EP4731799A1

EP4731799A1 - Batch process for the oxidative leaching of nickel and cobalt

Info

Publication number: EP4731799A1
Application number: EP24737432.5A
Authority: EP
Inventors: Margot NEVEN; Bart KLAASEN; Werner VERDICKT
Original assignee: Umicore NV SA
Current assignee: Umicore NV SA
Priority date: 2023-06-26
Filing date: 2024-06-26
Publication date: 2026-04-29
Also published as: WO2025003271A1

Abstract

The present invention provides a process for the batch preparation of a nickel or cobalt sulphate solution in a reactor, whereby metal particles containing nickel or cobalt, respectively, are reacted with sulphuric acid, and whereby hydrogen peroxide is added until the sulphuric acid is sufficiently depleted.

Description

BATCH PROCESS FOR THE OXIDATIVE LEACHING OF NICKEL AND COBALT

TECHNICAL FIELD

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

INTRODUCTION

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

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.

Next to lithium cobalt oxide, lithium manganese oxide and lithium iron phosphate, lithium nickel manganese cobalt oxide ("NMC", LiNixMn_yCo_zO2) and lithium nickel cobalt aluminium oxide ("NCA", LiNixCoyAlzOz) 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.

The rising demand for electric vehicles (EV) 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.

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 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: Ni + H2O2 + H2SO4 -> NiSO₄ + 2 H2O

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:

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

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.

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

JP 2011/126757 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.

Such processes may, however, suffer from entrainment of non-reacted metal fines in the resulting process output and slow leaching rates by using O2 as oxidizing agent, that is injected as finely dispersed bubbles of air or oxygen into a bed of metal nickel masses.

WO 2022/053 448 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, continuously 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.

SUMMARY

The current invention provides a solution for at least one of the above-mentioned problems by providing a batch 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.

The process is performed batchwise with a high initial acid concentration, controlled temperature, and controlled hydrogen peroxide (H2O2) injection rates.

The inventors have found that under such conditions, the conversion rate of nickel to nickel sulphate (NiSC ) is maximized and the formation of H2 is very limited. This optimizes the capacity of the column and increases process safety. Similar conclusions were deduced for the leaching of cobalt.

The inventive process is schematically shown in Figure 1.

Accordingly, the general inventive concept of the invention is a batch process for the preparation of a nickel or cobalt sulphate solution (N) in a reactor (100) comprising a reaction zone (10), 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 sulphuric acid solution via a feed section to said reaction section (10) to obtain a concentration or amount of sulphuric acid above a predetermined value, thereby contacting sulphuric acid with said metal particles containing nickel or cobalt in said reaction section (10); Hi. subsequently feeding hydrogen peroxide 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).

Preferably, said reactor (100) is a column reactor.

In another aspect, mixing is achieved by circulating the aqueous leaching solution through the reaction zone (100).

More particularly, the present invention provides in a first aspect a batch process for the preparation of a nickel or cobalt sulphate solution (N) 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 the reaction zone (10) of said column reactor (100); ii. feeding an aqueous sulphuric acid solution with a concentration higher than 160 g/L via a feed section to said reaction zone (10), and circulating said leach solution through said column reactor (100);

Hi. subsequently, feeding hydrogen peroxide in a stepwise or gradually decreasing amount to said circulating leach solution entering the reaction zone (10) until the concentration of sulphuric acid is below 20 g/L, thereby obtaining a nickel or cobalt sulphate solution, respectively; and iv. after step Hi., evacuating said nickel or cobalt sulphate solution from said column reactor (100).

The inventors have found that a gradually or stepwise decrease of the dosing of H2O2 during the batch process enables highly efficient use of hydrogen peroxide, in combination with a limited batch duration and minimal H2 formation.

In a preferred embodiment according to the first aspect of the invention, the initial hydrogen peroxide concentration in the oxidative leach solution entering the reaction zone in step Hi. is between 5 g/L and 30 g/L, preferably between 5 and 20 g/L, more preferably between 5 and 15 g/L, even more preferably about 10 g/L. In a preferred embodiment according to the first aspect of the invention, the hydrogen peroxide concentration in the oxidative leach solution entering the reaction zone in step iii. is stepwise or gradually decreased to a final hydrogen peroxide concentration between 1 g/L and 15 g/L, preferably between 1 and 10 g/L, more preferably between 1 and 5 g/L, even more preferably about 3 to 5 g/L.

In a preferred embodiment according to the first aspect of the invention, said aqueous sulphuric acid solution fed in step ii. has a concentration of sulphuric acid higher than 50 g/L, more preferably higher than 160 g/L, preferably from 200 g/L to 400 g/L, preferably between 100 and 300 g/L, more preferably between 150 and 250 g/L and even more preferably between 175 and 225 g/L, most preferably between 200 g/L and 300 g/L.

