Process and system for dissolving metal feedstock

Abstract

The present disclosure relates to a system and process for dissolving metal feedstock such as powdered nickel and / or cobalt, the system comprising a cooling loop that recycles and actively cools the reaction solution, optionally acting as the inlet for introducing at least one fluid reagent such as acid and / or oxidising agent into the reaction vessel The process of the disclosure provides for a safe and fast method of dissolving metal feedstocks that may then be used in downstream applications, such as in the production of active materials for electrochemical cells.

Description

[0001] PROCESS AND SYSTEM FOR DISSOLVING METAL FEEDSTOCK

[0002] TECHNICAL FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to a method and apparatus for dissolving metal feedstock. In particular, the disclosure provides a method and apparatus for dissolving metal feedstock to produce a metal sulphate for use in battery manufacturing, and more particularly a method and apparatus whose reaction parameter(s) may be monitored and controlled by a smart control system of the apparatus.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] Nickel (Ni) and cobalt (Co) are key elements for the manufacture of lithium-ion batteries, used as cathode active materials (CAMs) in the form of mixed metal oxides.

[0006] It is known that battery grade metal sulphate solutions can be prepared directly from metal feedstocks, by subjecting the feedstock to an aqueous leaching solution comprising at least one acid leaching agent and a liquid oxidizing agent in a process at elevated temperature and with agitation.

[0007] With use of lithium-ion battery technologies continuing to grow, the lack of suitability of various compositions and morphologies of raw metal feedstocks - whose respective abundances, environmental friendliness, and costs of acquisition often vary (or fluctuate) significantly - poses an increasing problem. Its solution could alleviate supply chain issues across many high value markets in which battery production is currently a manufacturing bottleneck.

[0008] Typically, metal feedstock introduced into leaching systems is unprocessed (raw) and has a relatively low surface-area-to-volume ratio. Such feedstocks may be sourced in powdered form, or as briquettes made by compressing such powder.

[0009] This tends to ensure that thermodynamic runaway of the highly exothermic dissolution process does not lead to unsafe conditions within the system. However, as a result, such systems are of limited flexibility, and may safely receive and process only specific metals, or feedstocks within a specific range of sizes, shapes, or compositions. Moreover, such systems tend to only be safely operable within a relatively restrictive range of system and / or reagent parameters. Conventional systems are typically only suited to a limited degree of parametrisation. For example, conventional systems may be limited in their suitability to:

[0010] • feedstocks containing a certain metal;

[0011] • feedstocks of a certain composition;

[0012] • feedstocks having a certain morphology;

[0013] • feedstocks having a certain surface-area-to-volume ratio;

[0014] • feedstocks of a certain quantity;

[0015] • feedstocks forming a certain concentration within the reaction vessel;

[0016] • acids of certain volumes;

[0017] • acids of certain concentrations;

[0018] • dilutants of certain volumes / ratios;

[0019] • feedstocks having undergone certain extents of repulping;

[0020] • leaching reactions having certain maximum durations;

[0021] • leaching reactions having certain maximum rates;

[0022] • leaching reactions involving certain agitation rates;

[0023] • certain modes of operation (e.g., batch versus continuous);

[0024] • certain excesses of feedstock;

[0025] • certain reaction pHs;

[0026] • certain starting and / or working temperatures.

[0027] The present inventors have realised that there exists a need for a system and process for metal sulphate production which provides improved flexibility and control over both operation efficiency and safety conditions. Such systems and processes would preferably be suited to a wider range of parametrisations than conventional, inflexible systems and processes (that is, less limited in their suitability for various leaching reaction reagents and conditions). In particular, the present inventors have realised that it is desirable to provide systems and processes suited for processing metal feedstock in powdered (high surface-area-to-volume ratio) form, which would allow for processing of a greater variety of feedstocks, e.g., feedstocks having different morphologies (pellets, chunks, blocks, powders, etc.), and / or different sizes, and / or different impurities, etc. Systems and processes of the art are currently unable to adequately provide this flexibility while maintaining both operational efficiency (e.g., in terms of cost, duration, and energy consumption) and acceptable (e.g., industry standard) safety margins, particularly given the increased risk of thermodynamic runaway presented by the high surface-area-to-volume ration of powdered feedstocks, and the kinetic uncertainty associated with powdered feedstocks of unknown (or imprecisely known) composition.

[0028] SUMMARY OF THE DISCLOSURE

[0029] In a first aspect according to the disclosure, there is provided a process for dissolving metal feedstock in a system. The process comprises receiving, by a reaction vessel of the system, reagents comprising a metal feedstock, sulphuric acid, oxidising agent, and water. The receiving is via one or more reagent introduction means. The process further comprises agitating, by an agitation means of the system, the reagents within the reaction vessel. The process further comprises cooling, by a cooling circuit of the system, at least a first region of the system. The cooling comprises conveying one or more fluids of the reagents through a working fluid loop of the cooling circuit. The cooling further comprises conveying a coolant through a coolant loop of the cooling circuit. The coolant is fluidly separated from and, at a heat transfer region of the cooling circuit, in heat exchange with the one or more fluids in the working fluid loop.

[0030] The acid and / or oxidising agent (preferably the oxidising agent) may be introduced into the reaction vessel via the working fluid loop of the cooling circuit.

[0031] The process may further comprise controlling, by a control means of the system, one or more reaction parameters of the system, thereby to adjust one or more reaction conditions within the system.

[0032] The process may further comprise, before controlling the one or more reaction parameters of the system, obtaining, by a sensing means of the system, reaction data indicative of the one or more reaction conditions within the system. The process may further comprise, before controlling the one or more reaction parameters of the system, receiving, by the control means, the reaction data from the sensing means. The controlling the one or more reaction parameters of the system may include controlling, based on the reaction data, the one or more reaction parameters of the system thereby to adjust the one or more reaction conditions.

[0033] The one or more reaction parameters may comprise one or more of: a rate of agitation of the reagents by the agitation means; a rate of introduction of the metal feedstock into the reaction vessel via the one or more reagent introduction means; a rate of introduction of the sulphuric acid into the reaction vessel via the one or more reagent introduction means; a rate of introduction of the hydrogen peroxide into the reaction vessel via the one or more reagent introduction means; a relative dosing, or relative dosings, of one or more of the reagents introduced into the reaction vessel; an amount of excess metal feedstock present in the reaction vessel; one or more cooling parameters; a rate of output of a product mixture from the reaction vessel; and a rate of output of metal sulphate from the reaction vessel. The one or more cooling parameters may comprise one or more of: a rate of flow of the one or more fluids through the working fluid loop; a rate of flow of the coolant through the coolant loop; a temperature of the coolant in the coolant loop; a heat capacity of the coolant; and a surface area and / or volume of the heat transfer region.

[0034] The system may further comprise an impurity removal circuit in fluid communication with the reaction vessel, the impurity removal circuit comprising one or more filtration stages, a feedstock reintroduction means and, optionally, one or more impurity removal stages. The process may further comprise capturing, by the one or more filtration stages, unreacted metal feedstock from a mixture formed in the reaction vessel, the mixture further comprising one or more impurities. The one or more reaction parameters may comprise a rate of capture of the unreacted metal feedstock from the mixture formed in the reaction vessel. The process may further comprise returning, by the feedstock reintroduction means, the unreacted metal feedstock into the reaction vessel. The one or more reaction parameters may comprise a rate of reintroduction of the unreacted metal feedstock into the reaction vessel. The process may further comprise removing, by the one or more impurity removal stages, at least some of the one or more impurities from the mixture. The one or more reaction parameters may comprise a rate of removal of one or more impurities from the mixture formed in the reaction vessel.

[0035] A conduit forming at least a part of the working fluid loop for conveying the one or more fluids of the reagents may also form at least a part of the one or more reagent introduction means. The receiving, by the reaction vessel, the reagents may include introducing at least one fluid of the one or more fluids of the reagents into the reaction vessel via the conduit which forms at least a part of the working fluid loop. The one or more reaction parameters may comprise a rate of introduction of the at least one fluid into the reaction vessel via the conduit which forms at least a part of the working fluid loop.

[0036] The one or more reagent introduction means may comprise a feedstock introduction means and at least one acid introduction means. The feedstock introduction means and the at least one acid introduction means may be distinct means. The one or more reagent introduction means may comprise a water introduction means. The water introduction means may be distinct from the feedstock introduction means and may be distinct from the at least one acid introduction means.

[0037] The process may further comprise, before receiving the metal feedstock of the reagents by the reaction vessel, repulping the metal feedstock by a repulping means of the system. The one or more reaction parameters may comprise an extent of repulping of the metal feedstock. The process may further comprise repulping the unreacted metal feedstock by a further repulping means of the system, after the capturing the unreacted metal feedstock from the mixture formed in the reaction vessel, and before the returning the unreacted metal feedstock into the reaction vessel. The one or more reaction parameters may comprise an extent of repulping of the metal feedstock. The one or more reaction parameters may comprise an extent of further repulping of the unreacted metal feedstock.

[0038] The one or more reaction conditions may comprise one or more reaction safety conditions and / or one or more reaction efficiency conditions.

[0039] The one or more reaction efficiency conditions may comprise one or more of: a yield of product metal sulphate; an atom economy of product metal sulphate; a production cost of product metal sulphate; a production rate of product metal sulphate; an amount of excess metal feedstock; a quantity of the one or more impurities within the mixture formed in the reaction vessel; a quantity of the one or more impurities removed from the mixture by the one or more impurity removal stages; a rate of capture of unreacted metal feedstock from the mixture by the one or more filtration stages; and a quantity of unreacted metal feedstock captured from the mixture by the one or more filtration stages.

