Method for producing nickel and cobalt salt aqueous solution, method for producing nickel sulfate and cobalt sulfate, and method for producing precursor compound for synthesizing positive electrode material

Abstract

Provided is a method for obtaining a salt aqueous solution containing nickel and cobalt by leaching nickel and cobalt in a shorter leaching time while effectively separating copper, nickel, and cobalt from a mixture containing nickel, cobalt, and copper, such as a highly corrosion-resistant alloy obtained by dry-treating a waste battery material.　The present invention is a method for producing a nickel and cobalt salt aqueous solution, the method comprising a step for bringing a mixture containing nickel, cobalt, and copper into contact with a mineral acid under conditions in which a sulfurizing agent is present, wherein the mixture is immersed in a mineral acid in an amount of 1 equivalent or more until the oxidation-reduction potential, at which a silver / silver chloride electrode is used as a reference electrode, reaches 70 mV after having reached a minimum value, and thereafter, a sulfurizing agent is added to the solution, whereby nickel and cobalt are leached from the mixture.

Description

Method for producing aqueous nickel and cobalt salt solutions, method for producing nickel sulfate and cobalt sulfate, method for producing precursor compounds for synthesizing positive electrode materials

[0001] The present invention relates to a method for producing an aqueous solution of nickel and cobalt salts by selectively leaching nickel and cobalt from a mixture such as an alloy containing nickel, cobalt, and copper with a mineral acid, a method for producing nickel sulfate and cobalt sulfate using the method, and a method for producing precursor compounds for the synthesis of positive electrode materials.

[0002] 2. Description of the Related Art Lightweight, high-power lithium-ion batteries (hereinafter also referred to as "LIBs") are installed in vehicles such as electric vehicles and hybrid vehicles, as well as in electronic devices such as mobile phones, smartphones, and personal computers.

[0003] LIBs are made by placing a negative electrode material, which uses copper foil as a negative electrode current collector and has graphite or other negative electrode active material fixed to its surface, and a positive electrode material, which uses aluminum foil as a positive electrode current collector and has lithium nickel oxide or lithium cobalt oxide fixed to its positive electrode current collector, together with a separator made of a porous polypropylene resin film, inside an outer can made of metal such as aluminum or iron, or plastic such as vinyl chloride, and then charging the battery with lithium hexafluorophosphate (LiPF ６ The structure is impregnated with an organic solvent containing an electrolyte such as .

[0004] When LIBs are incorporated into vehicles, electronic devices, etc., as described above, they eventually become unusable due to deterioration of the vehicle or electronic device, or due to the lifespan of the LIB, and become waste LIBs. Furthermore, cathode material scrap (waste cathode material) may be generated as a defective product during the cathode material manufacturing process. Such waste LIBs and waste cathode material are collectively referred to as "waste battery materials." These waste battery materials contain valuable components such as nickel, cobalt, and copper, and it is desirable to effectively recover and reuse these valuable components in order to make effective use of resources.

[0005] Generally, when attempting to efficiently recover valuable metals from metallic devices, components, or materials, a pyrometallurgical method is considered to be effective and efficient. The pyrometallurgical method involves placing the materials in a furnace or the like, melting them at high temperatures, and separating them into metal containing the valuable metals and slag to be disposed of. For example, Patent Document 1 discloses a method for recovering valuable metals by pyrometallurgical refining. By applying the method disclosed in Patent Document 1 to waste battery materials, an alloy containing nickel, cobalt, and copper can be obtained.

[0006] Although pyrometallurgy requires high temperatures and requires energy, it has the advantage that most of the impurities can be separated from the valuable metals as slag. Furthermore, the resulting slag is stable, which poses no environmental problems and is easy to dispose of.

[0007] However, the metal obtained is an alloy containing valuable metals, and in order to reuse it, it is necessary to purify it by separating the valuable metals from the alloy and removing impurities.

[0008] A commonly used method for separating elements in pyrometallurgy is to slowly cool the metal from a high-temperature molten state to take advantage of the difference in melting points. However, when metals with very similar melting points are combined, such as copper, nickel, and cobalt, the entire composition range melts uniformly, resulting in a mixed solidification and making it difficult to separate the individual elements.

[0009] Another method of element separation that has been carried out industrially is a method of roughly separating mixed matte, which is a sulfide of nickel and cobalt. In this method, matte containing copper, nickel, and cobalt is produced in a smelting process, and then slowly cooled to separate it into sulfides rich in copper and sulfides rich in nickel and cobalt. However, this method is merely a technology for separating copper from nickel and cobalt, and the separation is only rough, so additional processing such as electrolytic refining is required.

[0010] The same applies to the separation of copper and cobalt, and the separation of cobalt and nickel.

[0011] As described above, the separation and refinement of each element by pyrometallurgy is insufficient. In particular, when producing aqueous solutions or compounds for use as battery materials, high separation ability is required because, for example, the amount of copper contamination is strictly limited.

[0012] In contrast, hydrometallurgy using acid treatment, neutralization, solvent extraction, etc., can separate individual impurity elements from the valuable metals to be recovered, making it possible to recover nickel sulfate, cobalt sulfate, and mixtures of these with high purity.

[0013] However, when waste battery materials are hydrometallurgically refined, for example, hexafluorophosphate anion, an electrolyte component contained in waste LIB, is a difficult-to-treat substance that cannot be completely decomposed even with high-temperature, high-concentration sulfuric acid, and is contaminated with the acid solution from which valuable components are leached. Furthermore, since hexafluorophosphate anion is a water-soluble carbonate ester, phosphorus and fluorine are contained in the wastewater after valuable components are recovered, and therefore the wastewater cannot be released into public sea areas, etc., until these elements are removed.

