WO2024235745A1

WO2024235745A1 - Process for manufacturing an aqueous metal solution

Info

Publication number: WO2024235745A1
Application number: PCT/EP2024/062567
Authority: WO
Inventors: Andrew WILLSON; Maria Jose LACADENA
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2023-05-12
Filing date: 2024-05-07
Publication date: 2024-11-21
Anticipated expiration: 2025-11-12

Abstract

The invention relates to a process for manufacturing an aqueous metal solution by leaching solid metal objects with an aqueous leaching solution comprising at least one acid leaching agent.

Description

PROCESS FOR MANUFACTURING AN AQUEOUS METAL SOLUTION

TECHNICAL FIELD

TECHNICAL BACKGROUND

Nowadays the demand of electric vehicles (EV) increased. The current predominate battery energy storage technology for EVs is the lithium-ion battery (LIB). Therefore, also the sourcing of raw materials for this type of battery becomes an issue. LIBs of lithium (Li) nickel (Ni) manganese (Mn) cobalt (Co) oxides, also called NMC, have a sufficient long live and a less likelihood of fire or explosion. Hence, NMC are the leader for automotive applications, i.e., for EVs. The cathode used in NMC batteries is a combination of nickel:manganese:cobalt for instance in a weight ratio 8: 1 : 1 hence called NMC 811. To produce these cathodes, aqueous solutions of the metals are used, especially metal sulphate solutions are used.

However, even though much more of these metals will be needed in near future, most of these metals in the global supply chain are not actually suited for battery production. Battery demand requires high grade metal products to produce metal sulphate and currently, for example less than 10 % of nickel supply is in sulphate form. Hence, there is a need to capture the rising demand for producing aqueous metal solution and a lot of research is going on in this field.

The battery grade metal sulphate solutions are currently mainly produced by dissolving metal sulphate crystals. In the alternative, the metals can be sourced in powder form, or as briquettes made by compressing powder. These crystals, powders and briquettes are then dissolved in sulphuric acid to produce battery grade metal sulphate solutions.

In WO 2021/105365 a process for manufacturing nickel sulphate having a purity that is sufficient for batteries is described. In said process metal particles comprising nickel are leached with an aqueous sulphuric acid solution in presence of hydrogen peroxide. This process is usually carried out in batch mode, but for industrial applications a process, which can be conducted in a continuous mode, is of more interest.

WO 2022/053448 describes a process for producing metal sulphates, which can be carried out in a continuous mode. In said process electrolytically produced metal objects and an aqueous leaching solution comprising sulphuric acid and oxidizing agent in liquid form are added to the reaction vessel in a counter-current mode to obtain the desired metal sulphate solution. In particular, the metal objects are introduced from the top into a vertical reaction column and the leaching solution for dissolving the metal objects is introduced from the opposite direction. The obtained mixture is recirculated in the reaction vessel. However, in said process it cannot be ensured that the metal objects are maintained in the reaction column long enough for dissolving them entirely in the aqueous leaching solution. Due to dissolution (leaching) process, the metal objects shrink and form smaller particles, also called fines or fine particles. These fines, as the introduced metal objects, are subjected to the gravity. However, these fines have the tendency to float upwards in the reaction column, because the friction of the liquid on them drags them upwards and the velocity of the fines caused by this effect exceeds the gravity settling velocity when the fine particles become small enough. Therefore, at least a part of the fines is lost through the product overflow of the column for the production process. Moreover, the fines are present in the produced metal sulphate solution as impurities. Therefore, there is the need to separate the fines from the metal sulphate solution to obtain an aqueous metal sulphate solution in battery grade. However, this further process step also results into a decreased yield of the produced aqueous metal sulphate solution having the desired purity.

Hence, there was still the need to provide a process for the manufacturing of an aqueous metal solution having a purity suitable for producing batteries and which can be easily produced in high yields.

Present invention aim is to find a process for dissolving the metal solid objects and reducing the size of those objects to tiny particles that can be fully dissolved before leaving the reactor.

SUMMARY OF THE INVENTION

The present invention refers to a process for manufacturing an aqueous metal solution by leaching solid metal objects with an aqueous leaching solution comprising at least one acid leaching agent in a reactor vessel having a central draft tube surrounded by an annulus, at least one exit point from the annulus to a recirculation loop, a recirculation pump, and a product overflow, wherein the metal solid objects and the aqueous leaching solution are added from the top through the draft tube into the reactor vessel to form an upward flow in an annulus around the draft tube inside the reactor vessel, and wherein the recirculation loop is outside the reactor vessel. BRIEF DESCRIPTION OF THE DRAWING

Figure 1 schematically shows a reactor vessel suitable for carrying out the process of the invention. The reactor vessel (1) has exit points (10) and (11) to a recirculation loop (2), a recirculation pump (3), a product overflow (4), and a central draft tube (5) surrounded by an annulus (14), through which the solid metal objects (6), the leaching solution (7) and the recirculated mixture (8) are introduced into the reactor vessel (see feed line (6) for the solid metal objects, feed line (7) for the fresh leaching solution and feed line (8) for the recirculated mixture). The exit points (10) and (11) have regulatory valves (12) and (13) respectively. The reactor vessel may have a solid/liquid separator (9) that may be a magnetic filter.