[0040] The one or more reaction conditions may comprise one or more conditions associated with the first region of the system. The one or more conditions associated with the first region of the system may comprise one or more of: a temperature; a pH of the reagents; an oxidation reduction potential of the reagents; a homogeneity of the liquid phase mixture of the reagents; an amount of excess metal feedstock with respect to the other reagents; a rate of output of product mixture from the reaction vessel; and a rate of output of metal sulphate from the system. The one or more conditions associated with the first region of the system may comprise one or more of: a quantity of the one or more impurities within the mixture formed in the reaction vessel; a quantity of the one or more impurities removed from the mixture by the one or more impurity removal stages; a rate of capture of the unreacted metal feedstock from the mixture by the one or more filtration stages; and a quantity of unreacted metal feedstock captured from the mixture by the one or more filtration stages.

[0041] The first region may comprise one or more of: a region within the reaction vessel; a region within the working fluid loop; a region within the coolant loop; a region within the one or more reagent introduction means; and a region at or proximate the agitation means. The first region may comprise a region within the impurity removal circuit.

[0042] A sensor of the sensing means may be disposed at or within a second region of the system. The second region may comprise one or more of: a region within the reaction vessel; a region within the working fluid loop; a region within the coolant loop; a region within the one or more reagent introduction means; and a region at or proximate the agitation means. The second region may comprise a region within the impurity removal circuit.

[0043] The metal feedstock may be a powdered metal feedstock. The process may further comprise, before receiving the metal feedstock by the reaction vessel, forming, by a comminuting means of the system, the powdered metal feedstock from uncrushed metal feedstock. The one or more reaction parameters may comprise an extent of the comminuting of the metal feedstock. The metal feedstock may be a powdered metal feedstock selected from the group of powdered metal feedstocks consisting of: powdered Nickel feedstock, powdered Cobalt feedstock, and a mixture of powdered Nickel feedstock and powdered Cobalt feedstock. The D[4,3] of the powdered metal feedstock may be equal to or greater than 100 nm, preferably 1 pm, more preferably 10 pm; and equal to or below 10 mm, preferably 5 mm, more preferably 1 mm.

[0044] D[4,3] particle size may be understood as the volume-weighted mean particle size, i.e. the average diameter of spherical particles of an equivalent volume to the particles which are being measured.

[0045] The process may include outputting product metal sulphate.

[0046] The process may include operating in a batch mode of operation. The process may include operating in a continuous mode of operation.

[0047] The reaction chamber may be formed from polymeric material such as polyethylene, polypropylene or the like, preferably a fibre reinforced polymeric material. In a further aspect according to the disclosure, there is provided a system for dissolving metal feedstock. The system comprises a reaction vessel for receiving reagents, the reagents comprising a metal feedstock, sulphuric acid, hydrogen peroxide, and water. The system further comprises one or more reagent introduction means for introducing the reagents into the reaction vessel. The system further comprises an agitation means for agitating the reagents within the reaction vessel. The system further comprises a cooling circuit for cooling at least a first region of the system. The cooling system comprises a working fluid loop for conveying one or more fluids of the reagents. The cooling system further comprises a coolant loop for conveying a coolant. The coolant is fluidly separated from, and, at a heat transfer region of the cooling circuit, in heat exchange with, the one or more fluids in the working fluid loop.

[0048] The system may further comprise a control means for controlling one or more reaction parameters of the system, thereby to adjust one or more reaction conditions within the system.

[0049] The system may further comprise a sensing means for obtaining reaction data indicative of the one or more reaction conditions within the system. The control means may be for receiving the reaction data from the sensing means. The control means may be for controlling, based on the reaction data, the one or more reaction parameters of the system thereby to adjust the one or more reaction conditions.

[0050] The one or more reaction parameters may comprise one or more of: a rate of agitation of the reagents by the agitation means; a rate of introduction of the metal feedstock into the reaction vessel via the one or more reagent introduction means; a rate of introduction of the sulphuric acid into the reaction vessel via the one or more reagent introduction means; a rate of introduction of the hydrogen peroxide into the reaction vessel via the one or more reagent introduction means; a relative dosing, or relative dosings, of one or more of the reagents introduced into the reaction vessel; an amount of excess metal feedstock present in the reaction vessel; one or more cooling parameters; a rate of output of a product mixture from the reaction vessel; and a rate of output of metal sulphate from the reaction vessel. The one or more cooling parameters may comprise one or more of: a rate of flow of the one or more fluids through the working fluid loop; a rate of flow of the coolant through the coolant loop; a temperature of the coolant in the coolant loop; a heat capacity of the coolant; and a surface area and / or volume of the heat transfer region. The system may further comprise an impurity removal circuit in fluid communication with the reaction vessel. The impurity removal circuit may further comprise one or more filtration stages. The impurity removal circuit may further comprise a feedstock reintroduction means. The impurity removal circuit may further comprise one or more impurity removal stages. The impurity removal circuit may be for capturing, by the one or more filtration stages, unreacted metal feedstock from a mixture formed in the reaction vessel. The mixture may further comprise one or more impurities. The one or more reaction parameters may comprise a rate of capture of the unreacted metal feedstock from the mixture formed in the reaction vessel. The impurity removal circuit may be for returning, by the feedstock reintroduction means, the unreacted metal feedstock into the reaction vessel. The one or more reaction parameters may comprise a rate of reintroduction of the unreacted metal feedstock into the reaction vessel. The impurity removal circuit may be for removing, by the one or more impurity removal stages, at least some of the one or more impurities from the mixture. The one or more reaction parameters may comprise a rate of removal of one or more impurities from the mixture formed in the reaction vessel.

[0051] A conduit forming at least a part of the working fluid loop for conveying the one or more fluids of the reagents may also form at least a part of the one or more reagent introduction means. The conduit forming at least a part of the working fluid loop may be for introducing at least one fluid of the one or more fluids of the reagents into the reaction vessel. The one or more reaction parameters may comprise a rate of introduction of the at least one fluid into the reaction vessel via the conduit which forms at least a part of the working fluid loop.

[0052] The one or more reagent introduction means may comprise a feedstock introduction means and at least one acid introduction means. The feedstock introduction means and the at least one acid introduction means may be distinct means. The one or more reagent introduction means may comprise a water introduction means. The water introduction means may be distinct from the feedstock introduction means and may be distinct from the at least one acid introduction means.

[0053] The system may further comprise a repulping means for repulping the metal feedstock before the metal feedstock is received by the reaction vessel. The one or more reaction parameters may comprise an extent of repulping of the metal feedstock. The system may comprise a further repulping means for repulping the unreacted metal feedstock captured from the mixture formed in the reaction vessel, before the unreacted metal feedstock is returned into the reaction vessel. The one or more reaction parameters may comprise an extent of repulping of the metal feedstock. The one or more reaction parameters may comprise an extent of further repulping of the unreacted metal feedstock.

[0054] The one or more reaction conditions may comprise one or more reaction safety conditions and / or one or more reaction efficiency conditions.

[0055] The one or more reaction efficiency conditions may comprise one or more of: a yield of product metal sulphate; an atom economy of product metal sulphate; a production cost of product metal sulphate; a production rate of product metal sulphate; an amount of excess metal feedstock; a quantity of the one or more impurities within the mixture formed in the reaction vessel; a quantity of the one or more impurities removed from the mixture by the one or more impurity removal stages; a rate of capture of unreacted metal feedstock from the mixture by the one or more filtration stages; and a quantity of unreacted metal feedstock captured from the mixture by the one or more filtration stages.

[0056] The one or more reaction conditions may comprise one or more conditions associated with the first region of the system. The one or more conditions associated with the first region of the system may comprise one or more of: a temperature; a pH of the reagents; an oxidation reduction potential of the reagents; a homogeneity of the liquid phase mixture of the reagents; an amount of excess metal feedstock with respect to the other reagents; a rate of output of product mixture from the reaction vessel; and a rate of output of metal sulphate from the system. The one or more conditions associated with the first region of the system may comprise one or more of: a quantity of the one or more impurities within the mixture formed in the reaction vessel; a quantity of the one or more impurities removed from the mixture by the one or more impurity removal stages; a rate of capture of the unreacted metal feedstock from the mixture by the one or more filtration stages; and a quantity of unreacted metal feedstock captured from the mixture by the one or more filtration stages.

[0057] The first region may comprise one or more of: a region within the reaction vessel; a region within the working fluid loop; a region within the coolant loop; a region within the one or more reagent introduction means; and a region at or proximate the agitation means. The first region may comprise a region within the impurity removal circuit.

[0058] A sensor of the sensing means may be disposed at or within a second region of the system. The second region may comprise one or more of: a region within the reaction vessel; a region within the working fluid loop; a region within the coolant loop; a region within the one or more reagent introduction means; and a region at or proximate the agitation means. The second region may comprise a region within the impurity removal circuit.

[0059] The metal feedstock may be a powdered metal feedstock. The system may further comprise a comminuting means for forming the powdered metal feedstock from uncrushed metal feedstock before receiving the powdered metal feedstock by the reaction vessel. The one or more reaction parameters may comprise an extent of the comminuting of the metal feedstock. The metal feedstock may be a powdered metal feedstock selected from the group of powdered metal feedstocks consisting of: powdered Nickel feedstock, powdered Cobalt feedstock, and a mixture of powdered Nickel feedstock and powdered Cobalt feedstock.

[0060] The system may be configured to operate in a batch mode of operation. The system may be configured to operate in a continuous mode of operation.

[0061] The system may be configured to execute a process in accordance with the preceding aspect. The system may be configured to iterate some of the steps of the preceding aspect. The system may be configured to iterate all of the steps of the preceding aspect.