[0014] Furthermore, it is not easy to efficiently leach and refine valuable metals from waste battery materials using acid treatment alone. When valuable metal components are leached from waste battery materials using a highly oxidizing acid, impurities such as aluminum, iron, and manganese are also leached along with the valuable metal components. Furthermore, there are problems such as increased amounts of neutralizing agents and organic solvents required to treat these, increased wastewater treatment costs, and a complicated impurity separation process.

[0015] Thus, although hydrometallurgy has a higher separation efficiency than pyrometallurgy, recovering valuable metals from waste battery materials using only hydrometallurgy is not necessarily an advantageous method.

[0016] Therefore, attempts have been made to treat waste battery materials that are difficult to treat using either the above-mentioned pyrometallurgy or hydrometallurgy alone by combining pyrometallurgy and hydrometallurgy. In other words, this method involves removing most of the impurities that would otherwise be a heavy processing load in hydrometallurgy by pyrometallurgy, such as roasting the waste battery materials, and then more efficiently separating the remaining impurities by hydrometallurgy to recover valuable metals. In this combined method of pyrometallurgy and hydrometallurgy, fluorine and phosphorus compounds in the electrolyte are decomposed by pyrometallurgy and removed by volatilization or by being transferred to slag. Furthermore, organic components such as plastics and separators, which are structural components of waste LIBs, are also decomposed and removed by pyrometallurgy.

[0017] However, in the method combining pyrometallurgy and hydrometallurgy, the metal obtained through pyrometallurgy is an alloy containing copper, nickel, and cobalt, which is highly corrosion-resistant and refractory, and therefore presents a problem in that it cannot be easily dissolved in acid in the subsequent hydrometallurgy.

[0018] It is not particularly difficult to dissolve the above-mentioned highly corrosion-resistant alloy in acid using, for example, chlorine, and then separate copper, nickel, and cobalt from the resulting leached aqueous solution by known methods such as solvent extraction. However, this method is not preferred because of the corrosion of equipment caused by chlorine and the high cost of solvent extraction.

[0019] For example, Patent Document 2 discloses a method for recovering cobalt and nickel by separating copper, aluminum, and manganese by precipitation from an acidic solution containing copper, aluminum, and manganese together with cobalt and nickel, obtained by leaching an active material of an electrode material for a lithium-ion secondary battery with a mineral acid such as sulfuric acid. Specifically, Patent Document 2 discloses a copper removal process in which a sulfide is added to a leaching solution containing copper, aluminum, and manganese together with cobalt and nickel to form a copper sulfide precipitate, which is then subjected to solid-liquid separation to separate and remove copper from the leaching solution. In other words, Patent Document 2 discloses a copper removal technology for separating and removing copper from a leachate containing cobalt, nickel, and copper in an ionic state.

[0020] Patent Document 3 also discloses a method for recovering transition metals such as nickel and cobalt from lithium-ion batteries containing many impurity metals (e.g., iron, aluminum, copper, etc.) and carbon. Specifically, the method includes: separating a material A to be treated containing transition metals such as nickel and cobalt, impurity metals such as copper, and carbon from the positive electrode; mixing and heating the material A with aqua regia to obtain a material B to be treated, which is an aqueous solution in which the transition metals and impurity metals are ionized and eluted; and then introducing a sulfiding agent into the material B to precipitate the impurity metals, particularly copper, as copper sulfide, which is then separated and removed. In other words, Patent Document 3 also discloses a copper removal technology for separating and removing copper from an aqueous solution (material B) containing cobalt, nickel, and copper in ionic states.

[0021] On the other hand, Patent Document 4 does not disclose a copper removal technique from a leaching solution containing nickel, cobalt, and copper in an ionic state as disclosed in Patent Documents 2 and 3, but discloses a method for effectively separating copper from nickel and cobalt by selectively leaching nickel and cobalt from an alloy containing copper, nickel, and cobalt using sulfuric acid in an acid leaching process. Specifically, this method involves contacting an alloy containing copper, nickel, and cobalt with sulfuric acid under conditions in which a sulfurizing agent also exists, thereby obtaining a copper-containing solid and a leaching solution containing nickel and cobalt. Here, Patent Document 4 describes that it is preferable to contact the alloy to be treated with sulfuric acid and the sulfurizing agent simultaneously, or to contact the alloy with the sulfurizing agent first and then with sulfuric acid.

[0022] As described above, the method disclosed in Patent Document 4 is not a technique for removing copper from the leaching solution after the leaching treatment, but rather involves acid leaching in the presence of a sulfiding agent at the stage of the leaching treatment, and is an effective technique that can enhance the selectivity of nickel and cobalt during leaching.

[0023] However, when nickel and cobalt are leached from a mixture of nickel, cobalt, and copper, such as a highly corrosion-resistant alloy, it is desired to further improve selectivity while shortening the leaching time.

[0024] JP 2012-172169 A JP 2015-183292 A JP 2007-323868 A JP 2019-77912 A

[0025] The present invention has been proposed in view of the above circumstances, and has an object to provide a method for obtaining an aqueous salt solution containing nickel and cobalt by leaching nickel and cobalt in a shorter leaching time while effectively separating copper from the nickel and cobalt from a mixture containing nickel, cobalt, and copper, such as a highly corrosion-resistant alloy obtained by dry processing of waste battery material.

[0026] The present inventors have conducted extensive research and have found that the above-mentioned problems can be solved by a method comprising the steps of contacting a mixture containing nickel, cobalt, and copper with a mineral acid in the presence of a sulfiding agent to obtain solid copper sulfide and an aqueous salt solution containing nickel and cobalt, in which the mixture is immersed in the mineral acid for a predetermined period of time, and then a sulfiding agent is added to the solution to leach nickel and cobalt from the mixture, thereby completing the present invention.

