Method for producing hydroxide containing nickel and cobalt

Abstract

[Problem] To provide a method which enables the production of a hydroxide that contains nickel (Ni) and cobalt (Co), the hydroxide being usable as a precursor of a positive electrode active material, even if the starting material contains various impurities. [Solution] This method for producing a hydroxide containing Ni and Co comprises: a step for washing an NiCo mixed hydroxide with water; a first alkali cleaning step for cleaning the water-washed NiCo mixed hydroxide using a basic aqueous solution that has a predetermined concentration and liquid temperature for a predetermined cleaning time; a step for leaching the cleaned NiCo mixed hydroxide at a predetermined temperature using an aqueous ammonia solution that has a predetermined ammonium carbonate and / or ammonium hydrogen carbonate concentration; a thermal decomposition precipitation step for heating the thus-obtained leachate containing Ni and Co at a predetermined temperature so as to precipitate the Ni and Co in the form of a hydroxide; and a second alkali cleaning step for cleaning the precipitated hydroxide using a basic aqueous solution that has a predetermined concentration and liquid temperature for a predetermined cleaning time.

Description

Method for producing hydroxide containing nickel and cobalt

[0001] The present invention relates to a method for producing hydroxides containing nickel and cobalt.

[0002] Lithium-ion secondary batteries, which are charged and discharged 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, so demand for them has been increasing in recent years as batteries for electronic devices such as mobile phones and laptops, as power sources for electric vehicles and the like, and storage batteries for smart grids. A lithium-ion secondary battery has a basic structure consisting of a positive electrode and a negative electrode facing each other with a separator in between, and an electrolyte made of an organic electrolytic solution filled between them.

[0003] The active material contained in the positive electrode is a metal oxide containing lithium and having a layered rock salt or spinel crystal structure. Specifically, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), ternary lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LiMn ２ O ４ These active materials can be produced by mixing lithium hydroxide particles with metal hydroxide particles as a precursor and firing the mixture.

[0004] The above metal hydroxide particles can be produced by crystallization by adjusting the pH of a solution containing the target metal salt. For example, in the production of a precursor of lithium nickel cobalt manganese oxide, a sodium hydroxide solution is added to an aqueous solution containing the raw materials nickel sulfate, cobalt sulfate, and manganese sulfate, and a mixed hydroxide containing nickel hydroxide, cobalt hydroxide, and manganese hydroxide is produced by the resulting neutralization reaction. However, in the above neutralization reaction of the nickel sulfate raw material, sodium sulfate (mirabilite), which 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 the total amount of sodium sulfate in wastewater is regulated in some regions, it has sometimes been necessary to install costly treatment facilities to meet wastewater standards, or to limit the production amount of nickel hydroxide to reduce the amount of sodium sulfate discharged. [Formula 1] NiSO ４ +2NaOH→Ni(OH) ２ +Na ２ SO ４

[0005] In order to avoid the above problems, methods for producing nickel hydroxide that do not by-produce sodium sulfate 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 resulting aqueous ammonia solution containing nickel and hydroxyl ions, and the aqueous ammonia solution is then distilled under atmospheric pressure or reduced pressure to precipitate and recover nickel hydroxide.

[0006] Japanese Patent Application Publication No. 10-324524

[0007] Although nickel hydroxide can be produced without producing sodium sulfate as a by-product by using the technology of Patent Document 1, the technology of Patent Document 1 uses metallic nickel as a precursor raw material, which is therefore not economically advantageous. 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 impurities leached together with the nickel through a refining process before electrowinning, resulting in the metallic nickel being finally obtained in the form of a plate or lump. Therefore, in order to efficiently leach metallic nickel with an aqueous ammonia solution, a step of processing the plate or lump metallic nickel into a powder is required.

[0008] Furthermore, some positive electrode active materials, such as the above-mentioned NCM and NCA, contain cobalt. In this case, there is no particular problem if the precursor of the positive electrode active material contains cobalt in addition to nickel; in fact, it is often preferable for the precursor to contain a certain amount of cobalt. However, although many of the raw materials used to produce the above-mentioned metallic nickel generally contain cobalt, the cobalt is separated and removed from the nickel by a refining method such as solvent extraction in a pre-processing step of electrowinning, resulting in unnecessary separation costs. As such, since the method of producing nickel hydroxide using refined metallic nickel as a raw material requires many processes that increase costs, it would be preferable from the perspective of production costs if an unrefined raw material containing a wide variety of impurities, such as that obtained by processing nickel oxide ore or scrap, could be used as an alternative raw material to produce a hydroxide containing nickel and cobalt that can be used as a precursor of the positive electrode active material of a lithium-ion secondary battery.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a method capable of producing a hydroxide containing nickel and cobalt that can be used as a precursor for a positive electrode active material of a lithium ion secondary battery, even if the raw material contains a greater variety of impurities than purified metallic nickel.

[0010] In order to achieve the above object, the method for producing a hydroxide containing nickel and cobalt according to the present invention comprises a water washing step of washing a particulate nickel-cobalt mixed hydroxide with water, a first alkali washing step of washing the washed nickel-cobalt mixed hydroxide with an aqueous sodium hydroxide solution having a sodium hydroxide concentration of 1.0 mol / L or more and 8.0 mol / L or less and a solution temperature of 10°C or more and 90°C or less for 0.50 hours or more and 2.0 hours or less, and a second alkali washing step of washing the nickel-cobalt mixed hydroxide washed in the first alkali washing step with an aqueous sodium hydroxide solution having an ammonium carbonate and / or ammonium hydrogencarbonate concentration of 0.50 mol / L or more and 4.1 mol / L or less. the leaching step of leaching the nickel and cobalt in a slurry state at a temperature of 0°C to 60°C using an ammonia-containing aqueous solution containing the ammonia water; the thermal decomposition precipitation step of heating the leachate containing nickel and cobalt obtained by the leaching step at a temperature of 60°C to 100°C for 0.50 to 2.0 hours to precipitate the nickel and cobalt as hydroxides; and the second alkali washing step of washing the precipitated hydroxides with an aqueous sodium hydroxide solution having a sodium hydroxide concentration of 1.0 mol / L to 8.0 mol / L and a liquid temperature of 10°C to 90°C for 0.50 to 2.0 hours.

[0011] According to the present invention, even if a raw material contains more impurities than purified metallic nickel, it is possible to produce a hydroxide containing nickel and cobalt that can be used as a precursor for a positive electrode active material of a lithium ion secondary battery.

[0012] FIG. 1 is a block flow diagram of an embodiment of a method for producing hydroxides containing nickel and cobalt according to the present invention.