In a preferred embodiment according to the first aspect of the invention hydrogen peroxide is fed in step iii. to the reaction section (10) until the concentration of sulphuric acid is below 25 g/L, preferably below 20 g/L, more preferably between 0 and 12 g/L, even more preferably between 2 g/L and 10 g/L such as 2 g/L, 4 g/L, 6 g/L, 8 g/L, 10 g/L or 12 g/L.

In a preferred embodiment according to the first aspect of the invention, the molar ratio of the total amount of hydrogen peroxide fed in step iii. to the sulphuric acid amount fed in step ii. is between 0.6 and 1.1, preferably between 0.6 and 1.0, more preferably between 0.8 and 1.0, more preferably is about 0.9, even more preferably between 0.95 and 1.05, and most preferably between 0.95 and 0.99.

In a preferred embodiment according to the first aspect of the invention, at least 60 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 batch process is interrupted and the nickel or cobalt sulphate solution is evacuated, more preferably at least 80 wt%, even more preferably at least 90 wt%.

In a preferred embodiment according to the first aspect of the invention, mixing in the reaction zone (10) is achieved by circulating the aqueous leaching solution through said reactor (100) in counter-current.

In another aspect, the aqueous sulphuric acid solution is fed at a temperature from 60 °C to 80 °C, preferably from 70 °C to 80 °C, even more preferably from 75 °C to 80 °C. In another aspect, the reaction temperature at the top of the reaction zone (10) is higher than 80 °C to the boiling point of the leaching solution, preferably from 85 °C to 100 °C, even more preferably from 92 °C to 99 °C.

In another aspect, the metal particles containing nickel or cobalt are electrolytically obtained, and preferably are cut cathodes.

In another aspect, 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.

In another aspect, the reaction column (100) further comprises an H2 detector (40).

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. 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 another aspect, the reactor (100) comprises an insulation and/or heating jacket (50).

In another aspect, the pressure above the reaction zone (10) is atmospheric pressure or an under-pressure of less than 0.2 atm.

In another aspect, the hydrogen peroxide is fed via a feed section to said reaction section (10) at an initial rate of 20 preferably from 25.5 g.L^.min'¹ to 27.5 g.L^.min'¹.

In another aspect, the provision of hydrogen peroxide gradually or stepwise decreases to a final rate of 1 preferably from 2.5 g. Lamin’ ¹ to 10 g.L^.min^-1, even more preferably from 2.5 g.L^.min^-1 to 7.5 g.L^.min’¹.

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

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

■ one or more buffer tanks configured to receive a nickel or cobalt sulphate solution from said reactors (100), preferably column reactors (100). In a preferred embodiment, said buffer tank comprises an outflow valve.

DESCRIPTION OF THE FIGURES

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

Figure 1 shows schematically a batch process according to the invention in a reactor.

Figure 2 shows the cross section of a reactor (100) of the present invention.

Figure 3 shows the acid circulation, the inflow and outflow temperature, the hydrogen peroxide yield fraction and as well as the leach rate at varying hydrogen peroxide injection rates of Example 2.

Figure 4 shows the acid concentration, the hydrogen peroxide yield and the temperature in function of the reaction time of Example 2.

Figure 5 shows the acid concentration and the hydrogen peroxide injection rate in function of the reaction time of Example 3.

Figure 6 shows the hydrogen peroxide yield and the hydrogen peroxide injection rate in function of reaction time of Example 3.

Figure 7 shows the influence of the bed height on the fractional leach rate of Example 4.

DETAILED DESCRIPTION OF THE INVENTION

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.

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: "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.

"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.

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

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.

Batch process

The process of the present invention is a batch process, i.e. a discontinuous process.

A batch process has several advantages versus a continuous process, including handling feed or reagents variability (e.g. Ni metal reactivity, or H2O2 quality), suppressing H2 formation during leaching and metal loading, increasing throughput, enabling low residual acid content, enabling high metal concentrations in the product solution, and more flexibility in general.

In the context of the present invention, the term "batch" is to be considered as a process in which the process does not have any continuous flow conditions. In a preferred embodiment, the process does not have a continuous outflow of the produced nickel and/or cobalt sulphate solution.

Consequently, the bed volume of metal particles containing nickel or cobalt decreases over the reaction time in the reaction zone (10) of the batch reactor (100).

In one embodiment, the batch process is stopped and the nickel and/or cobalt sulphate solution is evacuated when the particles containing nickel and/or cobalt have fully reacted with the sulphuric acid and hydrogen peroxide.

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

In a preferred embodiment, the batch process is interrupted and the nickel or cobalt sulphate solution is evacuated when the nickel and/or cobalt sulphate solution has the desired, i.e. a predetermined, residual acid content.

In a preferred embodiment, the batch 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 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 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 a substantial 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 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.%. 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.