[0062] BRIEF DESCRIPTION OF THE FIGURES

[0063] Examples of the present disclosure are described below with reference to the accompanying drawings, in which:

[0064] Figure 1 is a schematic illustration depicting a known system for dissolving metal feedstock;

[0065] Figure 2a is a schematic illustration depicting a system for dissolving metal feedstock;

[0066] Figure 2b is a schematic illustration depicting a further system for dissolving metal feedstock;

[0067] Figure 3 is a schematic illustration depicting a yet further system for dissolving metal feedstock;

[0068] Figure 4 is a schematic illustration depicting a yet further system for dissolving metal feedstock; Figure 5 is a graph showing the remaining solids when dissolving nickel powder at various pH levels;

[0069] Figure 6 is a graph showing the leaching efficiency of nickel powder at various temperatures;

[0070] Figure 7 is a graph showing the leaching efficiency against the feeding time when dissolving nickel metal;

[0071] Figure 8 is a graph showing the pH variation over time when dissolving nickel metal with various ratios of acid and oxidising agent;

[0072] Figure 9 is a graph showing the leaching efficiency of various ratios of acid and oxidising agent when dissolving nickel metal;

[0073] Figure 10 is a graph showing the leaching efficiency of dissolving nickel / cobalt mixtures; and

[0074] Figure 11 is a graph showing the temperature variation as oxidising agent is periodically added to a reactor containing nickel metal.

[0075] DETAILED DESCRIPTION OF THE DISCLOSURE

[0076] Prior to outlining the present disclosure in more detail, a set of terms and conventions is first defined.

[0077] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0078] Metal feedstock

[0079] In the present context, the term "metal feedstock" refers to a raw or unprocessed metal used as a reagent to the industrial process described herein. In particular, in the present context, the term "metal feedstock" refers to a raw or unprocessed metal used as a reagent in a dissolution reaction for producing metal sulphates for producing a precursor of one or more components of electrochemical cells, e.g., cathode active materials for the manufacture of battery (electrochemical cell) cathodes.

[0080] As used herein, "cathode" denotes a cell's positive electrode, while "anode" denotes a cell's negative electrode.

[0081] Powdered

[0082] In the present context, the term "powdered", when used to refer to the morphology of metal feedstock for use in an industrial process, refers to an assembly of particles having been processed, e.g., by crushing, and / or grinding, and / or milling, and / or micronizing, so as to increase the feedstock's surface area relative to that of the metal feedstock in an uncrushed state, e.g., in unprocessed chunks of ore.

[0083] In the present context, the term "powdered metal feedstock" may refer to a metal feedstock whose morphology has been altered by the processing described above. In particular, the term "powdered metal feedstock" may refer to the powdered metal product produced by processing, as above, a briquette of metal feedstock, or may refer directly to the briquette of metal feedstock itself. Alternatively, the term "powdered metal feedstock" may refer to the powdered metal product produced by processing, as above, another suitable morphology of metal feedstock.

[0084] As used herein, the term "briquette" refers to a compressed block or chunk of powdered metal feedstock used as a reagent to the industrial process described herein. A briquette may be considered a metal feedstock whose processing, as above, produces a powdered metal feedstock, or may itself be considered a powdered metal feedstock compacted into a block or chunk.

[0085] Dissolving

[0086] In the present context, the term "dissolving" refers to the process by which a solute reacts in a solvent to form a solution. In particular, in the present context, the term "dissolving" refers to reaction of a metal feedstock with a solution of sulphuric acid and hydrogen peroxide, thereby to form a metal sulphate product.

[0087] In the present context, the term "dissolving", when used in reference to dissolution of the metal feedstock, may be used interchangeably with the term "leaching", which, in the context of metallurgy, refers specifically to the process, described herein, of treating metal feedstock with chemicals (e.g., sulphuric acid and hydrogen peroxide) thereby to produce soluble salts separable from insoluble impurities initially present within the feedstock.

[0088] Impurity

[0089] In the present context, the term "impurity" refers to a chemical substance inside a confined chemical phase which differs from the chemical composition of that phase. An impurity is a chemical substance, having a differed composition from a desired chemical product, whose presence (i) prevents the chemical product from being wholly characterised by its one-component-phase diagram, and / or (ii) prevents the chemical product from exhibiting perfect homogeneity, and / or (iii) allows the chemical product to be separable or purifiable from, or to be otherwise demonstrated to contain, at least a trace of another chemical species.

[0090] Agitating

[0091] In the present context, the term "agitation" refers to the process of moving one or more components of a mixture of reagents, to control their extent / rate of molecular contact, i.e., influence their collision rate, and thereby influence the kinetics of the reaction.

[0092] Comminution / comminuting

[0093] In the present context, the term "comminuting" (and the associated term "comminution") refers to the process of size reduction of an ore, i.e., metal feedstock, prior to its leaching. Comminuting may be achieved by, e.g., crushing, grinding, or milling, or micronizing, by any suitable means.

[0094] Repulping

[0095] In the present context, the term "repulping" refers to the process of diluting, e.g., with water, a metal feedstock. Repulping powdered metal feedstock tends to be an effective dilution strategy of metal feedstock reagents, to allow kinetic - and thus, in the case of highly exothermic dissolution reactions, thermodynamic - control of their leaching.

[0096] Mixture

[0097] In the present context, the term "mixture" refers to a chemical composition comprising two or more different chemical species which can be separated by physical methods. Examples of mixtures include solutions, suspensions and colloids.

[0098] In the present context, the term "mixture", unless stated otherwise, refers to the mixture comprising the specified leaching reagents (i.e., metal feedstock, sulphuric acid, hydrogen peroxide, and water) and any metal sulphate product present in the solution.

[0099] Filtration

[0100] In the present context, the term "mixture" refers to the physical process by which chemical species in the solid phase are separated from chemical species in the liquid or gaseous phase.

[0101] In the present context, the term "filtration" may refer to a physical process by which solid-phase impurities are removed from a mixture. Separation

[0102] In the present context, the term "separation" refers to the physical or chemical process by which two or more distinct chemical species in a mixture are separated such that at least one product mixture which results from the separation is purified in one of the distinct chemical species.

[0103] In the present context, the term "separation" may refer to a process by which impurities are removed from a mixture.

[0104] Dosing

[0105] In the present context, the term "dosing" refers to the process of feeding reagents, e.g., metal feedstock, and / or acids, and / or water, in relatively precise, specifically selected quantities / concentrations, thereby to influence reaction mixture concentrations, reaction kinetics, and reaction thermodynamics.

[0106] In the present context, the term "relative dosing" refers to the process of specifically selecting a quantity / concentration of one or more reagents based on a specifically selected (or known) quantity / concentration of one or more other reagents, and / or specifically adjusting a quantity / concentration of one or more reagents relative to a specifically selected (or known) quantity / concentration of one or more other reagents.

[0107] Oxidation reduction potential

[0108] In the present context, the term "oxidation reduction potential" refers to a measure of the tendency of a chemical system to be oxidized, i.e., to lose electrons, or conversely to be reduced, i.e., to gain electrons, relative to a reference species.

[0109] It will be understood by those skilled in the art that the oxidation reduction potential value of a chemical species is indicative of the thermodynamic favourability of a transfer of electrons to or from the species. More specifically, relatively negative oxidation reduction potential values are to be understood as indicative of relative strength as a reducing agent, while relatively positive oxidation reduction potential values are to be understood as indicative of relative strength as an oxidising agent.

[0110] It will be understood by those skilled in the art that multiple (e.g., conventional) reference species by which to measure oxidation reduction potentials are possible and envisaged. Batch operation

[0111] In the present context, the term "batch operation" refers to a process, according to the present disclosure, in which a series of steps are carried out on limited, distinct quantities ("batches") of materials introduced at the start of the process. In a batch operation, the series forming the process has a distinct beginning and end. A process carried out in batch operation produces a discrete and finite quantity of product per batch, and may be iterated over multiple (temporally spaced) batches.

[0112] The term "batch operation" may be considered to refer to a process having both continuous and discontinuous characteristics.

[0113] The term "batch operation" may, according to the present disclosure, connote a steady state operation of a system / process during the batch operation, or a variable state operation of a system / process during the batch operation.

[0114] The term "batch operation" may, according to the present disclosure, connote use of a control system to adjust a state of operation of the process / system, e.g., to maintain / adjust a steady state operation before, during, or after the batch operation, or to maintain / adjust a variable state operation before, during, or after the batch operation, or to transition between a steady state operation and a variable state operation before, during, or after the batch operation.

[0115] Continuous operation

[0116] In the present context, the term "continuous operation" refers to a process, according to the present disclosure, in which a series of steps are carried out on materials which are introduced continuously during the process. In a continuous operation, some or all of the steps forming the process occur contemporaneously, or at least partially temporally overlap.

[0117] In particular, in the present context, "continuous operation", unless stated otherwise, refers to a process, according to the present disclosure, in which metal sulphate product is produced and / or extracted from the system while, contemporaneously, one or more reagents (e.g., metal feedstock, and / or acids, and / or water) are dosed into the system.

[0118] By way of further example, in the present context, "continuous operation", may refer to a process, according to the present disclosure, in which two or more intermediate steps of the process (that is, steps occurring after reagent dosing and before product extraction) occur contemporaneously with each other. By way of further example, in the present context, "continuous operation", may refer to a process, according to the present disclosure, in which one or more intermediate steps of the process occur contemporaneously with a step of reagent dosing and / or a step of product extraction.

[0119] The term "continuous operation" may, according to the present disclosure, connote a steady state operation of a system / process during the continuous operation, or a variable (though continuous) state operation of a system / process during the continuous operation.

[0120] The term "continuous operation" may, according to the present disclosure, connote use of a control system to maintain / adjust a state of operation of the process / system, e.g., to maintain / adjust a steady state operation during the continuous process, or to maintain / adjust a variable state operation during the continuous process, or to transition between a steady state operation and a variable state operation during the continuous process.

[0121] About

[0122] Wherever the term "about" is employed herein in the context of amounts, for example absolute amounts, such as numbers, purities, concentrations, weights, sizes, etc., or relative amounts (e.g. percentages, equivalents or ratios), timeframes, and parameters such as temperatures, pressure, etc., it will be appreciated that such variables are approximate and as such may vary by ±10%, for example ± 5% and preferably ± 2% (e.g. ± 1%) from the actual numbers specified. This is the case even if such numbers are presented as percentages in the first place (for example 'about 10%' may mean ±10% about the number 10, which is anything between 9% and 11%).

[0123] System for dissolving metal feedstock

[0124] Figure 1 depicts a prior art system 100 for dissolving metal feedstock 102 via a leaching process, thereby to produce a metal sulphate.