[0013] An embodiment of a method for producing a nickel- and cobalt-containing hydroxide according to the present invention will be described below with reference to Figure 1. The hydroxide production method according to the embodiment of the present invention is a method for producing a hydroxide containing nickel and cobalt (hereinafter also referred to as a purified nickel-cobalt mixed hydroxide) that can be used as a precursor for the positive electrode active material of a lithium-ion secondary battery. The nickel- and cobalt-containing mixed hydroxide used as a raw material herein contains, in addition to the target metals nickel and cobalt, impurities such as calcium, magnesium, zinc, sulfur, silicon, manganese, iron, and aluminum. A nickel-cobalt mixed hydroxide containing such various impurities (hereinafter also simply referred to as a nickel-cobalt mixed hydroxide) may be referred to as a mixed hydroxide precipitate (MHP).

[0014] Specifically, the method for producing a nickel-cobalt-containing hydroxide according to an embodiment of the present invention includes a water-washing step in which a particulate nickel-cobalt mixed hydroxide is washed with water, preferably at room temperature, a first alkaline washing step in which the washed nickel-cobalt mixed hydroxide is washed for a predetermined time with an alkaline washing solution having a predetermined alkali concentration at a predetermined temperature, a leaching step in which the nickel-cobalt mixed hydroxide washed in the first alkaline washing step is leached with an ammonia-containing aqueous solution having a predetermined temperature and containing ammonium carbonate or ammonium bicarbonate at a predetermined concentration to leach the nickel and cobalt in the form of an ammine complex, a thermal decomposition precipitation step in which the nickel- and cobalt-containing leachate obtained by the leaching step is heated under predetermined conditions to thermally decompose the ammine complex into ammonia and carbonate and precipitate the nickel and cobalt as hydroxides, and a second alkaline washing step in which the precipitated hydroxides are washed for a predetermined time with an alkaline washing solution having a predetermined alkali concentration at a predetermined temperature. Each of these steps will be described in more detail below.

[0015] [Water-washing step] The water-washing step is a step in which mainly calcium and magnesium contained as impurities in the raw material nickel-cobalt mixed hydroxide in particulate form are removed using wash water. The temperature of the wash water used in this water-washing step is preferably 10°C or higher and 90°C or lower, and more preferably room temperature. There are no particular limitations on the specific washing method, but an example is a method in which the nickel-cobalt mixed hydroxide is added to wash water that has been placed in a container equipped with a stirrer in advance, and the mixture is held in the form of a slurry for approximately 0.50 to 1.0 hours while being stirred with the stirrer. After washing, the slurry is introduced into a solid-liquid separator such as a centrifuge or filter for solid-liquid separation, whereby a water-washed wet nickel-cobalt mixed hydroxide can be recovered.

[0016] [First alkaline washing step] The first alkaline washing step is a step in which impurities that are difficult to remove in the preceding water washing step, mainly zinc, sulfur, and silicon, are removed using an alkaline washing solution. The type of alkaline washing solution used in this first alkaline washing step is not particularly limited, and an aqueous caustic soda solution can be suitably used. When caustic soda is used, the sodium hydroxide concentration in the alkaline washing solution is preferably 1.0 mol / L or more and 8.0 mol / L or less. A specific embodiment of the first alkaline washing step is illustrated in Reference Example 3 described below.

[0017] If the sodium hydroxide concentration is less than 1.0 mol / L, the removal of zinc, sulfur, and silicon may be insufficient. In particular, zinc is contained in the mixed hydroxide of nickel and cobalt recovered as a precipitate in the subsequent thermal decomposition and precipitation step. Therefore, even if zinc is washed in the second alkaline washing step following the thermal decomposition and precipitation step, the alkaline washing solution will not have a chance to come into contact with the zinc inside the mixed hydroxide, making removal difficult. Therefore, it is desirable to sufficiently remove zinc in the first alkaline washing step.

[0018] Conversely, if the sodium hydroxide concentration exceeds 8.0 mol / L, zinc, sulfur, and silicon can be sufficiently removed, but nickel hydroxide and cobalt hydroxide may be oxidized to form oxides. Such conversion of hydroxides to oxides can lead to the disadvantage of making it difficult to leach nickel and cobalt in the subsequent leaching step. A sodium hydroxide concentration of 4.0 mol / L or more and 8.0 mol / L or less is more preferable because oxidation can be suppressed while removing zinc and sulfur, making it easier to avoid the above-mentioned disadvantages in the leaching step. On the other hand, if the sodium hydroxide concentration is 1.0 mol / L or more but less than 4.0 mol / L, the zinc removal rate will be lower than when the sodium hydroxide concentration is 4.0 mol / L or more, but oxidation tends to be suppressed, which is actually advantageous from the perspective of reducing nickel and cobalt loss. Therefore, it is preferable to appropriately select the concentration of sodium hydroxide depending on the use and purpose of the hydroxide containing nickel and cobalt (i.e., purified nickel-cobalt mixed hydroxide) as a precursor of the positive electrode active material of a lithium ion secondary battery.

[0019] The alkaline cleaning solution used in this first alkaline cleaning step preferably has a liquid temperature of 10° C. or higher and 90° C. or lower, more preferably 70° C. or higher and 90° C. If the liquid temperature is lower than 10° C., there is a risk that zinc, sulfur, and silicon will not be sufficiently removed, whereas if the liquid temperature exceeds 70° C., the removal rates of zinc, sulfur, and silicon can be maintained at a high level. However, if the liquid temperature exceeds 90° C., the removal rates of zinc, sulfur, and silicon will not be significantly improved, and instead, excessive loss of water due to evaporation will occur, which is disadvantageous in terms of cost.

[0020] The washing time for the first alkaline washing step is preferably 0.50 hours or more and 2.0 hours or less, more preferably 0.50 hours or more and 1.0 hour or less. By setting the washing time to 0.50 hours or more, the desired removal rates for zinc, sulfur, and silicon can be achieved. On the other hand, if the washing time exceeds 1.0 hour, the removal rates do not improve significantly. Therefore, setting the washing time to 1.0 hour or less allows for efficient and cost-effective removal of zinc, sulfur, and silicon. Furthermore, since particles of the nickel-cobalt mixed hydroxide washed in the previous water washing step often aggregate to form aggregates, if the washing time is less than 0.50 hours, it is difficult for the alkaline washing solution to reach the interior of these aggregates even when the alkaline washing is performed with stirring, resulting in the desired removal rate being unattainable. Conversely, if the washing time exceeds 2.0 hours, nickel hydroxide and cobalt hydroxide are easily oxidized, which may result in the difficulty of leaching the resulting nickel and cobalt oxides in the subsequent leaching step.

[0021] As mentioned above, zinc is easily included in the mixed hydroxide of nickel and cobalt produced in the thermal decomposition precipitation step, and in this case, zinc removal becomes difficult even when washing is performed in the second alkaline washing step that follows the thermal decomposition precipitation step. Therefore, it is desirable to determine the various washing conditions of this first alkaline washing step, i.e., sodium hydroxide concentration, washing temperature, and washing time, taking into consideration the zinc removal rate in the second alkaline washing step. Specifically, in this first alkaline washing step, it is preferable to remove zinc so that the zinc quality of the hydroxide containing nickel and cobalt obtained through the second alkaline washing step is the desired quality, and for example, a zinc removal rate of preferably 15% or more, more preferably 50% or more, and even more preferably about 80 to 90% is achieved.