[0027] (1) A first aspect of the present invention is a method for producing an aqueous solution of nickel and cobalt salts, comprising the step of contacting a mixture containing nickel, cobalt, and copper with a mineral acid in the presence of a sulfurizing agent, wherein the mixture is immersed in one equivalent or more of the mineral acid until the oxidation-reduction potential, using a silver / silver chloride reference electrode, reaches 70 mV after passing through a minimum value, and then one or more sulfurizing agents selected from hydrogen sulfide, solid sulfur, sodium hydrogen sulfide, and sodium sulfide are added to the solution, thereby leaching nickel and cobalt from the mixture.

[0028] (2) A second aspect of the present invention is a method for producing an aqueous solution of nickel and cobalt salts according to the first aspect, wherein the mixture is an alloy containing nickel, cobalt, and copper.

[0029] (3) A third aspect of the present invention is a method for producing an aqueous solution of nickel and cobalt salts according to the second aspect, wherein the alloy comprises an alloy obtained by heating, melting, and reducing used lithium ion batteries.

[0030] (4) A fourth aspect of the present invention is a method for producing an aqueous solution of nickel and cobalt salts according to any one of the first to third aspects, wherein the amount of the sulfiding agent added is 1 equivalent or more relative to the amount of copper contained in the mixture in terms of sulfur.

[0031] (5) A fifth aspect of the present invention is a method for producing nickel sulfate and cobalt sulfate from a mixture containing nickel, cobalt, and copper, comprising the steps of: carrying out the production method according to the first aspect of the present invention using sulfuric acid as the mineral acid to produce an aqueous solution of nickel and cobalt sulfate; purifying the aqueous solution of nickel and cobalt sulfate; and precipitating solid nickel sulfate and solid cobalt sulfate from the purified aqueous solution.

[0032] (6) A sixth aspect of the present invention is a method for producing a precursor compound for synthesizing a positive electrode material for a lithium ion battery, the method comprising the steps of: producing an aqueous solution of nickel and cobalt salts by the production method according to the first aspect of the present invention; purifying the aqueous salt solution to obtain an aqueous solution containing purified nickel and cobalt; and adding hydroxides or carbonates to the aqueous solution containing purified nickel and cobalt to precipitate nickel and cobalt as hydroxides or carbonates, thereby obtaining a solid suitable for synthesizing the positive electrode material for a lithium ion battery.

[0033] According to the present invention, nickel and cobalt can be leached from a mixture containing nickel, cobalt, and copper in a shorter leaching time while effectively separating the nickel and cobalt from the copper, and an aqueous solution of nickel and cobalt salts can be obtained effectively and efficiently.

[0034] 1 is a graph showing the change in oxidation-reduction potential versus a silver / silver chloride electrode when an alloy containing nickel, cobalt, and copper is immersed in an aqueous sulfuric acid solution.

[0035] Specific embodiments of the present invention (hereinafter also referred to as "present embodiments") will be described below, but the present invention is not limited to the following embodiments. Note that in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "X or more and Y or less."

[0036] 1. Method for Producing Aqueous Solution of Nickel and Cobalt Salts The method according to the present embodiment is a method for producing an aqueous solution of nickel and cobalt salts, which includes a step of bringing a mixture containing nickel, cobalt, and copper into contact with a mineral acid, and then adding a sulfiding agent to cause a reaction, thereby obtaining solid copper sulfide and an aqueous solution of nickel and cobalt salts (hereinafter also referred to as "aqueous solution of nickel and cobalt salts"), which is a leaching aqueous solution containing nickel and cobalt.

[0037] The "mixture containing nickel, cobalt, and copper" is a solid mixture containing nickel, cobalt, and copper, and examples thereof include alloys containing nickel, cobalt, and copper. Examples of such alloys include alloys obtained by heating, melting, and reducing waste battery materials, such as lithium-ion batteries (waste LIBs) discarded due to the deterioration of automobiles and electronic devices, or generated as lithium-ion batteries reach the end of their service life, and defective batteries and cathode material scrap (waste cathode material) generated during manufacturing processes. In other words, examples of such alloys include alloys obtained by dry-processing waste battery materials. Note that dry-processing can remove components such as organic solvents, aluminum, iron, manganese, phosphorus, fluorine, and carbon, resulting in alloys with reduced impurity components.

[0038] The alloy obtained by heating, melting, and reducing waste battery materials may be cast into a plate shape, for example. Alternatively, a powder such as atomized alloy powder obtained by atomizing a molten alloy obtained by heating, melting, and reducing waste battery materials may be used. Alternatively, these alloys may be pulverized into fine particles, or drawn into wires and appropriately cut into rods. The atomization method involves melting an alloy, contacting it with high-pressure gas or water, and scattering and rapidly solidifying the molten alloy to obtain a powder. When producing a powder such as atomized alloy powder, the particle size of the alloy powder is preferably approximately 300 μm or less, because this improves reactivity with mineral acids during wet processing. On the other hand, a particle size of approximately 10 μm or more is preferred, because a too small particle size increases costs and can also cause dust generation and fire.

[0039] The alloy obtained by dry processing of waste battery materials is refractory and highly corrosion-resistant. Conventionally, it has been difficult to efficiently and selectively leach nickel and cobalt from this alloy and separate copper from nickel and cobalt. In contrast, the method according to the present embodiment allows nickel and cobalt to be leached at a higher leaching rate while effectively separating them from copper, and while effectively shortening the leaching time.