DETAILED DESCRIPTION OF THE INVENTION

Before the issues of the invention are described in detail, the following should be considered:

As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

The terms "comprising", "comprises" and "comprised of as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of as used herein comprise the terms "consisting of, "consists" and "consists of.

Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

As used herein, the term "average" refers to number average unless indicated otherwise.

As used herein, the terms "% by weight", "wt.- %", "weight percentage", or "percentage by weight", and the terms "% by volume", "vol.- %", "volume percentage", or "percentage by volume", are used interchangeably.

The recitation of numerical ranges by end points includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

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.

The term “aqueous metal solution” as used herein refers to an aqueous solution of a metal salt, for example nickel sulphate (NiSCU), obtained by leaching a solid metal object with an acid leaching agent in water.

The term “continuous process” as used herein refers to a process, wherein the starting materials can be added to the reactor and the product can be collected without discontinuing the process. This does not exclude that also a continuous process is occasionally interrupted, for example for maintenance. A batch process on the other hand is characterized in that starting materials are added in specified amounts, and the process performed to produce a product and the products recovered, before a new batch can be produced.

The term “particles” as used herein intends to designate a particulate solid having a mean particle size ranging from the microns to the centimetres, and which may have any shape (powder, pellets, briquettes etc.).

The terms “plates, squares, rounds, crowns, tubes, and bars” as used herein refers to different geometric shapes of metallic cathode material.

The term “battery grades” as used herein refers to the quality, i.e., level of impurities presents in the produced end-product. Frequently, 99.9 % purity is required. The exact specifications may vary depending on the intended use and the specifications of the batteries, but this term is nevertheless well understood by a person skilled in the art.

The term “electrowinning” as used herein means a process where metals are recovered in an electrolytic cell. An aqueous solution containing metal sulphates is subjected to an electric potential, resulting in that metal cations are drawn to the surface of the negative pole, the cathode, where they are deposited as pure metal. The term “electrorefining” as used herein relates to a process, where impurities are removed. Anodes comprising impure metal ate subjected to an electric potential within an electrolytic cell, corroding the anodes into solution, and the refined, pure metal is deposited on the cathodes. Both electrowinning an electrorefining processes result in electrolytically produced metals on the cathode or forming the cathode and are available in different shapes.

In the following passages, different alternatives, embodiments and variants of the invention are defined in more detail. Each alternative and embodiment so defined may be combined with any other alternative and embodiment, and this for each variant unless clearly indicated to the contrary or clearly incompatible when the value range of a same parameter is disjoined. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

Furthermore, the particular features, structures or characteristics described in the present description may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.

The present invention refers to a process for manufacturing an aqueous metal solution by leaching solid metal objects (6) with an aqueous leaching solution (7) comprising at least one acid leaching agent in a reactor vessel (1) having a central draft tube (5) surrounded by an annulus (14), at least one exit point (10) or (11) from the annulus to a recirculation loop (2), a recirculation pump (3), and a product overflow (4), wherein the solid metal objects and the aqueous leaching solution are added from the top through the draft tube into the reactor vessel to form an upward flow in the annulus around the draft tube inside the reactor vessel, and wherein the recirculation loop is outside the reactor vessel. According to the invention the metal objects move in the draft tube in a co-current downward direction in respect to the downward flow of the liquid in the draft tube.

In an embodiment of the invention, it is preferred that there is no chemical compound other than the solid metal objects, the aqueous leaching solution, and the recirculated mixture is added to the reactor vessel, in particular that there is no gas supply into the reactor vessel. In another embodiment of the invention, it is preferred that there is no additional agitation in the reactor vessel, and especially that there is no axial flow impeller within the draft tube.

The leaching solution flows down the draft tube and then flows up into the annulus around the draft tube. Preferably, the ratio of the cross-sectional area of the draft tube and the cross-sectional area of said annulus around the draft tube is from 1 :0.5 to 1 : 10, more preferably from 1: 1 to 1 :8, even more preferred from 1 : 1.5 to 1 :6 or 1 :2 to 1 :4.

The dimension of the cross-sectional area of the annulus inside the reactor vessel depends on the dimension of the reactor vessel, and the dimension of the draft tube. . Furthermore, the diameter of the draft tube used in the process of the invention is preferably in a range, which ensures that the velocity of the downward flow of the aqueous leaching solution in the draft tube is higher than the velocity of the upward flow of the liquid in the annulus around the tube in the reactor vessel. Generally, the diameter of the draft tube used in industrial process is between 0.2 and 3.0 m.

