Continuous nickel oxidation leaching process

Abstract

The present invention provides a method for preparing a nickel sulfate solution in a column reactor, whereby nickel-containing metal particles react with an oxidative leach solution comprising sulfuric acid and hydrogen peroxide in water, resulting in substantial depletion of the acid in the oxidative leach solution.

Description

[Technical field]

[0001] The present invention relates to a method for producing nickel sulfate. [Background technology]

[0002] Secondary lithium-ion batteries (LIBs) have found widespread application in portable devices and electric vehicles, as well as specialized aerospace applications. Important properties of reusable batteries include charge / discharge efficiency, cycle durability, energy density, and safety. Much development has focused on improving the performance of the cathode of LIBs.

[0003] Following lithium cobalt oxide, lithium manganese oxide and lithium iron phosphate, lithium nickel manganese cobalt oxide ("NMC", LiNi x Mn y Co z O2) and lithium nickel cobalt aluminum oxide ("NCA", LiNi x Co y Al z O2) have attracted much attention due to their excellent performance. They can be easily obtained by mixing a suitable mixed metal precursor with a suitable lithium compound, followed by heat treatment of the mixture. Further processing steps, for example to dope with further elements, provide surface coating, improve crystallite size, etc., have been widely reported.

[0004] The growing demand for electric vehicles (EVs) is increasing the demand for high-purity nickel, especially high-purity nickel sulfate. In fact, nickel smelters for preparing high-purity nickel are considered to be the most important for the supply of battery materials for the next decade. Such nickel smelters should enable high-capacity and high-efficiency methods to obtain the desired nickel sulfate in the desired quantity and purity. Novel methods therefore need to be developed and optimized. Among other methods, oxidative leaching of Ni from high-purity nickel metal is considered one of the more promising avenues.

[0005] The process of leaching Ni metal in sulfuric acid in the presence of hydrogen peroxide proceeds according to the following reaction: Ni+H2O2+H2SO4→NiSO4+2H2O

[0006] This method, also known as oxidative leaching of Ni metal, is a highly exothermic (-423 kJ / mol) process.

[0007] WO 2021 / 105365 describes a method for producing nickel sulfate by leaching metal particles containing nickel in an aqueous sulfuric acid solution, comprising the steps of: - introducing the metal particles into the aqueous sulfuric acid solution; - introducing an aqueous hydrogen peroxide solution into the aqueous sulfuric acid solution containing the metal particles, the aqueous hydrogen peroxide solution being gradually introduced into the aqueous sulfuric acid solution containing the metal particles. Furthermore, new methods are needed that result in new methods that allow easy implementation, high processing capacity, and optimized use of the reactants. WO 2011 / 126757 describes a method for producing an aqueous nickel sulfate solution with a low content of free sulfuric acid. The method includes filling a metal dissolving column with metallic nickel mass, feeding heated sulfuric acid from the top of the metal dissolving column and simultaneously feeding air or oxygen from the bottom of the metal dissolving column. However, such methods may have the disadvantage of unreacted metal particles being entrained in the resulting process product. Summary of the Invention

[0008] The present invention provides a solution to at least one of the above mentioned problems by providing a method for oxidative leaching of Ni as claimed in claim 1. Preferably, the method is carried out in a column reactor under continuous flow conditions, in which the acid concentration in the oxidative leaching solution is substantially depleted. More specifically, the acid in the oxidative leaching solution is depleted to the extent that the temperature of the resulting nickel sulfate solution is increased to a temperature just below the boiling point of the solution. The inventors have found that under such conditions, the conversion of Ni to nickel sulfate is maximized and, accordingly, the capacity of the column is maximized. The method of the present invention is shown diagrammatically in Figure 1. [Brief description of the drawings]

[0009] For further guidance, figures are included to provide a better understanding of the teachings of the present invention, which are intended to aid in the explanation of the invention and are not intended to limit the invention of this disclosure.

[0010] The drawings and symbols contained therein have meanings commonly understood by one of ordinary skill in the art to which this invention pertains. [Figure 1] FIG. 1 shows a schematic diagram of the process according to the invention in a column reactor. [Diagram 2] FIG. 2 is a graph showing the dissolution rate of nickel in an oxidative leaching process according to the method of the invention (Y-axis, kg / h) as a function of the average acid concentration (X-axis, g / L sulphuric acid, calculated as the average of CSA,i and CSA,o) at a constant volumetric flow rate through the column. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Unless otherwise defined, all terms used in disclosing the present invention, including technical and scientific terms, have the meanings commonly understood by those skilled in the art to which the present invention belongs. As a further guide, definitions of terms are included to better understand the teachings of the present invention. As used herein, the following terms have the following meanings:

[0012] As used herein, "a," "an," and "the" refer to both the singular and the plural unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more compartments.

