Process for the oxidative leaching of nickel and / or cobalt with ferric iron

Abstract

The present invention provides a process to prepare a nickel and / or cobalt salt solution via oxidative leaching of nickel and / or cobalt with ferric iron. The process comprises the steps of: i. contacting metal particles containing nickel (0) and / or cobalt (0) in a leaching reactor (RL) with an aqueous ferric salt solution, thereby obtaining an aqueous nickel and / or cobalt salt solution, respectively, comprising a ferrous salt; and ii. contacting an aqueous nickel and / or cobalt salt solution comprising ferrous salt with an oxidizing agent in presence of a mineral acid in an oxidation reactor (RO), thereby obtaining an aqueous nickel and / or cobalt salt solution, respectively, comprising ferric salt.

Description

[0001] Process for the oxidative leaching of nickel and / or cobalt with ferric iron

[0002] TECHNICAL FIELD

[0003] The present invention relates to a process for manufacturing battery grade nickel or cobalt salt.

[0004] INTRODUCTION

[0005] Secondary lithium-ion batteries (LIB) have found widespread application in portable devices, electric vehicles, and specialized fields such as aerospace. 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 the LIB.

[0006] 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", LiNixCOyAIzC ) 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.

[0007] The rising demand for electric vehicles (EV) has led to an increased demand for high purity nickel and cobalt, especially for high purity nickel or cobalt salt. Effectively, refineries for preparing high purity nickel and / or cobalt are considered of paramount importance for the supply of battery materials in the next decade. Such nickel and cobalt refineries will need to allow for high capacities and high efficiency of the processes to yield the desired nickel and cobalt salts in a desired quantity and high purity. Therefore, novel processes need to be developed and optimized. Amongst other processes, the oxidative leaching of Ni or Co from a high purity nickel or cobalt metal is considered one of the more promising routes.

[0008] Bilczuk D. et al. ("Kinetic study of the dissolution of metallic nickel in sulphuric acid solutions in the presence of different oxidants", CANADIAN JOURNAL OF CHEMICAL ENGINEERING, vol. 94, no. 10, 5 August 2016 (2016-08-05), p. 1872-1879) studied the dissolution of metallic nickel particles (< 50 pm) in sulphuric acid solutions during a batch process in a single stirred reactor. Particularly, the effect of temperature, sulphuric acid concentration and oxidant type (H2O2, O2, or ferric sulphate) was investigated. The amount of ferric sulphate added corresponded to the theoretical stoichiometric amount needed to dissolve the nickel (1 g / L Ni, 1.9 g / L Fe). The dissolution of Ni in the ferric sulphate solution was observed to be pH sensitive, and fast only when the sulphuric acid concentration was increased to 1 mol / L.

[0009] WO2022 / 053448 Al describes that battery grade metal sulphate solutions can be prepared directly from electrolytically produced solid metal objects, such as nickel cathode plates, when these 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 and with vigorous mixing. The oxidizing agent is selected from hydrogen peroxide, halogens, halogen compounds such as chlorates and perchlorates, citric acid and oxalic acid.

[0010] WO2023 / 166118 Al discloses a process for the preparation of a nickel sulphate solution in a column reactor, whereby metal particles containing nickel are reacted with an oxidative leach solution comprising sulphuric acid and hydrogen peroxide in water and whereby the acid in the oxidative leaching solution is substantially depleted. Nickel metal can be added as Ni metal cut cathodes.

[0011] WO2021 / 105365 Al describes a process for manufacturing nickel sulphate by leaching metal particles comprising nickel in an aqueous sulphuric acid solution. The method includes 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. The nickel particles can be nickel powder or nickel briquettes.

[0012] WO2023 / 187107 Al discloses a method and apparatus for continuous dissolution of a substance in a solvent, wherein the substance to be dissolved can be Ni made by electroplating (electrolytic Ni), and the solvent contains sulfuric acid and hydrogen peroxide.

[0013] All such processes described above may, however, suffer from the high cost of hydrogen peroxide, or other suggested chemicals that are used as the oxidizing agent in an excess amount, and their limited availability on large scale. On the other hand, if O2 gas as an inexpensive reagent would be used directly by injection to a packed bed reactor with large metal pieces such Ni metal cut cathodes, the reaction between gaseous oxygen and the solid metal surface is highly inefficient and such leaching process is thus not economically feasible. Using a stoichiometric amount of ferric iron relative to the nickel to be dissolved is unfeasible for industrial applications due to the large quantity of iron introduced, which must subsequently be removed from the product stream. Similarly, employing a significant excess of sulfuric acid (H2SO4) as a leaching agent is not feasible, as the surplus acid must be neutralized to meet standard nickel and / or cobalt salt product specifications.

[0014] SUMMARY

[0015] The current invention provides in an alternative process, that further solves at least one of the above-mentioned problems by providing a process for the oxidative leaching of metal particles according to claim 1.

[0016] The leaching step of metal particles with ferric iron as an oxidizing agent in step i. of this process has fast kinetics, while ferric iron and other iron containing compounds used herein, are easy and safe to handle, and available at low cost. This process step has improved safety due to suppressed H2formation.

[0017] In step ii. of the process, ferrous iron is re-oxidized to ferric iron with an inexpensive oxidizing agent, so that overall, there is net consumption of an inexpensive oxidizing agent, preferably an oxygen-containing gas.

[0018] Preferably, the process is performed in a set-up with a buffering tank that is in fluid connection with the leaching reactor and oxidation reactor, whereby said leaching reactor is a packed bed reactor.

[0019] DESCRIPTION OF THE FIGURES

[0020] 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.

[0021] Figure 1A depicts an exemplary configuration for a continuous process consistent with some embodiments of the disclosure.

[0022] Figure IB depicts an exemplary configuration for a continuous process consistent with some embodiments of the disclosure. Figure 2 depicts an exemplary configuration for a (semi-)batch or continuous process consistent with some embodiments of the disclosure.

[0023] Figure 3 depicts a preferred configuration for a continuous process consistent with some embodiments of the disclosure.

[0024] DETAILED DESCRIPTION OF THE INVENTION

[0025] 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:

[0026] "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.

[0027] "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.

[0028] "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.

[0029] 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. "Pressure" or "partial pressure" as used herein is referring to absolute pressure, and in this case the units of "bar" or "bara" are equivalent to each other.

[0030] "Metal particles" as used herein is referring to pieces of matter that are composed of pure metallic elements or metallic alloys, which may have different sizes, shapes, and structures, for example including powders or large metal pieces.

[0031] The term "ferric iron" or "ferric ion" or "Fe3+" as used herein refers to the element iron in its +3-oxidation state.

[0032] The term "ferrous iron" or "ferrous ion" or "Fe2+" as used herein refers to the element iron in its +2-oxidation state.

[0033] "Oxidizing agent" as used herein is referring to a reagent that either oxidizes Ni (0) and Co (0) to Ni2+and Co2+, respectively, or to a reagent that oxidizes ferrous iron to ferric iron.

[0034] "Mineral acid" as used herein is to be considered equivalent to the term "inorganic acid" and refers to mineral acids that are very soluble in water, and that form hydrogen ions and the conjugate base when dissolved in water.

[0035] Any water used in the process may be high purity water, such as demineralized water or RO water.

[0036] In the context of the present invention, the term "continuous process" is to be considered as a process in which the produced solution has a substantially constant composition. Specifically, a continuous process is a process in which the produced solution has a constant composition within the range of what are considered normal process variations. Also, it is envisaged that liquid reagents which are fed to the reactor have a fixed composition under normal process conditions. More specifically, the produced solution has a composition whereby the concentration of each ingredient is within the range of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -3% or less of its average concentration. In a preferred embodiment, the present invention provides a continuous process which operates under steady-state conditions.

[0037] Preferably, a mineral acid, iron source, an oxidizing agent for ferrous iron and water are fed to the process according to the present invention at a substantially constant concentration and flow rate. Ni and / or cobalt metal particles may be fed to the process intermittently or gradually. Preferably, the present invention provides a process, preferably a continuous process, wherein the bed volume of metal particles contain- ing nickel is controlled in a column reactor within the range of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -3% or less of its average bed volume.

[0038] In one embodiment, the process is a discontinuous process, whereby the term "discontinuous" means that the process is interrupted when the produced solution is evacuated.