Without wishing to be bound by theory, due to use of a draft tube having a smaller diameter than the reactor vessel it is possible to obtain the desired difference between the velocity of the downward flow of the aqueous leaching solution in the draft tube and the velocity of the upward flow of the liquid in the annulus around the tube inside the reactor vessel. The ratio of the downward flow velocity of the aqueous leaching solution in the draft tube to the upward flow velocity of the liquid in the annulus can be altered by changing the ratio of the diameter of the draft tube to the diameter of the reactor vessel.

Especially, it is preferred that the difference in the velocities is such that the velocity of the upward flow of the liquid in the annulus around the draft tube inside the reactor vessel is slow enough to ensure that the metal solids, i.e., the solid metal objects and the fines formed in the leaching step, have enough time to dissolve entirely. In particular, due the different flow velocities between the high downward flow of the aqueous leaching solution in the draft tube and the lower upward flow of the liquid in the annulus around the draft tube, it is possible to keep the fines, which can be dragged upwards by the flow in the reactor vessel, long enough in the upward flow in an annulus around the draft tube inside the reactor vessel so that they have time to fully dissolve before reaching the product overflow of the reactor vessel.

The higher the downward velocity of the aqueous leaching solution in the draft tube, the higher the dissolution of the metal solid objects. The lower the upward velocity of the liquid in the annulus, the smaller the particles dragged upwards. The smaller the size of the particles that are dragged upwards, the greater the chance of dissolving the particles before they leave in the overflow.

Therefore, according to the invention, in an optimum configuration, i.e., the cross-sectional area of the annulus formed by the upward flow around the draft tube inside the reactor vessel is very large in comparison to the cross-sectional area of the draft tube, there is no need to separate the fines from the produced aqueous metal solution. Based on his general knowledge a person skilled in the art is able to determine the optimal ratio between the diameter of the draft tube and the diameter of the reactor vessel. Nevertheless, preferably a separator, as described below, is used in the process of the invention to avoid in any case that particles leave the reactor vessel.

In a preferred embodiment of the invention, the velocity of the downward flow of the aqueous leaching solution in the draft tube is more than the velocity of the upward flow of the liquid in the annulus around the draft tube inside the reactor vessel. The velocity of the downward flow of the aqueous leaching solution in the draft tube and the velocity of the upward flow of the liquid in the annulus around the draft tube can be easily determined by methods known in the art.

As the liquid flows upward in the annulus, particles smaller than a given size are dragged upwards, and the remaining particles bigger than said given size settle downwards according to the Stokes Law formula below:

V Settling of the particles [4gDp (detp - deni)/3/deni/C] 0.5 g = acceleration due to gravity = 10 (m/s²)

D_p = Particle diameter of the given size (m)

C = Drag coefficient (friction of the liquid on the particle) deni = Liquid density (kg/m³) den_p = Particle density (kg/m³)

The downward velocity of the aqueous leaching solution flow in the draft tube can be determined by dividing the sum of the flow from the recirculation pump and the flow of the additional fresh chemicals by the cross-sectional area of the draft tube.

The upward flow velocity of the liquid in the annulus can be calculated by multiplying the downward flow velocity of the aqueous leaching solution in the draft tube by the ratio of the cross-sectional area of draft tube divided by the cross-sectional area of the annulus.

Vup annulus Vdown draft tube * (Xsectional area of the draft tube / Xsectional area of the annulus ) If the upward velocity of the liquid in the annulus exceeds the settling velocity of the particle of a given diameter, then the particle will rise. The purpose of the invention is such that there is sufficient time available to dissolve the rising particles in the annulus before they leave the overflow line.

Preferably, the velocity of the downward flow of the aqueous leaching solution is preferably between 0.05 m/s and 2.0 m/s, more preferably between 0.10 m/s and 1.5 m/s, even more preferably between 0.20 m/s and 1.0 m/s, and the velocity of the upward flow of the liquid in the annuals around the draft tube inside the reactor vessel is from 0.012 to 1.0 m/s, preferably from 0.02 to 0.5 m/s, most preferably from 0.05 to 0.25 m/s.

The ratio between the downward flow velocity of the aqueous leaching solution in the draft tube and upward flow velocity of the liquid in the annulus around the draft tube is preferably in the range from 1 to 50, more preferably from 1.5 to 30 and even more preferably from 2 to 10. According to the invention, the upward flow velocity of the liquid in the annulus around the draft tube is slow enough to ensure that preferably at least 98 %, more preferably at least 98.5 %, even more preferably at least 99 % or 99.9 %, most preferably 100% of the solid metal objects including the metal fines formed during the dissolution are dissolved in the aqueous leaching solution. The quantity of the solid metal objects dissolved can be determined by measuring the concentration of metallic salt in the reactor mixture, or by measuring the difference between the weight of solid metal objects added from the top and the concentration of the metal particles in the manufactured/obtained aqueous metal solution.