[0013] As used herein, "about" referring to a measurable value, such as a parameter, amount, duration, etc., is meant to encompass variations of the specified value and from the specified value of no more than ±20%, preferably no more than ±10%, more preferably no more than ±5%, even more preferably no more than ±1%, and even more preferably no more than ±0.1%, insofar as such variations are appropriate for the practice of the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself specifically disclosed.

[0014] As used herein, "comprise," "comprising," "comprises," and "comprised of" are synonymous with "include," "including," "includes," or "contain," "containing," or "contains," and are inclusive or open-ended terms that specify the presence of what follows, e.g., components, and do not exclude or preclude the presence of additional, unrecited components, features, elements, materials, steps that are known in the art or disclosed herein.

[0015] The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range as well as the recited endpoints. All percentages are to be understood as percentages by weight, abbreviated as "wt. %," or percentages by volume, abbreviated as "vol. %," unless otherwise defined or a different meaning is apparent to one of ordinary skill in the art from its use and in the context in which it is used.

[0016] In the context of the present invention, the term "continuous process" shall be considered as a process in which the solution produced has a substantially constant composition. Specifically, a continuous process is a process in which the solution produced has a constant composition within what would be considered normal process variations. It is also assumed that the liquid reagents fed to the reactor have a fixed composition under normal process conditions. More specifically, the solution produced has a composition in which the concentration of each component is within ±20% or less of its average concentration, preferably ±10% or less, more preferably ±5% or less, and even more preferably ±3% or less. In a preferred embodiment, the present invention provides a continuous process operating under steady state conditions.

[0017] Preferably, sulfuric acid and hydrogen peroxide are fed to the process according to the invention at substantially constant concentrations and flow rates. Ni metal can be fed to the process intermittently or gradually. Preferably, the present invention provides a process, preferably a continuous process, in which the bed volume of nickel-containing metal particles is controlled in a column reactor within ±20% or less of its average bed volume, preferably ±10% or less, more preferably ±5% or less, even more preferably ±3% or less.

[0018] In the context of the present invention, the term "concentrated nickel sulfate solution" shall be considered as synonymous with the term "nickel sulfate solution having a nickel content of at least 60 g Ni / L", optionally including further inclusions such as sulfuric acid in an amount of less than 30 g / L H2SO4, preferably less than 20 g / L, more preferably less than 10 g / L. Preferably, the nickel sulfate solution has a nickel content of at least 60 g Ni / L, preferably at least 80 g Ni / L. The nickel sulfate solution preferably has a nickel sulfate content below the saturation point of nickel sulfate at the treatment temperature, i.e. at a temperature of about 90° C. or about 95° C. Preferably, the nickel sulfate solution has a Ni content of 80-200 g Ni / L, preferably 90-175 g Ni / L, more preferably 100-150 g Ni / L. Preferably, the nickel sulfate solution obtained from the oxidative leaching reaction has a nickel content of 110-140 g / L, more preferably 120-140 g / L, and most preferably the nickel sulfate solution has a nickel content of about 130 g / L.

[0019] In a first aspect, the present invention provides a method for preparing a nickel sulfate solution by oxidative leaching of nickel-containing metal particles in a column reactor having a feed at the bottom of the reactor, an outlet or overflow at the top or apex of the reactor, and a reaction section between the feed and the overflow. The method comprises: i. feeding nickel-containing metal particles into a reaction section of the column reactor; ii. feeding an oxidizing leachate comprising sulfuric acid and hydrogen peroxide in water to the reaction section via a feed section, whereby the oxidizing leachate is brought into contact with the metal particles containing nickel in the reaction section, whereby the residual amount of sulfuric acid (C SA,o obtaining a nickel sulfate solution containing iii. discharging the nickel sulfate solution from the overflow of the column reactor.

[0020] Preferably, the process according to the first aspect of the invention is a continuous process. Preferably, the process according to the first aspect of the invention is applied to prepare a concentrated nickel sulfate solution. The process is typically carried out under continuous flow conditions in a column reactor, where the acid in the oxidative leach solution is substantially depleted after passing through the column reactor. In particular, steps ii. and iii. are typically carried out under continuous flow conditions, and step i. can be carried out under continuous flow conditions or can be carried out gradually or intermittently. More particularly, the acid in the oxidative leach solution is depleted to the extent that the temperature of the resulting nickel sulfate solution is increased to a temperature just below the boiling point of the solution, ensuring that the capacity of the column is maximized for a target acid concentration in the nickel sulfate solution at the top of the reactor. The inventors have found that under such conditions, the conversion of Ni to nickel sulfate is maximized and, correspondingly, the capacity of the column is maximized.

