Method for producing metal ni / co particles, and method for producing positive electrode active material

Abstract

Provided is a method for producing metal Ni / Co with which it is possible to obtain metal Ni / Co particles serving as a raw material for a nickel salt or the like by removing impurities from a Ni- and Co-containing hydroxide through a simple process. This method for producing metal Ni / Co particles is characterized by including: a slurry step for mixing a hydroxide that contains an impurity element, Ni, and Co with water to prepare a slurry; a reduction step for mixing the slurry and a reducing agent to reduce the Ni and the Co in the hydroxide to obtain metal Ni / Co particles; an extraction step for magnetically separating the slurry after the reduction step to extract the metal Ni / Co particles; and a washing / drying step for washing and drying the metal Ni / Co particles obtained in the extraction step.

Description

Method for producing metal Ni / Co particles and method for producing positive electrode active material

[0001] The present disclosure relates to a method for producing metallic Ni / Co particles and a method for producing a positive electrode active material.

[0002] Nickel is widely used as a raw material for stainless steel, and as the sulfide ore that is the raw material for nickel is becoming scarce, technology for refining low-grade oxide ore has been developed and put into practical use.

[0003] For example, a production process known as the High Pressure Acid Leach (HPAL) method has been put into practical use, in which nickel oxide ores such as limonite or saprolite are placed in a pressure device such as an autoclave together with a sulfuric acid solution, and nickel is leached under high temperature and pressure of approximately 240° C. to 260° C. In a production process based on the HPAL method, nickel is leached into a sulfuric acid solution, and then excess acid is neutralized by adding a neutralizing agent, and the nickel is then separated from the leach residue by solid-liquid separation, and recovered as, for example, hydroxides containing Ni and Co.

[0004] Hydroxides containing Ni and Co are used as raw materials for producing nickel salts, particularly nickel sulfate, which are used in general electrolytic plating, as well as in electroless plating for hard disks, as catalysts, and as battery materials for lithium-ion batteries and nickel-metal hydride batteries.

[0005] In the high-temperature pressure acid leaching method, impurities such as zinc, magnesium, calcium, and manganese contained in the ore are easily leached out by the sulfuric acid solution and are therefore likely to be mixed into the hydroxide containing Ni and Co. Therefore, in order to obtain high-purity nickel salts and the like from the hydroxide containing Ni and Co, it is necessary to remove the impurities from the hydroxide containing Ni and Co.

[0006] For example, Patent Document 1 discloses a method for obtaining high-purity nickel sulfate with low impurities such as magnesium by treating a nickel-containing solution containing nickel and cobalt through a stepwise solvent extraction process.

[0007] JP 2013-100204 A JP 2017-25367 A

[0008] However, in the prior art, a complicated solvent extraction process is required to remove impurities from hydroxides containing Ni and Co to obtain high-purity nickel salts.

[0009] Therefore, the present disclosure aims to provide a method for producing metallic Ni / Co that can remove impurities from hydroxides containing Ni and Co in a simple process to obtain metallic Ni / Co particles that can be used as raw materials for nickel salts, etc.

[0010] A method for producing metallic Ni / Co particles according to one embodiment of the present disclosure is characterized by including a slurry process in which a hydroxide containing impurity elements, Ni, and Co is mixed with water to prepare a slurry; a reduction process in which the slurry is mixed with a reducing agent to reduce the Ni and Co in the hydroxide and obtain metallic Ni / Co particles; an extraction process in which the slurry after the reduction process is magnetically separated to extract the metallic Ni / Co particles; and a washing and drying process in which the metallic Ni / Co particles obtained in the extraction process are washed and dried.

[0011] Furthermore, a method for producing a positive electrode active material according to one aspect of the present disclosure is characterized in that a Ni- and Co-containing lithium composite oxide is produced using the metallic Ni / Co particles obtained by the method for producing metallic Ni / Co particles.

[0012] According to one aspect of the present disclosure, impurities can be removed from hydroxides containing Ni and Co in a simple process to obtain metallic Ni / Co particles that can be used as raw materials for nickel salts and the like.

[0013] 1 is a flow diagram of a method for producing metal Ni / Co particles according to an embodiment of the present invention. 2 is a powder X-ray diffraction pattern of the metal Ni / Co particles of Example 1. 3 is a scanning electron microscope (SEM) photograph of the metal Ni / Co particles of Example 1.

