Method for producing leach solution from hydroxide including nickel and cobalt

Abstract

[Problem] To provide a method for producing a leach solution that includes nickel ions and cobalt ions, using a raw material that includes nickel and cobalt and is less expensive than metallic nickel powder. [Solution] A leach solution including nickel ions and cobalt ions leached from hydroxide particles is obtained by subjecting a slurry to a leaching process under prescribed temperature conditions, said slurry having been obtained by mixing the hydroxide particles, which include nickel and cobalt, and aqueous ammonia that includes ammonium sulfate and has preferably been adjusted such that the ammonium sulfate concentration is within the range 0.5-4.1 mol / L.

Description

Method for producing leachate from hydroxide containing nickel and cobalt

[0001] The present invention relates to a method for producing a leach solution containing nickel ions and cobalt ions from a hydroxide containing nickel and cobalt.

[0002] Lithium-ion secondary batteries, which charge and discharge by the movement of lithium ions between a positive electrode and a negative electrode, have a high energy density and are resistant to deterioration even with repeated charging and discharging. As a result, demand for these batteries has been increasing in recent years for use in electronic devices such as mobile phones and laptops, as power sources for electric vehicles and other devices, and as storage batteries for smart grids. Lithium-ion secondary batteries have a structure in which an electrolyte is filled between a positive electrode and a negative electrode facing each other with a separator in between. Lithium nickel oxide is used as the active material for the positive electrode, which is the main component of the battery. Lithium nickel oxide can be produced by mixing lithium hydroxide with nickel hydroxide as a precursor and firing the mixture.

[0003] Nickel hydroxide as the precursor can be produced by a neutralization reaction that occurs when an aqueous sodium hydroxide solution is added to an aqueous nickel sulfate solution as a raw material. In this neutralization reaction of the nickel sulfate raw material, sodium sulfate (mirabilite) that is produced as a by-product in an equimolar amount with nickel hydroxide, as shown in the following formula 1, can sometimes be a problem. That is, since total wastewater volume restrictions are imposed on sodium sulfate in some regions, it has sometimes been necessary to install costly treatment facilities to meet the wastewater standards, or to limit the production volume of nickel hydroxide in order to suppress the discharge of sodium sulfate. [Formula 1] NiSO ４ +2NaOH→Ni(OH) ２ +Na ２ SO ４

[0004] Therefore, methods for producing nickel hydroxide that do not produce sodium sulfate as a by-product have been proposed. For example, Patent Document 1 proposes a technology in which oxygen is introduced into an aqueous ammonia solution containing powder of metallic nickel to leach the metallic nickel into the aqueous ammonia solution, seed crystals are added as needed to the aqueous ammonia solution containing nickel and hydroxyl ions, and the aqueous ammonia solution is evaporated under atmospheric pressure or reduced pressure to precipitate and recover nickel hydroxide.

[0005] Japanese Patent Application Publication No. 10-324524

[0006] Although nickel hydroxide can be produced without producing sodium sulfate as a by-product by using the technology of Patent Document 1, this technology is not economically advantageous because it uses metallic nickel as a precursor raw material. Specifically, metallic nickel is generally produced by leaching nickel from intermediate raw materials such as matte, sulfide, or hydroxide obtained by processing nickel ore using acid, chlorine, or the like, and then separating the impurities leached with the nickel through a refining process before electrowinning, resulting in the metallic nickel being in the form of a plate or block. Therefore, a step of processing the metallic nickel into powder is required to efficiently leach it with an aqueous ammonia solution.

[0007] In addition, as in the case of ternary positive electrode active materials such as lithium nickel cobalt manganate (NCM) and lithium nickel cobalt aluminum oxide (NCA), in which a portion of the nickel is replaced with an element such as cobalt, cobalt may be added to the precursor during the production of the lithium nickel oxide. In this case, the inclusion of cobalt in the nickel used as the precursor raw material is not a problem; rather, it is preferable for the nickel used as the precursor raw material to contain a certain amount of cobalt. However, although many of the intermediate raw materials used in the production of metallic nickel contain cobalt, they are subjected to a purification process such as a solvent extraction process to separate and remove cobalt from the nickel prior to electrowinning, resulting in unnecessary separation costs. As such, the method of producing nickel hydroxide using metallic nickel as a raw material requires many processes that increase costs, so there is a need for an alternative method of producing nickel hydroxide using unrefined intermediate raw materials containing a wide variety of impurities, for example, obtained by processing nickel oxide ore or scrap.