[0021] The depletion of sulfuric acid throughout the column reactor is determined by the sulfuric acid concentration (C SA,o ) of the sulfuric acid concentration (C SA,i ) in the context of the present invention, the inventors recommend that said ratio be maintained at a value between 0.90 and 0.01, preferably between 0.80 and 0.01, and more preferably between 0.70 and 0.02. In the context of the present invention, this ratio is called the "acid ratio".

[0022] FIG. 1 shows diagrammatically the process according to the invention in a column reactor.

[0023] The inventors have found that a desired, i.e. sufficiently low, acid ratio can be managed by maintaining a sufficiently low flow rate of oxidized leachate through the column reactor.

[0024] The inventors have found that the lower the flow rate of the oxidizing leachate through the column reactor, the easier it is to control the column reactor process. By keeping the flow rate of the oxidizing leachate low enough, the sulfuric acid is depleted at the top of the column reactor. Also, by keeping the flow rate of the oxidizing leachate to the column reactor low enough, the leaching reaction can be controlled so that the temperature of the nickel sulfate solution at the top of the column reactor remains below the boiling point of the solution, and the inlet temperature can be kept at a moderate to low temperature. A sufficiently low flow rate can control the progress of the leaching reaction to ensure complete consumption of the oxidizing agent, and preferably a sufficiently low flow rate is managed so that the temperature at the top of the column is just below the boiling point of the solution. Importantly, the inventors have recognized that carrying out the column reactor process at a sufficiently low flow rate will result in a higher average acid concentration in the column reactor, which will result in a faster conversion of Ni metal to NiSO4.

[0025] FIG. 2 shows the nickel dissolution rate (Y-axis, kg / h) in an oxidative leaching process according to the method of the present invention versus the average acid concentration (X-axis, g / L sulfuric acid, C) at a constant volumetric flow rate through the column. SA,i and C SA,o The results show that the higher the average acid concentration in the column, the higher the nickel dissolution rate. The maximum capacity of the continuous process can be obtained when the consumption of acid through the column is maximized, provided that the temperature at the top of the column reactor is controlled below the boiling point of the nickel sulfate solution.

[0026] On the other hand, processes carried out at higher ratios of the sulfuric acid concentration of the nickel sulfate solution obtained in step ii. to that of the oxidized leachate, for example at ratios of 0.95 to 1.0, will inevitably result in lower average acid concentrations in the reaction zone due to the higher flow rates, and therefore in such processes the conversion of Ni metal to NiSO4 will be slower and capacity will be reduced.

[0027] In a preferred embodiment, the invention provides a method according to the first aspect, wherein on a macroscopic scale, a 1D flow profile is maintained throughout the column.

[0028] In a preferred embodiment, the present invention relates to a method for determining the acid ratio, i.e., the sulfuric acid concentration (C SA,o ) of the sulfuric acid concentration (C SA,i The method according to the first aspect further provides a method for treating a catalysis comprising the steps of: (a) a ratio of 0.01 to 0.15, 0.02 to 0.10, 0.15 to 0.20, 0.25, 0.30, 0.35, or any value therebetween;

[0029] In a preferred embodiment, the present invention provides a method for treating a gas containing a volatile organic compound (VOC) comprising the steps of: SA,i and C SA,o Difference Δ ac is at least 5 g / L and at most 80 g / L sulfuric acid, preferably at least 10 g / L and at most 70 g / L sulfuric acid. ac is at least 15 g / L, more preferably at least 20 g / L. ac is at most 60 g / L or at most 50 g / L, more preferably at most 45 g / L. Most preferably, the difference in acid concentration Δ ac is about 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, or 45 g / L, or any value therebetween.

[0030] In a preferred embodiment, the oxidative leaching process, i.e., the column reactor, is controlled so that the nickel sulfate solution obtained from the column reactor has a residual sulfuric acid content (C SA,oLeaching with a low residual sulphuric acid content ensures that the sulphuric acid is economically used in the process. Preferably, the residual amount of sulphuric acid in the nickel sulphate solution is between 2g / L and 15g / L, more preferably between 2g / L and 10g / L, and most preferably the residual amount of sulphuric acid is about 2g / L, 4g / L, 6g / L, 8g / L or 10g / L, or any value therebetween.