[0014] Figure 1 shows a flow diagram of a method for producing metallic Ni / Co particles according to this embodiment. As shown in Figure 1, the method for producing metallic Ni / Co particles according to this embodiment includes a slurry process, a reduction process, an extraction process, and a washing and drying process. Specifically, the process includes a slurry process in which a hydroxide containing impurity elements, Ni, and Co is mixed with water to prepare a slurry, a reduction process in which the slurry is mixed with a reducing agent to reduce the Ni and Co in the hydroxide and obtain metallic Ni / Co particles, an extraction process in which the slurry after the reduction process is magnetically separated to extract the metallic Ni / Co particles, and a washing and drying process in which the metallic Ni / Co particles obtained in the extraction process are washed and dried. Each of these processes will be described in detail below.

[0015] (Slurry Process) The hydroxide containing impurity elements, Ni, and Co may be of any origin, and examples thereof include hydroxides containing Ni and Co obtained by a manufacturing process based on high-temperature acid leaching (HPAL) of nickel oxide ore, as described above. Examples of impurity elements contained in the hydroxide include Zn, Mg, Ca, Mn, Fe, B, and Cu. Hydroxides containing impurity elements, Ni and Co, are hydroxides containing Ni, Co, and impurity elements as constituent elements, and include, for example, nickel hydroxide, cobalt hydroxide, and hydroxides of impurity elements (e.g., zinc hydroxide, magnesium hydroxide, calcium hydroxide, manganese hydroxide, iron hydroxide, boron hydroxide, copper hydroxide, etc.). Furthermore, for example, hydroxides in which cobalt or impurity elements are solid-dissolved in nickel hydroxide, hydroxides in which nickel or impurity elements are solid-dissolved in cobalt hydroxide, and the like may also be included. Hydroxides containing impurity elements, Ni, and Co are hardly dissolved in water, and Ni, Co, and the impurity elements are not ionized in the slurry.

[0016] The water is not particularly limited, but is preferably, for example, ion-exchanged water, pure water, ultrapure water, etc. The water is preferably mixed with the hydroxide in an amount such that the solids concentration in the slurry is 0.1 g / L or more and 3.0 g / L or less. By setting the solids concentration in the slurry within the above range, the efficiency of reduction by the reducing agent in the subsequent step can be increased, and a decrease in the fluidity of the slurry can be suppressed, which may lead to an improvement in the recovery rate of the metal Ni / Co particles finally obtained.

[0017] (Reduction step) The reducing agent is not particularly limited as long as it can reduce Ni and Co in the hydroxide containing impurity elements, Ni, and Co, and obtain metallic Ni / Co particles, and examples thereof include hydrazine compounds such as hydrazine and hydrazine monohydrate, hypophosphorous acid, sodium borohydride, etc. Among these, hydrazine compounds such as hydrazine and hydrazine monohydrate are preferred in that they suppress the inclusion of impurities in the metallic Ni / Co particles.

[0018] In order to increase the reduction efficiency, the reducing agent is preferably prepared as an alkaline aqueous solution containing the reducing agent and mixed with the slurry. The alkaline aqueous solution containing the reducing agent can be obtained, for example, by dissolving a reducing agent such as a hydrazine compound in water and adding sodium hydroxide, potassium hydroxide, ammonia, or other water-soluble alkali to adjust the pH to alkaline. The pH of the alkaline aqueous solution containing the reducing agent is preferably, for example, 10 or more and 13 or less. Furthermore, in order to reduce the amount of water-soluble alkali added, a pH of 10 or more and 12 or less is more preferred.

[0019] The amount of reducing agent added is preferably 0.5 or more in molar ratio, which is the molar equivalent calculated from the chemical reaction formula, relative to the total amount of Ni and Co in the slurry in order to increase reduction efficiency. To further increase reduction efficiency, a molar ratio of 0.75 or more is more preferable, with the upper limit being 1.5 or less. For example, a molar ratio of 0.5 means that, although there are two reduction reaction formulas for hydrazine, when considering the standard electrode potential of Ni, formula (2) is considered to be the preferred reaction. In this case, four electrons are released per mole of hydrazine, so two moles of divalent Ni ions can be reduced. N2H4 + 2OH - →N2 + H2 + 2H2O + 2e- E = 1.587-0.06pH (1) N2H4+4OH - →N2 + 4H2O + 4e - E = -0.33-0.06pH (2)

[0020] The reaction temperature in the reduction step is, for example, preferably 50° C. or higher and 85° C. or lower, and more preferably 70° C. or higher, from the viewpoint of increasing the reduction efficiency.