Upfront loading of sulphuric acid and nickel or cobalt particles

The sulphuric acid solution is fed to the batch process upfront.

In a preferred embodiment of the invention, each batch leaching process uses each time a full amount of fresh sulphuric acid solution. The required concentration and volume of sulphuric acid that is loaded to the batch process upfront, is calculated with the knowledge of the target nickel or cobalt sulphate concentration in the product, and considering dilution during the process with H2O2, and considering water evaporation and potential compensation of evaporated water.

In a preferred embodiment, a stoichiometric amount of sulphuric acid is added versus the targeted total nickel or cobalt amount of the product solution.

The sulphuric acid solution is prepared by adding a predetermined amount of H2SO4 to a buffer tank or circulation tank, followed by diluting in water, thereby obtaining a temperature rise. If needed, further heating of the sulphuric acid solution is applied.

Nickel or cobalt metal may be fed to the batch process upfront.

In a preferred embodiment, Ni and Co are reloaded after evacuating the leach solution of the first batch process, before starting the next 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.

In an alternative embodiment, the Ni and Co particles are reloaded before evacuating the leaching solution, but after stopping the hydrogen peroxide 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. Nickel and cobalt

In a preferred embodiment, the nickel or cobalt is electrolytically produced and even more preferably is cut cathode material.

The inventors showed that the electrolytically produced nickel or cobalt cathodes can be successfully leached using the process of the present invention.

Leach solution

Leach solution means the aqueous solution comprising sulphuric acid in the reaction zone (10) of the reactor (100), into which the hydrogen peroxide is subsequently fed. In this context the terms leach solution, leaching solution, and oxidative leaching solution are used interchangeably.

In a preferred embodiment, the leaching is not a single-pass leaching. To enable a single-pass leaching the reactor or reaction column (100) needs to be cooled to ensure that the temperature does not exceed 100 °C, preferably does not exceed 99°C.

Concentrated nickel or cobalt sulphate solution

The batch 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.

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. The 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.

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.

Purification and further filtering

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, Mn, Fe, Al, F, C, Ca, Si, P, As, Cd, 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.

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 potassium hydroxide, potassium carbonate, nickel hydroxide, nickel 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.

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

Metal particles containing nickel or cobalt

In a preferred embodiment, the metal particles containing nickel or cobalt comprise nickel or cobalt in an amount of at least 97 wt.%, relative to the total weight of said metal particles, preferably at least 98 wt.% and more preferably at least 99 wt.%.

Said metal particles may further contain Co in an amount of up to 1 wt.%. Preferably said metal particles contain Ni in an amount of at least 99.5 wt.%.

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+ %.

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.

Hydrogen peroxide

Hydrogen peroxide used in the process is typically an aqueous solution with a hydrogen peroxide concentration of 30 to 60 wt.%, such as 50 wt.% or 35 wt% solution in water, and sulphuric acid has a concentration of 78 to 98 wt.% in water, preferably a 98 wt.% concentration in water.

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

In a preferred embodiment according to the first aspect of the invention, hydrogen peroxide is fed continuously during step iii. until the concentration of sulphuric acid is below 20 g/L. It was found that in order to achieve highly efficient use of hydrogen peroxide, in combination with a limited batch duration and minimal H2 formation, it is preferable to gradually or stepwise decrease the dosing of H2O2 during the batch process. In the initial phase of the oxidative leaching in step iii ., at high H2SO4 concentrations, the oxidative leaching is not kinetically limited by the acid concentration and the leaching rate is determined by the H2O2 dosing. The control of the heat balance is crucial in the strongly exothermic oxidizing leaching process. In this initial phase of the leaching process, the available cooling capacity sets an upper limit to the H2O2 dosing and thus the maximal leaching rate, because boiling due to reaction heat has a negative effect on hydrogen peroxide efficiency. By lowering the dosing of H2O2 when acid concentrations are low at the end of the process, the excessive decomposition of H2O2 to O2 is avoided.

In a preferred embodiment, the cumulative H2O2 efficiency for the full 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.

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.

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.

In a preferred embodiment, the present invention provides a process according to the first aspect, whereby the hydrogen peroxide concentration in said oxidative leach solution entering the reaction zone in step iii., initially is between 5 and 30 g/L, preferably between 5 and 20 g/L, more preferably between 5 and 15 g/L, even more preferably about 10 g/L.

In a preferred embodiment, the present invention provides a process according to the first aspect, whereby the hydrogen peroxide content of said oxidative leach solution entering the reaction zone in step iii. is gradually or stepwise decreased during step Hi. to a hydrogen peroxide concentration between 1 and 15 g/L, preferably between 1 and 10 g/L, more preferably between 1 and 5 g/L, even more preferably about 3 to 5 g/L.