[0031] In a preferred embodiment, the present invention provides a process according to the first aspect, wherein the oxidative leachate is fed to the reactor, i.e. the column reactor, at a temperature above 20°C, preferably above 30°C, preferably above 40°C, more preferably above 50°C. In particular, the oxidative leachate is fed to the reactor at a temperature between 50°C and 85°C, preferably between 65°C and 85°C, more preferably at a temperature of about 75°C. It is advantageous to provide a lower temperature oxidative leachate to the column, allowing a higher acid concentration. Such a higher acid concentration allows a higher Ni conversion and therefore a higher process capacity. However, the inventors have realised that to ensure a sufficiently high kinetics of the oxidative leaching reaction, it is appropriate to maintain a sufficiently high temperature of the oxidative leach solution entering the column. The desired temperature, for example 60°C, can be achieved by mixing room temperature sulphuric acid and / or hydrogen peroxide with a partially cooled fraction of the column effluent. Furthermore, maintaining a sufficiently high temperature allows an efficient cooling operation of the fraction of the effluent. Feed of the oxidized leachate at a lower temperature also ensures that decomposition of hydrogen peroxide in the feed solution is suppressed.

[0032] In a preferred embodiment, the present invention provides a process according to the first aspect, wherein the nickel sulfate solution is removed from the reactor at a temperature below the boiling point of the nickel sulfate solution, preferably at a temperature between 90° C. and 105° C., more preferably at a temperature between 95° C. and 100° C. Preferably, the nickel sulfate solution discharged from the reactor has a temperature between 95° C. and 99° C., for example 96° C., 97° C., 98° C. or 99° C.

[0033] In a preferred embodiment, the present invention provides a process according to the first aspect, wherein a first fraction φ1 of the nickel sulphate solution is cooled from a temperature above 90° C. to a temperature below 85° C., and the fraction φ1 is mixed with sulphuric acid and hydrogen peroxide in water to form an oxidized leachate before feeding the oxidized leachate to the reactor. Preferably, the first fraction φ1 is cooled from a temperature above 95° C. to a temperature below 85° C., preferably below 80° C., more preferably below 75° C., even more preferably below 70° C., more preferably from a temperature above 97° C. to a temperature below 85° C. Advantageously, the first fraction φ1 is cooled to a temperature above 50° C., preferably above 60° C., more preferably above 70° C.

[0034] The cooling can be carried out in a heat exchanger, such as a plate heat exchanger, a shell-and-tube heat exchanger, or in a reactor equipped with cooling means. Preferably, the heat exchanger consists of a reactor equipped with cooling means. Such a reactor can further buffer the volume of the first fraction φ1. Alternatively, the sulfuric acid and / or hydrogen peroxide can be preheated with heat recovered from the heat exchanger. Advantageously, the process conditions according to the process of the invention ensure that a constant temperature of the nickel sulfate solution at the top of the column reactor is achieved, which allows to simplify the cooling process.

[0035] In a preferred embodiment, the present invention provides a process according to the first aspect, wherein a first fraction φ1 of the nickel sulfate solution is mixed with sulfuric acid and / or hydrogen peroxide to form an oxidized leachate, and then the oxidized leachate is fed to the reactor. In a preferred embodiment, the volume ratio of the first fraction φ1 to the total volume of the nickel sulfate solution is between 0.70 and 0.98, preferably between 0.75 and 0.95, more preferably between 0.80 and 0.93, and most preferably equal to 0.80, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92 or any value therebetween.

[0036] In a preferred embodiment, the present invention provides a process according to the first aspect, wherein the heat recovered from the cooling step of the first fraction φ1 is at least partly used to heat the oxidized leachate and / or the reactor contents. Preferably, the heat is used to heat the oxidized leachate and / or the reactor contents to a temperature of between 55°C and 85°C, preferably between 60°C and 85°C, more preferably between 65°C and 80°C, most preferably to a temperature of about 65°C.

[0037] In a preferred embodiment, the present invention provides a method according to the first aspect, wherein the second fraction φ2 of the nickel sulfate solution is subjected to a purification step to reduce the concentration of one or more impurities in the second fraction φ2, the impurities comprising one or more selected from the list comprising Cu, Zn, Co, Mn, Fe, Al, F, C, Ca, Si, P, As, Cd, Sb and Mg. In a preferred embodiment, a base is added to the second fraction φ2 of the nickel sulfate solution to react with residual amounts of sulfuric acid present in the nickel sulfate solution before the second fraction is subjected to a further purification step, the base being selected from the group consisting of potassium hydroxide, potassium carbonate, nickel hydroxide, nickel carbonate, cobalt hydroxide, cobalt carbonate, manganese hydroxide, manganese carbonate, calcium hydroxide, calcium carbonate, sodium hydroxide, sodium carbonate, lithium hydroxide, lithium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, or a combination of two or more of the foregoing. Preferably, the base is added until the pH of the nickel sulfate solution is 2 to 5, preferably 2.5 to 4.5, more preferably 3.0 to 4.0.