[0125] The metal feedstock 102 may contain Nickel and / or Cobalt, and may be a Nickel-rich and / or Cobalt-rich ore. The metal feedstock 102 is typically introduced into the system 100 in raw / un processed form, e.g., in the form of one or more chunks of metal ore.

[0126] The system 100 comprises a reaction vessel 104 configured to receive, e.g., via an inlet (not shown), the metal feedstock 102. The reaction vessel 104 is also configured to receive, e.g., via said inlet or one or more further inlets (not shown), a quantity of sulphuric acid 106 and a quantity of oxidising agent 108. The sulphuric acid 106 and oxidising agent 108 may be introduced into the reaction vessel 104 together (e.g., premixed), i.e., as a piranha solution / etch, or as reagents dosed and / or introduced at different times and / or at different locations in the system 100.

[0127] The reaction vessel 104 is also configured to receive a quantity of water (not shown), either in the solution of acid 106, oxidising agent 108, or separately as a repulping species and / or dilutant to a leaching reaction.

[0128] The metal feedstock 102, sulphuric acid 106, oxidising agent 108, and water together comprise reagents 110 of a leaching process. Introduction of the reagents 110 into the reaction vessel 104, which may occur contemporaneously or separately, via the inlet and / or one or more further inlets (not shown), is indicated schematically in Figure 1 by a single-headed arrow and reference numeral 112.

[0129] The system 100 further comprises an agitation means 114, e.g., an impeller, configured to agitate the reagents 110, thereby to control their extent / rate of molecular contact, i.e., influence their collision rate, and influence the kinetics of the reaction.

[0130] In operation, the system 100 agitates the reagents 110, thereby to produce a product mixture 116 containing a quantity of (desired) metal sulphate 118 and a quantity of one or more impurities 120. Output of the product mixture 116 by the system 100, e.g., via one or more outlets (not shown), is indicated schematically in Figure 1 by a single-headed arrow and reference numeral 122. Extraction of the (soluble) metal sulphate 118 from the product mixture 116 is typically achieved by one or more known filtration and / or separation techniques, not described in detail here.

[0131] Typically, the metal feedstock 102 introduced into the system 100 has a low-surface area (unpowdered) morphology, and the system 100 is of limited flexibility, being configured to safely receive and process reagents 110 only within a specific, relatively restrictive range of system and / or reagent parameters. More specifically, a leaching process described herein is known to be highly exothermic, and care must be taken to avoid thermodynamic runaway during operation of the system 100.

[0132] For example, the system 100 may be suited only to certain parametrisation. In other words, the system 100 may be limited in its suitability for various leaching processes and conditions. Parameters according to which the system 100 is limited may include, e.g., feedstocks of a certain metal, and / or feedstocks having a certain morphology, and / or feedstocks having a certain surface-area-to-volume ratio, and / or feedstocks of a certain quantity, and / or feedstocks forming a certain concentration within the reaction vessel, and / or acids of certain volumes, and / or acids of certain concentrations, and / or dilutants (water) of certain volumes / ratios, and / or feedstocks having undergone certain extents of repulping, and / or reactions of certain maximum durations, and / or reactions of certain maximum rates, and / or certain agitation rates, and / or certain modes of operation (e.g., batch versus continuous), and / or certain excesses of feedstock, and / or certain reaction pHs, and / or certain starting and / or working temperatures, etc. Moreover, the system may need to be designed using resilient materials, such as metals having certain temperature and pressure tolerances, to ensure compliance with safety requirements in the event that there is unexpected increases in the temperature and / or pressure during the reaction. These requirements increase the capital cost of such systems.

[0133] Figure 2a depicts a further system 200 for dissolving metal feedstock 202 via a leaching process, thereby to produce a metal sulphate. As will be explained in detail below, the system 200 is a system according to the present disclosure which provides improved flexibility, control, and safety of a leaching process.

[0134] In the following detailed description, like numerals are, unless otherwise specified, used to denote like features of previously-described embodiments and the Figures to which they refer.

[0135] As will be explained in detail below, the system 200 is equipped to dynamically respond to one or more reaction conditions during a leaching process, thereby to provide improved flexibility, control, and safety. Advantageously, this affords the system 200 suitability to a wider range of parametrisations. Moreover, the improved control of the process allows for the reaction chamber 104 to be manufactured with reduced cost without compromising safety.

[0136] For instance, the reaction chamber of the disclosure may be formed from polymeric material such as polyethylene, polypropylene or the like, preferably a fibre reinforced polymeric material. Such materials are typically not suitable for high temperature reactions. However, the system of the disclosure has suitable control and safety that high temperatures and / or pressures usually not suitable for polymeric reaction chambers may be avoided. This can significantly reduce the CapEx for the system of the disclosure.

[0137] Preferably, the reaction chamber is formed from a fibre reinforced polymeric material.

[0138] In other words, the system 200 is less limited than the prior art system 100 in its suitability for various leaching processes and conditions. The parameters according to which the system 200 operate that are less limited than the prior art system 100 include, but are not limited to, those described above with reference to the limitations of the prior art system 100.

[0139] The metal feedstock 202 is introduced into the reaction vessel 104 in powdered, i.e., processed, form.

[0140] In particular, that the reaction vessel 104 is suited to receiving metal feedstock in powdered (high surface-area-to-volume ratio) form allows for processing of a greater variety of feedstocks, e.g., feedstocks having different morphologies (pellets, chunks, blocks, powders, etc.), and / or different sizes / volumes, and / or different impurity ratios.

[0141] In this embodiment, the metal feedstock 202 may contain Nickel and / or Cobalt, and may be derived from a Nickel-rich and / or Cobalt-rich ore.

[0142] Preferably, the metal feedstock is selected from powdered nickel, powdered cobalt, or mixtures thereof, more preferably the metal feedstock is powdered nickel.

[0143] Preferably the metal feedstock has D[4,3] equal to or greater than 100 nm, preferably 1 pm, more preferably 10 pm; and equal to or below 10 mm, preferably 5 mm, more preferably 1 mm, such as in the range of 100 nm to 10 mm, or 1 pm to 5 mm, or 10 pm to 5 mm, or 1 pm to 1 mm. Metal feedstocks having a D[4,3] below such ranges introduces drawbacks in that the metal feedstock may become difficult to produce and / or convey. Metal feedstocks having a D[4,3] above such ranges may damage the system during operation.

[0144] Returning to the description of Figure 2a, the system 200 comprises a reaction vessel 104 configured to receive, via a feedstock introduction means (not shown), the powdered metal feedstock 202. The reaction vessel 104 is also configured to receive, via one or more acid introduction means (not shown), a quantity of sulphuric acid 106 and a quantity of oxidising agent 108. The sulphuric acid 106 and oxidising agent 108 may be introduced into the reaction vessel 104 together (e.g., pre-mixed), i.e., as a piranha solution / etch, or as reagents dosed and / or introduced at different times and / or at different locations (e.g., via separate introduction means of the one or more acid introduction means) in the system 200.

[0145] The reaction vessel 104 is also configured to receive a quantity of water (not shown), either in the solution of acid 106, oxidising agent 108, or separately, via a water introduction means (not shown), as a repulping species and / or dilutant to a leaching reaction.

[0146] The powdered metal feedstock 202, sulphuric acid 106, oxidising agent 108, and water together comprise reagents 210 of a leaching process. Introduction of the reagents 210 into the reaction vessel 104, which may occur contemporaneously or separately, via the feedstock introduction means, the one or more acid introduction means, and the water introduction means, is indicated schematically in Figure 2 by a single-headed arrow and reference numeral 212.

[0147] The system 200 further comprises an agitation means 114, e.g., an impeller, configured to agitate the reagents 210, thereby to control their extent / rate of molecular contact, i.e., influence their collision rate, and influence the kinetics of the reaction. The agitation means 114 is driven by a driving means 215, e.g., a motor.

[0148] In operation, the agitation means 114 agitates the reagents 210, thereby to produce the product mixture 116 containing a quantity of metal sulphate 118 and a quantity of one or more impurities 120. Output of the product mixture 116 by the system 200, e.g., via one or more outlets (not shown), is indicated schematically in Figure 2 by a single-headed arrow and the reference numeral 122.

[0149] The system 200 further comprises a cooling circuit 216 comprising a working fluid loop 218 and a coolant loop 220. The working fluid loop 218 is in fluid communication with the reaction vessel 104 and is configured to convey one or more fluids of the reagents 210. The one or more fluids of the reagents 210 may be one, or two, or all three of the reagents 210 (namely, the sulphuric acid 106, the oxidising agent 108, and the water). The coolant loop 220 is configured to convey a coolant, the coolant being fluidly separated from, and in heat exchange with, the one or more fluids within the working fluid loop 218. The coolant may be, or comprise, e.g., water, or any other suitable fluid for storing heat. The coolant loop 220 is in fluid communication with a heat sink or other suitable means of transferring heat away from cooling circuit 216 (not shown). In this embodiment, the coolant loop 220 is supplied by a coolant supply (not shown),

[0150] In operation, in this embodiment, the working fluid loop 218 draws the one or more fluids of the reagents, e.g., draws at least some of the reagent mixture 210, from the reaction vessel 104 into the cooling circuit 216. During its passage through or proximate the coolant loop 220, and more specifically at a heat exchange region 222 of the cooling circuit 216, the received one or more fluids undergoes heat exchange with (i.e., transfers heat to) the coolant. The cooled one or more fluids is returned, via the working fluid loop 218, to the reaction vessel 104, thereby to cool the reagent mixture 210 therein.

[0151] In this manner, the cooling circuit 216 is configured to cool at least a first region 224 of the system 200, the first region 224 being, in this embodiment, some or all of the reaction vessel 104, and / or some or all of the impeller 114.

[0152] The rate of cooling of the first region 224 provided by the cooling circuit 216 varies with a number of controllable cooling parameters, including, e.g., a rate of throughflow of the one or more fluids taken from the reagent mixture 210, a rate of throughflow of coolant, a starting temperature of the coolant, a heat capacity of the coolant, a surface area and / or volume of the heat exchange region 222, etc.