Furthermore, to enhance the dissolution of the solid metal objects in the aqueous leaching solution, the mixture of the solid metal objects and the leaching solution is recirculated into the reactor via at least one exit point on the reactor vessel connected to a recirculation loop and a recirculation pump. At least one exit point is on the side of the reactor vessel which is opposite to the product overflow. A recirculating pump is placed on the circulation loop (2) after the at least one exit point, in a level lower than the level of the exit point.

In an embodiment of the invention, the reactor vessel has at least two exit points (10) and (11) from the annulus to the recirculation loop (2), the exits points are on the side of the reactor vessel which is opposite to the product overflow (4), the first exit point (10) is at the same level as the product overflow (4) and the second exit point (11) is below the first exit point (10).

According to this embodiment of the invention, in order to dissolve the tiny remaining particles of the solid metal object, at least some of the upward flow in the annulus around the draft tube needs to pass upward into the zone inside the reactor vessel between the two exit points (10) and (11). This zone, which is inside the reactor vessel between the two exit points (10) and (11), is defined as "particle destruction zone”.

The dimensions of the reactor vessel and the particle destruction zone can be economically optimised by allowing part of the upward flow in the annulus around the draft tube to rise to the top of the reactor vessel before being drawn into the recirculation loop, thus allowing a good concentration of the leaching solution going into top part of the reactor vessel. There are regulatory valves (12) and (13) at each exit points (10) and (11) respectively, so that at least part of the upward flow in the annulus around the draft tube is taken from the top exit point (10) for recycle, to ensure that enough leaching solution reaches the particles to make them dissolve.

The recirculation flow rate depends on the scale of the reactor vessel and a suitable flow rate can be determined by a person skilled in the art. Usually, the recirculation velocity is in the same range as the velocity of the downward flow of the aqueous leaching solution as indicated above. According to the invention, as mentioned above, the addition of the solid metal objects, the fresh aqueous leaching solution and the recirculated mixture into the reactor vessel is preferably operated in a co-current mode, i.e., all reactants (the solid metal objects, the fresh aqueous leaching solution as well as the recirculated mixture) are added into the reactor vessel from the same direction.

The process of the invention can be carried out in batch mode, in a semi- continuous mode or in a continuous mode. Preferably, the process is carried out in a continuous mode.

Furthermore, even though by using the process of the invention it is possible to dissolve the solid metal objects including the fines entirely and thus the use of liquid/solid separator is not absolutely necessary, nevertheless, as mentioned above, a liquid/solid separator is preferably used to produce an aqueous metal solution having a very high battery grade purity. For this purpose, the liquid/solid separator (9) is placed preferably after the product overflow of the reactor vessel. Different devices for separating solids from liquids are commercially available. Suitable separators are for example filters, decanters, wet scrubbers, hydrocylones, centrifuges, or magnetic separators. Preferably, the separator used in the process of the invention is a magnetic separator.

The magnetic separation can be performed using a magnetic filter, for example magnetic elements such as rods or plates positioned in the product flow path after the product overflow of the reactor vessel. Metal fines adhere to the magnetic filter and are removed from the product solution. When the magnetic filter reaches its capacity, it can be removed and cleaned, either mechanically or manually. The collected fines can be subjected to further leaching, recovered, or disposed, as desired.

According to the invention, the metal objects used in the process are selected from the group consisting of metal particles, briquettes, pellets and electrolytically produced solid metal objects. Preferably, the solid metal objects are metal particles.

The metal particles may have any shape for instance they are in form of a powder, or they are pellets or briquettes. From a chemical point of view, a powder may be preferred (hence, with particle size in the range of microns to the mm, typically between 50 pm and 5 mm, more preferably between 100 pm and 3 mm) to have a high surface to volume ratio but from an industrial point of view, pellets or briquettes might be easier to handle. These typically have dimensions in the range of the mm to the cm, typically between 10 and about 500 mm, more preferably between 15 and 45 mm. Furthermore, according to the invention, the solid metal objects may be electrolytically produced solid metal objects as for example described in WO 2022/053448, incorporated herein by reference. The electrolytically produced solid metal objects may be selected from the group consisting of cathode plates, squares, rounds, crowns and chippings. For carrying out the process of the invention, it preferred that for example the cathode plates are cut, chopped, or otherwise broken up into pieces of suitable size. Metallic nickel or cobalt cathodes typically have a regular shape but can have also irregular shape. The cathodes used can be full-size cathodes or any other size and shape cut from the initial full plate or other shapes produced in an electrowinning or electrorefining process. Nickel or cobalt containing off-grade materials of any shape can also be considered as material suitable for the process of the invention.

