 10 g / L. Preferably, said nickel sulphate solution has a nickel content of at least 60 g Ni / L, and preferably at least 80 g Ni / L. Said nickel sulphate solution preferably has a content of nickel sulphate below the saturation point of nickel sulphate at the processing temperature, i.e. at a temperature of about 90°C or of about 95°C.

[0089] Preferably, said nickel sulphate solution has a Ni content between 80 and 200 g Ni / L, preferably between 90 and 175 g Ni / L and more preferably between 100 and 150 g Ni / L. Preferably, said nickel sulphate solution obtained from the oxidative leaching reaction is a nickel sulphate solution having a nickel content of between 110 and 140 g / L, more preferably between 120 and 140 g / L, and most preferably said nickel sulphate solution having a nickel content of about 130 g / L.

[0090] The semi-batch process of the present invention allows to produce a "concentrated cobalt sulphate solution". This is to be considered as synonymous to the term "cobalt sulphate solution having a cobalt content of at least 60 g Co / L," optionally comprising further contents, such as sulphuric acid in an amount of less than 30 g / L H2SO4, preferably less than 20 g / L and more preferably less than 10 g / L. Preferably, said cobalt sulphate solution has a cobalt content of at least 60 g Co / L, and preferably at least 80 g Co / L.

[0091] Said cobalt sulphate solution preferably has a content of cobalt sulphate below the saturation point of cobalt sulphate at the processing temperature, i.e. at a temperature of about 90°C or of about 95°C. Preferably, said cobalt sulphate solution has a cobalt content between 80 and 200 g Co / L, preferably between 90 and 175 g Co / L and more preferably between 100 and 150 g Co / L. Preferably, said cobalt sulphate solution obtained from the oxidative leaching reaction is a cobalt sulphate solution having a cobalt content of between 110 and 140 g / L, more preferably between 120 and 140 g / L, and most preferably said cobalt sulphate solution having a cobalt content of about 130 g / L.

[0092] In a preferred embodiment, the nickel or cobalt sulphate solution is subjected to a purification step to reduce the concentration of one or more impurities, whereby said impurities comprise one or more impurities selected from the list comprising Cu, Zn, Co, Mn, Fe, Al, F, C, Ca, Si, P, As, Cd, Cr, Sb and Mg, and whereby said impurities may further comprise Co in the case of a process for preparing a nickel sulphate solution or Ni in the case of a process for preparing a cobalt sulphate solution.

[0093] In a preferred embodiment, a base is added to the said nickel or cobalt sulphate solution to react with the residual amount of sulphuric acid present in said nickel or cobalt sulphate solution, prior to subjecting it to a further purification step, whereby said base is selected from the group consisting of ammonium hydroxide, ammonium carbonate, potassium hydroxide, potassium carbonate, nickel or cobalt hydroxide, nickel or cobalt carbonate, cobalt hydroxide, cobalt carbonate, manganese hydroxide, manganese carbonate, calcium hydroxide, calcium carbonate, sodium hydroxide, sodium carbonate, lithium hydroxide, lithium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, or a combination of two or more of the aforementioned.

[0094] Preferably, said base is added until the pH of the nickel or cobalt sulphate solution is between 2 and 5, preferably between 2.5 and 4.5, and more preferably between 3.0 and 4.0.

[0095] In a preferred embodiment, the metal particles comprise nickel or cobalt, respectively, in an amount of at least 96 wt%, preferably 97 wt.%, relative to the total weight of said metal particles, preferably at least 98 wt.% and more preferably at least 99 wt.%. Preferably said metal particles contain Ni or Co in an amount of at least 99.5 wt.%, more preferably 99.9 wt%.

[0096] Said Ni metal particles may further contain Co in an amount of up to 1 wt .%.

[0097] In the context of the present invention, the nickel or cobalt metal feed preferably comprises highly pure nickel or cobalt metal, having a purity of typically 99.97+ %, 99.98+ %, or even 99.99+ %.

[0098] The nickel or cobalt metal may be fed to the reactor in the form of nickel or cobalt cut cathode metal, having a size of typically l"xl", 2"x2" or 4"x4", a shredded or cut full plate cathode metal obtained from an electrowinning process, nickel or cobalt metal rounds, or nickel or cobalt pellets, balls having diameter of about 0.5 cm. In a preferred embodiment, hydrogen peroxide used in the process is typically an aqueous solution with a hydrogen peroxide concentration of 30 to 60 wt.%, such as 35 wt. % or 50 wt.% solution in water and sulphuric acid has a concentration of 76 to 98 wt.% in water, preferably a 98 wt.% concentration in water.

[0099] Any water used in the process may be high purity water, such as demineralized water or RO water.

[0100] In one embodiment, the present invention provides a process according to the first aspect, whereby said oxidative leach solution comprises hydrogen peroxide in an amount of 1 to 50 g / L, preferably 1 to 30 g / L, and more preferably in an amount of 5 to 30 g / L.

[0101] More preferably, said oxidative leach solution comprises hydrogen peroxide in an amount of 5 to 20 g / L, more preferably in an amount of about 5 to 12 g / L, and even more preferably in an amount of about 7 to 10 g / L.

[0102] In a preferred embodiment, the hydrogen peroxide is fed at a constant supply rate to the reaction zone (10).

[0103] In one embodiment, the supply rate of the hydrogen peroxide is lowered at the end of the process.

[0104] The inventors found that feeding of the sulphuric acid at high concentrations results in an increased temperature and thus can be used to replace or reduce pre-heating of the aqueous medium.