[0040] As mentioned above, the term "waste battery material" as used in this specification refers not only to used batteries but also to defective batteries and cathode materials produced in the manufacturing process. Furthermore, the waste battery material is not limited to waste lithium-ion batteries, but may also be other waste batteries containing copper, nickel, or cobalt, such as nickel-metal hydride batteries. Furthermore, as long as the raw material contains waste batteries, it is not excluded that other metals, resins, and the like other than waste batteries may also be added as appropriate. In such cases, the waste batteries referred to in this specification include the other metals and resins.

[0041] As described above, the "aqueous solution of nickel and cobalt salts" is a leaching solution containing nickel and cobalt obtained by acid leaching. When sulfuric acid is used as the mineral acid, the aqueous solution becomes an aqueous solution of nickel and cobalt sulfates. When hydrochloric acid is used as the mineral acid, the aqueous solution becomes an aqueous solution of nickel and cobalt hydrochlorides.

[0042] [Step of Leaching Treatment] In the method according to the present embodiment, nickel and cobalt are leached from a mixture containing nickel, cobalt, and copper with a mineral acid in the presence of a sulfiding agent, i.e., the leaching treatment is carried out with a mineral acid in the coexistence of a sulfiding agent.

[0043] In this leaching process, the copper leached from the alloy can be precipitated as solid copper sulfide by the coexistence of a sulfiding agent, while the leached nickel and cobalt remain in the leaching solution. Because the precipitated copper sulfide has extremely low solubility in acid, it can be made to be almost absent from the leaching solution, and nickel and cobalt can be selectively present in the salt solution (leaching solution). In this way, copper can be effectively separated from nickel and cobalt.

[0044] The reaction that occurs when sulfuric acid is brought into contact with the sulfurizing agent in the presence of the sulfurizing agent is shown in the following reaction formula. The following reaction formula shows an example in which solid sulfur (S) is used as the sulfurizing agent. As shown in the following reaction formula, when a solid mixture containing nickel, cobalt, and copper is acid leached in the presence of the sulfurizing agent, the leached copper is sulfurized to produce solid copper sulfide (formula [1]). Meanwhile, when nickel and cobalt are leached with sulfuric acid, they become present as ions in the leaching solution (formulas [2] and [3]). Even if the leached nickel or cobalt reacts with the sulfurizing agent to produce sulfides, the sulfides of nickel and cobalt, which are highly soluble in acid, will decompose (formulas [2]' and [3]'). [Reaction formula] Cu + S → CuS ... [1] Ni + H ２ SO ４ → NiSO ４ +H ２ ...[2] NiS+H ２ SO ４ → NiSO ４ +H ２ S...[2]' Co+H ２ SO ４ → CoSO ４ +H ２ ...[3] CoS+H ２ SO ４ → NiSO ４+H ２ S...[3]'

[0045] The method according to the present embodiment is characterized in that, in the leaching treatment, a mixture containing nickel, cobalt, and copper is immersed in a mineral acid under predetermined conditions, and then a sulfurizing agent is added to a solution containing the mixture immersed in the mineral acid, thereby leaching nickel and cobalt from the mixture. In this respect, it differs from the prior art method disclosed in Patent Document 4, which either contacts the alloy to be treated with sulfuric acid and the sulfurizing agent simultaneously, or contacts the alloy with the sulfurizing agent first and then with sulfuric acid.

[0046] According to the method of the present embodiment, as will be shown in the examples described later, it is possible to shorten the leaching time of nickel and cobalt in particular in leaching treatments in the presence of a sulfiding agent.

[0047] This is thought to be because, in the leaching process, a mixture of alloys containing nickel, cobalt, and copper is first immersed in a mineral acid for a predetermined period of time, which changes the surface condition of the alloy. More specifically, it is thought that immersing the alloy in a mineral acid causes the passive film on the alloy surface to disappear, and the alloy surface becomes rough and the surface area to increase. As a result, it is thought that by subsequently adding a sulfiding agent to a solution containing the alloy whose surface condition has changed, the leaching rate of nickel and cobalt from the alloy increases rapidly, and nickel and cobalt are leached within a short time after the addition of the sulfiding agent.

[0048] The mineral acid used in the leaching treatment is an aqueous solution of one or more of sulfuric acid and hydrochloric acid. Among these, sulfuric acid is particularly preferred. As described above, an aqueous solution of nickel and cobalt sulfates can be obtained by leaching nickel and cobalt from the mixture with sulfuric acid. Also, an aqueous solution of nickel and cobalt hydrochlorides can be obtained by leaching nickel and cobalt from the mixture with hydrochloric acid.

[0049] The treatment of immersing a mixture of an alloy containing nickel, cobalt, and copper in a mineral acid (hereinafter, for convenience, this treatment will also be referred to as the "immersion treatment") is a treatment performed before adding a sulfiding agent to leach nickel and cobalt. In other words, the immersion treatment is positioned as a pretreatment for the leaching treatment in the presence of a sulfiding agent. The immersion treatment of a mixture in a mineral acid is performed by immersing the mixture in the mineral acid until the oxidation-reduction potential (ORP) of the solution reaches an extreme value (minimum value) and then reaches 70 mV relative to a silver / silver chloride electrode. The immersion treatment time is approximately 5 to 60 minutes.

[0050] Here, Figure 1 is a graph showing the change in ORP (based on a silver / silver chloride electrode) when an alloy containing nickel, cobalt, and copper was immersed in an aqueous solution of sulfuric acid, a mineral acid. The amount of sulfuric acid used was 5 equivalents relative to the total amount of nickel and cobalt contained in the alloy. As shown in the graph in Figure 1, when the alloy was immersed in the mineral acid, the ORP of the solution rapidly decreased, then reached a minimum value, and then gradually increased. As shown by this change in ORP, by immersing a mixture of alloys or the like in the mineral acid until the ORP reached a minimum value and then increased to approximately 70 mV, it is possible to effectively change the surface condition of the mixture.