[0022] That is, if the zinc and sulfur removal rates in the first alkaline washing step are 15% or more and 75% or more, respectively, the desired quality generally required for the hydroxide containing nickel and cobalt (i.e., purified nickel-cobalt mixed hydroxide) obtained as a precursor for the positive electrode active material of a lithium ion secondary battery through subsequent steps can be achieved. When a higher quality is required as a precursor for the positive electrode active material of a lithium ion secondary battery, it is desirable to adopt conditions in this first alkaline washing step that result in the zinc and sulfur removal rates of 50% or more and 90% or more, respectively.

[0023] Although there are no particular limitations on the specific washing method using an alkaline washing solution, one example is a method in which nickel-cobalt mixed hydroxide is added to an alkaline washing solution that has been placed in advance in a vessel equipped with a stirrer and a jacket, and the solution is stirred while controlling the temperature by introducing, for example, steam into the jacket, thereby maintaining the solution in a slurry state for a predetermined period of time. After alkaline washing, the slurry is introduced into a solid-liquid separator such as a centrifuge or filter for solid-liquid separation, whereby the alkali-washed wet nickel-cobalt mixed hydroxide can be recovered.

[0024] Since the washing wastewater discharged into the liquid phase in the solid-liquid separation after the alkaline washing contains impurities such as zinc, sulfur, and silicon, it is preferable to remove these impurities from the washing wastewater by an impurity removal method such as precipitation. This allows the washing wastewater to be reused as the alkaline washing solution. Here, precipitation is a technique for extracting solutes dissolved in a solution as precipitated particles, for example, by changing the washing wastewater from an unsaturated state to a supersaturated state, thereby promoting the generation and growth of crystal nuclei to obtain the precipitated particles.

[0025] [Leaching Step] The leaching step is a step in which the nickel-cobalt mixed hydroxide that has been alkali-washed in the previous first alkali washing step is leached with an ammonia-containing aqueous solution. Specifically, water is placed in a vessel equipped with a stirrer and a jacket, and ammonia water (NH ４ OH) and ammonium carbonate ((NH ４ ) ２ CO３ To prepare this ammonia-containing aqueous solution, ammonium bicarbonate (NH ) is added instead of or in addition to ammonium carbonate. ４ HCO ３ ) may also be used. Note that Figure 1 illustrates the case where only ammonium hydrogen carbonate is used. Next, the nickel-cobalt mixed hydroxide particles washed in the previous first alkali washing step are placed in a container containing the ammonia-containing aqueous solution prepared as described above, and the mixture is stirred and mixed with the stirrer to prepare a slurry having a uniform concentration.

[0026] In this state, the slurry temperature is maintained at a temperature of 0°C to 60°C, preferably 20°C to 50°C, to perform the leaching treatment. This allows nickel ions and cobalt ions to be leached from the nickel-cobalt mixed hydroxide particles, as shown in Reference Example 4 described below. On the other hand, manganese, iron, and aluminum, which are hardly leached in this leaching process, remain as leaching residue. After the leaching treatment, the slurry can be introduced into a solid-liquid separation device such as a centrifuge or filter to separate the leachate from the leaching residue. If the slurry temperature is below 0°C, the solubility of ammonium carbonate and ammonium bicarbonate in water decreases, resulting in supersaturation and precipitation, making successful leaching difficult. Conversely, if the slurry temperature exceeds 60°C, the ammonium carbonate and ammonium bicarbonate thermally decompose, making it difficult for both nickel and cobalt to maintain their ammine complex forms, also making successful leaching difficult. Furthermore, if the slurry temperature is set to 20°C or higher, the reaction rate can be increased, thereby increasing the production volume per unit time.

[0027] When ammonium carbonate is used to prepare the above-mentioned ammonia-containing aqueous solution, the ammonium carbonate concentration in the above-mentioned ammonia-containing aqueous solution is preferably in the range of 0.50 mol / L to 4.1 mol / L, more preferably in the range of 1.5 mol / L to 3.5 mol / L, and most preferably in the range of 2.0 mol / L to 3.0 mol / L. An ammonium carbonate concentration below 0.50 mol / L results in almost no leaching, while a concentration below 1.5 mol / L may result in a decrease in leaching rate. Conversely, an ammonium carbonate concentration above 3.5 mol / L results in almost no improvement in leaching rate and increases chemical costs, which is undesirable. Furthermore, an ammonium carbonate concentration above 4.1 mol / L may result in supersaturation and precipitation of ammonium carbonate, which may adversely affect the leaching process. The ammonium carbonate concentration can be measured by absorptiometry, ion chromatography, etc., and if the ammonium carbonate concentration is outside the above range, it can be adjusted by adjusting the amount of ammonium carbonate added.

[0028] In addition, even when ammonium hydrogen carbonate is used instead of ammonium carbonate in preparing the above-mentioned ammonia-containing aqueous solution, the concentration of ammonium hydrogen carbonate in the ammonia-containing aqueous solution is preferably in the range of 0.50 mol / L or more and 4.1 mol / L or less, more preferably in the range of 1.5 mol / L or more and 3.5 mol / L or less, and most preferably in the range of 2.0 mol / L or more and 3.0 mol / L or less, as described above.

[0029] Furthermore, the ammonia-containing aqueous solution used in the leaching treatment preferably has a free ammonia concentration in the range of 0.10 to 1.3 mol / L, which allows nickel and cobalt to be leached stably in the form of ammine complexes. If the free ammonia concentration is less than 0.10 mol / L, the formation of ammine complexes may become unstable, while if it exceeds 1.3 mol / L, it has almost no effect on the stable leaching in the form of the amine complexes, and 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 distillation.３ The form of 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.

[0030] In the method for producing a nickel- and cobalt-containing hydroxide according to an embodiment of the present invention, a mixed hydroxide of nickel and cobalt containing various impurities to be removed is used as a raw material. Therefore, in the leaching step, the mixed nickel-cobalt hydroxide that has been subjected to alkaline washing in the first alkaline washing step is subjected to leaching treatment with an ammonia-containing aqueous solution. However, the present invention is not limited to this. For example, as shown in Reference Example 5 described below, the leaching treatment can be performed on a mixed sulfide containing nickel and cobalt instead of the mixed nickel-cobalt hydroxide. In this case, the mixed sulfide containing nickel and cobalt can be produced by a high-pressure acid leaching method known as HPAL (High Pressure Acid Leach), in which sulfuric acid is added to nickel oxide ore under high temperature and pressure to perform acid leaching. Even when such a mixed sulfide is subjected to a leaching treatment, both nickel and cobalt form ammine complexes. Therefore, as shown in Reference Example 6 described later, by subjecting the mixed sulfide to a thermal decomposition precipitation step subsequent to the leaching treatment, nickel and cobalt can be precipitated as hydroxides and recovered as precipitates.