[0105] In a preferred embodiment, the acidic aqueous medium is fed to the reaction zone (10) at a temperature from 50 °C to 80 °C, preferably from 70 °C to 80 °C, even more preferably from 75 °C to 80 °C.

[0106] In a preferred embodiment, the reaction temperature at the top of the reaction zone (10) is higher than 80 °C, preferably from 85 °C to 100 °C, more preferably from 92 °C to 99 °C.

[0107] In a preferred embodiment, the sulphuric acid is fed at a higher acid concentration than the target concentration and the acidity of the acidic aqueous medium is subsequently reduced by the feeding of the aqueous medium, preferably water, or of the nickel or cobalt sulphate solution, respectively. In one embodiment, the sulfuric acid is fed at a constant supply rate until a sufficient amount of sulphate is present in the reactor to achieve a predetermined amount of nickel or cobalt sulphate respectively, and whereby subsequently hydrogen peroxide is dosed to achieved the desired degree of metal leaching to achieve the predetermined amount of metal sulphate in solution.

[0108] In a preferred embodiment, the acidity of the acidic aqueous medium is reduced at the end of the process cycle, i.e. prior to evacuation of the nickel or cobalt sulphate solution. In a preferred embodiment, the acidity of the acidic aqueous medium is reduced to 10 g / L or less prior to the evacuation of the nickel or cobalt sulphate solution.

[0109] The inventors further found that a concentration of sulphuric acid of around 20 g / L at the top of the reaction zone (10) throughout the leaching ensures that peroxide addition is kinetically limiting the reaction. The inventors observed a higher peroxide yield is enabled in this case due to lower residual hydrogen peroxide concentration in the nickel or cobalt sulphate solution. This also increases the quality of the nickel or cobalt sulphate solution through the lower hydrogen peroxide.

[0110] Accordingly, in a preferred embodiment, the sulphuric acid is decreased at the end of the leaching.

[0111] In a preferred embodiment, the circulation reactor is controlled to ensure that the nickel or cobalt sulphate solution obtained from said reactor in step v. has a residual sulphuric acid content of between 1 g / L and 20 g / L. Leaching to a lower residual sulphuric acid content ensures that sulphuric acid is used economically in the process. Preferably, the residual amount of sulphuric acid in said nickel or cobalt sulphate solution is between 2 g / L and 15 g / L, more preferably between 2 g / L and 10 g / L, and most preferably the residual amount of sulphuric acid is about 2 g / L, 4 g / L, 6 g / L, 8 g / L or 10 g / L, or any value there in between.

[0112] In a preferred embodiment, the nickel or cobalt sulphate solution obtained from said reactor and having a residual sulphuric acid content is used for leaching of compressed metal waste in a subsequent leaching column. In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the molar ratio of the overall consumption of hydrogen peroxide to the overall consumption of sulphuric acid for the leaching of one batch of metal particles is more than 0.9 and less than 1.1, preferably more than 0.95 and less than 1.00. In other words, the consumed hydrogen peroxide to consumed sulphuric acid after step iv. is more than 0.9 and less than 1.1, preferably more than 0.95 and less than 1.00.

[0113] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby sulphuric acid and hydrogen peroxide are fed in step iii. in a molar ratio of 1.5: 1.0 to 0.6: 1.0. Preferably, sulphuric acid and hydrogen peroxide are fed in step iii. in a molar ratio of 1.2: 1 :0 to 0.8: 1.0, and more preferably in a molar ratio of 1.1 : 1.0 to 0.9: 1 :0. Preferably, in a former stage of step iii., sulphuric acid is fed in an excess relative to the amount of hydrogen peroxide being fed to the reactor. In other words, in an early stage of step iii., sulphuric acid is present in an excess relative to the amount of hydrogen peroxide being present in the reaction zone (10). Using higher amounts of sulphuric acid in the former stage of the process ensure good leaching kinetics at the former stage of the process. Preferably, in a later stage of step iii., sulphuric acid is fed in a sub-stoichiometric amount relative to the amount of hydrogen peroxide being fed to the reactor. In other words, in an later stage of step iii., sulphuric acid is fed in a sub-stoichiometric amount relative to the amount of hydrogen peroxide being present in the reaction zone (10). Feeding lower amounts of sulphuric acid at the end of the process avoids high residual amounts of sulphuric acid in the target nickel or cobalt sulphate solution.

[0114] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby in an early stage of step iii. the molar ratio of sulphuric acid to hydrogen peroxide in the reaction zone (10) is between 2.50: 1.00 and 1.01 : 1.00, preferably between 2.00: 1.00 and 1.01 : 1.00, and whereby in a later stage of step iii. the molar ratio of sulphuric acid to hydrogen peroxide in the reaction zone (10) is between 0.60: 1 :00 and 0.99: 1.00.

[0115] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby the concentration of hydrogen peroxide in the feed to the reactor zone (10) is kept substantially constant in step iii. and preferably also in the first part of step iv. The inventors envisaged that controlling the hydrogen peroxide concentration in the reaction zone around a predetermined concentration during the oxidative leaching encourages good leaching kinetics, while subsequently stopping or reducing the peroxide supply while feeding sulphuric acid ensures that all peroxide is fully consumed, which is economically desired - provided that metallic particles are still present in the reaction zone.

[0116] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby sulfuric acid is fed at a constant supply rate until a sufficient amount of sulphate is present in the reactor to achieve a predetermined amount of nickel or cobalt sulphate respectively, and whereby subsequently hydrogen peroxide is dosed to achieved the desired degree of metal leaching to achieve the predetermined amount of metal sulphate in solution.