The metal of the solid metal objects used in the process of the invention is preferably a battery metal, which is preferably selected from the group consisting of nickel, manganese, cobalt, and a combination of a least two of them, more preferably the solid metal object comprises at least nickel. The term “solid metal objects comprising at least nickel” intends to designate either substantially pure Ni objects, objects of a substantially pure alloy comprising Ni or a mixture of substantially pure Ni objects with a substantially pure object of at least one other metal, for instance solid metal objects resulting from the recycling of a used nickel-manganese-cobalt cathode and hence, also comprising Co and Mn. In an embodiment, the metal solid objects in the process of the invention are selected from precious metals comprising gold, silver, platinum, palladium, rhodium, and ruthenium.

By the term “substantially pure” is meant containing less than 2 wt.-% impurities (i.e., compounds from another chemical nature), preferably less than 1 wt.-%.

As to the mixture of Ni objects with objects of at least one other metal, and to objects of a substantially pure alloy comprising Ni, these generally contain at least 60 wt.-% of Ni, preferably at least 70 wt.-% of Ni and even more preferably, 80 wt.-% of Ni or more.

As to the at least one other metal in the mixture of solid metal objects or in the alloy, it is preferably chosen between Co and Mn and more preferably, it is a mixture of both. The result of the process of the invention may be a mixed aqueous metal solution, which will be used by cathode manufacturers. In this embodiment, the mixed metal source may be originating from used batteries hence, comprise Ni:Mn:Co in a weight ration from about 1 : 1: 1 to about 8: 1 : 1, values close to the latter being preferred.

The acid leaching agent used in the process of the invention, preferably is selected from the group consisting of sulphuric acid, hydrochloric acid, phosphoric acid, nitric acid, oxalic acid, citric acid, and a combination of a least two of these, preferably the acid leaching agent is sulphuric acid.

The concentration of the acid leaching agent in the aqueous leaching solution used in the process of the invention is preferably 5 wt.-% or more, more preferably 20 wt.-% or more, even more preferably 30 wt.-% of more, based on the total weight of the aqueous leaching solution. Generally, the concentration of the acid leaching agent in the aqueous leaching solution is 99 wt.-% or less, preferably 80 wt.-% or less or even 60 wt.-% or less, based on the total weight of the aqueous leaching solution. In practice, good results are obtained when the acid leaching agent is used in a concentration of 20 wt.% up to 40 wt.-%, especially when the solid metal objects are in powder form, while for briquettes the concentration of the acid leaching agent should be between 15 wt.-% and 30 wt.-%, based on the total weight of the aqueous leaching solution.

Preferably, the process of the invention is carried out such that the obtained aqueous metal solution comprises no or only minor amounts of the acid leaching agent. For instance, the residual acid leaching agent concentration in the produced aqueous metal solution is between 0 to 10 g/1, preferably 0 to 6 g/1. According to the invention, the pH of the aqueous leaching solution is below 5, more preferably below 4, even more preferably below 1.

Furthermore, in general, it is preferred that the pH of the upward flow in the annulus around the draft tube inside the reactor vessel is maintained in an interval of -1.5 to 5, preferably in an interval of pH -1 to 4, more preferably in an interval of -1.2 to 3, and most preferably the pH is maintained between -1 to 1.

Moreover, to facilitate the dissolution of the solid metal objects the aqueous leaching solution may additionally comprise an oxidizing agent in liquid form. The oxidizing agent is selected preferably from the group consisting of hydrogen peroxide, persulphates, halogens, and halogen compounds such as chlorates and perchlorates, hypochlorites, more preferably the oxidizing agent is hydrogen peroxide.

The oxidizing agent in liquid form, in particular an aqueous hydrogen peroxide solution, used in the process of the invention preferably has a concentration of 20 wt.-% or more, more preferably of 30 wt.-% or more. It generally has a concentration of 60 wt.-% or less, preferably of 50 wt.-% or less or even 35 wt.-% or less. In practice, for example good results are obtained with an aqueous hydrogen peroxide solution having a concentration between 30 wt.-% and 60 wt.-%

In another embodiment of the process of the invention, it is possible to premix the oxidizing agent and the acid together before adding them to the draft tube.

Preferably, at least a part of the oxidizing agent in liquid form used in the process of the invention is added through the draft tube into the reactor vessel simultaneously with at least a part of the aqueous leaching solution.

In any event, when the oxidizing agent in liquid form is an aqueous hydrogen peroxide solution, the aqueous hydrogen peroxide solution introduction through the draft tube into the reactor vessel preferably starts before a substantial amount of hydrogen is generated, in particular before the explosive concentration of hydrogen is reached in the gas phase of/above the reactor vessel.

Furthermore, when the oxidizing agent is hydrogen peroxide, the starting pH of the aqueous leaching solution is preferably below 1, typically about 0.5 and the pH of the upward flow in the annulus around the draft tube inside the reactor vessel is preferably still below 3.