[0031] Specifically, water is first placed in a container equipped with a stirrer, and then ammonia water (NH ４ OH), and ammonium carbonate ((NH ４ ) ２ CO ３ Alternatively, instead of or in addition to ammonium carbonate, ammonium bicarbonate (NH ４ HCO ３) to prepare an ammonia-containing aqueous solution. Nickel-cobalt mixed sulfide particles are added to the container containing the ammonia-containing aqueous solution prepared in this manner, and the mixture is stirred and mixed with the stirrer to prepare a slurry having a uniform concentration. In this state, air or oxygen gas is blown into the slurry to create oxidizing conditions, thereby carrying out a leaching treatment. This allows nickel ions and cobalt ions to be leached from the nickel-cobalt mixed sulfide particles.

[0032] In the leaching treatment, it is preferable to maintain the temperature of the slurry at a temperature of 20° C. to 50° C., which can promote the leaching reaction. When preparing an ammonia-containing aqueous solution by adding ammonium carbonate in the leaching treatment, the ammonium carbonate concentration in the ammonia-containing aqueous 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.

[0033] [Pyrolysis and Precipitation Step] The pyrolysis and precipitation step involves heating the leachate produced in the previous leaching step, thereby thermally decomposing the nickel and cobalt ammine complexes, precipitating the nickel and cobalt as hydroxides, and recovering them 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. As shown in Reference Example 1 described below, this allows for the recovery of both nickel and cobalt as hydroxides with a recovery rate of 90% or more. That is, cobalt ammine complexes typically undergo pyrolysis to form divalent cobalt, but oxidizing this to trivalent cobalt promotes recovery as hydroxides. The ammonia and carbonic acid generated by pyrolysis in this pyrolysis and precipitation step are preferably recovered and reused as ammonia water containing ammonium carbonate or ammonium bicarbonate in the previous leaching step.

[0034] In this thermal decomposition precipitation step, it is preferable to heat the solution so that the temperature is 60° C. or higher and 100° C. or lower. If the solution temperature is lower than 60° C., it becomes difficult to decompose the nickel or cobalt ammine complexes, and the proportion of these ammine complexes that remain stable in their form increases, making it difficult to form precipitates. Note that, although the higher the temperature, the more efficiently these nickel or cobalt ammine complexes are decomposed, a solution temperature higher than 100° C. is undesirable from an economical point of view because of the increased facility costs and energy consumption costs.

[0035] Even if the liquid temperature is adjusted to within a temperature range of 60°C or higher and 100°C or lower in the thermal decomposition precipitation step as described above, if the holding time is too short, the thermal decomposition reaction will not proceed sufficiently, making it difficult to achieve the desired recovery rate. Therefore, in this thermal decomposition precipitation step, it is preferable to maintain the liquid temperature within a temperature range of 60°C or higher and 100°C or lower for 0.50 hours or higher and 2.0 hours or lower. This prevents the problem of large amounts of nickel and cobalt remaining in the form of ammine complexes in the treated liquid after the thermal decomposition precipitation step, and increases the recovery rate of the nickel-cobalt mixed hydroxide.

[0036] In the leaching process preceding the thermal decomposition precipitation process, manganese may be leached depending on the leaching conditions. In this case, the impurity manganese forms an ammine complex in the leachate, along with nickel and cobalt. Because the manganese ammine complex has a lower thermal decomposition temperature than the nickel and cobalt ammine complexes, manganese is more likely to undergo thermal decomposition and form a precipitate than nickel and cobalt. Therefore, within the temperature range of 60°C to 100°C, as described above, precipitates formed within less than 0.50 hours after reaching the lower limit of the temperature range tend to contain more manganese. Therefore, it is preferable to discard or recover the precipitate formed within this time period and reuse it as raw material for the leaching process. On the other hand, even if the retention time exceeds 2.0 hours, the amount of precipitated nickel-cobalt mixed hydroxide hardly increases.

[0037] [Second alkaline washing step] The second alkaline washing step is a step in which the nickel-cobalt mixed hydroxide recovered in the preceding thermal decomposition precipitation step is washed with an alkaline washing solution. This removes zinc, sulfur, and silicon that were not completely removed in the first alkaline washing step, as well as carbon derived from the ammonium carbonate and ammonium bicarbonate added in the leaching step, and makes it possible to produce a hydroxide containing high-purity nickel and cobalt with extremely few impurities that can be suitably used as a positive electrode active material for lithium-ion secondary batteries (i.e., a purified nickel-cobalt mixed hydroxide).

[0038] The type of alkaline cleaning solution used in this second alkaline cleaning step is not particularly limited, and as in the first alkaline cleaning step described above, an aqueous caustic soda solution can be suitably used. When caustic soda is used, the concentration of sodium hydroxide in the alkaline cleaning solution is preferably 1.0 mol / L or more and 8.0 mol / L or less, and in particular, the lower limit of the sodium hydroxide concentration is more preferably 2.0 mol / L or more. This allows the removal rate of carbon and sulfur impurities to be maintained at a high level, as shown in Reference Example 2 described below.

[0039] Furthermore, when zinc is present, as described above, it is present mainly in a form that is incorporated in the nickel-cobalt mixed hydroxide produced in the thermal decomposition and precipitation step, and therefore, although the removal rate is lower than in the first alkaline washing step, the zinc removal rate can be improved to some extent by setting the sodium hydroxide concentration higher. If the sodium hydroxide concentration is less than 1.0 mol / L, there is a risk that the removal of zinc, sulfur, and carbon will be insufficient, while if it exceeds 8.0 mol / L, there is the advantage that zinc and sulfur can be sufficiently removed, but there is a risk that nickel hydroxide and cobalt hydroxide will be oxidized to form oxides, in which case the recovery rate as hydroxides will decrease and the quality of the purified nickel-cobalt mixed hydroxide precursor will deteriorate.

[0040] In this second alkaline washing step, as in the first alkaline washing step, the temperature of the alkaline washing solution is preferably 10°C or higher and 90°C or lower, and more preferably 70°C or higher and 90°C or lower. If the solution temperature is lower than 10°C, there is a risk that the zinc and sulfur that were not completely removed in the first alkaline washing step and the carbon derived from ammonium carbonate and the like added in the leaching step will not be sufficiently removed, whereas a solution temperature higher than 70°C will enable the removal rates of these zinc, sulfur, and carbon to be maintained at a high level. However, if the solution temperature exceeds 90°C, the removal rates of these zinc, sulfur, and carbon will not be significantly improved and, instead, excessive loss of water due to evaporation will occur, which is disadvantageous in terms of cost.

[0041] Similarly to the first alkaline washing step, the washing time for the second alkaline washing step is preferably 0.50 hours to 2.0 hours, more preferably 0.75 hours to 1.0 hour. Because the nickel-cobalt mixed hydroxide particles produced in the thermal decomposition and precipitation step often aggregate to form aggregates, a washing time of less than 0.50 hours makes it difficult for the alkaline washing solution to reach the interior of the aggregates, even when alkaline washing is performed with stirring, resulting in difficulty in achieving the desired removal rate. Conversely, a washing time of more than 2.0 hours may lead to oxidation of nickel hydroxide and cobalt hydroxide, which may result in a decrease in the recovery rate of hydroxides.