[0117] In a preferred embodiment, the present invention provides a process according to the first aspect, whereby the acid ratio, i.e. the ratio of the sulphuric acid concentration (CSA,O) of said nickel or cobalt sulphate solution obtained from the column reactor to the sulphuric acid concentration (CSA ) of the oxidative leach solution which is fed to the column reactor, is lower than 0.70, lower than 0.65, lower than 0.60, lower than 0.55, or even lower than 0.50.

[0118] Preferably, said ratio is between 0.5 and 0.1. Preferably, said ratio is lower than 0.45 and even lower than 0.40. Preferably, said ratio is higher than 0.05. Most preferably, said ratio is about 0.10, about 0.15, about 0.20, about 0.25, 0.30, about 0.35 or any value there in between.

[0119] In a preferred embodiment, the present invention provides a process according to the first aspect, whereby the difference Aac in acid concentration CSA and CSA,O is at least 5 g / L sulphuric acid and at most 80 g / L sulphuric acid, preferably at least 10 g / L sulphuric acid and at most 70 g / L sulphuric acid.

[0120] Preferably, said difference Aac in acid concentration is at least 15 g / L or more preferably at least 20 g / L.

[0121] Preferably, said difference Aac in acid concentration is at most 60 g / L or at most 50 g / L and more preferably at most 45 g / L. Most preferably, said difference Aac in acid concentration is about 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L or 45 g / L, or any value there in between.

[0122] In a preferred embodiment, the feed of hydrogen peroxide and sulphuric acid is stopped, while the circulation of the leach solution is maintained until the residual peroxide is consumed.

[0123] In a preferred embodiment, the feed of hydrogen peroxide and sulphuric acid is stopped, while the circulation of the leach solution is maintained until the predetermined residual sulphuric acid concentration in the nickel or cobalt sulphate solution is reached.

[0124] In a first embodiment, the present invention provides a process according to the first aspect, whereby sulphuric acid and hydrogen peroxide are fed in a stoichiometric amount in said oxidative leach solution. Preferably, the molar ratio of sulphuric acid to hydrogen peroxide is between 1 : 1 and 1 : 1.2, more preferably between 1.0: 1.0 and 1 : 1.1.

[0125] In a second, alternative embodiment, the present invention provides a process according to the first aspect, whereby hydrogen peroxide is fed to the oxidative leach solution which is fed to the circulation reactor in a sub-stoichiometric amount relative to the amount of sulphuric acid present in said oxidative leach solution. E.g., the oxidative leach solution may comprise 0.4 mol / L hydrogen peroxide and 0.5 mol / L sulphuric acid.

[0126] Preferably, the molar ratio of hydrogen peroxide to sulphuric acid in the oxidative leach solution which is fed to the circulation reactor at the start of the semi-batch process is between 0.6 and 1.0, preferably between 0.8 and 1.0, and more preferably is about 0.9.

[0127] Processes according to the invention allow to operate with a sub-stoichiometric amount of hydrogen peroxide, whereby a residual amount of sulphuric acid in the formed nickel or cobalt sulphate solution is allowed.

[0128] An excess of hydrogen peroxide supports further depletion of the sulphuric acid.

[0129] An excess of hydrogen peroxide ensures that hydrogen peroxide is not the rate limiting factor for the process. Excess hydrogen peroxide can be recovered from the circulation reactor effluent.

[0130] In another preferred embodiment, the present invention provides a process according to the first aspect, whereby the gaseous atmosphere in the overflow zone (20) is treated in a scrubber to remove water and any hydrogen that may have formed.

[0131] In a preferred embodiment, the present invention provides a process according to the first aspect, whereby said oxidative leach solution is contacted with said metal particles at atmospheric pressure in the headspace of the circulation reactor above the reaction zone, i.e. 1 bar, or at an under-pressure of less than 0.5 bar, preferably less than 0.2 bar, and more preferably less than 0.1 bar.

[0132] Preferably, said oxidative leach solution is contacted with said metal particles under an atmosphere of oxygen, air or oxygen-enriched air.

[0133] In another preferred embodiment, the gaseous atmosphere in the overflow zone (20) is flushed with an inert gas, such as steam or N2. This allows for a straightforward removal of hydrogen gas in case hydrogen gas is formed in the circulation reactor.

[0134] In a preferred embodiment, the present invention provides a process according to the first aspect, whereby a bed volume consisting of said metal particles in the circulation reactor has a diameter Db and a height Hb, whereby the ratio of said height to said diameter Hb: Db is between 0.8 to 15, preferably between 0.9 and 10, more preferably between 1 and 5.

[0135] Preferably, the height and diameter of said bed volume are maintained substantially constant throughout the process.

[0136] The inventive process proceeds in a column. In the context of the present invention, the term "column" is to be considered equivalent to the term "circulation reactor", "packed bed" or "packed bed reactor", "tower" or "tower reactor" and refers to a circulation reactor having a substantially cylindrical form having an internal diameter D and a height H. The circulation reactor (100) consists of a vertically arranged cylindrical column and is arranged to operate without mechanical agitation, preferably in the up-flow mode, i.e. fluid flow from bottom to top of the column.

[0137] The circulation reactor (100) is further characterized by

[0138] ■ a feed section at the bottom of said cylindrical reactor for feeding liquid reagents such as an aqueous solution, sulphuric acid and hydrogen peroxide;

[0139] ■ a top section or an overflow zone (20) at the upper part or top end of the circulation reactor, at the opposite side of the feed section, characterized by an effluent for collecting the overflowing nickel or cobalt sulphate solution; and

[0140] ■ a middle section or a reaction section (10) in the middle of said cylindrical reactor, where the leaching reaction proceeds.