In this context, the term "initially" is to be considered as equivalent to "at its maximum", namely the initial concentration of hydrogen peroxide in the oxidative leach solution refers to the maximum concentration of hydrogen peroxide in the oxidative leach solution that is dosed for leaching in step Hi. For example, a short period of dosing very low amounts of hydrogen peroxide during the process start-up to bring the reagents to a stable temperature is not to be considered here.

In a preferred embodiment, the hydrogen peroxide feeding rate is gradually or step- wise decreased.

In a preferred embodiment, the hydrogen peroxide feeding rate is stepwise decreased during the batch process in at least 2 steps, more preferably in at least 3 steps, most preferably in at least 4 steps.

In the context of this invention, the terms hydrogen peroxide "dosing", or "feeding" or "injection" or "provision" or "supply" or "flow" are used interchangeably, and all refer to the amount of hydrogen peroxide that is added to the circulating oxidative leaching solution, just before said oxidative leaching solution is re-entering the reactor (100) at its bottom section.

Likewise, in the context of this invention, the terms hydrogen peroxide "dosing rate", or "feeding rate" or "injection rate" or "provision rate" or "supply rate" or "flow rate" are used interchangeably, and all refer to the amount of hydrogen peroxide per unit of time that is added to the circulating oxidative leaching solution, just before said oxidative leaching solution is re-entering the reactor (100) at its bottom section.

In a preferred embodiment, the hydrogen peroxide is fed at an initial rate of 20 g.L' ^min'¹ to 30 g.L'¹. min^-1, preferably from 25.5 g.L'¹. min'¹ to 27.5 g.L'¹. min'¹.

In a preferred embodiment, the provision of hydrogen peroxide gradually or stepwise decreases to a final rate of 1 g.L'¹. min'¹ to 15 g.L'¹. min'¹, preferably from 2.5 g.L' ^min'¹ to 10 g.L'¹. min'¹, even more preferably from 2.5 g.L'¹. min'¹ to 7.5 g.L'¹. min'

In a preferred embodiment, the feeding of the hydrogen peroxide is adjusted in function of the temperature at the top of the reactor. In a preferred embodiment, the feeding of the hydrogen peroxide is adjusted in function of the temperature at the top of the reactor and the recirculation flow rate.

In a preferred embodiment, the leaching rate is regularly determined by intermediate measurements of the residual acidity to calculate the equivalent hydrogen peroxide consumption over the past interval.

In one embodiment, when this consumption is equal to the supply rate of hydrogen peroxide, the flow rate is kept constant.

In one embodiment, when the supply rate exceeds consumption, the flow is reduced to ensure the addition of only a minimal excess of hydrogen peroxide is added during the batch.

In one embodiment, the supply rate of hydrogen peroxide is kept constant during the complete batch.

In a preferred embodiment, the supply rate is of hydrogen peroxide is kept constant during the complete batch, and said oxidative leach solution comprises hydrogen peroxide in an amount of 1 to 25 g/L, more preferably in an amount of about 1 to 15 g/L, and even more preferably in an amount of about 3 to 10 g/L.

The gradual or stepwise decrease of the hydrogen peroxide concentration is preferably carried out over a time frame of 5 to 10 hours.

In a preferred embodiment, the temperature of the inflow is increased to compensate for the lower exothermic effect of the reaction.

In a preferred embodiment, towards the end of the leaching, when the hydrogen peroxide flow is reduced, the temperature of the incoming flow is almost equal to the outflow temperature.

In a preferred embodiment, the lower limit of the H2O2 injection is determined as the minimal value for which no H2 is produced.

In one embodiment, the metal feed is fixed and stable in terms of reactivity, and H2O2 is fed according to a predetermined addition profile.

Preferably, the H2O2 injection rate is gradually or stepwise decreased with at least 20% over a time frame of the first 5 hours of the batch process, more preferably with at least 40%, most preferably with a least 60%. Preferably, the H2O2 injection rate is gradually or stepwise decreased with at least 20% over a time frame of the first 5 hours of the batch process, more preferably over a time frame of 4 hours, most preferably over a time frame of 3 hours.

Preferably, the H2O2 injection rate is gradually or stepwise decreased with at least 20% over the first half of the total batch duration, more preferably with at least 30%, even more preferably with a least 50%, most preferably with a least 70%.

Preferably, the H2O2 injection rate is gradually or stepwise decreased with at least 10% over the first quarter of the total batch duration, more preferably with at least 20%, even more preferably with a least 30%, most preferably with a least 60%.

Preferably, the H2O2 injection rate at the end of the batch process is less than 30% of the initial H2O2 injection rate, more preferably less than 20%, even more preferably less than 15%, most preferably about 10 to 15 %.