[0008] The present invention has been made in view of the above circumstances, and has an object to provide a method for producing a leachate containing nickel ions and cobalt ions using a raw material containing nickel and cobalt that is cheaper than metallic nickel.

[0009] In order to achieve the above object, the method for producing a leachate according to the present invention is characterized in that a slurry is obtained by mixing hydroxide particles containing nickel and cobalt with ammonia water containing ammonium sulfate, and the slurry is subjected to a leaching treatment under predetermined temperature conditions to obtain a leachate containing nickel ions and cobalt ions leached from the hydroxide particles.

[0010] According to the present invention, a leachate containing nickel ions and cobalt ions can be produced using raw materials containing nickel and cobalt, which are cheaper than metallic nickel, without by-producing sodium sulfate.

[0011] FIG. 1 is a block flow diagram of a method for producing nickel hydroxide containing cobalt, which method preferably includes the method for producing a leachate of the present invention.

[0012] Hereinafter, an embodiment of a method for producing a leachate containing nickel ions and cobalt ions according to the present invention will be described. The method for producing a leachate according to this embodiment of the present invention is included in a method for producing nickel hydroxide containing cobalt as a precursor by subjecting a raw material nickel-cobalt mixed hydroxide to a series of treatments, as shown in FIG. 1 . This raw material nickel-cobalt mixed hydroxide contains impurities such as calcium, magnesium, zinc, sulfur, silicon, manganese, iron, and aluminum. Nickel-cobalt mixed hydroxide containing such various impurities is sometimes referred to as a mixed hydroxide precipitate (MHP).

[0013] That is, the method for producing nickel hydroxide containing cobalt in FIG. 1 includes a water washing step in which nickel-cobalt mixed hydroxide particles (MHP) are washed preferably with water at room temperature to mainly remove calcium and magnesium, an alkali washing reduction step in which the nickel-cobalt mixed hydroxide particles washed in the water washing step are washed and reduced with an alkali washing solution made of an aqueous caustic soda solution at room temperature, preferably with a concentration of about 8 mol / L, which contains a reducing agent such as sodium sulfite, to mainly remove zinc, sulfur, and silicon, and a process for reducing the nickel-cobalt mixed hydroxide particles in the alkali washing step. The process includes a leaching step in which the reduced nickel-cobalt mixed hydroxide particles are leached with an ammonia-containing aqueous solution containing ammonium sulfate, a thermal decomposition precipitation step in which the leachate obtained by the leaching step is heated to thermally decompose the ammonium sulfate into ammonia and sulfur trioxide and precipitate nickel hydroxide and cobalt hydroxide as precursors, and an alkaline washing step in which the precipitated nickel hydroxide and cobalt hydroxide are washed with an alkaline washing solution, preferably an aqueous caustic soda solution at room temperature with a concentration of about 4 mol / L, to mainly remove carbon. Each of these steps will be described below.

[0014] (1) Water-washing step The water-washing step is a step in which impurities contained in the raw material nickel-cobalt mixed hydroxide, mainly calcium and magnesium, are removed using wash water preferably at a liquid temperature of 10 to 90°C, more preferably at room temperature. This water-washing step is not limited to, but a preferred method is to add the nickel-cobalt mixed hydroxide to wash water that has been placed in advance in a container equipped with a stirrer, and wash the mixture for 0.50 to 1.0 hour while stirring with the stirrer. After washing, the slurry containing the nickel-cobalt mixed hydroxide particles is introduced into a solid-liquid separator such as a centrifuge or filter for solid-liquid separation, whereby the washed, wet nickel-cobalt mixed hydroxide can be recovered.