[0141] Optionally, the circulation reactor (100) comprises a condensing section (30).

[0142] Figure 2 shows an exemplary cross-section of the circulation reactor (100) comprising an insulation and / or heating jacket (50), the column and coating (60) and a rubber layer (70).

[0143] Metal particles comprising nickel or cobalt are preferably fed at the top of the reactor and may be dosed gradually or intermittently to form a bed of metal particles on a support in said circulation reactor.

[0144] Said circulation reactor preferably comprises a support above the feed section for supporting a solid reagent such as nickel or cobalt metal.

[0145] Said support consists of a grid for supporting the nickel or cobalt metal.

[0146] Further, the circulation reactor (100) is preferably equipped with means to feed a solid reagent such as nickel or cobalt metal to the reaction zone (10) of the circulation reactor.

[0147] Further, the circulation reactor (100) is preferably also equipped with means for radially and uniformly distributing the oxidative leach solution in the feed section of the circulation reactor (100). The solid reagent can be dosed on the support by introduction of the nickel or cobalt metal at the top of the reactor, or at any position above the support. The overflow zone (20) is provided with an overflow outlet and overflow conduct (21) to receive a nickel or cobalt sulphate solution via an overflow mechanism.

[0148] In a preferred embodiment, the overflow conduct (21) comprises a filter preferably for filtering metal fines.

[0149] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby a liquid volume consisting of said oxidative leach solution in said circulation reactor (100) has a diameter DL and a height HL, whereby the ratio of said height to said diameter HL: DL is between 1.0 and 10.0, preferably between 1.5 and 8.0, more preferably between 2.0 and 5.0 and most preferably about 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0, or any value there in between.

[0150] A proper geometry of the liquid volume in the circulation reactor (100), especially a sufficiently high ratio HL: DL ensures that a 1-dimensional flow can be obtained throughout the column, and that small metallic particles resulting from reacted metallic feed particles are not upwardly entrained with the nickel or cobalt sulphate solution resulting from the oxidative leaching reaction, thereby entraining unreacted metal particles and thereby contaminating the obtained nickel or cobalt sulphate solution, as well as lowering the efficiency of the process.

[0151] In a preferred embodiment, said circulation reactor (100) is cylindrically shaped and has an internal diameter D and a height H, whereby the ratio of said height H to said diameter D is significantly higher than 1, such as between 1.0 and 10.0, preferably between 1.5 and 8.0, more preferably between 2.0 and 5.0 and most preferably about 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0, or any value there in between.

[0152] A proper geometry of the circulation reactor (100), especially a sufficiently high ratio H :D ensures that a 1-dimensional flow can be obtained throughout the column.

[0153] In preferred embodiment, the reaction column further comprises an H2 detector. The use of a circulation reactor helps to increase the batch size. Moreover, recirculation helps preserving the heat balance at the start of a new cycle.

[0154] In a preferred embodiment, mixing of the reactants in the reaction zone (10) is achieved by circulating the aqueous leaching solution. In this respect, a predetermined volume of said acidic aqueous medium or leach solution is continuously evacuated and recirculated to the feed section of the circulation reactor (100).

[0155] In the semi-batch process, the entire solution is circulated until the process is stopped to evacuate the product solution.

[0156] In the context of the present invention, the terms "circulation" or "circulate" and "recirculation" or "recirculate" are used interchangeably.

[0157] Circulation is particularly advantageous if the particles containing nickel or cobalt have a reduced flowability, such as for example nickel or cobalt cathodes.

[0158] In a preferred embodiment, the circulating leach solution passes through a heat exchanger for cooling or heating before re-entering the column reactor, to control the heat balance of the system and to maximize the leaching rate and capacity.

[0159] In a preferred embodiment, the heat recovered from the circulating leach solution is used in another parallel process. The batch process according to the current invention allows to operate the process based on the actual need for energy recuperation.

[0160] In a preferred embodiment according to the first aspect of the invention, the acidic aqueous medium is circulated in counter-current mode, whereby nickel or cobalt are loaded from the top of the reactor into the reactor, and whereby the leaching solution is fed to a bottom section of the reactor.

[0161] Counter-current means that the solution is removed from the top of the reaction zone (10) and returned to the bottom of the circulation reactor (100), which is countercurrent to the direction in which the metal particles have been added.

[0162] In a preferred embodiment, the acidic aqueous medium is circulated in counter-current and the Ni or Co particles are loaded from the top of the column reactor (100). Counter-current circulation, in combination with nickel loading from the top, has the advantage that the fines are accumulated in the lower area of the reaction zone (10). It is advantageous because it limits entrainment of particles, because the remainder of the bed acts as a filter, and further because it results in a concentrated reaction zone since the smallest particles accumulate at the bottom, near the inlet of the solution. The latter maximizes the temperature increase, which is beneficial for leaching the remainder of the metal particles higher up in the column reactor.

[0163] In a preferred embodiment, the height h of the reaction zone (10) is at least 1 m, and might be even higher such as from 1 m to 3 m, preferably from 1.5 m to 2.5 m. The inventors showed that a bed height of 1 m doubled the leach rate as compared to a 50 cm bed height. Accordingly, in a preferred embodiment, the initial bed height of the particles containing nickel or cobalt is at least 1 m, and might be even higher such as from 1 m to 3 m, preferably from 1.5 m to 2.5 m. In another aspect, the height h of the reaction zone (10) is at least 1 m, preferably from 1 m to 12 m, even more preferably from 3 m to 10 m.

[0164] However, the overall leaching capacity generally is limited by cooling needs and heating capacity.