[0153] In the system 200, control of a rate of agitation provided by the agitation means 114 provides a degree of freedom for control of the kinetics of a leaching process.

[0154] Similarly, further degrees of freedom for kinetic control may be provided by control / adjustment of one or more of the following reaction parameters:

[0155] • a rate of introduction of the powdered metal feedstock 202, via the feedstock introduction means, into the reaction vessel 104;

[0156] • a rate of introduction of the sulphuric acid 106, via the one or more acid introduction means, into the reaction vessel 104;

[0157] • a rate of introduction of the oxidising agent 108, via the one or more acid introduction means, into the reaction vessel 104;

[0158] • a relative dosing (or relative dosings) of one or more of the reagents 210 introduced 212 into the reaction vessel 104;

[0159] • an amount, or relative amount, of excess powdered metal feedstock 202 present in the reagent mixture 210; and • one or more of the controllable cooling parameters of the cooling circuit 216, namely: a rate of throughflow of the one or more fluids taken from the reagent mixture 210; a rate of throughflow of coolant; a temperature of the coolant drawn from the coolant supply; a heat capacity of the coolant; and a surface area and / or volume of the heat exchange region 222.

[0160] Each of these reaction parameters may be independently adjusted to control the kinetics of the leaching process in a manner which optimises operational efficiency, e.g., with respect to cost and / or duration, but maintains reaction conditions, e.g., a working temperature, and / or a pressure, and / or a pH, within an acceptable, i.e., safe, range.

[0161] One or more of the reaction parameters may be controlled by a control means 226 of the system 200, thereby to maintain / adjust one or more reaction safety conditions at the first region 224, i.e., at some or all of the reaction vessel 104, and / or at some or all of the impeller 114. The one or more reaction safety conditions may be one or more of:

[0162] • a temperature;

[0163] • a pressure;

[0164] • a pH of one or more reagents;

[0165] • an oxidation / reduction potential of one or more reagents;

[0166] • a homogeneity of the liquid phase mixture of the reagents; and

[0167] • an amount of excess metal feedstock.

[0168] One or more of the reaction parameters may also be controlled by the control means 226 to maintain / adjust one or more reaction efficiency conditions. The one or more reaction efficiency conditions may be one or more of:

[0169] • a yield of product metal sulphate;

[0170] • an atom economy of product metal sulphate;

[0171] • a production cost of product metal sulphate;

[0172] • a production rate of product metal sulphate; and

[0173] • an amount of excess metal feedstock. In this embodiment, the relatively large number of possible reaction parameters, and the means for their control, provides sufficient degrees of freedom for simultaneous control of the one or more reaction safety conditions and the one or more reaction efficiency conditions. In this manner, operational efficiency of the leaching process may be optimised, for a range of possible feedstocks, while ensuring that safety conditions remain within an acceptable range.

[0174] The control means in Figure 2a is schematically illustrated as a single entity communicatively coupled to each of the reaction vessel 104, motor 215, and cooling circuit 216. Indeed, in some embodiments, the control means 226 comprises a single means for control of each reaction parameter. Alternatively, in some embodiments, the control means 226 may comprise a plurality of distinct control means, each configured to control a respective one of the reaction parameters.

[0175] While, in this embodiment, the system 200 receives the metal feedstock in powdered form, thereby advantageously enabling the introduction and processing of a range of ores, the system 200 is equally suited to receiving the metal feedstock in an alternative, e.g., non-powdered form, such as that typically received by the prior art system 100. For example, the morphology of the metal feedstock received by the system 200 may be coarse or granular (i.e., not fine enough to be considered a powder). Alternatively, the metal feedstock may take the form of a briquette, or a chunk, or a block.

[0176] Figure 2b depicts a further embodiment of the system 200 for dissolving the powdered metal feedstock 202.

[0177] In this embodiment, the system 200 further comprises a sensing means 228 configured to obtain reaction data indicative of the one or more reaction safety conditions and / or the one or more reaction efficiency conditions. The sensing means 228 is further configured to transmit or convey the reaction data to the control means 226. The reaction data obtained by the control means 226 allows the control means 226 to better control one or more of the reaction parameters. In other words, reaction data obtained by the control means 226 via the sensing means 228 tends to allow for more dynamic, real-time monitoring and maintenance / adjustment of the one or more reaction safety conditions and / or the one or more reaction efficiency conditions, providing better optimisation of the leaching process within acceptable safety margins. The reaction data may include, e.g., one or more of temperature data, pressure data, pH data, oxidation reduction potential data, homogeneity data, and data indicative of a quantity of excess feedstock.

[0178] The sensing means 228 may include one or more sensors 230 disposed within a second region 232 of the system 200, thereby to obtain reaction data indicative of the one or more reaction safety conditions and / or the one or more reaction efficiency conditions in the second region 232. Preferably, the second region 232 of the system 200 is within, or is the same region as, or is a region proximate to, the first region 224 of the system 200, such that reaction data obtained is also strongly indicative of the first region 224 at which the one or more reaction safety conditions are being controlled. However, in some embodiments, the second region 232 in which the one or more sensors 230 is disposed is a region of the system 200 other than the first region 224, i.e., the reaction data obtained by the sensing means 228 is not directly indicative of the one or more reaction safety conditions at the first region 224, wherever in the system said first region 224 may be. In such embodiments, the one or more reaction safety conditions may be indirectly obtained from the gathered reaction data, such that the control means 226 is still able to control the one or more reaction parameters to maintain / adjust the one or more safety conditions to maintain safe working conditions of the system 200.

[0179] For example, in some embodiments, the first region 224 and / or the second region 232 is a region elsewhere in the system, e.g. : a region at or within the reaction vessel 104; a region at or proximate the agitation means 114; a region at or within the working fluid loop 218; a region at or within the coolant loop 220; a region at, within or proximate the feedstock introduction means; a region at, within or proximate the one or more acid introduction means; a region at, within or proximate the water introduction means; and a region at, within or proximate an outlet of the reaction vessel 104.

[0180] The sensing means 228 in Figure 2b is schematically illustrated as an entity distinct from and coupled to the one or more sensors 230 disposed in the second region 232, wherever in the system said second region 232 may be. However, in some embodiments, the sensing means 228 does not comprise any entity other than the one or more sensors 230, i.e., the sensing means 228 is wholly disposed within the second region 232, wherever in the system said second region 232 may be.

[0181] Figure 3 depicts a further embodiment of the system 200 for dissolving the powdered metal feedstock 202.

[0182] In this embodiment, the system 200 further comprises an impurity removal circuit 300 comprising one or more filtration stages 302 and, optionally, a feedstock reintroduction means 304. The impurity removal circuit 300 is in fluid communication with the reaction vessel 104, e.g., via an outlet (not shown) of the reaction vessel 104. The one or more impurities 120 present in the product mixture 116 is likely to comprise a quantity of unreacted (solid) metal feedstock 306.

[0183] The one or more filtration stages 302 is configured to capture the unreacted metal feedstock 306 from the product mixture 116 in, and / or output 122, from the reaction vessel 104.

[0184] The feedstock reintroduction means 304 may be configured to return the captured unreacted metal into the reaction vessel 104, i.e., back into the reagent mixture 210.

[0185] The impurity removal circuit 300 may further comprise one or more impurity removal stages (not shown), configured to remove some or all of the one or more impurities 120 from the product mixture 116 formed in and output 122 from the reaction vessel 104. The impurity removal from the product mixture 122 may occur before, during, or after the capturing of the unreacted metal feedstock 306 by the one or more filtration stages.

[0186] Impurities in the product mixture could be trace elements or insoluble that are desirable to remove to ensure sufficient purity of the product mixture 122. Insoluble moieties may be removed by filtration, with the filtrate being recirculated back into the reactor 104 upon separation. Trace elements may be removed by suitable means such as selective precipitation, ion exchange membranes or the like. Any soluble components obtained from these methods may be recirculated back into the reactor 104 following selective removal of the trace elements.

[0187] In this embodiment, control of a rate of capture of the unreacted metal feedstock 306 in the product mixture 116 in, and / or output 122, from the reaction vessel 104 provides a further degree for control of the kinetics of the leaching process. In other words, the rate of capture of the unreacted metal feedstock 306, which may have an attendant impact on the quantity of excess feedstock present in the reaction vessel 104, constitutes a further reaction parameter controllable / adjustable by the control means 226.

[0188] In this embodiment, control of a rate of reintroduction of the unreacted metal feedstock 306 into the reaction vessel 104 may provide a further degree for control of the kinetics of the leaching process. In other words, the rate of reintroduction of the unreacted metal feedstock 306 constitutes a further reaction parameter controllable / adjustable by the control means 226.

[0189] In some embodiments, control of a rate of removal of one or more impurities from the product mixture 116 in, or output 122 from, the reaction vessel 104 provides a further degree for control of the kinetics of the leaching process. In other words, the rate of removal of one or more impurities from the product mixture 116 may constitute a further reaction parameter controllable / adjustable by the control means 226.

[0190] Figure 4 depicts a further embodiment of the system 200 for dissolving the powdered metal feedstock 202.

[0191] In this embodiment, the system 200 may further comprise a repulping means 400 configured to repulp the powdered metal feedstock 202, prior to the introduction 212 of the feedstock into the reaction vessel 104. The repulping means 400 may be configured to repulp the powdered metal feedstock 202 by diluting the feedstock with a (variable) quantity of dilutant, e.g., water.

[0192] In this embodiment, control of an extent of repulping, e.g., control of a volume of dilutant (e.g., water), may provide a further degree for control of the kinetics of the leaching process. In other words, the extent of repulping by the repulping means 400 may constitute a further reaction parameter controllable / adjustable by the control means 226.