[0051] The amount of mineral acid is 1 equivalent or more relative to the total amount of nickel and cobalt contained in the mixture. Five equivalents or more is preferable, and 10 equivalents or more is more preferable. The upper limit of the amount of mineral acid is not particularly limited, but 15 equivalents or less is preferable. Therefore, the amount of mineral acid is preferably in the range of 1 to 15 equivalents relative to the total amount of nickel and cobalt contained in the mixture. For example, when sulfuric acid is used as the mineral acid, the amount of mineral acid is the equivalent calculated by the above reaction formulas [2] and [3].

[0052] Immersion treatment under these conditions can effectively change the surface condition of the mixture, such as an alloy, and subsequent leaching treatment in the presence of a sulfiding agent can effectively leach nickel and cobalt from the mixture in a short period of time. The immersion treatment is a treatment in which the mixture is in contact with acid. The ORP conditions described above, in particular, the conditions for immersion treatment until the ORP reaches 70 mV after reaching a minimum value, are indicative of the state in which the surface condition of the mixture has been sufficiently changed by the acid.

[0053] Although the immersion treatment time may be extended and continued until the ORP of the solution exceeds 70 mV after reaching a minimum value, the effect of shortening the leaching time after the addition of the sulfiding agent will not be further increased, and the total treatment time, including the time for subsequent leaching treatment, will increase as the immersion treatment time increases. For these reasons, from the viewpoint of treatment efficiency, it is preferable to continue the immersion treatment until the ORP of the solution reaches 70 mV after reaching a minimum value.

[0054] As described above, after the mixture has been immersed in the mineral acid for a predetermined period of time, a sulfurizing agent is added to the solution containing the mixture immersed in the mineral acid. This allows nickel and cobalt to be leached from the mixture. The sulfurizing agent used is one or more selected from hydrogen sulfide, solid sulfur, sodium hydrogen sulfide, and sodium sulfide. When solid sulfur is used, it is preferable to grind it appropriately to facilitate the sulfurization reaction.

[0055] The amount of sulfurizing agent to be added is not particularly limited, but is preferably 1 equivalent or more relative to the amount of copper contained in the mixture in sulfur equivalent. The amount of sulfurizing agent to be added is calculated from the equivalent amount forming the sulfurizing agent shown in the above reaction formula [1].

[0056] Regarding other conditions in the leaching treatment, it is preferable to determine appropriate ranges for the temperature, time, and slurry concentration obtained by adding a mineral acid and a sulfiding agent to the mixture through preliminary tests.

[0057] Furthermore, regarding the reaction of the leaching treatment, the ORP value rises sharply when the hydrogen-generating leaching of nickel and cobalt (reaction formulas [2] and [3] above) is completed. Therefore, the end point of nickel and cobalt leaching can be determined by measuring the ORP of the resulting leachate.

[0058] As described above in detail, the method according to the present embodiment makes it possible to leach nickel and cobalt from a solid mixture containing nickel, cobalt, and copper in a shorter leaching time while effectively separating the nickel and cobalt from the copper, thereby making it possible to effectively and efficiently produce an aqueous solution of nickel and cobalt salts with a low copper content.

[0059] [Step of performing reduction treatment] Although not an essential aspect, the aqueous nickel and cobalt salt solution, which is the leaching aqueous solution obtained through the above-described leaching treatment step, may be further subjected to a step of performing reduction treatment using a reducing agent.

[0060] In the above-described leaching process, some of the copper constituting the mixture of alloys or the like may be leached by the mineral acid without reacting with the sulfiding agent, resulting in the nickel and cobalt salt aqueous solution. Therefore, by adding a reducing agent to the nickel and cobalt salt aqueous solution obtained by the leaching process and performing a reduction process, the trace amounts of copper in the aqueous solution can be reduced, producing a copper-containing precipitate that can be removed by solid-liquid separation. This allows for the production of a nickel and cobalt salt aqueous solution with an even lower content of copper as an impurity.

[0061] As the reducing agent, for example, a metal less noble than copper can be used. Among these, it is preferable to use a metal containing nickel and cobalt and bring the leaching solution into contact with the metal to reduce copper. The method according to this embodiment produces an aqueous salt solution of nickel and cobalt, and by using a metal containing nickel and cobalt as the reducing agent, there is no need to separately recover the reducing agent in a subsequent step, which is industrially advantageous. In addition to the above-mentioned metals, sulfides can also be used as the reducing agent.

[0062] The method of reduction treatment is not particularly limited. When a solid or liquid reducing agent is used, the reducing agent may be added directly to the aqueous solution. When the reducing agent is a gas, the reducing agent may be added by bubbling into the aqueous solution.

[0063] It is preferable to conduct tests in advance to select optimal ranges for the amount of reducing agent added and the reaction temperature. In the reduction treatment, it is preferable to monitor the oxidation-reduction potential (ORP) and pH and control them by adding a reducing agent or the like as appropriate, and it is preferable to conduct tests in advance to select optimal ranges.

[0064] 2. Method for Producing Nickel Sulfate and Cobalt Sulfate According to the above-described method for producing an aqueous solution of nickel and cobalt salts, nickel and cobalt can be leached from a mixture of an alloy containing nickel, cobalt, and copper at a higher leaching rate and in a shorter leaching time while effectively separating the nickel and cobalt from the copper. For example, an aqueous solution of nickel and cobalt sulfates can be produced by using sulfuric acid as the mineral acid.