[0165] In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said oxidative leach solution comprising sulphuric acid and hydrogen peroxide optionally in water is fed in via a bottom section of said circulation reactor (100) to said reaction section, and whereby said nickel or cobalt sulphate solution is evacuated in step iii. via a top section of said circulation reactor (100) from said reaction section.

[0166] Preferably, said metal particles are fed via a top section of said column reactor to the reaction zone (10). In one embodiment, said metal particles may be fed before in one batch at the start of the semi-batch reaction, or after the completion of the semibatch reaction. Said metal particles may be fed continuously or intermittently, preferably intermittently.

[0167] In a preferred embodiment, said reaction zone (10) may also incorporate a mechanical impeller, i.e. an impeller that is attached to a motor by means of a rod for the purpose of solely mixing liquid reagents. Alternatively, a static mixer is used.

[0168] In a preferred embodiment, the reaction zone (10) comprises a plurality of vertical baffles placed diametrically opposite to each other and placed at a position between said inlet nozzles and the said impeller such that at least one baffle is placed on diametrically opposite ends of the reactor walls. In this embodiment, the impeller and the vertical baffles help in micro-level mixing of the reactants. The impeller improves reactor kinetics. The vertical baffles contribute towards ensuring the maximum mixing of the reactants within the reaction zone (10). The placement of the vertical baffles ensures that the reaction is limited to the reaction zone (10) and does not extend into the zones above the reaction zone (10).

[0169] Preferably, said reactor has a calming zone above the reaction zone (10). The calming zone has a tubular structure with a constant cross section, preferably equal to that of said reaction zone (10), or with a widening cross section whereby the diameter of said cross section is larger than the cross section of the reaction zone (10). The calming zone is in fluid communication with said reaction zone (10) and has the reaction zone (10) at its distal end and the overflow zone (20) at its proximal end.

[0170] The function of the calming zone is to achieve a non-turbulent liquid flow in which unreacted metal fines adapt a non-fluidised condition. This allows the unreacted or insufficiently reacted metal particles to return to the reaction zone (10).

[0171] The calming zone may comprise a plurality of horizontal baffles placed in the central, proximal, and distal parts of the calming zone. In this embodiment, at least two of the provided horizontal baffles may be downward type of baffles with a centre flow aperture adapted to slow down the speed of the reactant mixture.

[0172] In yet another embodiment, the provided central horizontal baffle is a conical type baffle with annular flow. In this embodiment, the placement of the horizontal baffles creates a curved flow path that allows for particles of a large size to settle down, while at the same time, allowing the upward flowing mixture to travel smoothly into the overflow zone (20).

[0173] In a preferred embodiment, the overflow zone (20) has a tubular structure, with a cross section equal to that of the calming zone and the reaction zone (10) and is placed at the proximal end of the circulation reactor (100). The overflow zone (20) is provided with an outlet to receive the formed nickel or cobalt sulphate solution. In a preferred embodiment, the nickel or cobalt sulphate solution is evacuated when the predetermined acid ratio and / or nickel or cobalt concentration is obtained.

[0174] In an embodiment, the nickel or cobalt sulphate solution is evacuated at the bottom of the reaction zone (10).

[0175] In a preferred embodiment, the particles containing nickel or cobalt are fed while the nickel or cobalt sulphate solution is evacuated. The inventors found that feeding the particles containing nickel or cobalt when the circulation reactor (100) is open eliminates the risk of H2 formation.

[0176] In a preferred embodiment, water is added during the evacuation of the nickel or cobalt sulphate solution. This further reduces the residual sulphuric acid and the residual hydrogen peroxide. This is particularly advantageous at higher nickel or cobalt concentrations. Higher nickel or cobalt concentrations in the nickel or cobalt sulphate solution increase the boiling point and thus allow for a higher temperature difference (delta T). Higher nickel and cobalt concentrations also increase the capacity per batch. After evacuation, a safer loading is possible due to the elimination of H2 risk as compared to a continuous process.

[0177] In a preferred embodiment, after evacuation of the nickel or cobalt sulphate solution, a new cycle is started with the following process steps:

[0178] ■ feeding the aqueous medium, preferably water, hydrogen peroxide and sulphuric acid to the reaction zone (10) of the circulation reactor (100) preferably through a feeding section at the bottom of the circulation reactor (100); preferably the sulphuric acid and / or hydrogen peroxide are fed at high concentrations in order to obtain a resulting solution with a high nickel or cobalt concentration.

[0179] ■ When the column starts to overflow and the circulation reactor (100) is filled, the oxidative leach solution is recirculated; in a preferred embodiment, the hydrogen peroxide and acid addition rate are constant in time; in another embodiment, the hydrogen peroxide and acid addition rate are adjusted in function of the acid consumption.

[0180] ■ The recirculation is continued until the target nickel or cobalt concentration or nickel or cobalt density is reached. In a preferred embodiment according to the first aspect of the invention, the aqueous leach solution is circulated from the top of the column reactor (100) to a buffer tank and from the buffer tank to the bottom section of the column reactor (100). In this embodiment the buffer tank is a circulation tank (200).

[0181] The circulation tank (200) may comprise a mechanical stirrer. In a preferred embodiment according to the first aspect of the invention, the circulation tank (200) does not have a stirrer, and mixing in the reaction zone (10) and in the circulation tank (200) is achieved by circulating the aqueous leach solution.

[0182] In a second aspect, the present invention provides a system for producing nickel or cobalt sulphate comprising:

[0183] ■ one or more circulation reactors (100), preferably column reactors, configured to operate a process for preparing a nickel or cobalt sulphate solution according to the invention; and

[0184] ■ one or more buffer tanks configured to receive a nickel or cobalt sulphate solution from said circulation reactors (100).