[0193] In this embodiment, the system 200 may further comprise a further repulping means 402 configured to repulp the captured unreacted metal feedstock 306, after its capture by the one or more filtration stages 302, and prior to its (optional) return to the reaction vessel 104. The further repulping means 404 may be configured to repulp the captured unreacted metal feedstock 306 by diluting the feedstock with a (variable) quantity of dilutant, e.g., water. In this embodiment, control of an extent of the further repulping, e.g., control of a volume of dilutant (e.g., water), may provide a further degree for control of the kinetics of the leaching process. In other words, the extent of further repulping by the further repulping means 402 may constitute a further reaction parameter controllable / adjustable by the control means 226.

[0194] The extent of repulping by the repulping means 400 and the extent of further repulping by the further repulping means 402 may be independently controllable by the control means 226.

[0195] As in above embodiments, in this embodiment, the first region 224 and / or the second region 232 may comprise one or more of, e.g., any of the following regions within the system 200: a region at or within the reaction vessel 104; a region at or proximate the agitation means 114; a region at or within the working fluid loop 218; a region at or within the coolant loop 220; a region at, within or proximate the feedstock introduction means; a region at, within or proximate the one or more acid introduction means; a region at, within or proximate the water introduction means; and a region at, within or proximate an outlet of the reaction vessel 104.

[0196] Furthermore, in the embodiment depicted in Figure 4, the first region 224 and / or the second region 232 may be a region within the impurity removal circuit 300.

[0197] In some embodiments of the system 200, at least one of the one or more acid introduction means may be at least partly formed of a conduit which also forms at least a part of the working fluid loop, particularly wherein the acid introduction means provides the acid and / or oxidising agent at a location after the heat exchange region 222.

[0198] In other words, in some embodiments, including those described above, at least one of the one or more acid introduction means by which the sulphuric acid and / or the oxidising agent is introduced into the reaction vessel is integrally formed with at least a part of the working fluid loop, wherein typically the sulphuric acid and / or the oxidising agent is introduced to the conduit of the working fluid loop after the heat exchange region. As such, the sulphuric acid and / or the oxidising agent, as the case may be, is introduced into the reaction vessel via the working fluid loop of the cooling circuit. Advantageously, the sulphuric acid and / or the oxidising agent, as the case may be, may thus be delivered into the reaction vessel cooled.

[0199] By adding the acid and / or oxidising agent (particularly the oxidising agent such as the hydrogen peroxide) in the working fluid loop 218 after the heat exchange region 222, the acid and / or oxidising agent are collocated in high concentrations at a temperature below the temperature of the reaction vessel 104. Upon entry to the reaction vessel 104, the high concentrations are diluted. As a result, the likelihood of forming highly reactive reaction products between the acid and oxidising agent such as Caro's acid (peroxymonosulphuric acid) in the reagent input stream are reduced, with such reactive reaction products only being formed in situ in the proximity of the metal feedstock 202. Moreover, the likelihood of decomposition of the oxidising agent due to exposure to high temperatures is reduced.

[0200] In some embodiments of the system 200, at least some of the feedstock introduction means may also be at least partly formed of a conduit which also forms at least a part of the working fluid loop 218. Accordingly, in such embodiments, the solution of metal feedstock is introduced into the reaction vessel 104 via the working fluid loop 218 of the cooling circuit 216. Advantageously, the solution of metal feedstock may thus be delivered into the reaction vessel 104 pre-cooled.

[0201] In the above embodiments of the system 200, adjusting a rate of output 122 of the product mixture 116 from the reaction vessel 104, e.g., via the impurity removal circuit 300 and / or via any other outlet of the reaction vessel 104, may influence the kinetics of a leaching reaction of the metal feedstock. The rate of output 122 may thus be considered a respective reaction parameter whose adjustment represents a degree of freedom in the kinetic control of the leaching reaction.

[0202] In some embodiments, the system 200 may be configured to output the product metal sulphate 118, e.g., via an outlet of the reaction vessel 104 or an outlet of the impurity removal circuit 300. In such embodiments, adjusting a rate of output of the metal sulphate 118 from the system 200 may influence the kinetics of a leaching reaction of the metal feedstock. The rate of output 122 may thus be considered a respective reaction parameter whose adjustment represents a degree of freedom in the kinetic control of the leaching reaction. In some embodiments, the system 200 may further comprise a comminuting means (not shown) configured to form the powdered metal feedstock from input metal feedstock (e.g., raw ore or non-powdered feedstock), thereby to standardise a surface- area-to-volume ratio of the feedstock prior to introduction into the reaction vessel. Advantageously, this tends to allow standardisation, e.g., by crushing, of the morphology (e.g., surface-area-to-volume ratio) of raw metal feedstocks (e.g., ores) suitable for leaching by the above-described systems and processes, making a greater range of raw metal feedstocks suited to the leaching process.

[0203] In such embodiments, adjusting an extent of the comminuting (e.g., control of a surface-area-to-volume ratio of the powdered metal feedstock 202, or, e.g., control of an average diameter of powder particle of the powdered metal feedstock 202) may influence the kinetics of a leaching reaction of the metal feedstock. The extent of the comminuting may thus be considered a respective reaction parameter whose adjustment represents a degree of freedom in the kinetic control of the leaching reaction.

[0204] The system may be configured to operate in batch mode or semi-batch mode, such that metal feedstock is added and substantially dissolved before any further feedstock is added to the reactor. In batch mode, the reaction is run until the metal feedstock is consumed. In semi-batch mode, more feedstock may be added while the reaction is still taking place. However, typically the amount of metal feedstock present in the reactor is smaller, for instance less than 50 wt% such as less than 25 wt% or even less than 10 wt%, than the amount of metal feedstock that is periodically added to the reactor.

[0205] Alternatively, the system may be configured to operate continuously (or semi- continuously) with metal feedstock being added either continuously or periodically while significant amounts of unreacted metal feedstock remain in the reactor. For instance, typically the amount of metal feedstock present in the reactor is larger than, the amount of metal feedstock that is periodically added to the reactor during each addition. For instance, in continuous or semi-continuous mode, the amount of metal feedstock added to the reactor during each addition step is typically less than 50wt% of the amount of metal feedstock already present in the reactor, such as less than 25wt% or even less than 10 wt%. Optionally, the metal feedstock may be continuously added to the reactor.

[0206] Thus, a system for dissolving metal feedstock is provided. In some embodiments, at least some of the features which, in the description of Figures 2a-4, distinguish one embodiment of the system 200 from another may be omitted from a given embodiment, and may be included in embodiments not explicitly described as including said feature. For example, in some embodiments of the system 200, only one of the repulping means 400 and the further repulping means 402 may be present. By way of further example, in some embodiments of the system 200, the system 200 is substantially as shown in Figures 2b-4, but may not comprise the one or more sensors 230 and / or may not comprise the sensing means 228. In such embodiments, control of the one or more parameters described in the corresponding embodiment may be performed by the control means 226 without first receiving reaction data (or may not be performed at all).

[0207] In some embodiments, one or more of the entities of the system 200 described above (and schematically indicated in Figures 2a-4 by way of connecting lines) as being controllable by the control means 226 may in fact not be controllable by the control means 226, e.g., may not be communicatively coupled to the control means 226. For example, in some embodiments, only one, or only two, or only three, or only four, or only five of the entities described as having the ability to adjust one or more reaction parameters may in fact be controllable by the control means 226. More specifically, in some embodiments, for example, only one, or only two, or only three, or only four, or only five of the agitation means 114, the cooling circuit 216, the one or more reagent introduction means, the impurity removal circuit 300, the repulping means 400, and the further repulping means 402 are controllable by the control means 226.

[0208] Advantageously, the configuration of the entities within the system 200 which perform the steps of a process for dissolving / leaching metal feedstock provide a plurality of degrees of freedom to adjust one or more reaction conditions via kinetic control. For example, a value of one or more reaction parameters described above may be selected / set so as to provide a desired one or more reaction conditions within the system.

[0209] For example, such selection may include predicting, and / or simulating, and / or calculating, and / or measuring, a coupling between each of the one or more reaction parameters and a respective one of the one or more reaction conditions, and / or a coupling between a group of reaction parameters and a respective one of the one or more reaction conditions. This may be done based on one or more predicted, and / or simulated, and / or calculated, and / or measured conditions, e.g., determined prior to execution of the leaching process. Such selection may include, additionally or alternatively, determining, based on condition monitoring carried out during or after execution of the leaching process, a coupling between each of the one or more reaction parameters and a respective one of the one or more reaction conditions, and / or a coupling between a group of reaction parameters and a respective one of the one or more reaction conditions. Such selection may include, additionally or alternatively, iterating the process 500 and determining, based on condition monitoring carried out during a previous iteration of the leaching process, an updated coupling between each of the one or more reaction parameters and a respective one of the one or more reaction conditions, and / or an updated coupling between a group of reaction parameters and a respective one of the one or more reaction conditions.

[0210] The ability to influence a desired one or more reaction conditions via control of the one or more reaction parameters within the system tends to facilitate optimisation of the leaching process while maintaining operation within acceptable safety margins.

[0211] As described above, the control means 226 provides a means of selecting / setting a value of one or more reaction parameters so as to provide a desired one or more reaction conditions within the system.

[0212] The configuration of the entities within the system 200, which vary depending on the embodiment of the system 200 in which the leaching process is implemented, provide a plurality of degrees of freedom to adjust the one or more reaction conditions via kinetic control. Advantageously, adjustment of the one or more reaction conditions facilitates optimisation of the leaching process while maintaining operation within acceptable safety margins. As described above, the one or more reaction conditions may include one or more reaction safety conditions and / or one or more reaction efficiency conditions.

[0213] The control of the one or more reaction parameters may include continuously or periodically controlling (i.e., selecting / setting) a value of one or more reaction parameters, thereby to adjust the one or more reaction conditions, contemporaneously with other steps of the leaching process.