[0042] Although there are no particular limitations on the specific washing method using an alkaline washing solution, an example is a method in which, as in the first alkaline washing step, the nickel-cobalt mixed hydroxide is added to an alkaline washing solution that has been placed in advance in a vessel equipped with a stirrer and a jacket, and the solution is stirred while controlling the temperature by introducing steam, for example, into the jacket, thereby maintaining the solution in a slurry state for a desired period of time. After alkaline washing, the slurry is introduced into a solid-liquid separator such as a centrifuge or a filter for solid-liquid separation, whereby the alkali-washed, wet nickel-cobalt mixed hydroxide can be recovered.

[0043] In the washing effluent discharged to the liquid phase side in the solid-liquid separation after the alkaline washing, the solubility of the carbon content in the washing effluent decreases as the liquid temperature decreases, so in this case too, by using a precipitation method similar to the first alkaline washing step described above, it is possible to precipitate the carbon content in the washing effluent as sodium carbonate. The washing effluent from which sodium carbonate has been removed in this way can be reused as an alkaline washing solution.

[0044] As described above, by employing the method for producing a hydroxide containing nickel and cobalt according to an embodiment of the present invention, it is possible to produce a high-purity hydroxide containing nickel and cobalt with extremely low impurities from a crude raw material nickel-cobalt mixed hydroxide, such as nickel-cobalt mixed hydroxide precipitate (MHP), without by-producing sodium sulfate. In particular, even if the crude raw material contains various impurities such as manganese, iron, and aluminum, these impurities can be easily separated and removed, making it possible to produce hydroxide at a lower cost than when expensive purified metallic nickel is used as a raw material.

[0045] Furthermore, in the method for producing a nickel- and cobalt-containing hydroxide according to an embodiment of the present invention, the raw material is washed in two stages using different washing solutions in a water washing step and a first alkaline washing step before being treated in the thermal decomposition precipitation step. Therefore, when MHP is used as the raw material, most of the impurities typically contained in the MHP, such as calcium, magnesium, zinc, sulfur, and silicon, can be removed. Therefore, the quality of the mixed hydroxide of nickel and cobalt obtained through the thermal decomposition precipitation step can be significantly improved compared to the raw material MHP. Next, the present invention will be described in more detail with reference to reference examples and examples, but the present invention is not limited in any way to the following reference examples and examples.

[0046] Reference Example 1 (Air Blow-in Test in Pyrolysis and Precipitation Step) Ammonium carbonate (NH ４ ) ２ CO ３An aqueous solution containing 28.82 g of nickel-cobalt mixed hydroxide was added to the resulting ammonium carbonate solution to prepare an ammonium carbonate solution with an ammonium carbonate concentration of 1.5 mol / L. 20 g of nickel-cobalt mixed hydroxide was added to the resulting ammonium carbonate solution to form a slurry, which was then stirred with a stirrer and maintained at a temperature of 20°C for 2.0 hours, thereby carrying out a leaching treatment.

[0047] After the above leaching treatment, the leaching residue was removed by solid-liquid separation through filtration. The resulting leachate was placed in a 500 mL separable flask and marked to confirm the liquid volume. Stirring was initiated while heating with a hot stirrer until the temperature reached 80°C or higher, while replenishing evaporated water with pure water. Once the temperature reached 80°C, air injection was initiated at a flow rate of 1.0 L / min, and thermal decomposition treatment was carried out under this condition for 6 hours. The resulting slurry containing the precipitate was filtered, and the nickel-cobalt mixed hydroxide of Sample 1 was recovered on the solid phase side. The resulting nickel-cobalt mixed hydroxide of Sample 1 was dried and then quantitatively analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to determine the recovery rates of nickel and cobalt.

[0048] For comparison, a precipitate was produced in the same manner as above, except that air was not blown in during the thermal decomposition treatment, and this was filtered in the same manner as above to recover the nickel-cobalt mixed hydroxide of Sample 2. The resulting nickel-cobalt mixed hydroxide of Sample 2 was dried and quantitatively analyzed in the same manner as above to determine the recovery rates of nickel and cobalt. The recovery rates of nickel and cobalt for Samples 1 and 2 are shown in Table 1 below.

[0049]

[0050] As can be seen from the results in Table 1 above, the recovery rate of cobalt in Sample 1 was significantly higher than that in Sample 2. This is thought to be because, by stirring while blowing air into the mixture during the thermal decomposition treatment, the divalent cobalt after the thermal decomposition of the ammine complex was efficiently oxidized to trivalent cobalt, thereby facilitating the recovery of cobalt as hydroxide.

[0051] Reference Example 2 (Alkali washing test in second alkaline washing step) (Experiment A1) 50 mL of an aqueous caustic soda solution with a sodium hydroxide concentration of 4.0 mol / L was placed in a beaker, and 5 g of the mixed hydroxide of nickel and cobalt recovered by the thermal decomposition treatment in Reference Example 1 was added to form a slurry, which was then kept at a liquid temperature of 80°C for 1.0 hour while stirring and mixing, thereby carrying out alkaline washing of the mixed hydroxide. After this alkaline washing, the slurry was subjected to solid-liquid separation by filtration, and the washing wastewater containing impurities was removed to obtain a hydroxide containing nickel and cobalt.

[0052] (Experiment A2) A mixed hydroxide of nickel and cobalt was treated in the same manner as in Experiment A1, except that 50 mL of an aqueous solution of caustic soda with a concentration of 6.0 mol / L was used instead of 4.0 mol / L of sodium hydroxide.

[0053] (Experiment A3) A mixed hydroxide of nickel and cobalt was treated in the same manner as in Experiment A1, except that 50 mL of an aqueous solution of caustic soda with a concentration of 8.0 mol / L was used instead of 4.0 mol / L of sodium hydroxide.