[0039] In the context of the present invention, the term "batch process", or "semi batch process" or "(semi-)batch process" has to be considered as a discontinuous process. Specifically, in the context of the current invention, the term "batch process", or "semi-batch process" or "(semi-)batch process" refers to a process whereby the process is interrupted to discharge the produced salt solution (<pi), and whereby solids, liquid, liquified or gaseous reagents may be fed to the process upfront or may be intermittently or may be periodically introduced during the process.

[0040] In one embodiment of the present invention, the process is executed as a batch or semi-batch process, whereby the bed volume of metal particles containing nickel or cobalt decreases over the reaction time in the reaction zone of the batch reactor.

[0041] In one embodiment, the batch or semi-batch process is stopped, and the nickel and / or cobalt salt solution (<pi) is evacuated when the particles containing nickel and / or cobalt have fully reacted with the leaching solution, and thereby have been fully dissolved.

[0042] In one embodiment, the batch or semi-batch process is interrupted, and the nickel and / or cobalt salt solution (<pi) is evacuated before the particles containing nickel or cobalt have fully dissolved. Preferably, at least 1 wt.% of the initial amount of particles containing nickel or cobalt introduced in the leaching reactor have not dissolved when the process is interrupted and the nickel or cobalt salt 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 and / or cobalt introduced in the leaching reactor have not dissolved when the process is interrupted, and the nickel or cobalt salt solution is evacuated.

[0043] In one embodiment, the reaction is stopped, and the solutions are withdrawn from the process when the leaching rate of the metal particles is low.

[0044] In a preferred embodiment of the present invention, the process is executed as a batch or semi-batch process, whereby the process is interrupted, and the nickel and / or cobalt salt solution (<pi) is evacuated when said solution has the desired, targeted specification, i.e. a predetermined nickel and / or cobalt content and residual acid content.

[0045] "Leaching reactor" as used herein is referring to the reactor wherein the leaching of metal particles with an oxidizing agent takes places so that Ni and / or Co is dissolved, and an aqueous Ni and / or Co salt solution is formed.

[0046] The leaching reactor of the inventive process is preferably a packed bed reactor. In the context of the present invention, the term "packed bed reactor" is to be considered equivalent to the term "packed bed", "column" or "column reactor", "tower" or "tower reactor" and refers to a packed bed reactor having a substantially cylindrical form having an internal diameter D and a height H.

[0047] "Oxidation reactor" as used herein is referring to the reactor wherein ferrous iron is oxidized to ferrous iron.

[0048] As used herein, the term "buffering tank" is equivalent to "buffer tank", "storage tank", "mixing tank", "tank" or "vessel" and herein is referring to a vessel that is suitable for containing a relatively large volume of fluids compared to the reactors wherein the leaching and oxidation steps occur. The tank may be constructed of any suitable material and may be open to the environment or closed to operate under pressure. Buffering tanks herein are further configured to include one or more inlets and outlets for receiving and / or releasing fluids according to the current inventive process.

[0049] As used herein, the term "product salt solution (<pi)" refers to any nickel and / or cobalt salt solution evacuated from the process, at any position in the system thus referring for example to the solution cpiA, cpiB, or epic as depicted in Figures 1 to 3.

[0050] As used herein, the term "nickel and / or cobalt" includes the terms "nickel and cobalt", "nickel" and "cobalt". The appropriate designation will be clear to a skilled person based on the context in which it is used. E.g., leaching of metal particles containing nickel (0) leads to the formation of a nickel salt; leaching of metal particles containing cobalt (0) leads to the formation of a cobalt salt; and leaching of metal particles containing nickel (0) and cobalt (0) leads to the formation of a mixed nickel-cobalt salt.

[0051] In a first aspect, the invention provides a process comprising the steps of: i. contacting metal particles containing nickel (0) and / or cobalt (0) in a leaching reactor (RL) with an aqueous ferric salt solution, thereby obtaining an aqueous nickel and / or cobalt salt solution, respectively, comprising a ferrous salt; and ii. contacting an aqueous nickel and / or cobalt salt solution comprising ferrous salt with an oxidizing agent in presence of a mineral acid in an oxidation reactor (Ro), thereby obtaining an aqueous nickel and / or cobalt salt solution comprising ferric salt.

[0052] In one embodiment, the invention provides a process according to the first aspect of the invention, whereby at least a part of ferrous salt formed in step i. is oxidized to ferric salt in step ii. in the oxidation reactor (Ro), and at least a part of the ferric salt formed in step ii. is used as an oxidizing agent in step i. in the leaching reactor (RL) .

[0053] In step i. of this process, the leaching of metal particles using ferric iron as an oxidizing agent occurs with fast kinetics. Ferric iron salts and other iron-containing compounds used in this step are easy and safe to handle, and they are also cost-effective. Additionally, the leaching step with ferric iron enhances safety by reducing hydrogen gas formation. In step ii., ferrous iron is re-oxidized to ferric iron using an inexpensive oxidizing agent, preferably an oxygen-containing gas. This ensures that the overall process only consumes a low-cost, readily available oxidizing agent for leaching the metal particles. Another benefit of this invention is that it offers an alternative to single-step leaching processes in the prior art that use hydrogen peroxide as an oxidizing agent, which requires specific safety measures and suffers from limited availability for use on a large scale.

[0054] In one embodiment, the invention provides a process according to the first aspect of the invention, whereby the aqueous ferric salt solution flows over said metal particles. In a preferred embodiment, said aqueous ferric salt solution flows through said leaching reactor (RL) . Said aqueous ferric salt solution may be an aqueous nickel and / or cobalt salt solution comprising a ferric salt. Said leaching reactor (RL) may be configured with an inlet and outlet to circulate said aqueous ferric salt solution through said reactor via an circulation loop outside the reactor using a circulation pump. Said solution may be fed at the bottom of said leaching reactor and tapped off at the top of said leaching reactor or may be fed at the top of said reactor and tapped off at the bottom of said reactor.

[0055] Surprisingly, the inventors found that the use of ferric iron as a leaching agent improved significantly the leaching kinetics with increasing the flow of the leaching solution through the leaching reactor. Moreover, in contrast to ferric iron, the inventors did not observe a similar improvement of the leaching kinetics with increasing the flow of the leaching solution through the leaching reactor when using e.g. hydrogen peroxide as an oxidizing agent.

[0056] Preferably, the regeneration of ferric iron in step ii. occurs in a different reactor vessel than the one used for the leaching of metal particles in step i. This allows the reactor vessel for iron oxidation (Ro) to be of a different type than the leaching vessel (RL) and to operate under different conditions, such as varying temperature, pressure, and flow rate. Conducting both reactions simultaneously in a single vessel is not industrially practical due to the significantly different optimal conditions required for each reaction. More specifically, the metal particles containing nickel (0) and / or cobalt (0) are contacted in said leaching reactor (RL) with an aqueous ferric salt solution to yield an aqueous nickel and / or cobalt salt solution, respectively, comprising a ferrous salt. This resulting nickel and / or cobalt salt solution comprising said ferrous salt is then at least partially transferred to an oxidation reactor (Ro). In said oxidation reactor (Ro), the ferrous salt is oxidized to a ferric salt. The obtained ferric salt solution, comprising also nickel and / or cobalt salt, respectively, is subsequently at least partially transferred to the leaching reaction, where it acts as a leaching agent for leaching metal particles containing nickel (0) and / or cobalt (0). Accordingly, a loop system is created wherein a mineral acid and an inexpensive oxidizing agent, such as oxygen, are consumed to produce a nickel and / or cobalt salt solution. The target nickel and / or cobalt salt solution having a sufficiently high nickel and / or cobalt concentration, herein also called the product salt solution (<pi), may be evacuated from the system at any position in the loop system, such as after the leaching reactor or after the oxidation reactor.

[0057] In a preferred embodiment, the first and second reaction vessel (Ro and RL) are in fluid connection with each other, whereby at least a part of ferrous salt formed in step i. is oxidized to ferric salt in step ii. in the oxidation reactor (Ro), and at least a part of the ferric salt formed in step ii. is used as an oxidizing agent in step i. in the leaching reactor (RL) .