[0185] The one or more circulation reactors (100) are configured to operate a process for the preparation of a nickel or cobalt sulphate solution (N) in a circulation reactor (100) comprising a reaction zone (10) having a height h, an overflow zone (20) and optionally a condensing section (30), said process comprising the steps of: i. feeding metal particles containing nickel or cobalt, respectively, to the reaction section (10) of said reactor (100); ii. feeding an aqueous solution, preferably water, via a feed section to said reaction section (10), thereby contacting this solution with said metal particles containing nickel or cobalt in said reaction section (10); iii. subsequently feeding hydrogen peroxide and sulfuric acid to said reaction section (10) to stimulate the leaching of the metal particles until the concentration or amount of sulphuric acid in the reactor is below a predetermined value; iv. oxidative leaching of the metal particles containing nickel or cobalt in the reaction zone (10), thereby obtaining a nickel or cobalt sulphate solution, respectively; and v. after step iv., evacuating said nickel or cobalt sulphate solution from said reactor (100). In a preferred embodiment, the one or more buffer tanks are in fluid communication with the circulation reactors (100), preferably with the overflow zone (20) of the circulation reactors (100).

[0186] In a preferred embodiment, the one or more buffer tanks are configured to receive the nickel or cobalt sulphate solution from the circulation reactors (100).

[0187] In a preferred embodiment, the present invention provides a system according to the second aspect of the invention wherein the buffer tanks comprise an outflow valve.

[0188] In a preferred embodiment, the buffer tanks are configured to produce a constant outflow of nickel or cobalt sulphate solution.

[0189] EXAMPLES

[0190] The following examples are intended to further clarify the present invention and it is nowhere intended to limit the scope of the present invention.

[0191] Example 1 - Circulation reaction column and feeding

[0192] Figure 1 shows schematically a process according to the invention in a circulation reactor (100) with the following reference numerals.

[0193] 100 Circulation reactor

[0194] 10 Reaction zone

[0195] 20 Overflow zone

[0196] 21 Overflow conduct optionally containing filter

[0197] 30 Condensing section

[0198] 40 H2 detector

[0199] 50 Heating and / or insulation jacket (exterior)

[0200] 60 Column and coating layer

[0201] 70 Rubber layer

[0202] 200 Circulation or buffer tank

[0203] The circulation reactor (100) comprises a comprising a reaction zone (10) having a height h, an overflow zone (20), an overflow conduct (21) optionally containing a filter, means to evacuate the acidic aqueous medium at a predetermined volume of said acidic aqueous medium and means to circulate said evacuated acidic aqueous medium to the feed section of the circulation reactor (100); optionally a condensing section (30) and optionally a H2 measurement device (40).

[0204] Figure 2 shows an exemplary cross section of the circulation reactor (100) comprising an insulation and / or heating jacket (50), the column and coating (60) and a rubber layer (70).

[0205] The aqueous medium and optionally the sulphuric acid solution inflow of the column goes through a heat exchanger. This allows preheating without the need to preheat the whole circulation tank (200), thus limiting evaporation losses in this reactor.

[0206] Secondly, the column is wrapped in a heating and insulation jacket (50) so that additional heat can be introduced. This allows preheating of the column and avoiding heat losses through the wall.

[0207] In a preferred embodiment, the process of the invention comprises the following steps:

[0208] • Feeding nickel and water to the reaction zone (10) of the circulation reactor (100);

[0209] • Heating the water and the reaction zone (10) by partially evacuating the water and circulating until the nickel bed in the reaction zone (10) has an elevated temperature;

[0210] • Feeding sulphuric acid and hydrogen peroxide while circulating over the bed (upwards flow); in a preferred embodiment, leaching is done in countercurrent flow;

[0211] • Dissolving the nickel until the target nickel concentration or nickel density is reached;

[0212] • Stopping the feed of hydrogen peroxide and sulphuric acid while maintaining circulation, until all residual hydrogen peroxide is consumed, and the level of residual sulphuric acid is sufficiently low. ■ When the nickel sulphate solution has the predetermined nickel and residual sulphuric acid level, the nickel sulphate solution is evacuated from the circulation reactor; in a preferred embodiment, the nickel sulphate solution is evacuated from the bottom of the circulation reactor (100);

[0213] ■ Optionally new particles containing nickel are filled on top of the bed.

[0214] In a preferred embodiment, the process comprises the further step of:

[0215] ■ feeding water, hydrogen peroxide and sulphuric acid to the bottom of the reaction zone (10) at high concentrations of sulphuric acid and hydrogen peroxide; in a preferred embodiment, preheated water is fed to the reaction zone (10); this enables a smooth start of the leaching process.

[0216] ■ After the column starts to overflow and the circulation tank (200) is (partially) filled, the water supply is stopped and the acidic aqueous medium recirculated.

[0217] ■ Recirculation is continued until the target nickel concentration or nickel density is reached;

[0218] ■ The feed of hydrogen peroxide and sulphuric acid is stopped;

[0219] ■ Recirculation is continued until all residual hydrogen peroxide is consumed and until the concentration of residual sulphuric acid is sufficiently low;

[0220] ■ The nickel sulphate solution is evacuated; and

[0221] ■ Optionally, a new process is started.

[0222] Example 2 - Reaction zone temperature during and between cycles

[0223] Based on piloting according to Example 1, the inventors observed that contact with a hot bed of particles containing nickel is sufficient to start the leaching reaction.

[0224] The inventors further observed that the temperature of the liquid feed can be relatively low if the reaction bed has the required temperature.