[0054] The alkaline washing conditions for Experiments A1 to A3, the removal rates of zinc, sulfur, and carbon by the alkaline washing, and the zinc, sulfur, and carbon contents in the mixed hydroxide after alkaline washing are shown in Table 2 below. The removal rates shown in Table 2 were determined from the mass balance of the zinc, sulfur, and carbon contents obtained by quantitatively analyzing the post-washing liquid (washing wastewater) and the post-washing mixed hydroxide (NiCo mixed hydroxide). For example, in the case of zinc, the zinc content L was calculated by multiplying the zinc concentration determined by quantitative analysis of the post-washing liquid by the volume of the post-washing liquid. Ｚｎ The zinc content S is calculated by multiplying the zinc content determined by quantitatively analyzing the washed mixed hydroxide (dry matter) by the dry matter amount of the mixed hydroxide. Ｚｎ and calculate the contents L Ｚｎ , S Ｚｎ The removal rate was calculated by substituting the above into the following formula 2. [Formula 2] Removal rate = L Ｚｎ / (L Ｚｎ +S Ｚｎ ) 100

[0055]

[0056] As can be seen from Table 2 above, by performing alkaline cleaning using a caustic soda solution with a sodium hydroxide concentration of 4.0 mol / L or more and 8.0 mol / L or less, it is possible to maintain a carbon and sulfur removal rate of 80% or more, and by increasing the sodium hydroxide concentration, it is possible to improve the zinc removal rate. The zinc removal rate was inferior to that of Reference Example 3 described below. This is thought to be because the zinc was present in a form enclosed within the mixed hydroxide of nickel and cobalt recovered in the thermal decomposition and precipitation step, making it difficult for the alkaline cleaning solution to come into contact with the zinc. Note that all of the mixed hydroxides in Experiments A1 to A3 had a quality suitable for use as positive electrode active materials in lithium-ion secondary batteries.

[0057] Reference Example 3 (Alkali Cleaning Test in First Alkali Cleaning Step) (Experiment B1) 400 g (dry weight) of MHP and 1.85 L of pure water were placed in a beaker as raw materials, and then a water-washing treatment was carried out by maintaining the slurry temperature at 20°C while stirring and mixing for 30 minutes. After the water-washing treatment, the washing liquid was separated and removed by filtration, and 14 g of the solid nickel-cobalt mixed hydroxide was added to a beaker containing 140 mL of a caustic soda solution having a sodium hydroxide concentration of 6.0 mol / L, and alkaline washing was carried out by maintaining the liquid temperature at 20°C while stirring and mixing for 2.0 hours. After this alkaline washing, the slurry was subjected to solid-liquid separation by filtration, and the washing wastewater containing impurities was removed to obtain a nickel-cobalt mixed hydroxide.

[0058] (Experiment B2) A nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B1, except that the liquid temperature during alkali washing was changed from 20°C to 80°C.

[0059] (Experiment B3) A nickel-cobalt mixed hydroxide was subjected to a water-washing treatment and an alkali-washing treatment in the same manner as in Experiment B1, except that 140 mL of an aqueous caustic soda solution having a sodium hydroxide concentration of 4.0 mol / L was used instead of 6.0 mol / L, the temperature during the alkali washing was changed to 80°C instead of 20°C, and the retention time for the alkali washing was changed to 1.0 hour instead of 2.0 hours.

[0060] (Experiment B4) A nickel-cobalt mixed hydroxide was subjected to a water-washing treatment and an alkali-washing treatment in the same manner as in Experiment B1, except that the liquid temperature during the alkali-washing was changed from 20°C to 80°C, and the retention time of the alkali-washing was changed from 2.0 hours to 1.0 hour.

[0061] (Experiment B5) A nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B4, except that 140 mL of an aqueous caustic soda solution having a concentration of 8.0 mol / L was used instead of 6.0 mol / L of sodium hydroxide.

[0062] (Experiment B6) The nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B3, except that the retention time for alkali washing was changed from 1.0 hour to 0.50 hour.

[0063] (Experiment B7) The nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B3, except that the retention time for alkali washing was changed from 1.0 hour to 2.0 hours.

[0064] (Experiment B8) The nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B4, except that the retention time for alkali washing was changed to 0.50 hour instead of 1.0 hour.

[0065] (Experiment B9) The nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B4, except that the retention time for alkali washing was changed from 1.0 hour to 2.0 hours.

[0066] (Experiment B10) A nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B5, except that the retention time for alkali washing was changed to 0.50 hour instead of 1.0 hour.

[0067] (Experiment B11) A nickel-cobalt mixed hydroxide was subjected to water washing treatment and alkali washing treatment in the same manner as in Experiment B5, except that the retention time for alkali washing was changed from 1.0 hour to 2.0 hours.

[0068] The alkaline washing conditions for Experiments B1 to B11, the respective removal rates of zinc and sulfur by the alkaline washing, and the contents of zinc, sulfur, and carbon in the mixed hydroxide (NiCo mixed hydroxide) after alkaline washing are shown in Table 3. The removal rates and contents in Table 3 were determined in the same manner as in Reference Example 2.

[0069]

[0070] As can be seen from Table 3 above, by using an aqueous caustic soda solution with a sodium hydroxide concentration of 4.0 mol / L or more and 8.0 mol / L or less, and performing alkaline washing under the conditions of a liquid temperature during washing of 20°C or more and 80°C or less and a washing time of 0.50 hours or more and 2.0 hours or less, it is possible to remove zinc at a removal rate of 15% or more and sulfur at a removal rate of 75% or more.

[0071] [Reference Example 4] (Ammonium carbonate leaching test in leaching process) (Experiment C1) Ammonium carbonate ((NH ４ ) ２ CO ３ An aqueous solution containing 28.82 g of nickel-cobalt mixed hydroxide (MHP) having the composition shown in Table 4 below was added to the resulting aqueous solution containing ammonia to prepare an aqueous solution containing ammonia with an ammonium carbonate concentration of 1.5 mol / L. 20 g of powdered nickel-cobalt mixed hydroxide (MHP) having the composition shown in Table 4 below was mixed with the resulting aqueous solution containing ammonia to prepare a slurry, which was stirred with a stirrer while maintaining the liquid temperature at 20°C for 2.0 hours to carry out a leaching treatment.

[0072]

[0073] After the leaching treatment, solid-liquid separation was performed by filtration, yielding a leaching residue with a dry mass of 10.8 g and 270 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 3. [Formula 3] 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

[0074] As a result, the leaching rate of nickel was 71.2% and the leaching rate of cobalt was 65.3%, and a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions was produced.

[0075] (Experiment C2) Ammonium carbonate ((NH ４ ) ２ CO ３ Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Experiment C1, except that an ammonia-containing aqueous solution with an ammonium carbonate concentration of 3.0 mol / L was prepared by changing the amount of added ammonia (NH3) from 28.82 g to 57.65 g, resulting in a leaching residue with a dry mass of 6.30 g and a leachate of 310 mL. The element concentrations of the resulting leachate residue and leachate were measured in the same manner as in Experiment C1, and the leaching rate of nickel was 90.3%, and the leaching rate of cobalt was 84.6%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

[0076] (Experiment C3) Ammonium carbonate ((NH ４ ) ２ CO ３ Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Experiment C1, except that an ammonia-containing aqueous solution with an ammonium carbonate concentration of 4.1 mol / L was prepared by changing the amount of added ammonia (NH3) from 28.82 g to 115.30 g, resulting in the production of a leaching residue with a dry mass of 5.53 g and a leachate of 355 mL. The element concentrations of the resulting leachate residue and leachate were measured in the same manner as in Experiment C1, and the nickel leaching rate was 94.4% and the cobalt leaching rate was 88.9%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions was produced.