[0058] In a preferred embodiment, said leaching reactor (RL) and the oxidation reactor (Ro) are in fluid connection with a buffering tank (TB) .

[0059] Preferably at least a part of the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. is fed to a buffering tank (TB), and / or at least a part of said aqueous nickel and / or cobalt salt solution comprising ferric salt used for leaching in step i. is obtained from a buffering tank (TB).

[0060] Preferably, at least a part of the aqueous nickel and / or cobalt salt solution comprising ferric salt formed in step ii. is fed to a buffering tank (TB), and / or whereby at least a part of said aqueous nickel and / or cobalt salt solution comprising ferrous salt to be oxidized in step ii. is obtained from a buffering tank (TB) .

[0061] Even more preferably, the leaching reactor (RL) and the oxidation reactor (Ro) are in fluid connection with one single buffering tank (TB) . Such a set-up allows to decouple the flow rate over the oxidation reactor, from that over the leaching reactor. Decoupling those flow rates enables improved process control. Moreover, it enables a larger system volume without the need for more expensive reactor capacity. A large system volume is especially advantageous for batch mode operation of the process.

[0062] In a preferred embodiment, the leaching reactor may be a packed bed or column reactor or may be an agitated reactor without suspension of the metal particles.

[0063] In one or more embodiments, the leaching reactor is an agitated reactor, wherein the particles are either settled at the bottom or collected in a structure that holds the particles in place that is permeable for the solution, e.g. by using a mesh structure or buckets, and that is agitated by an impeller or by a circulation flow.

[0064] Preferably the leaching reactor is a packed bed reactor. During the leaching process, bed aging takes place whereby the median particle diameter of the metal particles containing nickel (0) and / or cobalt (0) decreases, and thereby the leaching rate increases.

[0065] The process according to the first aspect of the invention may be performed as a batch, semi-batch or a continuous process. The product salt solution (<pi) may be intermittently or continuously collected either after the leaching reactor (<PIA), after the oxidation reactor (<PIB), or from a buffer tank (epic).

[0066] Preferably, the process is a continuous process. In one embodiment, at least a part (<PIB) of the aqueous nickel and / or cobalt salt solution comprising ferric salt formed in step ii. (CJ ) is continuously collected with a substantially constant composition. Collection of the product salt solution (<piB) after the oxidation reactor (Ro) may be advantageous in view of a further iron removal step, for which it is beneficial to start already with a high Fe3+content.

[0067] Preferably, at least a part (<PIA) of the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. (cpz) is continuously collected with a substantially constant composition. Collection of the product salt solution (<PIA) after the leaching reactor (RL) is advantageous in view of optimal chemical efficiency, as all Fe3+produced can be used for the leaching reaction.

[0068] In a preferred embodiment of a continuous process, the volume ratio (cpiA / ic / cpz) of the continuously collected product stream (cpiA / ic) to the total stream after the leaching reactor (cpz) as shown in Figure 1A, 2 and 3, is between 0.66 % and 33.5%, preferably between 0.8 and 20%, more preferably between 1 and 10%, even more preferably between 1.2 to 5%, more preferably about 1.5 %, 2% or 2.5%.

[0069] In a preferred embodiment of a continuous process, the volume ratio (<PIB / <P4) of the continuously collected product stream (<piB) to the total stream after the oxidation reactor (CJ ) as shown in Figure IB, is between 0.66 % and 33.5%, preferably between 0.8 and 20%, more preferably between 1 and 10%, even more preferably between 1.2 to 5%, more preferably about 1.5 %, 2% or 2.5%.

[0070] In a first embodiment, the present invention provides a continuous process according to the first aspect of the invention, whereby an aqueous nickel and / or cobalt salt solution comprising ferric salt is fed to a column reactor via a bottom section of said leaching reactor ( L) to the reaction section, and whereby said aqueous nickel and / or cobalt salt solution comprising ferrous salt is evacuated from the reaction section via a top section of said leaching reactor (RL) . At least a part <p3, of said solution recovered via a top section of RL, is transferred to a separate oxidation reactor (Ro). The other part, cpiA, is the product salt solution that is continuously collected. In Roat least part of ferrous iron is oxidized to ferric iron prior to being reintroduced into the column reactor (RL) . Such a process is depicted in Figure 1A. In an alternative configuration depicted in Figure IB, at least a part <ps, of the solution recovered from Ro, is transferred to a separate leaching reactor (RL) . The other part, cpiB, is the product salt solution that is continuously collected. The configuration of Figure 1A and IB has the advantage of a high chemical efficiency because all of the Fe3+produced in Rois circulated directly to RL, and similarly, all Fe2+produced in R is circulated to Ro.

[0071] In a second embodiment, the present invention provides a (semi-)batch or continuous process according to the first aspect of the invention, whereby an aqueous nickel and / or cobalt salt solution comprising ferric salt is fed to a column reactor via a bottom section of said leaching reactor (RL) to the reaction section, and whereby said aqueous nickel and / or cobalt salt solution comprising ferrous salt is evacuated from the reaction section via a top section of said leaching reactor (RL) . Said solution recovered via a top section of RL, is transferred to the buffering tank (TB). The product salt solution, epic, is intermittently or continuously collected via the buffering tank (TB).

[0072] The oxidation reactor (Ro) obtains an aqueous nickel and / or cobalt salt solution comprising ferrous salt (<pB) from the buffering tank (TB) and feeds aqueous nickel and / or cobalt salt solution comprising ferric salt back to TB, and TBfeeds the leaching reactor (RL) . This configuration has the advantage of enabling a large system volume, and different flow settings for the leaching versus the oxidation reaction. Such a process is depicted in Figure 2. Further this configuration allows for flexible process control and is suitable for both (semi-)batch and continuous operations.

[0073] In a third embodiment, the present invention provides a continuous process according to the first aspect of the invention, whereby an aqueous nickel and / or cobalt salt solution comprising ferric salt is fed to a column reactor via a bottom section of said leaching reactor (RL) to the reaction section, and whereby said aqueous nickel and / or cobalt salt solution comprising ferrous salt is evacuated from the reaction section via a top section of said leaching reactor (RL) . Said solution recovered via a top section of RL, is transferred to the buffering tank (TB). The product salt solution, epic, is continuously collected via the buffering tank (TB).

[0074] The oxidation reactor (Ro) obtains an aqueous nickel and / or cobalt salt solution comprising ferrous salt (<pB) from the buffering tank (TB) and feeds the solution after oxidation directly back to the leaching reactor (RL) . This configuration has the advantage of enabling a large system volume and different flow settings for the leaching versus the oxidation reaction, while maintaining a high concentration of ferric iron for the leaching reaction. Such a process is depicted in Figure 3. The flow rate over the leaching reactor is defined as the volume of the aqueous ferric salt solution that enters the leaching reactor per weight of the metal particles in the reactor per unit of time, expressed as L.kg’Th’1. The aqueous ferric salt solution that enters the leaching reactor may be an aqueous nickel and / or cobalt salt solution comprising a ferric salt (<ps). Preferably, the flow rate over the leaching reactor is substantially kept constant during a (semi-)batch or continuous process. The flow rate of the aqueous ferric salt solution fed to said leaching reactor (RL) may be higher than 0.05 L.kg'Th'1, or higher than 0.10 L.kg'Th'1, or higher than 0.20 L.kg'Th'1, or higher than 0.30 L.kg’Th’1, or higher than 0.50 L.kg’Th’1, or higher than 1.0 L.kg’Th’1, or higher than 1.5 L.kg'Th'1, or higher than 5 L.kg'Th'1, or higher than 7.5 L.kg' Th-1. In contrast with hydrogen peroxide, ferric iron showed a strong impact on the leaching kinetics in the leaching reactor at increasing flow rate of the leaching solution (<p5) through the leaching reactor (RL) . The inventors observed that it is advantageous specifically when ferric iron as an oxidizing agent for leaching of metal particles containing Ni° and / or Co0is used, to set a high flow rate through the leaching reactor to increase the leaching rate. The leaching rate is typically expressed as g metal leached per kg of metal in the leaching reactor per hour. The improvement in leaching kinetics with higher flow rates of the leaching solution (<ps) through the leaching reactor was observed at all tested flow rates. No upper limit to this phenomenon was observed. However, for practical reasons the flow rate may be limited to not more than 100 L.kg'Th'1, or not more than 50 L.kg'Th'1, or not more than 20 L.kg'Th'1, or not more than 10 L.kg'Th'1. Practically, the upper limit of the flow rate may be determined by the set-up or equipment availability.