In a preferred embodiment of the invention, the solid metal object comprises at least Ni, and the aqueous leaching solution comprises sulphuric acid as leaching agent and hydrogen peroxide as oxidizing agent. In this preferred embodiment, the starting materials (both the aqueous sulphuric acid solution (H2SO4) and the aqueous hydrogen peroxide solution (H2O2) may be more concentrated than described above, i.e., typically 96 wt.-% for H2SO4 and up to 70 wt.-% for H2O2.

In fact, the concentrations of the reactive chemical species used in the process are linked. They depend on the specific type of the reactive chemical species, but also in which form the solid metal objects are used, for example in general the dissolution of particles is easier than of electrolytically produced solid metal objects. Based on his general knowledge, a person skilled in the art knows in which molar ratios the reactive chemical species have to be used in order to obtain an optimal leaching result.

Ideally, it would be advantageous to use amounts of solid metal objects, e.g. Ni, leaching agent., e.g. H2SO4, and oxidizing agent, e.g. H2O2, as close as possible to their stoichiometric amounts, which means for example a molar ratio Ni:H2SO4:H2O2 about 1 : 1 : 1 (see the following reaction scheme):

Ni + H2O2 + H2SO4 - ► NiSO₄ + 2 H2O

However, since, for example, in practice it is difficult or even impossible to avoid some H2O2 decomposition (unless by adjusting the dosing rate and/or with a small excess of sulphuric acid), the amount of H2O2 is used preferably slightly higher, for instance of at least 5 % (i.e. 1.05 mol vs 1 mol of the other species), generally at least 10 % and even higher, compared to the molar amount of the other species. As mentioned above, based on his general knowledge a person skilled in the art is able to determine the optimal ratio for the reactive chemical species used in the process of the invention, for example it is preferred, especially in case the solid metal objects are used in form of metal particles, briquettes or pellets, to use a molar ratio of Ni:H2SO4:H2O2 between 1 : 1 : 1.3 and 1 : 1 :1.1, typically equal to 1:1:1 2.

In preferred embodiment, especially, when the solid metal objects are metal particles comprising nickel, a molar excess of H2SO4:Ni may be used. In practice, good results can be obtained with a molar ratio H2SO4:Ni of 1.1 : 1 and in particular, with a molar ratio Ni:H2SO4:H2O2 of 1 : 1.1 : 1.2, in case the solid metal objects are metal particles, briquettes or pellets.

The water used in the process of the invention is preferably present in an amount sufficient to solubilize the metal salt obtained by the leaching process of the invention, for example NiSCU. This means that water is used in an amount at least equal to the amount required to get an aqueous solution saturated with the metal salt throughout the process including the cooling down of the solution to room temperature. Preferably, the amount of water is slightly higher to ensure that the final metal salt concentration is close to but still below saturation. With respect to NiSO4, good results are obtained if a final NiSCU concentration between 80% and 90% of its molar concentration at saturation at room temperature is used.

According to the invention, it is preferred that the leaching process is conducted such that the temperature of the upward flow the annulus around the draft tube inside the reactor vessel is maintained between 50 °C and up to the boiling point of the leaching solution, i.e., generally the temperature is maintained in an interval between 50 °C and 100 °C, more preferably between 60 and 85 °C, or even more preferably between 65 and 75 °C. According to one embodiment of the invention, the upward flow in the annulus around the draft tube inside the reactor is cooled or pressurized to prevent boiling.

Preferably external heating can be applied when starting the leaching process of the invention. However, usually the dilution of the acid leaching agent and the leaching reaction itself are exothermic reactions, and during operation also the recirculation pump will contribute to an increase in temperature. It is contemplated that a high production rate and a high recirculation rate will require cooling, whereas a low production rate as well as the start-up of the process will require heating. Cooling and heating is preferably achieved using heat exchanges in the recirculation loop. The advantage of this is that by avoiding traditional methods of heating, such as the injection of steam, one also avoids the introduction of impurities, such as iron, frequently encountered in process waters. Furthermore, redistribution of the heat, produced by the exothermic reaction, throughout the system reduces the need for specific cooling of the reactor vessel.

The leaching reaction of the invention can be conducted at atmospheric pressure or under a pressure of up to 10 bar with the addition of nitrogen, oxygen, or air. In the presence of oxygen or air under pressure, lower (sub-stoichiometric) amounts of H2O2, which is the preferred oxidizing agent, might be used since the oxygen could carry out part of the oxidation.

Furthermore, the process of the invention may be operated in a duration of from minutes to several hours. Preferably, the duration time of the process is between 60 minutes and 36 hours, more preferably between 4 hours and 24 hours, even more preferably between 6 and 12 hours.