[0077] (Experiment C4) Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Experiment C1, except that the liquid temperature during the leaching treatment was changed from 20° C. to 50° C., resulting in a leaching residue with a dry mass of 6.07 g and 203 mL of leachate. The element concentrations of the obtained leach residue and leachate were measured in the same manner as in Experiment C1, and the nickel leaching rate was found to be 73.9%, and the cobalt leaching rate was 73.6%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

[0078] (Experiment C5) Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Experiment C2, except that the liquid temperature during the leaching treatment was changed from 20° C. to 50° C., resulting in a leaching residue with a dry mass of 3.57 g and 235 mL of leachate. The element concentrations of the obtained leach residue and leachate were measured in the same manner as in Experiment C1, and the nickel leaching rate was 92.5%, and the cobalt leaching rate was 87.3%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

[0079] (Experiment C6) Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Experiment C3, except that the liquid temperature during the leaching treatment was changed from 20° C. to 50° C., resulting in a leaching residue with a dry mass of 5.05 g and 415 mL of leachate. The element concentrations of the obtained leach residue and leachate were measured in the same manner as in Experiment C1, and the nickel leaching rate was 95.2%, and the cobalt leaching rate was 89.2%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

[0080] (Experiment C7) 20 g of powdered nickel-cobalt mixed hydroxide (MHP) having the composition shown in Table 4 above was mixed with 25% ammonia water placed in a container to form a slurry, which was then stirred with a stirrer while maintaining the liquid temperature at 20°C for 2.0 hours to carry out a leaching treatment. Thereafter, solid-liquid separation was carried out in the same manner as in Experiment C1 to obtain 150 mL of leachate. The element concentrations of this leachate were measured in the same manner as in Experiment C1 to determine the leaching rate of each element.

[0081] As a result, the leaching rate of nickel was 14.6%, and the leaching rate of cobalt was 0.2%, which was insufficient compared to experiments C1 to C3, in which leaching treatment was carried out at the same temperature, and almost no cobalt ions were leached. In experiment C7, the leaching rate of each element was calculated using the following formula 4. [Formula 4] Leaching rate of element α = mass of element α in leaching solution / mass of element α in MHP × 100

[0082] (Experiment C8) The leaching treatment of MHP and the subsequent solid-liquid separation and concentration measurement were carried out in the same manner as in Experiment C7, except that the liquid temperature during the leaching treatment was changed from 20°C to 50°C. The nickel leaching rate was 17.5% and the cobalt leaching rate was 0.3%, which was insufficient for nickel ions to be leached compared to Experiments C4 to C6, in which the leaching treatment was carried out at the same temperature, and almost no cobalt ions were leached. The leaching rates were calculated in the same way as in Experiment C7. The measurement results of Experiments C1 to C8 above are summarized in Table 5 below.

[0083]

[0084] [Reference Example 5] (Oxygen Blow Leaching Test of NiCo Mixed Sulfide (MS)) (Experiment D1) Ammonium carbonate (NH ４ ) ２ CO ３ An aqueous solution containing 28.82 g of ammonium carbonate was added to the resulting ammonia-containing aqueous solution to prepare an ammonia-containing aqueous solution with an ammonium carbonate concentration of 1.5 mol / L. 18 g of powdered nickel-cobalt mixed sulfide (MS) having the composition shown in Table 6 below was mixed with the resulting ammonia-containing aqueous solution to prepare a slurry. While oxygen gas was blown into the slurry from an oxygen cylinder at a flow rate of 1 L / min, the slurry was stirred with a stirrer and held at a liquid temperature of 50°C for 2 hours, whereby a leaching treatment was carried out.

[0085]

[0086] After the leaching treatment, solid-liquid separation was performed by filtration, yielding a leaching residue with a dry mass of 15.2 g and 205 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 5. [Formula 5] 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

[0087] As a result, the leaching rate of nickel was 18.3% and the leaching rate of cobalt was 7.2%, and a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions was produced.

[0088] (Experiment D2) Ammonium carbonate ((NH ４ ) ２ CO ３ Leaching of MS and subsequent solid-liquid separation were carried out in the same manner as in Experiment D1, except that an ammonia-containing aqueous solution with an ammonium carbonate concentration of 3.0 mol / L was prepared by changing the amount of added ammonia (NH3) from 28.82 g to 57.65 g, resulting in a leaching residue with a dry mass of 9.80 g and a leachate of 238 mL. The element concentrations of the resulting leachate residue and leachate were measured in the same manner as in Experiment D1, and the nickel leaching rate was 44.7%, and the cobalt leaching rate was 24.5%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

[0089] (Experiment D3) Ammonium carbonate ((NH ４ ) ２ CO ３ Leaching of MS and subsequent solid-liquid separation were carried out in the same manner as in Experiment D1, except that the amount of ammonium carbonate added was changed from 28.82 g to 115.30 g, thereby preparing an ammonia-containing aqueous solution with an ammonium carbonate concentration of 4.1 mol / L. As a result, a leaching residue with a dry mass of 7.84 g and 200 mL of leachate were obtained. The element concentrations of the obtained leachate residue and leachate were measured in the same manner as in Experiment D1, and the leaching rate of nickel was 45.1%, and the leaching rate of cobalt was 39.4%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

[0090] (Experiment D4) Leaching of MS and subsequent solid-liquid separation were carried out in the same manner as in Experiment D2, except that the liquid temperature during the leaching treatment was changed from 50° C. to 20° C., resulting in a leaching residue with a dry mass of 12.6 g and 220 mL of leachate. The element concentrations of the obtained leach residue and leachate were measured in the same manner as in Experiment D1, and the nickel leaching rate was found to be 27.7%, and the cobalt leaching rate was found to be 21.6%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

[0091] (Experiment D5) Experiment D5 was carried out in the same manner as Experiment D1, except that ammonium carbonate was used in the leaching treatment in Experiment D1, but this was replaced with ammonium bicarbonate. As a result, it was confirmed that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions, almost equivalent to that in Experiment D1, could be obtained.

[0092] (Experiment D6) Leaching of MS and subsequent solid-liquid separation were carried out in the same manner as in Experiment D1, except that 200 mL of 25% aqueous ammonia was used as the leaching solution instead of the aqueous ammonia containing ammonium carbonate. 200 mL of leaching solution was obtained. The element concentrations of this leaching solution were measured in the same manner as in Experiment D1, and the leaching rates of each element were determined. As a result, the leaching rate of nickel was 14.6%, and the leaching rate of cobalt was 0.2%. Compared to Experiments D1 to D3, in which the leaching was carried out at the same temperature, the leaching of nickel ions was insufficient, and almost no cobalt ions were leached. In Experiment D6, the leaching rate of each element was calculated using the following formula 6. [Formula 6] Leaching rate of element α = mass of element α in leaching solution / mass of element α in MS × 100

[0093] (Experiment D7) MS leaching treatment and subsequent solid-liquid separation and concentration measurement were carried out in the same manner as in Experiment D6, except that the liquid temperature during the leaching treatment was changed from 50°C to 20°C. The nickel leaching rate was 14.6% and the cobalt leaching rate was 0.2%, which showed insufficient leaching of nickel ions and almost no leaching of cobalt ions compared to Experiment D4, in which the leaching treatment was carried out at the same temperature. The leaching rates were calculated in the same way as in Experiment D6. The measurement results of Experiments D1 to D7, excluding Experiment D5, are summarized in Table 7 below.