[0038] In a preferred embodiment, the present invention provides a method according to the first aspect, wherein the metal particles containing nickel comprise nickel in an amount of at least 97% by weight, preferably at least 98% by weight, more preferably at least 99% by weight, based on the total weight of the metal particles. The metal particles may further comprise Co in an amount of up to 1% by weight. Preferably, the metal particles contain Ni in an amount of at least 99.5% by weight. In the context of the present invention, the Ni metal feed preferably comprises highly pure Ni metal, typically having a purity of 99.97+%, 99.98+%, or even 99.99+%. Ni metal can be fed to the reactor in the form of Ni cut cathode metal, i.e., chopped or chopped full plate cathode metal obtained from an electrowinning process, typically having a size of 1 inch x 1 inch, 2 inch x 2 inch, or 4 inch x 4 inch; Ni metal rounds; or Ni pellets, i.e., balls having a diameter of about 0.5 cm. The hydrogen peroxide used in the process is typically a 30-60% by weight, for example 50% by weight, solution in water, and the sulfuric acid has a concentration of 78-98% by weight in water, preferably 98% by weight in water. Any water used in the process may be high purity water, such as demineralized water or RO water.

[0039] In a preferred embodiment, the present invention provides a method according to the first aspect, wherein the oxidative leachate comprises sulphuric acid in an amount of 10 to 150 g / L, preferably in an amount of 15 to 100 g / L.Preferably, the oxidative leachate comprises sulphuric acid in an amount of 20 to 80 g / L, more preferably in an amount of 20 to 60 g / L.

[0040] In a preferred embodiment, the present invention provides a method according to the first aspect, wherein the oxidized leachate comprises hydrogen peroxide in an amount of 1-50 g / L, preferably 1-30 g / L, more preferably 5-30 g / L. More preferably, the oxidized leachate comprises hydrogen peroxide in an amount of 5-20 g / L, more preferably about 5-12 g / L, even more preferably about 7-10 g / L.

[0041] In a first preferred embodiment, the present invention provides a method according to the first aspect, wherein hydrogen peroxide is present in the oxidative leachate fed to the column reactor in substoichiometric amounts relative to the amount of sulfuric acid present in the oxidative leachate. For example, the oxidative leachate may comprise 0.4 mol / L hydrogen peroxide and 0.5 mol / L sulfuric acid. Preferably, the molar ratio of hydrogen peroxide to sulfuric acid in the oxidative leachate fed to the column reactor is between 0.6 and 1.0, preferably between 0.8 and 1.0, more preferably about 0.9. The method according to the present invention may be carried out with substoichiometric amounts of hydrogen peroxide, thereby allowing for residual amounts of sulfuric acid in the nickel sulfate solution formed. In a second alternative embodiment, the present invention provides a method according to the first aspect, wherein sulfuric acid and hydrogen peroxide are present in stoichiometric amounts in the oxidative leachate. Preferably, the molar ratio of sulfuric acid to hydrogen peroxide is between 1:1 and 1:1.2, more preferably between 1.0:1.0 and 1:1.1. The excess hydrogen peroxide promotes further depletion of sulfuric acid. The excess hydrogen peroxide ensures that hydrogen peroxide is not the rate limiting factor of the process. The excess hydrogen peroxide can be recovered from the column reactor effluent.

[0042] In a preferred embodiment, the present invention provides a process according to the first aspect, wherein the gas atmosphere in the overflow of the column reactor is circulated through a scrubber. Preferably, the scrubber is cooled. Preferably, the scrubber and the circulation reactor are integrated into one single unit. Preferably, the circulation reactor is maintained at a temperature between 50° C. and 90° C., preferably at a temperature of about 65° C. or about 85° C., more preferably at a temperature of about 75° C. Lower temperatures are more favorable for the efficiency of the scrubbing operation.

[0043] In a preferred embodiment, the present invention provides a process according to the first aspect, wherein the oxidative leachate is contacted with the metal particles at atmospheric pressure, i.e. 1 bar, or under reduced pressure of less than 0.5 bar, preferably less than 0.2 bar, more preferably less than 0.1 bar. Preferably, the oxidative leachate is contacted with the metal particles under an atmosphere of oxygen, air or oxygen-enriched air. In another preferred embodiment, the gas atmosphere in the overflow is flushed with an inert gas, such as N2. This allows easy removal of hydrogen gas if it is formed in the column reactor.

[0044] In another preferred embodiment, the present invention provides a method according to the first aspect, wherein the gas atmosphere in the overflow is treated in a scrubber to remove water and any hydrogen which may have been formed.