[0065] By utilizing such a method for producing an aqueous solution of nickel and cobalt salts, nickel sulfate and cobalt sulfate can be produced with effectively reduced impurities such as copper. Therefore, the method for producing nickel sulfate and cobalt sulfate can be defined as follows.

[0066] That is, the method for producing nickel sulfate and cobalt sulfate includes the steps of: carrying out a method for producing an aqueous nickel and cobalt sulfate solution on a mixture containing nickel, cobalt, and copper using sulfuric acid as the mineral acid; purifying the aqueous nickel and cobalt sulfate solution; and precipitating solid nickel sulfate and solid cobalt sulfate from the purified aqueous solution.

[0067] [Step for Producing an Aqueous Solution of Nickel and Cobalt Sulfates] The aqueous solution of nickel and cobalt sulfates can be produced by carrying out the above-described method for producing an aqueous solution of nickel and cobalt salts using sulfuric acid as the mineral acid. For example, an aqueous solution of nickel and cobalt sulfates with an extremely low copper content can be produced from a mixture containing nickel, cobalt, and copper, such as an alloy obtained by heating, melting, and reducing used lithium-ion batteries. Therefore, a detailed description thereof will be omitted here.

[0068] [Step of purifying the aqueous sulfate solution] The aqueous nickel and cobalt sulfate solution produced here contains nickel and cobalt, but may contain impurities such as iron, zinc, and phosphorus due to raw materials such as alloys obtained by heating, melting, and reducing waste lithium-ion batteries. Therefore, the produced aqueous nickel and cobalt sulfate solution is subjected to a purification process to remove impurities and obtain a purified aqueous solution. The purified aqueous solution is an aqueous sulfate solution in which nickel and cobalt are concentrated.

[0069] The purification treatment for the aqueous solution of nickel and cobalt sulfates is not particularly limited, but examples thereof include a solution purification treatment, a solvent extraction treatment, etc. In the purification treatment, any treatment may be carried out alone or two or more treatments may be carried out in combination depending on the types of impurity components contained in the aqueous solution.

[0070] (Liquid Purification Treatment) Examples of the liquid purification treatment include oxidation treatment and oxidation neutralization treatment.

[0071] Specifically, in the oxidation neutralization treatment, an oxidizing agent is added to an aqueous solution of nickel and cobalt sulfates to cause an oxidation reaction, and a neutralizing agent is added to control the pH of the solution within a predetermined range, thereby producing precipitates of impurity components such as iron and phosphorus contained in the aqueous solution. In this way, by performing the oxidation neutralization treatment as a solution purification treatment, the impurity components can be separated as precipitates, and a purified aqueous solution of nickel and cobalt sulfates can be obtained.

[0072] As the oxidizing agent, conventionally known oxidizing agents such as hydrogen peroxide, hypochlorous acid, oxygen, etc. are usable. The addition of the oxidizing agent is preferably controlled within a predetermined range by monitoring the oxidation-reduction potential (ORP) of the aqueous solution. Specifically, the oxidizing agent is added to the solution to control the ORP, for example, within a range of 380 mV to 430 mV based on a silver / silver chloride electrode.

[0073] After the oxidizing agent is added to cause an oxidation reaction, a neutralizing agent is added to adjust the pH of the aqueous solution to preferably within the range of 3.8 to 4.5. By controlling the pH within this range and carrying out the neutralization treatment, impurities such as iron and phosphorus can be effectively precipitated. Conventionally known alkalis such as sodium hydroxide and potassium hydroxide can be used as the neutralizing agent.

[0074] In the oxidation neutralization treatment, the oxidizing agent may be added after the neutralizing agent is added to the aqueous solution of nickel and cobalt sulfates. However, it is preferable to add the oxidizing agent and the neutralizing agent simultaneously, or to add the oxidizing agent first and then the neutralizing agent.

[0075] (Solvent Extraction Treatment) In the solvent extraction treatment, impurity components contained in the aqueous solution of nickel and cobalt sulfates or the aqueous solution obtained through the solution purification treatment are selectively extracted into an organic solvent, and the impurity components are separated and removed to obtain a purified aqueous solution of nickel and cobalt sulfates. Alternatively, nickel and cobalt contained in the aqueous solution of nickel and cobalt sulfates may be selectively extracted into an organic solvent, and then stripped with sulfuric acid to separate and remove the impurity components to obtain a purified aqueous solution of nickel sulfate or cobalt sulfate.

[0076] The solvent extraction treatment can be carried out by a conventionally known method using an acidic extractant or the like. The extractant to be used is selected depending on the metal element to be extracted. Furthermore, during extraction, the extractant is diluted with a hydrocarbon organic solvent or the like. The concentration of the extractant in the organic solvent is not particularly limited, but taking into consideration phase separation and the like, it is preferably 5% by volume to 30% by volume, and more preferably 10% by volume to 25% by volume.

[0077] [Step of Precipitating Nickel Sulfate and Cobalt Sulfate] The aqueous solution purified as described above is an aqueous sulfate solution in which nickel and cobalt are concentrated. Therefore, by precipitating nickel sulfate and cobalt sulfate from such an aqueous solution, nickel sulfate and cobalt sulfate can be obtained in solid form.

[0078] The method for precipitating nickel sulfate and cobalt sulfate is not particularly limited, and examples thereof include a method in which water in an aqueous solution is evaporated using a crystallizer to precipitate crystals of nickel sulfate and cobalt sulfate.