[0214] The improved ability to actively control a desired one or more reaction conditions within the system, before, during, or after an iteration of the leaching process, tends to better facilitate optimisation while maintaining safe operation. In some embodiments described above, a non-exhaustive plurality of adjustable reaction parameters associated with entities of the system are identified as providing degrees of freedom for kinetic control of a leaching reaction. Embodiments benefit from at least one such degree of freedom for kinetic control of a leaching reaction. That is, such embodiments comprise one or more reaction parameters controllable to adjust one or more reaction conditions, the one or more reaction parameters comprising one or more parameters selected from the following, non-exhaustive, list:

[0215] • a rate of agitation of the reagent mixture provided by the agitation means;

[0216] • a rate of introduction of the powdered metal feedstock, via the feedstock introduction means, into the reaction vessel;

[0217] • a rate of introduction of the sulphuric acid, via the one or more acid introduction means, into the reaction vessel;

[0218] • a rate of introduction of the hydrogen peroxide, via the one or more acid introduction means, into the reaction vessel;

[0219] • a relative dosing (or relative dosings) of one or more of the reagents introduced into the reaction vessel;

[0220] • an amount, or relative amount, of excess powdered metal feedstock present in the reagent mixture; and

[0221] • one or more of the controllable cooling parameters of the cooling circuit, i.e., one or more of:

[0222] - a rate of throughflow of the one or more fluids taken from the reagent mixture;

[0223] - a rate of throughflow of coolant;

[0224] - a temperature of the coolant drawn from the coolant supply;

[0225] - a heat capacity of the coolant; and

[0226] - a surface area and / or volume of the heat transfer region;

[0227] • a rate of output of the product mixture from the reaction vessel;

[0228] • a rate of capture of the unreacted metal feedstock from the product mixture in, and / or output from, the reaction vessel;

[0229] • a rate of reintroduction of the unreacted metal feedstock into the reaction vessel;

[0230] • a rate of removal of one or more impurities from the product mixture in, or output from, the reaction vessel;

[0231] • an extent of the repulping of the metal feedstock;

[0232] • an extent of the further repulping of the unreacted metal feedstock; and

[0233] • an extent of the comminuting of the metal feedstock prior to introduction into the reaction vessel. In embodiments described above, a non-exhaustive list of reaction conditions is identified, the reaction conditions comprising one or more safety conditions and / or one or more safety conditions. The safety conditions and reaction efficiency conditions are identified as indicative of safety margins and operational efficiency, respectively, of a leaching reaction. Said kinetic control facilitates at least one safety condition and / or at least one efficiency condition (preferably, at least one safety condition and at least one efficiency condition) being maintained at, or adjusted to, a desired value or state, or maintained at, or adjusted to, within a desired range of values or states.

[0234] The one or more reaction safety conditions may be associated with (e.g., representative of) a condition(s) within the first region of the system (which may be the same region as the second region, or a different region to the second region, or a region overlapping with the second region).

[0235] In embodiments described above, the one or more reaction safety conditions comprises one or more conditions selected from the following, non-exhaustive, list:

[0236] • a temperature;

[0237] • a pH of the one or more of the reagents;

[0238] • an oxidation reduction potential of one or more of the reagents;

[0239] • a homogeneity of the liquid phase mixture of two or more of the reagents;

[0240] • an amount of excess metal feedstock with respect to the other reagents;

[0241] • a rate of output of the product mixture the reaction vessel; and

[0242] • a production rate of product metal sulphate.

[0243] In embodiments described above, the one or more reaction efficiency conditions comprises one or more conditions selected from the following, non-exhaustive, list:

[0244] • a yield of product metal sulphate;

[0245] • an atom economy of product metal sulphate;

[0246] • a production cost of product metal sulphate;

[0247] • a production rate of product metal sulphate;

[0248] • an amount of excess metal feedstock;

[0249] • a quantity of one or more impurities within the product mixture;

[0250] • a quantity of one or more impurities removed from the product mixture by the one or more impurity removal stages;

[0251] • a rate of capture of unreacted metal feedstock from the product mixture in, and / or output from, the reaction vessel; and • a quantity of unreacted metal feedstock captured from the product mixture in, and / or output from, the reaction vessel.

[0252] In embodiments described above, the first region is a region cooled by the cooling circuit, and is the region associated with the one or more reaction safety conditions to be maintained within safe margins.

[0253] In these embodiments, the first region comprises one or more of:

[0254] • a region within the reaction vessel;

[0255] • a region within the working fluid loop;

[0256] • a region within the coolant loop;

[0257] • a region within the one or more reagent introduction means;

[0258] • a region at or proximate the agitation means; and

[0259] • a region within the impurity removal circuit.

[0260] In embodiments described above, reaction data may be obtained by one or more sensors in the second region. This reaction data is indicative of the one or more reaction safety conditions and / or the one or more reaction efficiency conditions in the second region. Since it is the one or more reaction safety conditions associated with the first region which are of interest, and which are directly influenced by control of the one or more reaction parameters, the second region is preferably within, or the same region as, or a region proximate to, the first region.

[0261] Advantageously, this tends to ensure that reaction data obtained is strongly indicative a current one or more reaction safety conditions at the first region.

[0262] Nonetheless, in some embodiments, the second region is a region other than the first region, such that the reaction data obtained by is indirectly indicative of the one or more reaction safety conditions at the first region. In such embodiments, the one or more reaction safety conditions associated with the first region may be indirectly obtained from the gathered reaction data. In such embodiments, the control means is advantageously still able to control the one or more reaction parameters to maintain / adjust the one or more safety conditions to maintain safe working conditions of the system. In such embodiments, the second region may comprise one or more of:

[0263] • a region within the reaction vessel; and / or

[0264] • a region within the working fluid loop; and / or

[0265] • a region within the coolant loop; and / or • a region within the one or more introduction means; and / or

[0266] • a region at or proximate the agitation means; and / or

[0267] • a region within the impurity removal circuit.

[0268] The product metal sulphate may be used in the production of active materials such as cathode active materials in battery cathodes (i.e. electrochemical cells).

[0269] Reagents and Conditions

[0270] The process of the disclosure is typically carried out using water as the solvent.

[0271] The process of the disclosure involves an oxidising agent.

[0272] The oxidising agent may be selected from hydrogen peroxide, persulphate (such as hydrogen persulphate (H2S2O8), sodium persulphate (Na2S20s), potassium persulphate (K2S2O8), sodium hydrogenpersulphate (NaHS2Os), or potassium hydrogenpersulphate (KHS2O8), preferably hydrogen persulphate, sodium persulphate, or sodium hydrogenpersulphate, more preferably sodium persulphate (Na2S20s)), or ozone.

[0273] When the oxidising agent is ozone, the ozone is preferably generated in situ and dissolved in water, which is then added to the reaction vessel.

[0274] Suitable methods to generate ozone include UV or corona discharge.

[0275] UV zone generators utilise UV light for instance with a wavelength of 185 nm applied to a gas stream (such as air or concentrated oxygen), resulting in diatomic oxygen splitting and forming ozone. Likewise, corona discharge uses an arc discharge (or corona) applied to air or concentrated oxygen to enrich the gas stream with ozone. The gas stream may then be bubbled through water to capture the ozone for use as the oxidising agent in the method of the disclosure.

[0276] When using ozone as the oxidising agent, the system of the disclosure preferable comprises an ozone generation system (such as a UV ozone generator or corona discharge ozone generator) configured to generate ozone for use as the oxidising agent, for instance as ozone dissolved in water.

[0277] Ozone is typically difficult to incorporate into industrial processes, as it can be difficult to accurately and reliably control the level of ozone in any input stream (at least in compared to other molecular oxidising agents that may be prepared as stock solutions). The control provided by the system and process of the disclosure advantageously allows the dynamic adjustment required to tolerate ozone as an oxidising agent.

[0278] The temperature and pH of the reaction will depend on a number of factors, such as solubility and stability of the reagents and solubilised products, reaction kinetics, and propensity for side reactions.

[0279] Suitable reaction temperatures include from 5 to 95 °C.

[0280] For hydrogen peroxide, suitable reaction conditions include a temperature of from 10 to 60 °C, preferably from 20 to 50 °C, more preferably from 25 to 45 °C, most preferably from 30 to 45 °C.

[0281] For ozone, suitable reaction conditions include a temperature of from 10 to 60 °C, preferably from 20 to 50 °C, more preferably from 25 to 45 °C, most preferably from 30 to 45 °C.

[0282] For persulphate, suitable reaction conditions include a temperature of from 5 to 95 °C, such as from 20 to 90 °C, preferably from 50 to 90 °C, more preferably from 65 to 90 °C, most preferably from 75 to 85 °C.

[0283] Suitable pH for the reaction mixture range from above pH 0, such as from pH 0.5 to pH 3, preferably from pH 0.8 to pH 3; preferably from pH 1 to pH 2.5, more preferably from pH 1 to pH 2.

[0284] Although the sulphuric acid solubilises the metal with a stoichiometric consumption of oxidising agent, the reaction may be viable over a range of ratios for the acid and oxidising agent. For instance, the either the acid or the oxidising agent may be in excess.

[0285] Using a large excess of acid will typically result in the reaction mixture having a lower pH. This has been found to result in lower overall consumption of the metal feedstock. Additionally, it may require additional processing downstream to neutralise the acidity reaction product. Likewise, using a large excess of oxidising agent may result in all of the acid being consumed in the solubilisation reaction, such that the pH may not be maintained at a suitably low level.

[0286] Suitable molar ratios of oxidising agent (e.g. hydrogen peroxide) : acid therefore include from 0.8: 1 to 1.3: 1, preferably from 0.85: 1 to 1.2: 1, more preferably from 0.9: 1 to 1.15: 1.

[0287] Typically, the oxidising agent is added at a suitable rate to ensure a positive oxidationreduction potential (ORP), such as an ORP of at least 400 mV preferably at least 500 mV.

[0288] The process may be carried out for as long as needed to solubilise the metal feedstock. The process time will vary depending on scale and conditions such as pH and temperature. However, controlling these conditions within the suitable values set out above, typical reaction times may vary from 15 minutes to 4 hours, such as from 30 minutes to 3 hours, preferably from 45 minutes to 2 hours, more preferably from 60 to 90 minutes for a suitably sized commercial reactor.