[0075] The process according to the first aspect of the present invention, allows efficient leaching of large metal particles by contacting them with an aqueous ferric salt solution. The reactivity of such large metal particles with a mineral acid such as aqueous sulphuric acid is low. In addition, such large metal particles may not be suspended, and therefore cannot directly and efficiently react with a gaseous reagent such as oxygen.

[0076] In a preferred embodiment according to the first aspect of the invention, said metal particles containing nickel (0) and / or cobalt (0) introduced to the leaching reactor (RL) have a median particle diameter of at least 100 pm, preferably at least 250 pm, even more preferably at least 500 pm or most preferably more than 1 mm. Preferably, said metal particles have a median particle diameter of at most 2 m, and preferably less than 1 m, more preferably less than 200 mm, and most preferably less than 100 mm.

[0077] A suitable method to measure those metal particles having a diameter up to 100 mm, is the dry sieving method, whereby the median particle diameter is determined as the opening size at which 50% of the amount of metal particles is retained on sieves with larger openings and 50% is retained on sieves with smaller openings. The particle size determination, especially for larger particles (>100 mm), may be done by directly measuring the diameters of the individual pieces, optionally assisted by microscopy and / or automated image analysis.

[0078] In preferred embodiments the metal particles are electrolytically produced and are fed as shredded or cut full plate cathode metal obtained from an electrowinning process.

[0079] In preferred embodiments the metal particles are electrolytically produced, and are fed to the reactor in the form of electrolytic rounds or pellets, or balls having a diameter of about 0.5 cm.

[0080] In preferred embodiments the metal particles are electrolytically produced and are fed to the reactor in the form of cut Ni or Co cathode metal, having a size of typically l"xl", 2"x2" or 4"x4".

[0081] In some embodiments the metal particles are electrolytically produced, and are fed to the reactor in the form of full plate Ni or Co cathode metal, having a size of typically 1200 mm x 1200 mm.

[0082] In preferred embodiments, the metal particles are granules or briquettes or metal shots or pellets or balls.

[0083] The metal particles may be a combination of the different types of metal particles described above.

[0084] In some embodiments, metal particles containing nickel (0) and / or cobalt (0) comprise elemental Ni particles or elemental Co particles, or a combination thereof.

[0085] In some embodiments, metal particles containing nickel (0) and / or cobalt (0) comprise alloys containing nickel and / or cobalt, obtained from either battery smelting, ferronickel processing, or from superalloy recycling, and combinations thereof.

[0086] In a preferred embodiment, metal particles containing nickel (0) and / or cobalt (0) comprise nickel and cobalt in an amount of at least 96 wt.%, relative to the total weight of said metal particles, preferably 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.%.

[0087] More preferably, said metal particles containing nickel (0) and / or cobalt (0) comprise Ni and / or cobalt in an amount of at least 99.5 wt.%.

[0088] Most preferably, the metal feed preferably comprises highly pure Ni metal or highly pure Co metal, having a purity of typically 99.97+ %, 99.98+ %, or even 99.99+ %. Even more preferably, the metal feed preferably comprises highly pure Ni metal having a purity of typically 99.97+ %, 99.98+ %, or even 99.99+ %.

[0089] In some embodiments, metal particles containing nickel (0) and / or cobalt (0) may comprise Cu in an amount lower than 1 wt%, or lower than 0.5 wt%, or lower than 0.1 wt%, or said the metal particles containing nickel (0) and / or cobalt (0) may not comprise Cu. The inventors observed that the presence of Cu may decrease the metal leaching reaction rate.

[0090] An increased temperature versus room temperature is desired for fast reaction kinetics for the oxidative leaching reaction with ferric iron.

[0091] In a preferred embodiment, the present invention provides a process according to the first aspect, whereby said aqueous ferric salt solution is fed to said leaching reactor (R. ) in step i. at an inlet temperature (Tiniet) at a temperature between 50°C and 98°C, preferably above 70°C, and more preferably above 75°C, preferably at a temperature below 95°C, most preferably at a temperature of about 80°C, 85°C, 90°C or any temperature there in between.

[0092] In steady-state conditions, the leaching reactor (RL) in step i. operates at a temperature (TRL) of at least the inlet temperature (Tiniet) of the feed solution. In a preferred embodiment, the present invention provides a process according to the first aspect, whereby the leaching reactor (RL) in step i. operates at a temperature (TR) of at least Tiniet and lower than the boiling point of the aqueous nickel and / or cobalt salt solution, preferably above 60°C, and more preferably above 75°C, preferably at a temperature of 95°C or below, most preferably at a temperature of about 80°C, 85°C, 90°C, 95°C or any temperature there in between.

[0093] The outlet temperature for RL of the aqueous nickel and / or cobalt salt solution is higher than the inlet temperature (Tiniet), as there is a temperature increase over the column. Preferably the nickel and / or cobalt salt solution is evacuated from said reactor at a temperature below the boiling point of said solution, more preferably at a temperature between 85°C and the boiling point, more preferably between 93°C and 100°C.

[0094] An increased temperature versus room temperature also strongly enhances the reaction rate of the oxidation of ferrous to ferric iron.

[0095] The desired operation temperature for the oxidation reactor to oxidize ferrous to ferric iron, that is an exothermic reaction, is in between the inlet temperature of the leaching reactor and 150°C, in order to avoid the need for extensive cooling between the two reactors and / or evaporation of the solution.

[0096] In a preferred embodiment, the present invention provides a process according to the first aspect, whereby the oxidation reactor (Ro) in step ii. operates at a temperature between 50°C and 150°C, preferably above 80°C, preferably at a temperature below 120°C, more preferably below 100°C, most preferably at a temperature of about 85°C, 90°C, 95°C, 98°C or any temperature there in between.

[0097] In a preferred embodiment, the oxidation reactor is a pressure reactor that operates at pressures higher than atmospheric pressure.

[0098] In a preferred embodiment, the aqueous nickel and / or cobalt salt solution containing ferric iron is cooled between the oxidation reactor and the leaching reactor. Cooling may proceed in a heat exchanger such as a plate heat exchanger, a shell-and-tube heat exchanger, or in a reactor with cooling means.

[0099] In a preferred embodiment, the present invention provides a process whereby heat recovered from the cooling step is, at least in part, used for heating the reagents and / or the content of said reactors.

[0100] In the leaching reactor, ferric iron reacts stoichiometrically with the metal particles, meaning that two Fe3+atoms react with either one Ni° or Co0atom to form Ni2+or Co2+, respectively.

[0101] In one embodiment, in the leaching reactor (RL), leaching of Ni metal particles in sulphuric acid occurs via the following chemical reaction:

[0102] Ni° + Fe2(SO4)3-> NiS04+ 2 FeS04

[0103] Especially when Ni metal cut cathodes are leached, the following leaching reaction with sulfuric acid only is minimal :

[0104] Ni° + H2S04-> NiS04+ H2

[0105] This implies that H2 formation is negligible. In addition, the presence of ferric ions as an oxidizing agent further suppresses any H2 formation during leaching of Ni (0) and / or Co (0) metal particles in mineral acids. In a further embodiment, when Ni and / or Co metal cut cathodes are leached in an aqueous H2SO4 solution, the extent of the chemical reaction with any dissolved O2 is minimal, compared to the dissolution by ferric iron.

[0106] Preferably, leaching of the metal particles in step i. is performed with ferric iron as the predominant oxidizing agent. Preferably, ferric iron constitutes at least 70 mol% of the total oxidizing agents present, more preferably more than 90 mol%, most preferably more than 95 mol%. This means that ferric iron is the most abundant oxidizing agent for Ni and / or Co, and that other oxidizing agents such as dissolved O2 or H2O2, are present in a significantly lower amount than ferric iron. The mineral acid itself is not considered as an oxidizing agent in the context of this invention.

[0107] All forms of ferric iron may act as an oxidizing agent in step i. In one or more embodiments, ferric iron is present in a precipitated solid, or as Fe3+in solution, or as a mixture of both forms. Preferably, ferric iron in the leaching step, step i., is predominantly present as Fe3+in solution. More preferably, Fe3+in solution constitutes at least 70 mol% of the total ferric iron present in step i., more preferably more than 90 mol%.