Sulphuric acid

In a preferred embodiment, the sulphuric acid is fed at a concentration from 200 g/L to 400 g/L, preferably from 225 g/L to 375 g/L, even more preferably from 250 g/L to 350 g/L. In an even more preferred embodiment according to the first aspect of the invention, the sulphuric acid is fed with a concentration higher than 160 g/L, preferably between from 200 g/L to 300 g/L.

In a preferred embodiment, the sulphuric acid is fed at a temperature from 60 °C to 80 °C, preferably from 70 °C to 80 °C, even more preferably from 75 °C to 80 °C.

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.

Residual sulphuric acid

In a preferred embodiment, the reactor is controlled to ensure that the nickel or cobalt sulphate solution obtained from said reactor has a residual sulphuric acid content (CSA,O), i.e., the sulphuric acid content when evacuating the target nickel or cobalt sulphate solution from the reactor, 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.

In a preferred embodiment, the nickel or cobalt sulphate solution obtained from said circulation reactor and having a residual sulphuric acid content (CSA,O) is used for leaching of compressed metal waste in a subsequent leaching reactor, i.e. leaching column.

Delta sulphuric acid consumption

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 the target nickel or cobalt sulphate solution obtained from the reactor to the sulphuric acid concentration (CSA ) of the oxidative leach solution which is initially fed to the reactor, i.e., at the start of the batch reaction, is lower than 0.70, lower than 0.65, lower than 0.60, lower than 0.55, or even lower than 0.50. Preferably, said ratio is between 0.5 and 0.05. 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.

In a further preferred embodiment, said ratio is lower than 0.05. Preferably said ratio is between 0.05 and 0.001, most preferably between 0.05 and 0.005, even more preferably between 0.03 and 0.01.

Ratio of hydrogen peroxide to sulphuric acid

In a first preferred embodiment, the present invention provides a process according to the first aspect, whereby hydrogen peroxide is fed to the reactor during the batch reaction in a sub-stoichiometric amount relative to the amount of sulphuric acid added in step ii. of the process. E.g., the oxidative leach solution may comprise 0.4 mol/L hydrogen peroxide and 0.5 mol/L sulphuric acid.

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.

In a second, alternative embodiment, the present invention provides a process according to the first aspect, whereby sulphuric acid and hydrogen peroxide are present 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.

An excess of hydrogen peroxide supports further depletion of the sulphuric acid. 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 reactor effluent.

Off-gas treatment

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.

Pressure

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

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 reactor. Bed height h

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 reaction zone 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.

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

Column reactor

The inventive process can proceed in a column. In the context of the present invention, the term "column" is to be considered equivalent to the term "column reactor", "packed bed" or "packed bed reactor", "tower" or "tower reactor" and refers to a column reactor having a substantially cylindrical form having an internal diameter D and a height H.

The column reactor (100) consists of a vertically arranged cylindrical column and is arranged to operate without mechanical agitation, preferably in the upflow mode, i.e. fluid flow from bottom to top of the column.

The column reactor (100) is further characterized by

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

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

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

Optionally, the column reactor (100) comprises a condensing section (30).

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

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

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

Further, the column 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 column reactor.

Further, the column reactor (100) is preferably also equipped with means for radially and uniformly distributing the oxidative leach solution in the feed section of the column 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.

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

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 column 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.

A proper geometry of the liquid volume in the column 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.

In a preferred embodiment, said column 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.

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

In preferred embodiment, the reaction column further comprises an H2 detector.

Bed height h

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, more preferably from 2.5 m to 10 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, more preferably from 1 m to 10 m.

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

At a sufficiently high sulphuric acid level, for example as from 50 g/L, more preferably as from 100 g/L to 300 g/L, the impact of the bed height is less pronounced as compared to lower sulphuric acid levels, for example less than 50 g/L.

Feeding into reaction zone

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 in water is fed in via a bottom section of said column reactor (100) to said reaction section, and whereby said nickel or cobalt sulphate solution is evacuated in step iv. via a top section of said column reactor (100) from said reaction section.

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 batch reaction, or after the completion of the batch reaction. Alternatively, said metal particles may be fed continuously or intermittently, preferably intermittently.

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.

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).

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.

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). 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.

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). 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 column reactor (100). The overflow zone (20) is provided with an outlet to receive the formed nickel or cobalt sulphate solution.

Circulation

In a preferred embodiment, mixing of the reactants in the reaction zone (10) is achieved by circulating the aqueous leaching solution. A predetermined volume of said acidic aqueous medium and/or leach solution is continuously evacuated and recirculated to the feed section of the circulation reactor (100). In the context of the present invention, the circulation reactor is a column reactor.

In a preferred embodiment, a predetermined volume of said acidic aqueous medium and/or leach solution is continuously evacuated at the top of the column reactor, and recirculated to the feed section of the column reactor (100) throughout step ii. and step iii.

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

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

In a preferred embodiment, the circulation rate is higher than 3 bed volumes per hour, more preferably between 5 and 20 bed volumes per hour, even more preferably 5 to 10 bed volumes per hour.