The aqueous metal solution obtained by the process of the invention is generally brought or kept at atmospheric pressure and cooled down to room temperature before eventually being further processed to isolate the metal salt produced, for example by crystallization. However, the pure aqueous metal salt solution obtained by the process of the invention can also be used directly as a feed material for producing the cathode material.

The above-described process can be carried out with the aid of an arrangement comprising at least on reactor vessel as schematically shown in Figure 1. The arrangement comprises at least one reactor vessel (1) with exit points (10) and (11) to a recirculation loop (2), a recirculation pump (3), a product overflow (4), optionally a solid/liquid separator (9) after the product overflow, and a central draft tube (5), surrounded by an annulus (14). The solid metal objects (6) and the leaching solution (7) are added through the top of the central draft tube (5) into the reactor vessel. Additionally, a heat exchanger (not shown) may be arranged in the recirculation loop for heating or cooling the leaching solution as necessary. Additionally, regulatory valves (12) and (13) regulates the flow at the exits points (10) and (11). With the aid of a pump (not shown) the product solution having preferably a metal content of at least 100 g per litre, more preferably at least 150 g/1, even more preferred at least 200 g/1, can be withdrawn through the product overflow from the reactor vessel. A feeder can be arranged for automatically feeding the solid metal objects through the draft tube into the reactor vessel without interrupting the leaching process of the invention. The rate of feeding the solid metal objects, the addition of fresh leaching agent and optional oxidizing agent, the temperature and the rate of recirculation are adjusted so that a continuous output of the metal salt solution meeting the desired quality parameters is achieved.

The reactor vessel and the associated equipment, pipes and vessels or tanks are made of material resistant to strong acids and oxidizing agents, for example made of a polymer composite, duplex stainless steel, coated metal, or polymer liners. Such examples might include a fiber reinforced polymer or a ceramic or glass coated metal.

Examples

Example 1 - Batch reaction:

The test was carried out in a double jacket reactor of 4 liters capacity with a diameter of 140 mm and a height of 320 mm, comprising a draft tube inside of 50 mm of diameter and 400 mm of length. The draft tube was placed about 5 cm above the bottom of the reactor.

Raw material:

• Nickel plates containing 99.8 wt% Nickel - Nickel plates are broken Nickel Cathode Squares with max size of 50 mm from Goodfellow.

• Sulphuric acid with 98 wt% concentration from Merck.

• Hydrogen peroxide with 50 wt% concentration from Solvay.

The reactor equipment was connected to the heating and cooling water systems. Auxiliary equipment such as peristaltic pump, temperature sensor, pH sensor. The nickel plates are packed inside the draft tube, with a total amount of 763 grams for the test. Then 1275.5 ml of sulphuric acid solution (20% w/w) was introduced inside the reactor and heated to 70°C. The solution recirculates through the draft tube with the support of a pump with at a flow rate of ~1 L/hour. Once the solution reached the set temperature, the addition of hydrogen peroxide (50% w/w) starts progressively at a dosing rate of 0.8 ml/min. The total amount of hydrogen peroxide introduced was 176.7 grams, dosed for over 3 hours and the total reaction time was 8 hours. A sample was taken every hour for the analysis of nickel by ICP-OES (Inductively coupled plasma - optical emission spectrometry).

After 8 hours, the solution was extracted from the reactor and measured the concentration of hydrogen peroxide. The remaining nickel was extracted, rinsed with distilled water, dried, and then weighed. The remaining amount of nickel was 626.84 grams.

Figure 2 shows the amount of nickel in g/L (liter of leached solution) dissolved over time (hour), it can be seen that the concentration of nickel increases specially in the first three hours of the reaction during the addition of hydrogen peroxide. Once all the peroxide is introduced in the reactor the kinetics of nickel dissolution decreases, where nickel reacts with the remaining peroxide in the solution.

Figure 3 shows hydrogen peroxide concentration in the leached solution over time measured by potentiometric titration with Cerium (IV) sulphate, starting at 3 hours of reaction. On the X axis the time is expressed in hours, and on the Y axis the hydrogen peroxide is expressed in percentage. The concentration decreases progressively to a point where hydrogen peroxide can no longer be detected. The peroxide efficiency was calculated based on the amount of nickel dissolved.

The moles of nickel reacted divided by the moles of hydrogen peroxide.

Peroxide efficiency: ((Ni (grams) final - Ni (grams) initial)/ Ni MW) / (H2O2 (grams as 100%) / H2O2 MW) x 100

The peroxide efficiency at the end of the reaction was 89% and the final pH was 0.56.

Example 2 - Continuous reaction:

The test was carried in the same reactor as in Example 1. Auxiliary equipment such as peristaltic pump, temperature sensor, pH sensor. Two storage tanks, one for the sulphuric acid and the other for hydrogen peroxide, where two pumps would pump the chemicals to the top of the draft tube which is pack with the nickel plate. The bottom of the reaction presents two exit with 10 mm diameter each, one for the recirculation of the leach solution, and the other for the overflow of the nickel sulphate solution.