[0079] 3. Method for Producing Precursor Compound for Synthesizing Positive Electrode Material for Lithium-Ion Batteries Furthermore, a precursor compound for synthesizing a positive electrode material for lithium-ion batteries can be produced from the aqueous solution of nickel and cobalt salts produced by the above-described method for producing an aqueous solution of nickel and cobalt salts. Because the aqueous solution of nickel and cobalt salts is an aqueous solution in which the copper content is effectively reduced, by producing a precursor compound for the positive electrode material using this aqueous solution, it is possible to obtain a precursor compound that contains almost no impurities such as copper.

[0080] Specifically, the method for producing a precursor compound for synthesizing a positive electrode material for a lithium-ion battery includes the steps of: carrying out a method for producing a nickel and cobalt salt aqueous solution on a mixture containing nickel, cobalt, and copper to produce a salt aqueous solution containing nickel and cobalt; purifying the obtained salt aqueous solution to obtain a purified aqueous solution containing nickel and cobalt; and adding hydroxide or carbonate to the purified aqueous solution containing nickel and cobalt to precipitate nickel and cobalt as hydroxide or carbonate, thereby obtaining a solid suitable for synthesizing a positive electrode material for a lithium-ion battery.

[0081] [Step of Producing an Aqueous Solution of Nickel and Cobalt Salts] The aqueous solution of nickel and cobalt salts can be produced by carrying out the method for producing an aqueous solution of nickel and cobalt salts described above. Therefore, a detailed description thereof will be omitted here. For example, an aqueous solution of nickel and cobalt salts containing an extremely low copper content can be produced from a mixture containing nickel, cobalt, and copper, such as an alloy obtained by heating, melting, and reducing used lithium-ion batteries.

[0082] [Step of purifying the salt solution] As described above in detail, in the step of purifying the salt solution, treatments such as solution purification and solvent extraction can be performed alone or in combination of two or more depending on the types of impurities contained in the salt solution, thereby obtaining a purified aqueous solution in which the impurities are reduced and nickel and cobalt are concentrated.

[0083] [Step of Obtaining a Solid Suitable for the Synthesis of a Positive Electrode Material for Lithium-Ion Batteries] Next, hydroxides or carbonates are added to the aqueous solution containing the purified nickel and cobalt, thereby precipitating the nickel and cobalt as hydroxides or carbonates. By this process, a solid containing nickel and cobalt can be obtained.

[0084] The nickel and cobalt hydroxides or carbonates thus deposited can be effectively used as raw materials for precursor compounds for synthesizing a positive electrode material for a lithium ion battery having a desired composition.

[0085] Specifically, for example, by adding manganese sulfate or the like to the precipitated hydroxide or carbonate of nickel and cobalt, a precursor compound for synthesizing a ternary cathode material (NMC) containing nickel, manganese, and cobalt as main components can be obtained.

[0086] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[0087] [Example] Used lithium-ion batteries were subjected to a dry process in which they were heated, melted, and reduced to obtain a molten alloy containing nickel, cobalt, and copper. This was poured into a small crucible with a hole in the bottom, and high-pressure gas or water was sprayed onto the molten alloy that flowed out from the hole, causing it to scatter and solidify. The molten alloy was then sieved to obtain an atomized alloy powder with a particle size of 300 μm or less. Table 1 below shows the results of an analysis of the obtained alloy powder using an ICP analyzer.

[0088]

[0089] Next, in each example, 1.0 g of the above alloy powder was sampled. Also, in each example, 0.37 g of solid sulfur was prepared, which was 1 equivalent of forming copper sulfide as shown in the above reaction formula [1] relative to the amount of copper contained in the alloy powder. Also, in each example, sulfuric acid was sampled in an amount equivalent to 5 equivalents relative to the total amount of nickel and cobalt contained in the alloy powder, and this was diluted to 50 ml to prepare a sulfuric acid aqueous solution. The amount of sulfuric acid was the equivalent calculated using the above reaction formulas [2] and [3].

[0090] In each example, an alloy powder was added to the prepared sulfuric acid aqueous solution, and the alloy powder was immersed in the sulfuric acid aqueous solution in the absence of a sulfurizing agent. The solution was stirred at 200 rpm under predetermined temperature conditions until the oxidation-reduction potential (ORP) of the solution relative to a silver / silver chloride electrode reached an extreme value (minimum value) and then reached 70 mV, as shown in Table 2 below. This treatment is referred to as the "immersion treatment" for convenience. Note that "ORP upon addition of S" in Table 2 refers to the ORP at the end of the immersion treatment. Furthermore, as shown in Table 2, the immersion treatment times in Examples 1 to 5 were 10 minutes, 15 minutes, 30 minutes, 45 minutes, and 60 minutes, respectively.

[0091] Thereafter, solid sulfur as a sulfiding agent was added to the sample obtained by immersing the alloy powder in an aqueous sulfuric acid solution, and the mixture was stirred at a rotation speed of 200 rpm under predetermined temperature conditions to perform a leaching treatment to leach nickel and cobalt from the alloy powder.

[0092] In the leaching treatment, the time required for 95% of the nickel and cobalt contained in the alloy powder to be leached (leaching time) was measured. Table 2 below shows the treatment conditions, as well as the leaching time after addition of the sulfiding agent and the total reaction time (total time of immersion and leaching). The leaching rates of nickel and cobalt were calculated based on the analysis results using an ICP-5100 optical emission spectrometer manufactured by Agilent.

[0093] In Comparative Example 1, the alloy powder having the same analytical values ​​as in the Examples and shown in Table 1 above was used, and leaching treatment was carried out using only sulfuric acid without the coexistence of a sulfurizing agent, with the other conditions being the same as in the Examples.

[0094] In Comparative Example 1, the leaching time was limited to 2 hours because the leaching rate of nickel and cobalt was extremely slow. Table 2 below shows the treatment conditions and the measurement results of the total reaction time.