[0021] (Extraction Process) Because the metallic Ni / Co particles contained in the slurry after the reduction process are magnetic, the metallic Ni / Co particles can be extracted (recovered) from the slurry by subjecting the slurry to magnetic separation. Specific methods for magnetic separation are, for example, as follows. The slurry is passed through a flow path provided in a magnetic separation device, and a magnet is placed on the outside of the wall of this flow path, thereby causing the metallic Ni / Co particles to adhere to the wall of the flow path. The metallic Ni / Co particles adhered to the wall may be recovered, for example, manually or by backwashing with water. The metallic Ni / Co particles can be easily recovered by using the UK series (recovery device) manufactured by Sumitomo Heavy Industries Finetech, Ltd.

[0022] (Washing and Drying Process) Washing of the metallic Ni / Co particles is, for example, a process of mixing the metallic Ni / Co particles obtained in the extraction process with water to form a slurry and stirring the mixture. This washing process can remove impurities present on the surface of the metallic Ni / Co particles. The washing time is not particularly limited, but is, for example, 5 minutes to 1 hour. The temperature of the water used for washing is, for example, 10°C to 40°C. The washing process is preferably repeated three or more times, more preferably five or more times. It is also more preferable to strengthen the washing process using ultrasonic waves. The method for recovering the metallic Ni / Co particles after washing may be the same as the extraction process, but it is preferable to use the UK series (recovery device) manufactured by Sumitomo Heavy Industries Finetech, Ltd. The water used for washing is, for example, ion-exchanged water, pure water, ultrapure water, etc.

[0023] Drying is a process in which, for example, the slurry containing the washed metallic Ni / Co particles is filtered to separate the metallic Ni / Co particles, and the metallic Ni / Co particles are dried in the air or under reduced pressure. The filtration of the slurry can be performed using, for example, a suction filter, a filter press, a centrifuge, or the like. The drying temperature is, for example, 80°C or higher and 120°C or lower. The drying time is, for example, 30 minutes or higher and 5 hours or shorter.

[0024] In this manner, impurities are removed from hydroxides containing Ni and Co to obtain metallic Ni / Co particles. In this embodiment, high-purity metallic Ni / Co particles can be obtained by a simpler process than conventional methods, since a complicated solvent extraction process is not required for hydroxides containing impurities, Ni, and Co. The obtained metallic Ni / Co particles can be used as a raw material for nickel salts, particularly nickel sulfate, for example.

[0025] An example of a method for producing a positive electrode active material in which metallic Ni / Co particles are used to produce a Ni and Co-containing lithium composite oxide will be described below.

[0026] The metallic Ni / Co particles are dissolved in sulfuric acid to prepare a solution containing nickel sulfate and cobalt sulfate. While sulfuric acid is preferred for dissolving the metallic Ni / Co particles, any acid solution capable of dissolving the metallic Ni / Co particles, such as hydrochloric acid or nitric acid, may be used. Hereinafter, the solution containing nickel sulfate and cobalt sulfate will be referred to as a Ni- and Co-containing solution.

[0027] Next, the prepared Ni- and Co-containing solution is used to obtain a Ni- and Co-containing hydroxide by a crystallization method. Specifically, the reaction vessel is heated to 40 to 60°C, and the Ni- and Co-containing solution and an aqueous solution containing an ammonium ion donor are added dropwise. At this time, an aqueous solution of an alkali metal hydroxide may be added dropwise in an amount sufficient to keep the reaction solution alkaline, for example, at a pH of 10 to 14. By this method, a Ni- and Co-containing hydroxide is obtained.

[0028] Next, the obtained hydroxide containing Ni and Co is roasted to obtain an oxide containing Ni and Co. The roasting conditions are not particularly limited, and are, for example, from 500°C to 1100°C.

[0029] Next, the obtained Ni- and Co-containing oxide is mixed with a lithium compound. The lithium compound is not particularly limited and may be a hydroxide, oxide, carbonate, or the like of lithium. Compounds composed of elements other than Ni, Co, and Li may also be added. The mixing method is not particularly limited, as long as the respective compounds are sufficiently mixed to the extent that the Ni- and Co-containing oxides are not destroyed. For example, a general mixer can be used for mixing, such as a dry mixer or a mixing granulator such as a shaker mixer, a Lödige mixer, a Julia mixer, or a V-blender. The mixing ratio of the Ni- and Co-containing oxide to the lithium compound is not particularly limited, and it is preferable to adjust the molar ratio (Li / Me ratio) of the amount of lithium (Li) in the lithium compound to the total amount of metal elements Me other than Li (e.g., Ni, Co, and other elements) so that it is 0.95 to 1.25.