[0108] Iron may be introduced when the process starts as any form of iron oxide, iron hydroxide, iron-oxyhydroxide, iron chloride, iron sulphate, or metallic iron, or any combination thereof.

[0109] Iron may be supplied to the process to compensate for iron loss via the product salt solution (<pi) . In some embodiments, iron is introduced continuously or intermittently to the process under the form of iron oxide, iron hydroxide, iron-oxyhydroxide, iron chloride, iron sulphate, metallic iron, or any combination thereof. In a preferred embodiment, iron is recirculated into to the process after it is isolated from the product salt solution (<pi).

[0110] Iron may be also contained in the metal particles, in which case less iron should be additionally introduced and / or recirculated into the process.

[0111] In one embodiment, the total iron concentration in solution, both in step i. and step ii., is between 2 and 30 g / L, preferably between 5 and 20 g / L, most preferably between 5 and 15 g / L. The total iron concentration refers to the total amount of iron, including both Fe2+and Fe3+, that is present in the solution sampled at any point in the process. In a preferred embodiment, the total iron concentration in solution at the start of the process, both in step i. and step ii ., is between 2 and 30 g / L, preferably between 5 and 20 g / L, most preferably between 5 and 15 g / L.

[0112] In a preferred embodiment, the total iron concentration in solution, both in step i. and step ii., is kept substantially constant during the process.

[0113] The inventors noticed a positive correlation between the leach rate and the total iron concentration in solution. However, the added iron must be removed from the product stream (<pi), necessitating a balance between optimal reaction kinetics and minimal effort for iron removal.

[0114] In one embodiment, the iron amount in the product salt solution (cpi) before iron removal is sub-stoichiometric versus the total nickel and cobalt amount. In other words, the molar ratio of the moles of iron versus the total moles of nickel and cobalt in the product salt solution (<pi) is lower than 2. The molar ratio of iron versus the total of nickel and cobalt in the product salt solution (<pi) may be lower than 1.0 or lower than 0.5 or lower than 0.25 or lower than 0.15. The molar ratio of iron versus the total of nickel and cobalt in the product salt solution (<pi) may be higher 0.01 or higher than 0.02 or higher than 0.05.

[0115] In one embodiment, at least a part of said aqueous nickel and / or cobalt salt solution obtained in step i. and / or at least a part of said aqueous nickel and / or cobalt salt solution obtained in step ii. is evacuated from the process, and said evacuated solution (<piA, <PIB ,<pic in Figures 1 to 3) has a molar ratio of iron to the total of nickel and cobalt that is lower than 2, or lower than 1.0, or lower than 0.5 or lower than 0.25 or lower than 0.15.

[0116] In one embodiment, at least a part of said aqueous nickel and / or cobalt salt solution obtained in step i. and / or at least a part of said aqueous nickel and / or cobalt salt solution obtained in step ii. is evacuated from the process, and said evacuated solution (<piA, cpiB, <Pic in Figures 1 to 3) has a molar ratio of iron to the total of nickel and cobalt that is higher 0.01 or higher than 0.02 or higher than 0.05.

[0117] The ratio of ferrous iron to the total content of ferrous and ferric iron of the aqueous nickel and / or cobalt salt solution comprising ferrous salt obtained in step i. is at least 0.05, preferably at least 0.1, more preferably at least 0.15, most preferably at least 0.25. The ratio of ferrous iron to the total content of ferrous and ferric iron of the aqueous nickel and / or cobalt salt solution comprising ferrous salt obtained in step i. is at most equal to 1.

[0118] The ratio of ferric iron to the total content of ferrous and ferric iron of the aqueous nickel and / or cobalt salt solution comprising ferric salt obtained in step ii. is at least 0.05, preferably at least 0.1, more preferably at least 0.5, most preferably at least 0.7.

[0119] The ratio of ferric iron to the total content of ferrous and ferric iron of the aqueous nickel and / or cobalt salt solution comprising ferrous salt obtained in step ii. is at most equal to 1. It is advantageous to produce a solution with high fraction of ferric iron in step ii. in order to maximize the leaching capacity in the leaching reactor. Yet, this ratio may not be set too high, since it then become more economically interesting to increase the performance of the leaching reactor (e.g. by adding more metal particles) so to establish a more balanced operation.

[0120] The ratio of ferrous iron or ferric iron to the total content of ferrous and ferric iron in solution may be considered either as a molar ratio or weight ratio, since both units are equivalent for this ratio.

[0121] The leaching reaction can be initiated by addition of Ni salt or Co salt or Cl anions to the matrix. Preferably the leaching reaction is initiated by addition of Ni sulphate, Co sulphate, nickel chloride or cobalt chloride to the matrix.

[0122] In some embodiments catalytic elements may be added to accelerate the leaching kinetics and / or iron oxidation kinetics. In some embodiments chloride anions, copper cations or a mixture thereof, are added.

[0123] The oxidation in step ii. is performed with an oxidizing agent for ferrous iron, selected of the group consisting of: ozone, hydrogen peroxide, CL, and oxygen-containing gas such as oxygen, oxygen enriched air, or air. Preferably, the oxidizing agent is an oxygen-containing gas. In a preferred embodiment, the oxidizing agent is oxygen with a purity level between 85 and 99 vol%.

[0124] The pressure has an important direct effect on kinetics of iron oxidation in the oxidation reactor. The impact of pressure on the kinetics is higher than that of temperature or the effect of the mineral acid concentration to boost the oxidation rate. In a preferred embodiment, the oxidation reactor is a stirred reactor that is an autoclave that can withstand high pressure. In some embodiments, the oxidation reactor is made of stainless steel, or enamel lined.

[0125] In one embodiment, the absolute pressure in the atmosphere above the aqueous nickel and / or cobalt solution in the oxidation reactor is between 1 bar and 100 bar, preferably said pressure is higher than 2 bar, higher than 5 bar, higher than 10 bar, higher than 15 bar, or even higher than 20 bar.

[0126] Increasing the absolute pressure of the oxygen-containing gas used as oxidizing agent results in an elevated oxygen partial pressure and an increase of the oxidation kinetics.

[0127] In one embodiment, the inventive process according to the first aspect of the invention proceeds with an oxidation reactor (Ro) whereby an atmosphere above the nickel and / or cobalt salt solution in said oxidation reactor (Ro) contains a gaseous oxidizing agent at a partial pressure between 1 bar and 100 bar, or said partial pressure may be higher than 2 bar, higher than 5 bar, higher than 10 bar, higher than 15 bar, or even higher than 20 bar. Said gaseous oxidizing agent may be oxygen, chlorine and / or ozone. In one specific embodiment said gaseous oxidizing agent comprises oxygen.

[0128] In one embodiment, the partial pressure of oxygen in the atmosphere above the aqueous nickel and / or cobalt solution in the oxidation reactor (Ro) is between 1 bar and 100 bar, preferably said pressure is higher than 2 bar, higher than 5 bar, higher than 10 bar, higher than 15 bar, or even higher than 20 bar.

[0129] Practically, the upper pressure limit is determined by side equipment to deliver counterpressure to the reactor.

[0130] For example, the oxidation of ferrous sulphate with oxygen is described by the following reaction:

[0131] 4 FeS04+ O2+ 2 H2S04-> 2 Fe2(SO4)3+ 2 H2O

[0132] This oxidation reaction is exothermic, which must be considered during process design.

[0133] The oxidation of ferrous iron to ferric iron in step ii. according to the first aspect of the invention, requires high shear mixing of the oxidizing agent and the aqueous solution at high pressure. In some embodiments, high shear mixing of the oxidizing agent and the aqueous solution at high pressure occurs in an oxidation reactor that is a stirred reactor, static mixer or radial pump. In a stirred reactor, the reactor shape, stirrer type, and / or high agitation speed may prevent the reaction from being limited by the mass transfer of oxygen from the gas phase to the liquid phase.

[0134] The oxidation reactor operating volume is defined as the volume of solution in the oxidation reactor during the process. In one embodiment, the volume of solution in the oxidation reactor is maintained substantially constant during the process.