In one experimental run, the draft tube was packed with 1467.3 grams, the temperature was maintained at 70°C, 50% w/w hydrogen peroxide was added at a flow rate of 35ml/h, and 20% w/w sulphuric acid was added at a flow rate of 184ml/h. The solution recirculates through the draft tube with the support of a pump with at a flow rate of ~1 L/hour. The process was running in continue for 27 hours, exhibiting stable hydrogen peroxide concentrations over time at about 0.6%.

Nickel sulphate solution was constantly removed, from the overflow where fines were not present. Samples were taken every hour for the first 8 hours and then every 2 hours to measure the concentration of nickel by ICP-OES. The concentration of nickel in g/1 in the leached solution is shown in Figure 4 as a function of time (in hour). The final pH of the leached solution was 0.2.

Claims

1. A process for manufacturing an aqueous metal solution by leaching solid metal objects with an aqueous leaching solution comprising at least one acid leaching agent in a reactor vessel having a central draft tube surrounded by an annulus, at least one exit point from the annulus to a recirculation loop, a recirculation pump, and a product overflow, wherein the solid metal objects and the aqueous leaching solution are added from the top through the draft tube into the reactor vessel to form an upward flow in the annulus around the draft tube inside the reactor vessel, and wherein the recirculation loop is outside the reactor vessel.

2. The process according to claim 1, wherein the reactor vessel has at least two exit points from the annulus to the recirculation loop, the exit points are on the side of the reactor vessel which is opposite to the product overflow, the first exit point is at the same level as the product overflow and the second exit point is below the first exit point.

3. The process according to claim 1 or 2, wherein the velocity of the downward flow of the aqueous leaching solution in the draft tube is higher than the velocity of the upward flow of the liquid in the annulus around the draft tube in the reactor vessel, preferably the ratio of the velocity of the downward flow of the aqueous leaching solution in the draft tube to the velocity of the upward flow of the liquid in the annulus around the draft tube inside the reactor vessel, is in the range from 1 to 50, more preferably from 1.5 to 30, and even more preferably from 2 to 10.

4. The process according to any one of the preceding claims, wherein the ratio of the cross-sectional area of the draft tube and the cross-sectional area of the annulus around the draft tube in the reactor vessel is from 1 :0.5 to 1 : 10.

5. The process according to any one of the preceding claims, wherein the upward flow velocity of the liquid in the annulus around the draft tube inside the reactor vessel is slow enough such that the solid metal objects are entirely dissolved in the mixture.

6. The process according to any one of the preceding claims, wherein the mixture recirculated in the recirculation loop is added from the top through the draft tube into the reactor vessel.

7. The process according to claim 5, wherein the addition of the solid metal objects, the aqueous leaching solution and the recirculated mixture into the reactor vessel is operated in a co-current mode.

8. The process according to any one of the preceding claims, wherein the process is a continuous process.

9. The process according to any one of the preceding claims, wherein the reactor vessel has a solid/liquid separator after the product overflow, which is preferably a filter, a decanter, a wet scrubber, a hydrocylone, a centrifuge, or a magnetic separator.

10. The process according to any one of the preceding claims, wherein the solid metal objects are selected from the group consisting of solid metal particles, briquettes, pellets and electrolytically produced solid metal objects, such as cathode plates, squares, rounds, crowns and chippings.

11. The process according to any one of the preceding claims, wherein the solid metal objects are metal particles, which have preferably a particle size between 50 pm and 5 mm, or metal pellets or metal briquettes, which have preferably a dimension in the range of between 10 to 500 mm.

12. The process according to any one of the preceding claims, wherein the metal of the solid metal object is a battery metal or a noble metal, preferably selected from the group consisting of nickel, manganese, cobalt, gold, silver, platinum, palladium, rhodium, and ruthenium, and a combination of a least two of them, more preferably the solid metal object comprises at least nickel.

13. The process according to any one of the preceding claims, wherein the acid leaching agent is selected from the group consisting of sulphuric acid, hydrochloric acid, phosphoric acid, nitric acid, oxalic acid, citric acid, and a combination of a least two of these, preferably the acid leaching agent comprises sulphuric acid.

14. The process according to any one of the preceding claims, wherein the aqueous leaching solution additionally comprises an oxidizing agent in liquid form, which is preferably selected from the group consisting of hydrogen peroxide, persulphates, halogens, and halogen compounds such as chlorates and perchlorates, hypochlorites, more preferably the oxidizing agent is hydrogen peroxide.

15. The process according to any one of the preceding claims, wherein the temperature of the upward flow in the annulus around the draft tube inside the reactor vessel is maintained between 50°C and up to the boiling point of the leaching solution.