In another embodiment, the circulation rate is varied during the process.

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.

In a preferred embodiment, the circulating leach solution is cooled in the first part of leaching in step iii.

In a preferred embodiment, the circulating leach solution is cooled in the first part of leaching in step iii. and heated a second part of step iii.

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. Counter-current circulation

In a preferred embodiment of the first aspect of the invention, the acidic aqueous medium is circulated in counter-current. 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). In the context of the present invention, the circulation reactor is a column reactor.

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 Ni or Co loading from the top, has the advantage that the fines are accumulated in the lower area of the reaction zone (10).

System

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

■ one or more buffer tanks configured to receive a nickel or cobalt sulphate solution from said reactors (100), preferably column reactors.

The one or more reactors (100) are configured to operate a batch process for the preparation of a nickel or cobalt sulphate solution (N) in a 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 sulphuric acid solution via a feed section to said reaction section (10) to obtain a concentration of sulphuric acid is above a predetermined value, thereby contacting sulphuric acid with said metal particles containing nickel or cobalt in said reaction section (10); iii. subsequently feeding hydrogen peroxide to said reaction section (10) to stimulate the leaching of the metal particles until the concentration of sulphuric acid 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 reactors (100), preferably with the overflow zone (20) of the reactors (100).

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

In a preferred embodiment, the buffer tanks comprise an outflow valve.

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

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 or circulation vessel (200).

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.

EXAMPLES

The following examples are intended to further clarify the present invention, and is nowhere intended to limit the scope of the present invention.

Example 1 - Reaction column and feeding

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

100 Column reactor

10 Reaction zone

20 Overflow zone 21 Overflow conduct optionally containing filter

30 Condensing section

40 H2 detector

50 Heating and/or insulation jacket (exterior)

60 Column and coating layer

70 Viton rubber layer

200 Circulation tank

The column 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, optionally a condensing section (30) and optionally a H2 measurement device (40).

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

The aqueous sulphuric acid solution inflow of the column goes through a heat exchanger. This allows preheating of the solution without the need to preheat the whole circulation tank 200, limiting evaporation losses in this reactor. 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.

In a preferred embodiment, the following process steps are carried out:

■ Prepare the acid solution by adding the stoichiometric amount of acid to the water and heat up to the required starting temperature. By adding the acid to the water, a temperature rise is already obtained.

■ Start to circulate the acid solution over the reaction zone with a limited hydrogen peroxide injection rate to heat up the column.

■ When temperature is stable, increase the hydrogen peroxide injection to reach the maximal leach rate and/or maximal temperature at the overflow zone (20), ideally just below boiling point. The circulating leach solution passes through a heat exchanger for cooling before re-entering the reaction zone (10). ■ Acid is consumed as the leaching progresses and the leach rate will decline. Adjust the hydrogen peroxide injection to limit the excess of hydrogen peroxide added, in line with the decreasing leaching rate.

■ Significant evaporation will occur during the leaching which must be compensated for during the batch.

■ At the end of the leach, the reaction heat becomes so low that cooling is no longer required and even heating may be necessary to minimize batch time. A temperature just below the boiling point, around 100 °C, is optimal to maintain maximal leach rates at low acidity towards the end of the leach.

Controlling the hydrogen peroxide injection rate ensures at least a cumulative hydrogen peroxide efficiency of > 80%.

Example 2 - Selecting the initial hydrogen peroxide injection rate

The aqueous sulphuric acid solution is supplied to the column reactor (100) upfront. The supply of peroxide is gradually and stepwise decreased during the batch, in line with decreasing reactivity.

To achieve this, the leaching rate is regularly determined by intermediate measurements of the residual acidity in the system.

The equivalent hydrogen peroxide consumption over the past interval is calculated. When this consumption is equal to the supply rate of peroxide, the flowrate is kept constant. When the supply rate exceeds consumption, the flow is reduced to ensure the addition of only a minimal excess of peroxide is added during the batch. This excess hydrogen peroxide will not be consumed for leaching but rather decompose. Consequently, the overall hydrogen peroxide efficiency declines.

The feed is more reactive at high temperature. However, high temperatures also increase peroxide decomposition and therefore reduce peroxide efficiency. Hence a balance is needed between reactivity and decomposition. The temperature is kept below the boiling point at around 95 °C. Heat is released during the exothermic leaching reaction (423.8 kJ/mol Ni leached). Hence, in order to maintain 95 °C at the overflow zone (20), an adjustment of the inflow temperature is needed.

Yet, to start such a batch, the reactivity of the particular feed at the start of the batch needs to be assessed in order to define the initial rate of peroxide supply. This is done in an upfront test that screens for the maximal leaching rate and the corresponding maximal hydrogen peroxide dosing rate. This test is illustrated in Example 2.