[0135] In one embodiment, the flow rate over the oxidation reactor is between 1 and 40 reactor operating volumes per hour. Preferably, the flow rate over the oxidation reactor is between 2 and 30 reactor operating volumes per hour, more preferably between 2 and 10 reactor operating volumes per hour.

[0136] In one embodiment, at least a part of the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. is subjected to an iron removal process.

[0137] In one embodiment, at least a part of said aqueous nickel and / or cobalt salt solution obtained in step i. and / or at least a part of said aqueous nickel and / or cobalt salt solution obtained in step ii. is evacuated from the process, and said evacuated solution (<piA, cpiB, <Pic in Figures 1 to 3) is subjected to an iron removal process.

[0138] Preferably, iron removal and recovery occur without the introduction of any sodium or ammonium cations.

[0139] In one embodiment, Fe removal from the product salt solution <pi is done via ionexchange with an extractant, said extractant being a phosphorus-containing extractant such as di-(2-ethyl hexyl) phosphoric acid (D2EHPA) or bis(2,4,4-trimethylpen- tyljphosphinic acid, or a carboxylic acid such as neodecanoic acid. Preferably, the extractant is D2EHPA. Said ion-exchange can occur via solvent extraction or a fixed bed extraction.

[0140] In a preferred embodiment, the Fe removal from the product salt solution <pi is done via hydrolysis with a base. 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, lithium hydroxide, lithium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, sodium hydroxide, sodium carbonate, ammonium hydroxide, or a combination of two or more of the aforementioned. Preferably, said base is calcium hydroxide or calcium carbonate, nickel hydroxide, nickel carbonate, cobalt hydroxide, or cobalt carbonate.

[0141] Preferably, said base is added until the pH of the product solution is between 1 and 5, preferably between 1 and 4.5, and more preferably between 3.0 and 4.0. In one embodiment, the Fe removal via hydrolysis with a base occurs via a batch or continuous process in a stirred reactor.

[0142] In one embodiment, iron in the product salt solution <pi is first reduced with a metallic reagent such as Ni, Co or Mn metal, so that Fe is predominantly present as Fe2+, and then oxidized and precipitated with said base as Fe3+after which the iron cake is more easily filtered off.

[0143] In a preferred embodiment, Fe removal via hydrolysis from the product salt solution <pi is done with Co or Ni powder, or Co or Ni briquettes that react with the residual acid under oxidizing conditions with excess reagent. In one embodiment, the Fe removal via hydrolysis with Co or Ni powder, occurs via a batch or continuous process in a stirred reactor. In one embodiment, the Fe removal via hydrolysis with Co or Ni briquettes occurs in a packed bed column reactor.

[0144] In one embodiment, said product salt solution <pi is subjected to further purification steps after iron removal, for example to separate Co from Ni, or to reduce the concentration of one or more impurities, whereby said impurities comprise one or more selected from the list comprising Cu, Cr, Pb, Zn, Mn, Al, F, C, Ca, Si, P, As, Cd, Sb, Ni, Co and Mg, or to even further reduce the iron content.

[0145] In some embodiments, the nickel and / or cobalt salt solution in step i. and step ii. comprises nickel and / or cobalt chloride, or nitrate, or phosphate or sulphate, or combinations thereof. Preferably, said nickel and / or cobalt salt solution comprises a sulphate and / or chloride salt.

[0146] In a preferred embodiment, the nickel and / or cobalt salt solution is nickel and / or cobalt sulphate and has battery-grade purity after the purification steps.

[0147] In one embodiment, the nickel and / or cobalt salt solution is a mixture of nickel and / or cobalt sulphate and nickel and / or cobalt chloride salt, that is further processed and converted to a nickel and / or cobalt carbonate salt.

[0148] The target concentration for nickel and / or cobalt salt in the product salt solution <pi is at least 60 g / L of Ni and / or Co, optionally comprising further components, such as sulphuric acid or hydrochloric acid.

[0149] In a preferred embodiment, said product salt solution <pi has a nickel content of at least 60 g Ni / L, and preferably at least 80 g Ni / L. Said nickel salt solution preferably has a content of nickel salt below the saturation point of nickel at the processing temperature, i.e. at a temperature of about 90°C or of about 95°C. Preferably, said nickel salt solution has a Ni content between 80 and 200 g Ni / L,

[0150] In one or more preferred embodiments, the said nickel salt solution is a nickel sulphate solution and has a Ni content between 90 and 175 g Ni / L and more preferably between 100 and 150 g Ni / L. Even more 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 is having a nickel content of about 130 g / L.

[0151] In one or more embodiments, said nickel salt solution is a nickel chloride solution and has a Ni content between 150 and 200 g Ni / L, most preferably said nickel chloride solution is having a nickel content of about 175 g / L.

[0152] In a preferred embodiment, said solution <pi has a cobalt content of at least 60 g Co / L, and preferably at least 80 g Co / L. Said cobalt salt solution preferably has a content of cobalt salt below the saturation point of cobalt at the processing temperature, i.e. at a temperature of about 90°C or of about 95°C. Preferably, said cobalt salt solution has a Co content between 80 and 200 g Co / L.

[0153] In one or more preferred embodiments, said cobalt salt solution is a cobalt sulphate solution and has a Co content between 90 and 175 g Co / L and more preferably between 100 and 150 g Co / L. Even more 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 is having a cobalt content of about 130 g / L.

[0154] In one or more embodiments, said cobalt salt solution is a cobalt chloride solution and has a Co content between 150 and 200 g Co / L, most preferably said cobalt chloride solution is having a cobalt content of about 175 g / L.

[0155] The residual acid content of the aqueous nickel and / or cobalt salt solution is about constant throughout the different process steps, and is kept within a certain range, whereby the upper limit is determined by the specification for the final nickel and / or cobalt product, and whereby a minimum amount of acid is needed to avoid Fe-pre- cipitation. The lowest residual acid contents can be more easily obtained from a batch process. It is undesirable that an excess of residual acid in the product stream needs to be neutralized.

[0156] In a preferred embodiment, the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. has a residual acid content of between 1 g / L and 20 g / L. Preferably, the residual acid is hydrochloric acid and the hydrochloric acid content is between 1 g / L and 10 g / L, and most preferably the residual amount of hydrochloric acid is about 1 g / L, 2 g / L, 6 g / L, 8 g / L or 10 g / L, or any value there in between.

[0157] More preferably, the residual acid is sulphuric acid, and the sulphuric acid content is 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.

[0158] In one embodiment, up to about 15 g / L of iron was used at a sulfuric acid concentration of about 10 g / L without significant iron precipitation.

[0159] In the entire loop process, several reagents need to be replenished: The mineral acid is consumed during the iron oxidation step, iron and acid may be removed via the product salt solution (<pi) and water evaporation may occur due to the elevated temperatures.

[0160] In one embodiment according to the invention, no acid is consumed during the leaching step (step i.), and the acid content of the solution that enters the leaching reactor equals that of the solution leaving the leaching reactor.

[0161] In one embodiment according to the invention, a mineral acid is consumed during the oxidation step of ferrous to ferric iron (step ii.) and may be added in a stoichiometric amount to compensate for its consumption by iron oxidation, and to compensate for the amount discharged with the product stream <pi. The impact of the acidity in the reactor on the oxidation rate of iron was assessed as limited.

[0162] In one embodiment, the mineral acid is fed to the process in the leaching reactor, right before the entrance of the solution to the oxidation reactor, in the oxidation reactor, or to a buffering tank (TB) . In a preferred embodiment, the mineral acid is fed to the oxidation reactor in order to avoid or minimize iron precipitation.

[0163] The mineral acid may be sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid, or mixtures thereof. In a preferred embodiment, the mineral acid is sulphuric acid or hydrochloric acid. Hydrochloric acid has a concentration of maximum 38 wt.% in water. Sulphuric acid has a concentration of 78 to 98 wt.% in water, preferably a 98 wt.% concentration in water. Even more preferably, sulphuric acid and / or hydrochloric acid is fed to the oxidation reactor (Ro).

[0164] In a preferred embodiment, the oxidation reactor is operated under acidic conditions at a concentration lower than 300 g / L H2SO4. The inventors observed that a minimal concentration of H2SO4, not more than 10 g / L, is required to initiate the reaction. On average, it was observed that the oxidation rate increases with a factor of about 2 when the sulphuric acid concentration decreased from 130 g / L to 10 g / L.