[0045] In a preferred embodiment, the present invention relates to a bed volume of the metal particles in a column reactor having a diameter D b and height H b and the ratio of the height to the diameter H b :D b is between 0.8 and 5, preferably between 1 and 5. Preferably, the height and diameter of the bed volume are maintained substantially constant throughout the process.

[0046] The process of the invention proceeds in a column. In the context of the present invention, the term "column" shall be considered equivalent to the terms "column reactor", "packed bed" or "packed bed reactor", "tower" or "tower reactor" and refers to a column reactor having a substantially cylindrical form with an internal diameter D and a height H. A column reactor consists of a vertically arranged cylindrical column, arranged to operate without mechanical stirring, preferably in an upflow mode, i.e., fluid flow from the bottom to the top of the column. A column reactor is further characterized by (i) a feed section at the bottom of the cylindrical reactor for feeding liquid reagents, such as an aqueous solution containing sulfuric acid and hydrogen peroxide, (ii) a top or overflow section at the top or top end of the column reactor, opposite the feed section, characterized by an effluent for collecting the overflowing nickel sulfate solution, and (iii) a middle or reaction section in the middle of the cylindrical reactor, where the leaching reaction proceeds. Metal particles containing nickel are preferably fed to the top of the reactor and can be gradually or intermittently introduced to form a bed of metal particles on a support in the column reactor. The column reactor preferably comprises a support above the feed for supporting a solid reagent such as Ni metal. The support comprises a grid for supporting Ni metal. The column reactor further preferably comprises means for feeding a solid reagent such as Ni metal to the reaction zone of the column reactor. The column reactor further preferably comprises means for radially and uniformly distributing the oxidized leachate to the feed of the column reactor. The solid reagent may be loaded onto the support by introducing Ni metal at the top of the reactor or any position above the support. The overflow zone is provided with an outlet for receiving nickel sulfate solution via an overflow mechanism.

[0047] In a preferred embodiment, the present invention relates to a column reactor having a liquid volume of the oxidized leachate with a diameter of D L and height H L and the ratio of the height to the diameter H L :D Lis between 1.0 and 10.0, preferably between 1.5 and 8.0, more preferably between 2.0 and 5.0, most preferably about 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0, or any value therebetween. L :D L The ratio ensures that one-dimensional flow can be obtained throughout the column and that small metallic particles resulting from the reacted metallic feed particles are not entrained upwards into the nickel sulfate solution resulting from the oxidation leaching reaction, thereby entraining unreacted metallic particles and thereby contaminating the resulting nickel sulfate solution and further reducing the efficiency of the process.

[0048] In a preferred embodiment, the column reactor is cylindrical and has an internal diameter D and a height H, the ratio of the height H to the diameter D being significantly higher than 1, for example 1.0-10.0, preferably 1.5-8.0, more preferably 2.0-5.0, most preferably about 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0, or any value therebetween. An appropriate geometry of the column reactor, and in particular a sufficiently high H:D ratio, ensures that one-dimensional flow can be obtained throughout the column.

[0049] In a preferred embodiment, the present invention provides a process according to the first aspect of the present invention, wherein in step ii., the oxidized leachate comprising sulfuric acid and hydrogen peroxide in water is fed to the reaction zone through the bottom of the column reactor, and in step iii., the nickel sulfate solution is discharged from the reaction zone through the top of the column reactor. Preferably, the metal particles are fed to the reaction zone through the top of the column reactor. The metal particles may be fed continuously or intermittently, preferably intermittently.

[0050] In a preferred embodiment, the reaction zone can also incorporate a mechanical impeller, i.e., an impeller attached to a motor by a rod, for simply mixing the liquid reagents. Alternatively, a static mixer is used. In a preferred embodiment, the reaction zone includes a plurality of vertical baffles, which are diametrically positioned with respect to each other and are located between the inlet nozzle and the impeller, such that at least one baffle is located at the diametrically opposite end of the reactor wall. In this embodiment, the impeller and the vertical baffles serve to mix the reactants at a micro level. The impeller improves the reaction rate of the reactor. The vertical baffles help ensure maximum mixing of the reactants in the reaction zone. The placement of the vertical baffles ensures that the reaction is confined to the reaction zone and does not extend to zones above the reaction zone.