[0015] (2) Alkaline Washing Reduction Process The alkaline washing reduction process removes impurities, primarily zinc, sulfur, and silicon, that are difficult to remove in the previous water washing process by washing with an alkaline washing solution, such as a caustic soda solution with a concentration of 1.0 to 8.0 mol / L. The washing wastewater discharged after this washing process contains impurities such as zinc, sulfur, and silicon, and is then repeatedly treated as an alkaline washing solution after removing these impurities using a precipitation method or other method. Here, precipitation refers to a technique for extracting solutes dissolved in a solution as precipitated particles. For example, the solution can be converted from an undersaturated state to a supersaturated state, promoting the formation and growth of crystal nuclei, thereby obtaining the precipitated particles. Furthermore, manganese, iron, and aluminum that are not leached in the leaching process remain as leaching residue and are separated and removed from the leachate by solid-liquid separation methods such as filtration. Furthermore, the ammonia and sulfur trioxide generated by thermal decomposition in the thermal decomposition precipitation means are recovered and reused as ammonia water containing ammonium sulfate in the preceding leaching step, and the carbon content in the cleaning solution discharged after cleaning in the alkaline cleaning step decreases in solubility as the temperature of the cleaning wastewater decreases, so in this case too, the carbon content can be precipitated as sodium carbonate by using the precipitation method as described above. After removing the sodium carbonate in this way, the cleaning wastewater is reused as an alkaline cleaning solution.

[0016] (3) Leaching Step The leaching step is a step in which the nickel-cobalt mixed hydroxide washed in the previous alkaline washing and reduction step is leached with an ammonium sulfate aqueous solution. Specifically, water is first placed in a vessel equipped with a stirrer, and ammonia (NH ３ ) water and ammonium sulfate ((NH4) ２ SO ４ ) to prepare an aqueous ammonium sulfate solution. Next, nickel-cobalt mixed hydroxide particles are added to the container containing the prepared ammonium sulfate solution, and the mixture is stirred and mixed with the stirrer to prepare a slurry having a uniform concentration. In this state, the temperature of the slurry is maintained preferably at a temperature of 20°C or higher and 60°C or lower to carry out the leaching treatment. This allows nickel ions and cobalt ions to be leached from the nickel-cobalt mixed hydroxide particles. If the slurry temperature is lower than 20°C, the reaction rate is too slow, resulting in a decrease in production efficiency. Conversely, if the slurry temperature exceeds 60°C, ammonium sulfate is easily thermally decomposed, making it difficult to leach it. Note that if the slurry temperature is lower than 0°C, water freezes, making it difficult to prepare an ammonium sulfate solution.

[0017] During this leaching treatment, the ammonium sulfate concentration in the aqueous ammonium sulfate solution is preferably adjusted to a range of 0.50 mol / L to 4.1 mol / L, more preferably 1.5 mol / L to 3.5 mol / L, and most preferably 2.0 mol / L to 3.0 mol / L. An ammonium sulfate concentration below 1.5 mol / L may result in a decrease in the leaching rate, and particularly below 0.50 mol / L may result in the inability to achieve the desired effects of the present invention. Conversely, increasing the ammonium sulfate concentration beyond approximately 3.5 mol / L is undesirable because it increases the cost of neutralization, even though the leaching rate remains relatively unchanged. Furthermore, exceeding 4.1 mol / L may result in supersaturation of ammonium sulfate, resulting in precipitation, which may adversely affect the leaching treatment. The ammonium sulfate concentration can be measured by absorptiometry, ion chromatography, or other methods. If the ammonium sulfate concentration is outside the above range, it can be adjusted by adjusting the amount of ammonium sulfate added.

[0018] In addition, during the above-mentioned leaching treatment, it is preferable to adjust the free ammonia concentration in the slurry to within the range of 0.1 to 1.3 mol / L. If the free ammonia concentration is within this range, nickel and cobalt can be leached stably in the form of ammine complexes. Even if this free ammonia concentration exceeds 1.3 mol / L, it has almost no effect on the stable leaching in the form of the above-mentioned amine complexes, and it is undesirable because it increases costs and increases the load on wastewater treatment. Note that free ammonia refers to molecular ammonia (NH ３ ) and its concentration is measured by separating it by distillation and then changing the form to NH ４ ＋ and measured by absorptiometry. If the free ammonia concentration is outside the above range, it can be adjusted by adjusting the amount of aqueous ammonia added.