[0030] The mixture is then calcined to obtain a lithium composite oxide containing Ni and Co. The calcination temperature is, for example, in the range of 650°C or higher and 1100°C or lower. The calcination atmosphere may be an oxygen atmosphere, a dry air atmosphere that has been subjected to dehumidification and decarbonation treatment, or the like. The calcination furnace is not particularly limited, and may be an electric furnace, kiln, tubular furnace, pusher furnace, or the like. The obtained lithium composite oxide containing Ni and Co may be washed and dried as necessary.

[0031] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples.

[0032] Example 1: 50 g of hydroxide containing impurity elements (e.g., Zn, Mg, Ca), Ni, and Co was mixed with 400 L of pure water to prepare a slurry with a solid concentration of 0.13 g / L. Hydrazine monohydrate was added to the slurry. The amount of hydrazine monohydrate added was 1.25 in molar ratio relative to the total amount of Ni and Co in the slurry. The solution containing the slurry and hydrazine monohydrate was heated to 90°C and stirred for 30 minutes. After stirring, the slurry was subjected to magnetic separation, and a solid containing metallic Ni / Co particles was extracted from the slurry. The extracted solid was washed and dried, and the purity of Ni and Co in the dried solid was measured and found to be 98.6%.

[0033] Figure 2 shows the powder X-ray diffraction pattern of the metallic Ni / Co particles of Example 1. The peaks observed at 2θ = 44 to 45, 2θ = 51.1 to 52.1, and 2θ = 75.6 to 76.9 shown in Figure 2 are peaks attributed to metallic Ni and metallic Co.

[0034] Fig. 3 shows a scanning electron microscope (SEM) photograph of the metallic Ni / Co particles of Example 1. Looking at the SEM photograph of Fig. 3, the metallic Ni / Co particles obtained in Example 1 were particles with a particle size of about 1 µm.

[0035] Example 2 A solid material containing metallic Ni / Co particles was obtained in the same manner as in Example 1, except that 50 g of hydroxide containing impurity elements (Zn, Mg, Ca, etc.), Ni, and Co was mixed with 100 L of pure water to prepare a slurry with a solid content of 0.5 g / L. The purity of Ni and Co in the dried solid material was measured and found to be 98.8%.

[0036] Example 3 A solid material containing metallic Ni / Co particles was obtained in the same manner as in Example 1, except that 50 g of hydroxide containing impurity elements (Zn, Mg, Ca, etc.), Ni, and Co was mixed with 20 L of pure water to prepare a slurry with a solid content of 2.5 g / L. The purity of Ni and Co in the dried solid material was measured and found to be 98.6%.

[0037] According to Examples 1 to 3, it can be said that impurities were removed from hydroxides containing Ni and Co in a simple process, and high-purity metallic Ni / Co particles were obtained.

[0038] [Notes] (1) A method for producing metallic Ni / Co particles, comprising: a slurrying step of mixing a hydroxide containing impurity elements, Ni, and Co with water to prepare a slurry; a reduction step of mixing the slurry with a reducing agent to reduce the Ni and Co in the hydroxide and obtain metallic Ni / Co particles; an extraction step of magnetically separating the slurry after the reduction step to extract the metallic Ni / Co particles; and a washing and drying step of washing and drying the metallic Ni / Co particles obtained in the extraction step. (2) The method for producing metallic Ni / Co particles according to (1), wherein the reducing agent includes at least one of hydrazine and hydrazine monohydrate. (3) The method for producing metallic Ni / Co particles according to (1) or (2), wherein the solids concentration of the slurry is 0.1 g / L or more and 3.0 g / L or less. (4) A method for producing a positive electrode active material, comprising producing a Ni- and Co-containing lithium composite oxide using the metallic Ni / Co particles obtained by the method for producing metallic Ni / Co particles according to any one of (1) to (3) above.

Claims

1. A method for producing metallic Ni / Co particles, comprising: a slurry process for mixing a hydroxide containing impurity elements, Ni, and Co with water to prepare a slurry; a reduction process for mixing the slurry with a reducing agent to reduce the Ni and Co in the hydroxide and obtain metallic Ni / Co particles; an extraction process for magnetically separating the slurry after the reduction process to extract the metallic Ni / Co particles; and a washing and drying process for washing and drying the metallic Ni / Co particles obtained in the extraction process.

2. The method for producing metallic Ni / Co particles as described in claim 1, wherein the reducing agent includes at least one of hydrazine and hydrazine monohydrate.

3. A method for producing metallic Ni / Co particles as described in claim 1 or 2, wherein the solids concentration of the slurry is 0.1 g / L or more and 3.0 g / L or less.

4. A method for producing a positive electrode active material, comprising the steps of: preparing a Ni- and Co-containing lithium composite oxide using metallic Ni / Co particles obtained by the method for producing metallic Ni / Co particles according to claim 1 or 2.

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