[0095] Comparative Examples 2 and 3: In Comparative Examples 2 and 3, the same alloy powders as in the Examples, whose analytical values ​​are shown in Table 1, were used, and a leaching process was carried out to leach nickel and cobalt from the alloy powder as follows. In Comparative Examples 2 and 3, as in the Examples, 0.37 g of solid sulfur was prepared, which was 1 equivalent of forming copper sulfide as shown in the above reaction formula [1] relative to the amount of copper contained in the alloy powder. Furthermore, sulfuric acid was dispensed in an amount equivalent to 5 equivalents relative to the total amount of nickel and cobalt contained in the alloy powder, and this was diluted to 50 ml to prepare an aqueous sulfuric acid solution.

[0096] That is, in Comparative Example 2, 1.0 g of alloy powder and 0.37 g of solid sulfur as a sulfurizing agent were simultaneously added to the prepared sulfuric acid aqueous solution, and the mixture was stirred at a rotation speed of 200 rpm under a predetermined temperature condition to perform a leaching treatment to leach nickel and cobalt from the alloy powder. That is, in Comparative Example 2, the immersion treatment of immersing the alloy powder in a sulfuric acid aqueous solution in advance was not performed.

[0097] On the other hand, in Comparative Example 3, similar to the Example, alloy powder was added to the prepared sulfuric acid aqueous solution, and the alloy powder was immersed in the sulfuric acid aqueous solution in the absence of a sulfurizing agent, but the immersion treatment was continued until the ORP of the solution reached its extreme value (minimum value). The immersion time in Comparative Example 3 was 5 minutes.

[0098] In Comparative Example 3, a sample of alloy powder immersed in a sulfuric acid aqueous solution was then subjected to a leaching treatment in which solid sulfur, which is a sulfiding agent, was added to the sample, and the mixture was stirred at a rotation speed of 200 rpm under a predetermined temperature condition to leach nickel and cobalt from the alloy powder.

[0099] In Comparative Examples 2 and 3, the time required for 95% of the nickel and cobalt contained in the alloy powder to be leached was measured in the same manner as in the Examples. Table 2 below shows the measurement results of the leaching time and total reaction time after addition of the sulfiding agent, along with the treatment conditions.

[0100]

[0101] In Examples 1 to 5, which are specific examples of the present invention, the leaching time after the addition of the sulfurizing agent was shorter than in Comparative Example 2, in which sulfur was simultaneously added, and nickel and cobalt were able to be leached effectively and efficiently. This is thought to be because the surface condition of the alloy changed when the alloy was immersed in a sulfuric acid aqueous solution for a certain period of time without adding a sulfurizing agent, and then the sulfurizing agent was added and the leaching treatment was performed, which resulted in a rapid increase in the leaching rate of nickel and cobalt.

[0102] Furthermore, the results of Examples 4 and 5 show that the longer the immersion time, the greater the change in the surface condition of the alloy, and as a result, the shorter the leaching time after the addition of the sulfiding agent. However, as the immersion time is increased, the total reaction time for the immersion treatment and the leaching treatment after the addition of the sulfiding agent is inevitably increased.

[0103] On the other hand, in Comparative Example 1, the leaching treatment was performed without adding a sulfurizing agent, and therefore the leaching rate of nickel and cobalt was only about 10%. In Comparative Example 3, although 95% of the nickel and cobalt could be leached, the immersion treatment for the alloy powder was insufficient because the immersion treatment was terminated and the sulfurizing agent was added before the ORP of the solution reached its minimum value, and the leaching time after the addition of the sulfurizing agent was only about the same as in Comparative Example 2.

Claims

1. A method for producing an aqueous solution of nickel and cobalt salts, comprising the step of contacting a mixture containing nickel, cobalt, and copper with a mineral acid in the presence of a sulfiding agent, wherein the mixture is immersed in at least one equivalent of the mineral acid until the oxidation-reduction potential, using a silver / silver chloride reference electrode, reaches 70 mV after passing through a minimum value, and then one or more sulfiding agents selected from hydrogen sulfide, solid sulfur, sodium hydrogen sulfide, and sodium sulfide are added to the solution, thereby leaching nickel and cobalt from the mixture.

2. The method for producing an aqueous solution of nickel and cobalt salts according to claim 1, wherein the mixture is an alloy containing nickel, cobalt, and copper.

3. The method for producing an aqueous solution of nickel and cobalt salts according to claim 2, wherein the alloy includes an alloy obtained by heating, melting, and reducing waste lithium-ion batteries.

4. The method for producing an aqueous solution of nickel and cobalt salts according to any one of claims 1 to 3, wherein the amount of the sulfurizing agent added is 1 equivalent or more relative to the amount of copper contained in the mixture in terms of sulfur.

5. A method for producing nickel sulfate and cobalt sulfate from a mixture containing nickel, cobalt, and copper, comprising the steps of: carrying out the production method according to claim 1 using sulfuric acid as the mineral acid to produce an aqueous solution of nickel and cobalt sulfates; purifying the aqueous solution of nickel and cobalt sulfates; and precipitating solid nickel sulfate and cobalt sulfate from the purified aqueous solution.

6. A method for producing a precursor compound for synthesizing a positive electrode material for a lithium ion battery, comprising the steps of: producing an aqueous solution of nickel and cobalt salts by the production method described in claim 1; purifying the aqueous salt solution to obtain an aqueous solution containing purified nickel and cobalt; and adding hydroxides or carbonates to the aqueous solution containing purified nickel and cobalt to precipitate nickel and cobalt as hydroxides or carbonates, thereby obtaining a solid suitable for synthesizing the positive electrode material for a lithium ion battery.

Images