[0019] (4) Pyrolysis and Precipitation Step In the pyrolysis and precipitation step, the leachate produced in the previous leaching step is heated, preferably by maintaining the temperature at 60°C to 100°C for 0.50 to 2.0 hours, thereby thermally decomposing the nickel and cobalt ammine complexes and precipitating the nickel and cobalt hydroxides, which are then recovered as a precipitate. In this pyrolysis and precipitation step, stirring is preferably performed while blowing in an oxidizing agent, such as air, which promotes the oxidation of cobalt, enabling the recovery of both nickel and cobalt as hydroxides with a high recovery rate. That is, cobalt ammine complexes usually undergo thermal decomposition to divalent cobalt, but oxidizing this to trivalent cobalt promotes recovery as hydroxides. The ammonia and sulfur trioxide generated by the pyrolysis in this pyrolysis and precipitation step are preferably recovered and reused as the ammonia water containing ammonium sulfate used in the previous leaching step.

[0020] (5) Alkaline Washing Step In the alkaline washing step, the nickel-cobalt mixed hydroxide recovered in the preceding thermal decomposition precipitation step is washed, preferably with the same alkaline washing solution as that used in the alkaline washing and reduction step described above. This removes zinc, sulfur, and silicon that were not completely removed in the alkaline washing and reduction step, as well as carbon derived from the ammonium sulfate added in the leaching step, making it possible to produce a high-purity precursor with extremely few impurities that can be suitably used as a positive electrode active material for lithium-ion secondary batteries.

[0021] As described above, the method for producing a leachate according to an embodiment of the present invention makes it possible to produce a leachate containing nickel and cobalt from raw material nickel-cobalt mixed hydroxide particles without by-producing sodium sulfate, and also makes it possible to easily separate and remove impurities such as manganese, iron, and aluminum contained in the raw material, so that the leachate can be produced more inexpensively than when expensive metallic nickel is used as the raw material. The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0022] (Example) 185 mL of pure water and 15 mL of ammonia water with a concentration of 25% by mass were placed in a container, and ammonium sulfate (NH4) ２ SO ４ To the resulting ammonium sulfate solution, 20 g of powdered nickel-cobalt mixed hydroxide (MHP) having the composition shown in Table 1 below was mixed to prepare a slurry, which was stirred with a stirrer while maintaining the liquid temperature at 50°C for 2 hours, thereby carrying out a leaching treatment.

[0023]

[0024] After the leaching treatment, solid-liquid separation was performed by filtration, yielding a leaching residue with a dry mass of 12.5 g and 204 mL of leaching solution. The element concentrations in the leaching residue and leaching solution were measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the leaching rate of each element was calculated using the following formula 2. [Formula 2] Leaching rate of element α = mass of element α in leaching solution / (mass of element α in leaching solution + mass of element α in leaching residue) × 100

[0025] As a result, the leaching rate of nickel was 45.6% and the leaching rate of cobalt was 15.4%, and a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions was produced.

[0026] (Comparative Example) 20 g of powdered nickel-cobalt mixed hydroxide (MHP) having the composition shown in Table 1 above was mixed with 200 mL of 25% ammonia water placed in a container to form a slurry, which was then stirred with a stirrer while maintaining the liquid temperature at 50°C for 2 hours to carry out a leaching treatment. Thereafter, solid-liquid separation was carried out in the same manner as in the Examples to obtain 200 mL of leachate. The element concentrations of this leachate were measured in the same manner as in the Examples to determine the leaching rate of each element.

[0027] As a result, the leaching rate of nickel was 14.6% and the leaching rate of cobalt was 0.2%, meaning that about one-third of the nickel was leached compared to the example in which leaching treatment was carried out at the same temperature, but almost no cobalt was leached. In this comparative example, the leaching rate of each element was calculated using the following formula 3. The measurement results of the above example and comparative example are summarized in Table 2 below. [Formula 3] Leaching rate of element α = mass of element α in leachate / mass of element α in MHP × 100

[0028]

Claims

1. A method for producing a leachate from a hydroxide containing nickel and cobalt, comprising: mixing hydroxide particles containing nickel and cobalt with ammonia water containing ammonium sulfate to obtain a slurry; and subjecting the slurry to a leaching treatment under specified temperature conditions to obtain a leachate containing nickel ions and cobalt ions leached from the hydroxide particles.

2. A method for producing a leachate from a hydroxide containing nickel and cobalt according to claim 1, characterized in that the concentration of ammonium sulfate in the ammonia water containing ammonium sulfate is adjusted to be within the range of 0.50 to 4.1 mol / L.

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