[0165] In one embodiment, a mineral acid solution comprising iron is reintroduced to the process. Said acid solution comprising iron may be prepared by dissolving the iron cake, obtained from iron removal from the product salt solution <pi by hydrolysis using a base, in a diluted acid solution.

[0166] In an alternative embodiment, said mineral acid solution comprising iron comprises an iron-rich aqueous acidic eluate, resulting from iron removal from the product salt solution <pi via ion-exchange with an extractant.

[0167] Said acid solution comprising iron, may be reintroduced either to the leaching reactor, to the oxidation reactor, right before the entrance of the leaching or oxidation reactor, or to a buffering tank (TB).

[0168] In a preferred embodiment, the mineral acid solution or the mineral acid solution comprising iron, is reintroduced to the process right after evacuation of the product salt solution <pi, so that the residual acid concentration in the product salt solution <pi is minimal.

[0169] Preferably the leaching reactor is a packed bed reactor. In said packed bed reactor, the fluid may flow from bottom to top of the column, or the fluid may flow from the top to bottom of the column. Said column reactor consists of a vertically arranged cylindrical column and is arranged to operate without mechanical agitation, preferably in the up-flow mode, i.e. fluid flows from bottom to top of the column.

[0170] The flow rate of the solution over the packed bed leaching reactor is expressed in bed volumes per hour of solution entering the packed bed reactor, whereby 1 bed volume equals the volume of an empty reactor until the bed height of the metal particles. In a preferred embodiment, the flow rate is at least one bed volume per hour, so that the residence time is maximum one hour. More preferably, the flow rate is between 2 and 40 bed volumes per hour. Most preferably, the flow rate is between 10 and 30 bed volumes per hour. The inventors surprisingly found that over this full range of flow rates, an increase of the flow rate further increases the leaching rate, i.e. the amount of metal leached per total amount of metal in the column per unit of time increases. Therefore, a high flow rate can be exploited to increase the leach rate and the overall throughput of the process of the current invention.

[0171] The column reactor is further characterized by (i) a feed section at the bottom of said cylindrical reactor for feeding liquid reagents such as an aqueous nickel and / or cobalt salt solution comprising ferric salt.; (ii) a top section or an overflow section 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 aqueous nickel and / or cobalt salt solution comprising ferrous salt; (iii) a middle section or a reaction section in the middle of said cylindrical reactor, where the leaching reaction proceeds. Metal particles 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 Ni or Co metal. Said support consists of a grid for supporting the metal. Further, the column reactor is preferably equipped with means to feed a solid reagent such as Ni or Co metal to the reaction zone of the column reactor. Further, the column reactor is preferably also equipped with means for radially and uniformly distributing the oxidative leach solution in the feed section of the column reactor. The solid reagent can be dosed on the support by introduction of the Ni or Co metal at the top of the reactor, or at any position above the support. The overflow zone is provided with an outlet to receive a nickel or cobalt salt solution via an overflow mechanism.

[0172] 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 has a diameter DL and a height HL, whereby the ratio of said height to said diameter H : D 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, 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 metal salt solution resulting from the oxidative leaching reaction, thereby entraining unreacted metal particles and thereby contaminating the obtained product solution, as well as lowering the efficiency of the process. In a preferred embodiment, the present invention provides a process, whereby a bed volume consisting of said metal particles in the column 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 5, preferably between 1 and 5. Preferably, the height and diameter of said bed volume are maintained substantially constant throughout the process.

[0173] In a preferred embodiment, the present invention provides a process according to the first aspect, whereby, on a macroscopic scale, a ID flow profile is maintained throughout the column.

[0174] In a preferred embodiment, said column reactor 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, especially a sufficiently high ratio H: D ensures that a 1-dimen- sional flow can be obtained throughout the column.

[0175] In a preferred embodiment, the present invention provides a process whereby the leach solution is contacted with said metal particles at atmospheric pressure, 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 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 section is flushed with an inert gas, such as N2. This allows for a straightforward removal of hydrogen gas, in case hydrogen gas is formed in the column reactor.

[0176] In a preferred embodiment, the present invention provides a process whereby a gaseous atmosphere in the overflow section of said column reactor is circulated through a scrubber. Preferably, said scrubber is cooled. Preferably, said scrubber and circulation reactor are integrated in one single unit. Preferably, said circulation reactor is maintained at a temperature between 60°C and 95°C, preferably at a temperature of about 75°C and 95°C, and more preferably at a temperature of about 75°C, 80°C or 85°C , or any temperature there in between. Lower temperatures favour the efficiency of the scrubbing operation.

[0177] In another preferred embodiment, the present invention provides a process according to the first aspect, whereby the gaseous atmosphere in the overflow section is treated in a scrubber to remove water and any hydrogen that may have formed. According to the first aspect of the invention, the process steps i. and ii. may occur simultaneously or sequentially and may occur in the same reactor or in separate reactors which may be fluidically connected. The solution to be processed in step ii. may be the solution obtained in step i., a part of the solution obtained in step i., or may be any other solution. Similarly, the solution to be processed in step i. may be the solution obtained in step ii., a part of the solution obtained in step ii., or may be any other solution.

[0178] The process according to the current invention may use a single pressurized pack bed reactor. The process according to the current invention may use a first reaction vessel for the leaching of the metal particles (RL), and a second, separate, reaction vessel for the oxidation of iron (Ro). Preferably, step i. and step ii. of the process take place in separate reactors.

[0179] EXAMPLES

[0180] The following examples are intended to further clarify the present invention and are nowhere intended to limit the scope of the present invention.

[0181] EXAMPLE 1

[0182] Figure 1A shows schematically a process according to the invention whereby metallic nickel is oxidized by ferric iron in a column reactor and whereby the ferrous iron formed is oxidized in a separate oxidation reactor.

[0183] The column reactor RL has an internal diameter D and a height H, whereby the ratio H: D is about 2.35. The reaction zone of the column reactor RL is provided with Ni metal cut cathodes having a dimension of about 50 mm (or 2") by 50 mm (or 2") and having a nickel content of 99.97%. The metal particles containing nickel are intermittently fed on the support plate above the reactor feed section; metal particles feed omitted in Figure 1A. The Ni metal is provided in a bed, said bed having a bed volume characterized by a height and diameter, whereby the ratio of said height to said diameter is about 3.

[0184] An aqueous ferric iron sulphate solution having an iron content of about 15 g / L and a sulphuric acid content of about 10 g / L and also containing nickel sulphate is fed to the column reactor at a temperature of about 89°C via a bottom section and is brought into contact with the metallic nickel particles to yield the oxidation of Ni° to N i2+. The aqueous ferric iron sulphate solution is fed to the column reactor at a flow rate of about 6 times the bed volume per hour, whereby the bed volume BV is defined as the volume of the reactor up to the height of the bed. At the top of the column reactor a nickel sulphate solution having a nickel content of about 120 g / L, further comprising ferrous and ferric iron sulphate, is tapped off at a temperature of about 91°C due to the exothermic nature of the oxidation reaction. The content of ferrous iron, relative to the total content of iron in the nickel sulphate solution, is about 54%. Gases which may have accumulated at the top of the column reactor are treated in a scrubbing unit.

[0185] Nickel hydroxide is added to a fraction <piAof the aqueous nickel sulphate solution which is tapped off at the top of the column reactor to form an iron hydroxide precipitate that is filtered off. Alternatively, ferric iron in the nickel sulphate solution is first reduced to ferrous iron before adding nickel hydroxide. This ensures the formation of ferric hydroxide, which is more easily filtered off. The precipitate is resuspended in an aqueous medium and re-introduced into the circuit.

[0186] A fraction <p3of the aqueous nickel sulphate solution enters the iron oxidation reactor (Ro) which is an autoclave operating at 10 bara, equipped with a mechanical stirrer. Herein ferrous iron is oxidized by introducing sulfuric acid and oxygen through the aqueous medium resulting in a temperature increase up to a temperature of 93°C. The ferric iron solution which is formed is eventually tapped off and introduced in the nickel leaching reactor RL after cooling to 89°C.