[0094]

[0095] Reference Example 6 (Pyrolysis and Precipitation Test of Leachate of NiCo Mixed Sulfide (MS)) A vessel was charged with 185 mL of pure water and 15 mL of ammonia water with a concentration of 25 mass %, and ammonium carbonate (NH ４ ) ２ CO ３ An aqueous solution containing 28.82 g of ammonium carbonate was added to prepare an aqueous ammonia-containing solution with an ammonium carbonate concentration of 1.5 mol / L. 18 g of powdered nickel-cobalt mixed sulfide (MS) having the composition shown in Table 6 above was mixed with the resulting aqueous ammonia-containing solution to prepare a slurry. The resulting slurry was stirred with a stirrer and held at a temperature of 20°C for 2 hours to carry out a leaching treatment.

[0096] After the leaching treatment, the leaching residue was removed by solid-liquid separation through filtration. The resulting leaching solution, consisting of an ammoniacal solution of nickel and cobalt, was placed in a 500 mL separable flask and marked to confirm the liquid volume. Stirring was initiated while heating with a hot stirrer until the temperature reached 80°C or higher, and evaporated water was replenished with purified water. Once the temperature reached 80°C, thermal decomposition treatment was carried out over 6 hours. The resulting slurry containing the precipitate was filtered, and the nickel and cobalt hydroxides were separated and recovered from the decomposition solution. The resulting hydroxides were dried and quantitatively analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The recovery rates of nickel and cobalt hydroxides were 70.8% and 85.8%, respectively.

[0097] Example 1 A raw material, nickel-cobalt mixed hydroxide (MHP), was treated according to the block flow diagram of Figure 1. Specifically, first, in the water-washing step, 400 g (dry weight) of MHP as the raw material and 1.85 L of pure water were placed in a beaker, and the water was washed by stirring and mixing while maintaining the water temperature at 20°C.

[0098] Next, in the first alkaline washing step, 381.4 g (dry weight) of MHP obtained by the above water washing treatment was placed in a beaker together with 1.55 L of an 8.0 mol / L aqueous sodium hydroxide solution, and alkaline washing was carried out by stirring and mixing while adjusting the temperature to 20° C. The washing time was 0.50 hours.

[0099] Next, in the leaching step, 183 g (dry weight) of MHP that had been alkaline washed in the first alkaline washing step was placed in a beaker together with 1.0 L of a 25% aqueous ammonia solution, 0.6 L of pure water, and 253 g of ammonium hydrogen carbonate, and the mixture was adjusted to a temperature of 20° C. and stirred to perform leaching. The ammonium hydrogen carbonate concentration at this time was 2.0 mol / L.

[0100] Next, in the thermal decomposition precipitation step, 1.6 L of the leachate obtained by the above leaching treatment was placed in a beaker, heated to a temperature of 80°C, and maintained at this temperature for 2.0 hours to generate a mixed hydroxide of nickel and cobalt. Stirring was continued while maintaining the heating temperature. Then, solid-liquid separation was performed to obtain a mixed hydroxide of nickel and cobalt in the solid phase and a liquid after solid-liquid separation in the liquid phase.

[0101] Finally, in the second alkaline washing step, 89 g (dry weight) of the mixed hydroxide of nickel and cobalt obtained in the thermal decomposition and precipitation step was placed in a beaker together with 0.83 L of an 8.0 mol / L aqueous sodium hydroxide solution, and alkaline washing was carried out by stirring and mixing while adjusting the temperature to 20°C. The washing time was 0.50 hours. The compositions (grades) of the MHP used as the raw material and the intermediate products produced in each of the above series of steps were quantitatively analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and are shown in Table 8 below.

[0102]

[0103] The results in Table 8 above demonstrate that by sequentially undergoing the water washing step, first alkali washing step, leaching step, thermal decomposition precipitation step, and second alkali washing step that satisfy the requirements of the present invention, it is possible to produce a hydroxide containing nickel and cobalt of a quality that can be used as a precursor for a positive electrode active material for a lithium ion battery, even if the raw material contains a relatively large amount of impurities in addition to the target metals nickel and cobalt.

[0104] [Example 2] The same procedure as in Example 1 was carried out except that ammonium bicarbonate was used in the leaching step instead of ammonium carbonate. As a result, it was confirmed that the mixed hydroxide of nickel and cobalt obtained through the second alkali washing step had a quality almost equivalent to that shown in Table 8 above.

[0105] As described above, even when ammonium carbonate is used instead of ammonium bicarbonate, by sequentially carrying out the water washing step, first alkali washing step, leaching step, thermal decomposition precipitation step, and second alkali washing step that satisfy the requirements of the present invention, it is possible to produce a hydroxide containing nickel and cobalt that can be used as a precursor of a positive electrode active material for a lithium ion battery, even if the raw material contains a relatively large amount of impurities in addition to the target metals nickel and cobalt.

Claims

1. A washing step of washing a particulate nickel-cobalt mixed hydroxide with water; a first alkali washing step of washing the washed nickel-cobalt mixed hydroxide with an aqueous sodium hydroxide solution having a sodium hydroxide concentration of 1.0 mol / L to 8.0 mol / L and a liquid temperature of 10°C to 90°C for 0.50 hours to 2.0 hours; a leaching step of leaching the nickel-cobalt mixed hydroxide washed in the first alkali washing step in a slurry state at a temperature of 0°C to 60°C using an ammonia-containing aqueous solution containing ammonium carbonate and / or ammonium hydrogen carbonate in an aqueous ammonia solution having a concentration of 0.50 mol / L to 4.1 mol / L; and a thermal decomposition precipitation step of heating the leachate containing nickel and cobalt obtained by the leaching treatment at a temperature of 60°C to 100°C for 0.50 hours to 2.0 hours to precipitate the nickel and cobalt as hydroxides. and a second alkali washing step of washing the precipitated hydroxide with an aqueous sodium hydroxide solution having a sodium hydroxide concentration of 1.0 mol / L or more and 8.0 mol / L or less and a liquid temperature of 10°C or more and 90°C or less for 0.50 hours or more and 2.0 hours or less.

2. The method for producing hydroxides containing nickel and cobalt according to claim 1, wherein air is blown into the leachate in the thermal decomposition and precipitation step.

3. A method for producing a hydroxide containing nickel and cobalt as described in claim 1 or 2, wherein the sodium hydroxide concentration of the aqueous sodium hydroxide solution used in the first alkaline washing step and / or the second alkaline washing step is 4.0 mol / L or more and 8.0 mol / L or less and the liquid temperature is 70°C or more and 90°C or less.

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