Ni cathodes with a size of l"xl" were used as nickel particles. Other types of cathodes can be equally suitable for the process of the present invention. About 40 L of about 250 gram/L H2SO4 solution was circulated over the reactor column with a bed volume of about 7.5 L and a flow rate of 8.5 bed volumes per hour. The hydrogen peroxide was injected as a 35 wt% aqueous solution.

In a first experiment shown in Figure 3 the initial hydrogen peroxide input was set at 20 g.min^-1. The hydrogen peroxide addition (35 wt% solution) was increased to 40 g/min in order to increase reaction rate (and temperature). This resulted in an overshoot in temperature, boiling of the solution and therefore a negative effect on the hydrogen peroxide efficiency. Consequently, an injection rate of 40 g.min^-1 is too high. Accordingly, the present invention teaches to keep the injection rate at 30 g.min^-1 or less. An initial injection rate of 25 g.min^-1 produces optimal hydrogen peroxide efficiency.

In a second experiment shown in Figure 4, the initial hydrogen peroxide injection was directly set at 25 g.min^-1, that is the optimal initial hydrogen peroxide injection rate. Figure 4 shows the acid concentration, the hydrogen peroxide yield and the temperature in function of the reaction time.

Example 3 - Leach rates at variable hydrogen peroxide injection rate

The conditions of Example 1 and Example 2 were applied with the following precisions. The batch time was 14.5 h for a 25 L batch process with a bed height of 1 m Ni cathodes (±26 kg), a column diameter of about 0.1 m, and a flow rate of 5.1 bed volumes per hour.

The supply of peroxide is gradually and stepwise decreased during the batch, in line with decreasing reactivity. To achieve this, the leaching rate is regularly determined by intermediate measurements of the residual acidity in the system. The equivalent hydrogen peroxide consumption over the past interval is calculated. When this consumption is equal to the supply rate of peroxide, the flowrate is kept constant. When the supply rate exceeds consumption, the flow is reduced to ensure the addition of only a minimal excess of peroxide is added during the batch. The temperature is kept below the boiling point at around 95 °C. In order to maintain 95 °C at the overflow zone (20), an adjustment of the inflow temperature is needed.

The results are shown in Figure 5 and Figure 6. Figure 5 shows the acid concentration, the leach rate, and the stepwise decreasing hydrogen peroxide injection. In Figure 5 the leach rate is expressed as g nickel leached per kg of nickel in the column per hour, and the H2O2 injection as gram of hydrogen peroxide (35 wt% solution) per minute.

The initial leach rate is > 20 g Ni.kg^-1of Ni in the column reactor.h'¹ at high acid concentration. The reactivity of the feed declines during the batch. Therefore, the hydrogen peroxide injection is regularly balanced to reach a hydrogen peroxide efficiency as close as possible to 100% (stoichiometric). The H2O2 concentration in the oxidative leaching solution entering the reaction zone was decreased from about 13 g/L to about 3 g/L during the experiment. The yield on H2O2 is shown in Figure 6.

A total cumulative (average) rate of 12 g.kg'Th'¹ is obtained when leaching from high acidity until a final acid concentration of 6 g/L is obtained. The total peroxide supplied was 110% stoichiometric vs Ni or 0.64 kg l- Ch/kg Ni leached ( = 1.82 kg H2O2 (35 wt.%)/kg Ni leached).

The scatter in the first part of the leach shown in Figure 5 and Figure 6 is probably linked to variations on (manual) acid titrations. In an industrial setup, less variability is expected. Despite this scatter, on average a good efficiency is obtained by gradually reducing the H2O2 dosing rate from 25 g/min to 6 g/min over 5 hours.

In parallel, the temperature of the inflow is increased to compensate for the lower exothermic effect of the reaction. Towards the end of the leaching, when the hydrogen peroxide flow is reduced, the temperature of the incoming flow is almost equal to the outflow temperature. This is necessary to be able to use the last acid and thus achieve a low acid concentration.

The H2 formation was very limited and mainly present at the start of the leach as a result of a high acid concentration.

The experiment of Example 3 was repeated for different nickel feeds, namely pellets (Example 3b), cut cathodes (Example 3c), and rounds (Example 3d), with a similar H2O2 dosing strategy. The used parameters and results are shown in the table below in comparison to Example 3:

In these examples controlling the hydrogen peroxide injection rate ensured at least a cumulative hydrogen peroxide efficiency of 88% or more (see also table above).

In addition, the average fractional leaching rates (g Ni/ kg Ni in column per hour) during the experiment as a function of the decreasing H2SO4 concentration are shown below:

Average fractional leach rates at different acid concentration ranges.

Example 4 - Influence of bed height

The influence of the bed height was tested with the l"xl" cathodes. At the start of the experiment, the column is filled with 0.5 m bed height Ni metal. The results were compared with a test using a bed height of 1 m.