[0051] Preferably, the reactor has a calming zone above the reaction zone. The calming zone has a tubular structure with a constant cross section, preferably equal to the cross section of the reaction zone, or with an enlarged cross section, the diameter of which is greater than the cross section of the reaction zone. The calming zone is in fluid communication with the reaction zone, with the reaction zone at its distal end and an overflow zone at its proximal end. The function of the calming zone is to provide a non-turbulent liquid flow in which the unreacted metal particles conform to a non-flowing state. This allows the unreacted or under-reacted metal particles to be returned to the reaction zone. The calming zone may include a number of horizontal baffles located at the central, proximal and distal portions of the calming zone. In this embodiment, at least two of the provided horizontal baffles may be downward-facing baffles with a central flow opening adapted to slow down the velocity of the reaction mixture. In yet another embodiment, the provided central horizontal baffle is a conical baffle with annular flow. In this embodiment, the horizontal baffle arrangement creates a curved flow path that allows larger sized particles to settle while simultaneously allowing the upward flowing mixture to move smoothly into the overflow zone.

[0052] In a preferred embodiment, the overflow zone has a tubular structure, the cross section of which is equal to the cross sections of the settling zone and the reaction zone, and is located at the proximal end of the reactor, the overflow zone being provided with an outlet for receiving the nickel sulfate solution formed. EXAMPLES

[0053] The following examples are intended to further clarify the invention, but are not intended to limit the scope of the invention.

[0054] Example 1 FIG. 1 shows diagrammatically the process according to the invention in a column reactor.

[0055] The oxidized leachate is prepared by mixing an aqueous sulfuric acid solution A with a hydrogen peroxide solution P in water. The mixture is then mixed with a fraction φ1 of the effluent of the column reactor, to obtain an oxidized leachate of about T i = 60°C. The column reactor has an internal diameter D and a height H, the ratio H:D being about 2.35. The fraction φ1 is cooled from a temperature of about 98°C to a temperature of about 65°C before mixing it with sulfuric acid and hydrogen peroxide. The oxidized leachate thus prepared has a temperature of about 60°C and a sulfuric acid content of about 45 g / L and is fed to the reaction zone of the column reactor via a feed.

[0056] The reaction zone includes a Ni metal cut cathode having dimensions of approximately 50 mm x 50 mm and a nickel content of 99.97%. Metal particles containing nickel are intermittently fed onto a support plate above the reactor feed. The metal particle feed is omitted in FIG. 1. The Ni metal is provided in a bed, the bed having a bed volume characterized by a height and a diameter, the ratio of the height to the diameter being approximately 3. Upon contact with the sulfuric acid and hydrogen peroxide, a residual amount of sulfuric acid, C SA,o A nickel sulfate solution N is formed with a sulfuric acid content of about 7 g / L. The ratio of the sulfuric acid concentration in the effluent to that in the feed solution is about 0.15. Due to the exothermic nature of the reaction, the temperature To is about 98°C.

[0057] A first fraction φ1 of the nickel sulfate solution N is cooled from a temperature of about 98° C. to a temperature of about 65° C. and then mixed with a mixture of sulfuric acid A and hydrogen peroxide P in water. A second fraction φ2 of the nickel sulfate solution N is further treated to a pH of about 3.5 and then treated to remove impurities. Any gases that may have formed in the atmosphere at the top of the column reactor are treated in a scrubbing unit.

[0058] Example 2 The oxidized leachate is prepared by mixing an aqueous sulfuric acid solution A with a hydrogen peroxide solution P in water. The mixture is then mixed with a fraction φ1 of the effluent of the column reactor, to obtain an oxidized leachate of about T i = 75°C. The column reactor has an internal diameter D and a height H, the ratio H:D being about 2.6. The fraction φ1 is cooled from a temperature of about 98°C to a temperature of about 75°C before mixing it with sulfuric acid and hydrogen peroxide. The oxidized leachate thus prepared has a temperature of about 75°C and a sulfuric acid content of about 31 g / L and is fed to the reaction zone of the column reactor via a feed.

[0059] The reaction zone includes a Ni metal cut cathode having dimensions of approximately 50 mm x 50 mm and a thickness of 13 mm, and a nickel content of 99.97%. Metal particles containing nickel are intermittently fed onto a support plate above the reactor feed. The metal particle feed is omitted in FIG. 1. The Ni metal is provided in a bed, the bed having a bed volume characterized by a height and a diameter, the ratio of the height to the diameter being approximately 5. Upon contact with the sulfuric acid and hydrogen peroxide, a residual amount of sulfuric acid, C SA,o A nickel sulfate solution N is formed with a sulfuric acid content of about 10 g / L. The ratio of the sulfuric acid concentration in the effluent to that in the feed solution is about 0.32. Due to the exothermic nature of the reaction, the temperature T o is about 98°C.

[0060] A first fraction φ1 of the nickel sulfate solution N is cooled from a temperature of about 98° C. to a temperature of about 75° C. and then mixed with a mixture of sulfuric acid A and hydrogen peroxide P in water. A second fraction φ2 of said nickel sulfate solution N is further treated to remove impurities. Gases that may have formed in the atmosphere at the top of the column reactor are treated in a scrubbing unit.