[0289] In this context, the "reaction time" is the time of exposure of the metal feedstock to the reactant solution. This is effectively the time that any batch reactor is maintained in reaction conditions once all the reagents have been added. Addition of any reagents, for instance addition of the acid and oxidising agent, is usually controlled to ensure the temperature is maintained at the desired level, and is added at the appropriate rate depending on the amount of metal feedstock in the batch that needs to be solublised.

[0290] Even so, these timeframes are surprisingly fast particularly for lower temperature reactors (e.g. having reaction temperatures of around 40 °C. The lower reaction times may be achieved at such low temperatures as the reaction conditions may be set to allow fast dissolution of the metal, with the heat from this exothermic reaction being removed via the cooling loop.

[0291] Examples

[0292] Example 1

[0293] Various reactions were carried out using hydrogen peroxide as the oxidising agent in a small scale reactor having a cooling means. Using nickel powder as a feedstock, Figure 5 shows a plot of the remaining solids for reactions carried out at various pH values. The plot shows a general downward trend, showing that more residual solids remain at lower pH values. Values above pH 1 tend to have the lowest residual solids.

[0294] Figure 6 shows the leaching efficiency of reactions at different temperatures. Generally speaking, leaching efficiency is consistently high in the temperature range of 30 to 60 °C, with highest leaching efficiency being observed at 40 °C.

[0295] Figure 7 shows the leaching efficiency compared to the feeding time (i.e. the time over which the reagents were added to the system). Generally speaking, the leaching efficiency was independent of the feeding time. However, it is notable that the heat generated during shorter feeding times was significantly higher, which requires efficient heat exchange via the cooling loop to mitigate.

[0296] Figure 8 shows the pH trends for reactions carried out with differing molar excess of acid, varying from 0% (i.e. stoichiometric peroxide : acid), 5% and 10% excess. The resultant leaching efficiencies were similar (91.96, 91.03 and 89.88). However, the excess of acid beyond 10% can reduce the pH significantly, which begins to impact efficiency and residual metal feedstock as shown in Figure 5. This can also be seen in Figure 9, which shows the leaching efficiency vs excess of hydrogen peroxide. Thus, lower amounts of peroxide (corresponding to excess of acid) result in reduced efficiency. The same is found if too much peroxide is used, particularly over 20% molar excess.

[0297] Cobalt impurities were added to the nickel feedstock in the form of cobalt peroxide. Figure 10 shows that similar leaching efficiencies can be obtained for a wide range of Ni:Co ratios.

[0298] Example 2

[0299] Studies were carried out using sodium persulphate as the oxidising agent.

[0300] In an initial study, sodium persulphate was added all at once to an acidified solution of metallic nickel powder. The temperature immediately increased 20 °C, before beginning to decrease after about 7 minutes. The leaching efficiency was about 50%. In an exemplary study, sodium persulphate was added batchwise in 10 minute intervals to an acidified solution of nickel powder being suspended in water. Figure 11 shows the temperature increasing before being modified by the cooling jacket. The resultant reaction had approximately 50% leaching efficiency.

[0301] In a similar study, sodium persulphate was added continuously with the reaction conditions held at 70 °C. The resultant process had a similar leaching efficiency of about 50%. These studies show that similar leaching efficiencies may be achieved independently of how sodium persulphate is added to the reaction mixture. However, optimal reaction conditions are considered to occur at elevated temperatures.

Claims

CLAIMS1. A process for dissolving metal feedstock (102, 202) in a system (200), the process comprising: receiving (212), by a reaction vessel (104) of the system, reagents (210) comprising a metal feedstock (102, 202), sulphuric acid (106), oxidising agent (108), and water, the receiving (212) being via one or more reagent introduction means; agitating, by an agitation means (114) of the system (200), the reagents (210) within the reaction vessel (104); and cooling, by a cooling circuit (216) of the system (200), at least a first region (224) of the system (200), wherein the cooling comprises: conveying one or more fluids of the reagents (210) through a working fluid loop (218) of the cooling circuit (216); and conveying a coolant through a coolant loop (220) of the cooling circuit (216), the coolant being fluidly separated from and, at a heat transfer region (222) of the cooling circuit (216), in heat exchange with the one or more fluids in the working fluid loop (218).

2. The process of claim 1, wherein the sulphuric acid (106) and / or oxidising agent (108) is introduced into the reaction vessel (104) via the working fluid loop (218) of the cooling circuit (216).

3. The process of claim 1 or claim 2, wherein the metal feedstock (102, 202) is selected from powdered nickel, powdered cobalt, and mixtures thereof; and the oxidising agent (108) is selected from hydrogen peroxide, persulphate or ozone.

4. The process of any preceding claim, further comprising: obtaining, by a sensing means (228) of the system (200), reaction data indicative of one or more reaction conditions within the system (200); receiving, by control means (226), the reaction data from the sensing means (228); and controlling, by the control means (226), one or more reaction parameters of the system (200), thereby to adjust one or more reaction conditions within the system (200).

5. The process of claim 4, wherein the one or more reaction parameters comprises one or more of: a rate of agitation of the reagents by the agitation means (114); a rate of introduction of the metal feedstock (102, 202) into the reaction vessel (104) via the one or more reagent introduction means; a rate of introduction of the sulphuric acid (106) into the reaction vessel (104) via the one or more reagent introduction means; a rate of introduction of the oxidising agent (108) into the reaction vessel (104) via the one or more reagent introduction means; a relative dosing, or relative dosings, of one or more of the reagents (210) introduced into the reaction vessel (104); an amount of excess metal feedstock present in the reaction vessel (104); one or more cooling parameters comprising at least one of: a rate of flow of the one or more fluids through the working fluid loop (218); a rate of flow of the coolant through the coolant loop (220); a temperature of the coolant in the coolant loop (220); a heat capacity of the coolant; and a surface area and / or volume of the heat transfer region (222); a rate of output of a product mixture (116) from the reaction vessel (104); and a rate of output of metal sulphate (118) from the reaction vessel (104).

6. The process of any preceding claim, wherein: the system (200) further comprises an impurity removal circuit (300) in fluid communication with the reaction vessel (104), the impurity removal circuit (300) comprising one or more filtration stages (302), a feedstock reintroduction means (304) and, optionally, one or more impurity removal stages; and the process further comprises: capturing, by the one or more filtration stages (302), unreacted metal feedstock (306) from a mixture (116) formed in the reaction vessel (104), the mixture (116) further comprising one or more impurities (120), wherein, optionally: the process is in accordance with claim 4 or any claim dependent on claim 4 and the one or more reaction parameters comprises a rate of capture of the unreacted metal feedstock (306) from the mixture (116) formed in the reaction vessel (104);returning, by the feedstock reintroduction means (304), the unreacted metal feedstock (306) into the reaction vessel (104), wherein, optionally: the process is in accordance with claim 4 or any claim dependent on claim 4 and the one or more reaction parameters comprises a rate of reintroduction of the unreacted metal feedstock (306) into the reaction vessel (104); and optionally, removing, by the one or more impurity removal stages (302), at least some of the one or more impurities (120) from the mixture (116), wherein, optionally: the process is in accordance with claim 2 or any claim dependent on claim 2 and the one or more reaction parameters comprises a rate of removal of one or more impurities (120) from the mixture (116) formed in the reaction vessel (104).

7. A system (200) for dissolving metal feedstock (102, 202), the system comprising: a reaction vessel (104) for receiving (212) reagents (210), the reagents comprising a metal feedstock (102, 202), sulphuric acid (106), oxidising agent (108), and water; one or more reagent introduction means for introducing the reagents (210) into the reaction vessel (104); an agitation means (114) for agitating the reagents (210) within the reaction vessel (104); and a cooling circuit (216) for cooling at least a first region (224) of the system (200), the cooling circuit (216) comprising: a working fluid loop (218) for conveying one or more fluids of the reagents (210); and a coolant loop (220) for conveying a coolant, the coolant being fluidly separated from, and, at a heat transfer region (222) of the cooling circuit (216), in heat exchange with, the one or more fluids in the working fluid loop (218).

8. The system of claim 7, further comprising a conduit forming at least a part of the working fluid loop (218) for conveying the one or more fluids of the reagents (210) also forms at least a part of the one or more introduction means; the conduit forming at least a part of the working fluid loop (218) is for introducing at least one fluid of the one or more fluids of the reagents (210) into the reaction vessel (104).

9. The system (200) of claim 7 or claim 8, further comprising a sensing means (228) for obtaining reaction data indicative of one or more reaction conditions within the system (200); and a control means (226) for controlling one or more reaction parameters of the system (200), thereby to adjust one or more reaction conditions within the system (200); wherein the control means (226) is for receiving the reaction data from the sensing means (228); and the control means (226) is for controlling, based on the reaction data, the one or more reaction parameters of the system (200) thereby to adjust the one or more reaction conditions; wherein the one or more reaction parameters comprises one or more of: a rate of agitation of the reagents (210) by the agitation means (114); a rate of introduction of the metal feedstock (102, 202) into the reaction vessel (104) via the one or more reagent introduction means. a rate of introduction of the sulphuric acid (106) into the reaction vessel (104) via the one or more reagent introduction means; a rate of introduction of the oxidising agent (108) into the reaction vessel (104) via the one or more reagent introduction means; a relative dosing, or relative dosings, of one or more of the reagents (210) introduced into the reaction vessel (104); an amount of excess metal feedstock present in the reaction vessel (104); one or more cooling parameters comprising at least one of: a rate of flow of the one or more fluids through the working fluid loop (218); a rate of flow of the coolant through the coolant loop (220); a temperature of the coolant in the coolant loop (220); a heat capacity of the coolant; and a surface area and / or volume of the heat transfer region (222); a rate of output of a product mixture (116) from the reaction vessel (104); and a rate of output of metal sulphate (118) from the reaction vessel (104);10. The process or system of any preceding claim, wherein the reaction vessel (104) is formed from a fibre reinforced polymeric material.

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