For both scenarios, a full leach batch was performed, as described in example 1. This resulted in leaching rates presented in Figure 7.

The fractional leach rate is expressed per kg of Ni in the reaction column. Different bed heights are compared. Doubling the bed height allows to leach at least twice as fast.

An increased bed height also leads to a more efficient use per kg inventory, represented by the slightly higher leaching rate. In industrial settings the leach height might be even higher such as from 1 m to 3 m, preferably from 1.5 m to 2.5 m.

With increased bed heights, overall leaching capacity generally is limited by cooling needs (in the first part) and heating capacity (in the second part) of the batch process In industrial settings the heat losses will be relatively lower than in the experiments discussed herein on pilot scale.

Comparative Example 5 - Single pass leaching

In a single pass leaching configuration, the hydrogen peroxide injection rates are adapted to match the inflow of acid at least at a stoichiometric level. Accordingly, the nickel cathode metal would be partially dissolved, and the residual acid could be used to process finer nickel materials. The reactor or reaction column (100) needs cooling to ensure that the temperature does not exceed 100 °C, preferably does not exceed 99°C.

Single pass leaching, without cooling the reaction column, does not work for oxidative leaching with H2O2, because in this case the H2O2 injection rates needs to match the inflow of acid at least at a stoichiometric level since all Ni needs to be dissolved in one pass. Yet this introduces so much enthalpy that the temperature will by default exceed 100°C, significantly contributing to H2O2 decomposition, which will then again accelerate heat. Therefore, recirculation of the leaching solution with cooling of the overflow is preferred.

Comparative Example 6 -Constant maximal H2O2 addition rate

An experiment was designed whereby the optimal initial H2O2 addition rate determined in Example 2 of 25 g. min^-1 was set, and kept constant for about the whole batch duration. Hereby the duration of the batch process would be minimized, however, due to excessive H2O2 decomposition, it is not practically feasible to apply this high H2O2 injection rate for the whole experiment, and the experiment was stopped.

Claims

1. A batch process for the preparation of a nickel or cobalt sulphate solution (N) 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 the reaction zone (10) of said column reactor (100); ii. feeding an aqueous sulphuric acid solution with a concentration higher than 160 g/L via a feed section to said reaction zone (10), and circulating said leach solution through said column reactor (100); iii. subsequently, feeding hydrogen peroxide in a stepwise or gradually decreasing amount to said circulating leach solution entering the reaction zone (10) until the concentration of sulphuric acid is below 20 g/L, thereby obtaining a nickel or cobalt sulphate solution, respectively; and iv. after step iii., evacuating said nickel or cobalt sulphate solution from said column reactor (100).

2. Batch process according to claim 1, whereby the initial hydrogen peroxide concentration in said leach solution entering the reaction zone (10) in step iii. is between 5 g/L and 30 g/L.

3. Batch process according to claim 1 or 2, whereby the hydrogen peroxide concentration in said leach solution entering the reaction zone (10) in step iii. is stepwise or gradually decreased to a final hydrogen peroxide concentration between 1 g/L and 15 g/L.

4. Batch process according to any one of the preceding claims, whereby said aqueous sulphuric acid solution fed in step ii. has a concentration of sulphuric acid between 200 g/L and 300 g/L.

5. Batch process according to any one of the preceding claims, whereby hydrogen peroxide is fed in step iii. until the concentration of sulphuric acid is between 2 g/L and 10 g/L.

6. Batch process according to any one of the preceding claims, whereby the molar ratio of the total amount of hydrogen peroxide fed in step iii. to the sulphuric acid amount fed in step ii. is between 0.95 and 0.99.

7. Batch process according to any one of the preceding claims, whereby 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 batch process is interrupted and the nickel or cobalt sulphate solution is evacuated.

8. Batch process according to any one of the preceding claims, whereby mixing in the reaction zone (10) is achieved by circulating the aqueous leaching solution through said reactor (100) in counter-current.

9. Batch process according to any one of the preceding claims, whereby the aqueous sulphuric acid solution is fed at a temperature from 60 °C to 80 °C, preferably from 70 °C to 80 °C.

10. Batch process according to any one of the preceding claims, 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 92 °C to 99 °C.

11. Batch process according to any one of the preceding claims, whereby the metal particles containing nickel or cobalt are electrolytically obtained.

12. Batch process according to any one of the preceding claims, 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.%, relative to the total weight of said metal particles.

13. Batch process according to any one of the preceding claims, whereby the reactor (100) further comprises a H2 detector (40).

14. Batch process according to any one of the preceding claims, whereby the reactor (100) comprises an insulation and/or heating jacket (50).

15. Batch process according to any one of the preceding claims, whereby the pressure in the reaction zone (10) is atmospheric pressure or an under-pressure of less than 0.2 atm.