Claims

1. 1. A process for preparing a nickel sulphate solution (N) in a column reactor (R) by oxidative leaching of nickel-containing metal particles, comprising: i. feeding nickel-containing metal particles into a reaction section of the column reactor; ii. feeding an oxidizing leachate comprising sulfuric acid and hydrogen peroxide in water to the reaction zone via a feed zone, whereby the oxidizing leachate is brought into contact with the metal particles comprising nickel in the reaction zone, whereby the residual amount of sulfuric acid (C ＳＡ，ｏ obtaining a nickel sulfate solution containing iii. Discharging the nickel sulfate solution from the column reactor; The sulfuric acid concentration (C) of the nickel sulfate solution obtained in step ii. ＳＡ，ｏ ) of the sulfuric acid concentration of the oxidized leachate (C ＳＡ，ｉ ) is 0.90 to 0.

01.

2. 2. The method according to claim 1, wherein in step ii., the oxidized leachate comprising sulfuric acid and hydrogen peroxide in water is fed to the reaction section through the bottom of the column reactor, and in step iii., the nickel sulfate solution is discharged from the reaction section through the top of the column reactor.

3. The sulfuric acid concentration (C) of the nickel sulfate solution obtained in step ii. ＳＡ，ｏ ) of the sulfuric acid concentration of the oxidized leachate (C ＳＡ，ｉ 3. The method according to claim 1, wherein the ratio of 0.70 to 0.

02.

4. The liquid volume of the oxidized leachate in the column reactor has a diameter D Ｌ and height H Ｌ and a ratio H of the height to the diameter. Ｌ :D Ｌ The method according to any one of claims 1 to 3, wherein is between 1.0 and 10.0, preferably between 1.5 and 8.

0.

5. A process as claimed in any one of claims 1 to 4, wherein the oxidized leachate is fed to the reactor at a temperature of from 50°C to 85°C.

6. 6. The process of any one of claims 1 to 5, wherein the nickel sulfate solution is removed from the reactor at a temperature of from 90°C to 100°C.

7. A first fraction φ of the nickel sulfate solution １ is cooled from a temperature above 90° C. to a temperature below 85° C., and the fraction φ １ is mixed with sulphuric acid and / or hydrogen peroxide to form an oxidized leachate before feeding the oxidized leachate to the reactor.

8. A first fraction φ of the nickel sulfate solution １ is mixed with sulfuric acid and / or hydrogen peroxide to form an oxidized leachate, the oxidized leachate is then fed to the reactor, and the first fraction φ １ The method according to any one of claims 1 to 7, wherein the volume ratio of said nickel sulfate solution to the total volume of said nickel sulfate solution is from 0.70 to 0.

95.

9. The first fraction φ １ 9. The method according to claim 7 or 8, wherein heat recovered from the cooling step of step 1 above is used at least in part to heat the oxidized leachate and / or the contents of the reactor.

10. A second fraction φ of the nickel sulfate solution ２ is the second fraction φ ２ 10. The method of claim 1, wherein the sintered material is subjected to a purification step to reduce the concentration of one or more impurities in the sintered material, said impurities comprising one or more selected from the list comprising Cu, Zn, Co, Mn, Fe, Al, F, C, Ca, Si, P, As, Cd, Sb and Mg.

11. 11. The method according to any one of claims 1 to 10, wherein the nickel-containing metal particles comprise nickel in an amount of at least 96 wt. % relative to the total weight of the metal particles.

12. 12. The method according to any one of claims 1 to 11, wherein the oxidized leachate comprises sulfuric acid in an amount of 20 to 100 g / L.

13. 13. The method according to any one of claims 1 to 12, wherein the oxidized leachate comprises hydrogen peroxide in an amount of 1.5 to 30 g / L.

14. 14. A process according to any one of the preceding claims, wherein hydrogen peroxide is present in the oxidized leachate fed to the column reactor in a sub-stoichiometric amount relative to the amount of sulphuric acid present in the oxidized leachate.

15. The process according to any one of claims 1 to 14, wherein the gas atmosphere in the overflow of the column reactor is circulated through a scrubber.

16. A method according to any one of the preceding claims, wherein the oxidative leachate is contacted with the metal particles at atmospheric pressure or at a reduced pressure of less than 0.2 atm.

17. The column reactor is controlled so that the nickel sulfate solution obtained from the column reactor has a residual sulfuric acid content (C ＳＡ，ｏ 17. The method according to claim 1, wherein it is ensured that the .

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