[0225] The inventors further observed that pre-heating of the aqueous medium, preferably the water is required if the reaction bed does not have the temperature required to start the leaching reaction.

[0226] Accordingly, the inventors found that the time between two consecutive cycles should be kept short to ensure a sufficient temperature of the reaction zone (10).

[0227] Example 3 - Increase of sulphuric acid During piloting according to Example 1, the inventors observed higher leaching rates when operating at 12 g / L acid as compared to 10 g / L at the top of the reaction zone. The inventors believe that a concentration of sulphuric acid of 20 g / L at the top of the reaction zone (10) throughout the leaching ensures that feeding of hydrogen peroxide is kinetically limiting the reaction.

[0228] Consequently, the inventors believe that there is no benefit in working at higher acid concentrations than 20 g / L. The inventors observed further that difference with working at 10 g / L is significant.

[0229] Example 4 - Different phases of the semi-batch process

[0230] Figure 3 shows schematically a process according to the invention in a column reactor. In a preferred embodiment, the semi-batch process according the first aspect of the invention is comprising the following phases:

[0231] Phase 0: Loading the column reactor and the circulation tank

[0232] • Feeding metal particles containing nickel or cobalt and an aqueous medium to the reaction zone of the column reactor;

[0233] • Heating the aqueous medium and the reaction zone by evacuating the aqueous medium from the top of the column reactor and circulating the aqueous medium until the nickel bed in the reaction zone has an elevated temperature;

[0234] Phase 1 : Leaching

[0235] • Continuously feeding sulphuric acid and hydrogen peroxide while circulating over the bed (upwards flow); in a preferred embodiment, leaching is done in countercurrent flow of the leaching solution to the direction in which the cathodes have been added;

[0236] • Dissolving the metal particles containing nickel or cobalt until the target nickel or cobalt concentration or nickel or cobalt density is reached;

[0237] Phase 2: Residual acid removal

[0238] • If the imposed leaching rate during phase 1 is not fully reached, sulphuric acid and hydrogen peroxide will build up in the system.

[0239] • The acid removal step is initiated by stopping the sulphuric acid dosing, while the hydrogen peroxide dosing continues, yet preferably at a reduced rate.

[0240] • As the acid concentration decreases, additional heating may be required.

[0241] Phase 3: Hydrogen peroxide removal Stopping the feed of hydrogen peroxide and sulphuric acid while maintaining circulation, until all residual hydrogen peroxide is consumed, and the level of residual sulphuric acid is sufficiently low.

[0242] Phase 4: Discharging the system

[0243] ■ When the nickel sulphate solution has the predetermined nickel and residual sulphuric acid level, the nickel sulphate solution is evacuated from the column reactor; in a preferred embodiment, the nickel sulphate solution is evacuated from the bottom of the column reactor.

[0244] ■ Optionally new particles containing nickel or cobalt are filled on top of the bed.

[0245] Example 5 - Leach rate of semi-batch process

[0246] The experimental set-up that was used is represented in Figure 3. The column reactor is packed with 850 kg of nickel cut cathodes. Initially these are 2" x 2" when fed to the reactor, yet most of the cut cathodes in the reactor have already reduced dimensions due to partial dissolution in earlier leaching operations. The reactor diameter is 35.5 cm and the reactor is 4 m high from bottom to the overflow at the top. The circulation tank is filled with 300 L of water, the mixer inside the circulation tank is turned on (75 rpm) and the circulation pumps are started with a flow rate of 900 L / h. The solution is heated until the column inlet temperature is around 75°C and the outlet temperature is around 73°C meaning that the cathode bed in the column reactor is completely preheated. Then sulfuric acid is added to the solution until a concentration of 15 g / L H2SO4 is obtained. Next, both H2SO4 and H2O2 are dosed to the system: These reagents are dosed stoichiometrically (meaning 1 mol FhSC per 1 mol H2O2) to the solution just before entering the bottom of the reactor column with a constant rate of 23.8 kg / h of an 78% aqueous H2SO4 solution, equalling 190 mol / h H2SO4.

[0247] As the leaching reaction starts to take place, the temperature at the column outlet gradually increases until it reaches a stable value around 95 to 98°C. The leaching rate is 12.42 kg Ni / ton Ni in the column reactor / hour.

[0248] Water is dosed to compensate for evaporation. This phase is completed at the point when the solution has reached a density of 1.37 g / mL, which corresponds to a Ni concentration of 150 g / L. The acid removal phase is started by stopping the H2SO4 dosing while the column inlet temperature is increased to 80°C. The peroxide dosing during the acid removal was reduced to 25% of the dosing rate during the leaching phase. When the free acid content inside the buffer vessel is 12 g / l H2SO4, the system is ready to transition to the peroxide removal phase. The dosing of H2O2 is completely stopped while the sampling method and water dosing continue. The peroxide removal phase ends when the peroxide concentration approaches 0 g / l H2O2.

[0249] The final solution is drained from the column towards the circulation tank by reversing the pumping direction until a flow rate of around 700 L / h is reached.

[0250] The overall, cumulative, peroxide efficiency is 97.3%. The residual acid concentration is 9.6 g / l H2SO4. The maximum concentration of H2SO4 reached in the overflow of the reactor was 20.5 g / L. The maximum H2O2 concentration measured was 2.5 g / L. At the end of the batch, about 10 % of nickel in the column had reacted.

[0251] The leaching phase was about 8 hours, the acid removal step about 1 hour and the peroxide removal step took about 1 hour. The total time to complete the batch process was about 10 hours. This corresponds to an average leach rate over the total duration of the semi-batch process of 9.95 kg Ni / ton Ni per hour.