[0187] EXAMPLE 2

[0188] A semi-batch process according to Example 1 is executed with an additional buffer tank in fluid connection with the leaching reactor and the oxidation reactor, as depicted in Figure 2. In this configuration, the outflow of the leaching reactor is guided to a buffering tank TB, where the nickel sulphate solution from the leaching reactor is mixed with the ferric iron solution coming from the iron oxidation reactor Ro. This is advantageous because the leaching reactor and the oxidation reactor can be dimensioned smaller compared to the leaching reactor and the oxidation reactor of Example 1. An aqueous sulphuric acid flow is periodically introduced to the buffering tank. Further, a fraction <p3of the aqueous nickel sulphate solution is led to an oxidation reactor for oxidizing the ferrous iron to ferric iron by vigorously stirring under a pressurized atmosphere of air. Both the flows to the leaching reactor, as well as the flow to the oxidation reactor start from the buffer tank. This has the advantage that a separate flow rate can be set for each loop, however, both loops are working at the same, averaged, iron contents.

[0189] Once a nickel sulphate concentration of 120 g / L with a residual sulphuric acid content of 5 g / L is obtained in the buffering tank, the process is stopped, the product solution <pi is collected, and submitted to the iron removal step.

[0190] EXAMPLE 3

[0191] A continuous process according to Example 1, is executed with an additional buffer tank in fluid connection with the leaching reactor and the oxidation reactor, as depicted in Figure 3. In this configuration, the outflow of the leaching reactor is guided to a buffering tank TB, where the nickel sulphate solution from the leaching reactor is mixed with the ferric iron solution coming from the iron oxidation reactor Ro. This is advantageous because the leaching reactor and the oxidation reactor can be dimensioned smaller compared to the leaching reactor and the oxidation reactor of Example 1. From the buffering tank, an aqueous nickel sulphate solution is continuously tapped off as the nickel sulphate solution <pi.

[0192] Further, a fraction <p3of the aqueous nickel sulphate solution is led to an oxidation reactor for oxidizing the ferrous iron to ferric iron by vigorously stirring under a pressurized atmosphere of air. An aqueous sulphuric acid flow is introduced to the oxidation reactor. From there, the aqueous nickel sulphate solution containing ferric iron is now directly led to the leaching reactor. This has the advantage that leaching occurs at high concentration of ferric iron.

[0193] EXAMPLE 4

[0194] A leaching column is loaded with 1 inch by 1 inch Ni cut cathodes, until a bed height of 100 cm is reached. The amount of Ni corresponds to 32.5 kg and a bed volume of 7.85 L, whereby the bed volume is defined as the volume of the column up to the height of the bed. A set-up as depicted in Figure 2 is used. A starting solution containing 30 g / L H2SO4 and 30 g / L Ni added as nickel sulphate and 15 g / L Fe added as ferrous sulphate is prepared. 60 L of this solution is loaded in the autoclave (Ro), 15 L in the buffer tank (TB) and 10 L in the leaching column (RL). The reactor operating volume of the autoclave is defined as the amount of solution in the autoclave, herein 60 L. The autoclave is agitated at 278 rpm. The solution is heated separately in the autoclave to 98°C, the buffer tank to 85°C and the leaching column to 85°C. Subsequently, the autoclave is pressurized with O2 gas to 7 bara. Then circulation of the solution is started. The column pump is activated at a flow rate of 25 bed volumes / hour, and the autoclave pump is activated at 2.33 reactor volumes / hour. A constant volume of 60 L is maintained in the autoclave, the leaching column and the buffer vessel by adding water. H2SO4 is added to the buffer tank to maintain a constant pH value. Ni cathodes are added to the leaching column to maintain the cathode bed height. After reaching a steady state, a product stream with a nickel concentration of 120 g / L is collected from the buffer tank. The leaching rate is 6.4 g Ni / kg Ni in the column / hour.

Claims

CLAIMS1. A process comprising the steps of: i. contacting metal particles containing nickel (0) and / or cobalt (0) in a leaching reactor (RL) with an aqueous ferric salt solution, thereby obtaining an aqueous nickel and / or cobalt salt solution, respectively, comprising a ferrous salt; and ii. contacting an aqueous nickel and / or cobalt salt solution comprising ferrous salt with an oxidizing agent in presence of a mineral acid in an oxidation reactor (Ro), thereby obtaining an aqueous nickel and / or cobalt salt solution, respectively, comprising a ferric salt, whereby at least a part of said ferrous salt formed in step i. is oxidized to ferric salt in step ii., and whereby at least a part of said ferric salt formed in step ii. is used as an oxidizing agent in step i.

2. Process according to claim 1, whereby at least a part of said aqueous nickel and / or cobalt salt solution obtained in step i. and / or at least a part of said aqueous nickel and / or cobalt salt solution obtained in step ii. is evacuated from the process, and whereby said evacuated solution (<piA, cpiB, epic) has a molar ratio of iron to the total of nickel and cobalt that is lower than 2, and higher than 0.01.

3. Process according to claim 1 or 2, whereby said aqueous ferric salt solution flows through said leaching reactor (Ri_).

4. Process according to any of claims 1 to 3, whereby said aqueous ferric salt solution is fed to said leaching reactor (RL) at a flow rate between 0.10 and 20 L per kg of said metal particles in said leaching reactor (RL) per hour.

5. Process according to any of claims 1 to 4, whereby at least a part of the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. is fed to a buffering tank (TB), and / or whereby at least a part of said aqueous nickel and / or cobalt salt solution comprising ferric salt is obtained from a buffering tank (TB) .

6. Process according to any of claims 1 to 5, whereby at least a part of the aqueous nickel and / or cobalt salt solution comprising ferric salt formed in step ii. is fed to a buffering tank (TB), and / or whereby at least a part of said aqueous nickel and / or cobalt salt solution comprising ferrous salt is obtained from a buffering tank (TB).

7. Process according to any of claims 1 to 6, whereby the total iron concentration in said aqueous nickel and / or cobalt salt solution in step i. and step ii. is between 2 and 30 g / L.

8. Process according to any of claims 1 to 7, whereby the oxidizing agent in step ii. is selected of the group consisting of: oxygen-containing gas, ozone, hydrogen peroxide and CL.

9. Process according to any of claims 1 to 8, whereby an atmosphere above the nickel and / or cobalt salt solution in said oxidation reactor (Ro) contains a gaseous oxidizing agent at a partial pressure between 1 bar and 100 bar.

10. Process according to any of claims 1 to 9, whereby said leaching reactor (R.L) is a packed bed reactor.

11. Process according to any of claims 1 to 10, whereby said metal particles containing nickel (0) and / or cobalt (0) have a median particle diameter of more than 1 mm.

12. Process according to any of claims 1 to 11, whereby said aqueous ferric salt solution is fed to said leaching reactor (R.L) in step i. at an inlet temperature (Tiniet) between 50°C and 98°C.

13. Process according to any of claims 1 to 12, whereby step ii. is performed at a temperature between 50°C and 150°C.

14. Process according to any of claims 1 to 13, whereby leaching in step i. is performed with ferric iron as an oxidizing agent that constitutes at least 70 mol% of the total oxidizing agents present.

15. Process according to any of claims 1 to 14, whereby the ratio of ferrous iron to the total content of ferrous and ferric iron of the aqueous nickel and / or cobalt salt solution comprising ferrous salt obtained in step i. is at least 0.05.

16. Process according to any of claims 1 to 15, whereby the ratio of ferric iron to the total content of ferrous and ferric iron of the aqueous nickel and / or cobalt salt solution comprising ferric salt obtained in step ii. is at least 0.05.

17. Process according to any of claims 1 to 16, whereby at least a part of the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. is subjected to an iron removal process.

18. Process according to any of claims 1 to 17, whereby at least a part of the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. is continuously collected.

19. Process according to any of claims 1 to 18, whereby said nickel and / or cobalt salt solution comprises a sulphate and / or chloride salt.

20. Process according to any of claims 1 to 19, whereby sulphuric acid and / or hydrochloric acid is fed to said oxidation reactor (Ro).

21. Process according to any of claims 1 to 20, whereby the aqueous nickel and / or cobalt salt solution comprising ferrous salt formed in step i. has a residual acid content of between 1 g / L and 20 g / L.

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