[0252] Comparative Example 6 - Leach rate of continuous process

[0253] A continuous process was executed in the same column that was used in Example 5, yet using a continuous dosing of acid, hydroxide peroxide and Ni cut cathodes. In this example, the circulation reactor is filled with 300 L of a nickel sulphate solution with a concentration of 120 g / L Ni. While heating to 80°C, this solution is pumped over the reactor with a constant flowrate of 900 L / h. After reaching a stable temperature, acid and peroxide solution dosing was started at a 1 : 1 stoichiometric molar ratio and at a very low rate of 50 mol hhSC / h. Meanwhile water was continuously added to the circulation reactor to maintain the concentration of the solution around 120 g / L. Furthermore, a fraction of the solution from the overflow of the column is continuously taken out, to maintain the system at a constant volume: This evacuated fraction is the product solution, which is continuously harvested. Meanwhile the outflow of Ni in the product solution was compensated for by adding additional cut cathodes to the reactor.

[0254] Gradually the addition rate of H2SO4 and H2O2 is increased, until the product solution reaches a free acid concentration of 10 g / l, which is comparable to the solution in Example 5.

[0255] It was found that in this way, a maximal leach rate of 7.4 kg Ni / ton Ni per hour could be achieved without exceeding 10 g / L H2SO4 in the product solution. A further increase of leach rate would result in a more incomplete reaction and hence more residual acid in the product solution. Thus, the average leach rate in Example 5 is 34 % higher than in a corresponding continuous process with a similar yield on hydrogen peroxide. This is explained by the lower amount of free acid in solution, and hence less aggressive leach conditions, that can be applied in a continuous process for a similar product quality.

Claims

CLAIMS1. A semi-batch process for the preparation of a nickel or cobalt sulphate solution in a column reactor (100) comprising a reaction zone (10), said process comprising the steps of: i. feeding metal particles containing nickel or cobalt, respectively, to a reaction zone (10) of said column reactor (100); ii. feeding an aqueous medium to said reaction zone (10); iii. feeding sulphuric acid and hydrogen peroxide via a feed section to the reaction zone (10), thereby contacting hydrogen peroxide with said metal particles containing nickel or cobalt in an acidic aqueous medium; iv. simultaneously with step iii., circulating said acidic aqueous medium by evacuating a fraction of said acidic aqueous medium from said reactor (100) and by recirculating the evacuated fraction to said reactor (100) until a concentration of nickel or cobalt of at least 80 g / L, respectively, and a residual acid concentration below 20 g / L in said nickel or cobalt sulphate solution is achieved; and v. after step iv. evacuating said nickel or cobalt sulphate solution from said column reactor (100).

2. Process according to claim 1, whereby feeding of sulphuric acid and hydrogen peroxide in step iii. comprises the subsequent steps of: a. feeding sulphuric acid and hydrogen peroxide in a molar ratio of sulphuric acid to hydrogen peroxide of 0.9: 1.0 to 1.1 : 1.0; b. feeding hydrogen peroxide to further reduce the residual acid concentration of said nickel or cobalt sulphate solution.

3. Process according to claim 2, whereby the sulphuric acid content of the acidic aqueous medium in step iii. a. entering the bottom of the reaction zone (10) is between 15 and 60 g / L.

4. Process according to any of claims 1 to 3, whereby the residual amount of sulphuric acid of said nickel or cobalt sulphate solution evacuated in step v. is between 2 g / L and 15 g / L.

5. Process according to any of claims 1 to 4, whereby the concentration of nickel or cobalt in said nickel or cobalt sulphate solution, respectively, evacuated in step v. is between 80 g / L and 200 g / L.

6. Process according to any of claims 1 to 5, whereby circulating in step iv. is continued after step iii. is ended, until hydrogen peroxide in the nickel or cobalt sulphate solution is substantially exhausted.

7. Process according to any of claims 1 to 6, whereby the molar ratio of the total amount of hydrogen peroxide fed in step iii. to the total amount of sulphuric acid fed in step ii. and iii. is more than 0.9 and less than 1.1.

8. Process according to any of claims 1 to 7, whereby at least 80 wt.% of the initial amount of particles containing nickel or cobalt introduced in the column reactor have not reacted with the sulphuric acid and hydrogen peroxide when the process is interrupted and the nickel or cobalt sulphate solution is evacuated.

9. Process according to any of claims 1 to 8, whereby said aqueous medium fed in step ii. comprises sulphuric acid in a concentration of 5 to 30 g / L.

10. Process according to any of claims 1 to 9, whereby the aqueous medium entering the reaction zone (10) in steps ii., iii. and iv. has a temperature from 50 °C to 80 °C, preferably from 70 °C to 80 °C, even more preferably from 75 °C to 80 °C.

11. Process according to any of claims 1 to 10, whereby the reaction temperature at the top of the reaction zone (10) is between 80 °C and the boiling point of the leaching solution, preferably from 85 °C to 99 °C.

12. Process according to any of claims 1 to 11, whereby the metal particles containing nickel or cobalt are electrolytically obtained.

13. Process according to any of claims 1 to 12, whereby said metal particles containing nickel or cobalt comprise nickel or cobalt, respectively, in an amount of at least 96 wt.% relative to the total weight of said metal particles.

14. Process according to any of claims 1 to 13, whereby the column reactor (100) comprises an insulation jacket (50).

15. Process according to any of claims 1 to 14, whereby the pressure in the headspace above the reaction zone (10) is atmospheric pressure or an under-pressure of less than 0.2 atm.

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