Method for recovering lithium compound

Abstract

To provide a method for efficiently recovering a lithium compound.SOLUTION: A method for recovering a lithium compound includes stirring, in water, particles that are obtained by pulverizing a used positive electrode reaction vessel from which positive electrode material powder and positive electrode material powder precursor have been removed, then separating the particles from an aqueous solution, adding a flocculant to the obtained aqueous solution and stirring the aqueous solution, further separating aggregates from an aqueous solution, and removing water from the obtained aqueous solution to obtain powder with an average particle size of 500 μm or less. It is preferable that the average particle size of the powder is 300 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering lithium compounds from a used positive electrode reaction vessel of a lithium secondary battery. [Background technology]

[0002] The cathode material for lithium secondary batteries is manufactured in a reaction vessel (also called a reaction crucible). The raw material for the cathode, lithium hydroxide (LiOH·H2O), is used in excess when mixing with the precursor and firing to improve the high capacity performance of lithium secondary batteries. As a result, after manufacturing the cathode material, the excess lithium component must be removed through a water washing process. Furthermore, the corrosion reaction of excess lithium hydroxide, which occurs during the high-temperature manufacturing process of the cathode material, corrodes the reaction vessel used in manufacturing the cathode material, requiring replacement every 30 days or so. Conventionally, used reaction vessels have been discarded, but because the reaction vessels contain a high concentration of lithium hydroxide, the lithium compounds can be recovered and reused as positive electrode material, allowing for effective use of resources.

[0003] Therefore, Patent Document 1 discloses a method for recovering nickel, cobalt, manganese and lithium compounds from a used reaction vessel.

[0004] [Patent Document 1] Korean Publication No. 102408888 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional recovery methods require special equipment because they use highly corrosive hydrochloric acid. In addition, when lithium compounds are extracted from used reactor vessels using acids such as hydrochloric acid, the amount of metals recovered other than lithium (particularly aluminum) increases, which reduces the yield of lithium compounds in the subsequent purification process. There are methods for selectively recovering lithium using electrosorption, which uses a combination of a sorptive medium such as membrane capacitive deionization (MCDI) and an electric field, but this method only processes lithium ions that are attracted to the electrode, which has the problem of low lithium recovery.

[0006] An object of the present invention is to provide a method for efficiently recovering lithium compounds. [Means for solving the problem]

[0007] <1> The method for recovering a lithium compound of the present invention comprises crushing a used cathode reaction vessel from which the cathode material powder and cathode material powder precursor have been removed, stirring the resulting particles in water, separating the particles from the aqueous solution, adding a flocculant to the resulting aqueous solution and stirring, further separating the flocculates from the aqueous solution, and removing water from the resulting aqueous solution to obtain a powder having an average particle size of 500 μm or less. <2> The average particle size of the powder is 300 μm or less. <1> A method for recovering lithium compounds. <3> <1> or <2> A method for recovering lithium chloride by reacting the lithium compound obtained by the recovery method of 1) with hydrochloric acid. <4> <3> A method for recovering lithium carbonate, which comprises reacting the lithium chloride compound obtained by the recovery method of 1) with sodium carbonate. <5> <3> A method for recovering lithium carbonate by reacting the lithium chloride compound obtained by the recovery method of 1) with carbon dioxide. [Effects of the Invention]

[0008] According to the present invention described above, a method for efficiently recovering a lithium compound and a method for recovering lithium carbonate can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0009] The method for recovering a lithium compound of the present invention involves grinding a used cathode reaction vessel, from which the cathode material powder and cathode material powder precursor have been removed, and stirring the resulting particles in water, separating the particles from the aqueous solution, adding a flocculant to the resulting aqueous solution and stirring, further separating the flocculates from the aqueous solution, and removing water from the resulting aqueous solution (hereinafter also referred to as the drying step), thereby recovering a lithium compound in powder having an average particle size of 500 μm or less.

[0010] The lithium compound recovery method of the present invention involves crushing a used cathode reaction vessel, from which the cathode material powder and cathode material powder precursor have been removed, and agitating the resulting particles in water. The particles are then separated from the aqueous solution to obtain an aqueous solution. The resulting aqueous solution contains not only lithium compounds but also silicon compounds and aluminum compounds derived from the cathode reaction vessel. When a flocculant is added to the resulting aqueous solution and stirred, the charged fine particles in the aqueous solution react with the flocculant (which typically has a charge) to form flocculants. The flocculants are then separated from the aqueous solution, and the resulting aqueous solution (extract) is dried to obtain a powder of lithium compounds with an average particle size of 500 μm or less. The resulting lithium compounds are a mixture containing lithium compounds, which are then reacted with hydrochloric acid in the next step to obtain lithium chloride. When the extract is not processed into a powder but is instead subjected to the lithium chloride and lithium carbonate recovery process in a liquid state, these compounds are recovered from a dilute aqueous solution containing little active ingredient, resulting in a low yield of the final lithium carbonate. In this specification, the yield is increased by drying the powdered lithium compounds to form a powder and then reacting it with hydrochloric acid. However, when the average particle size of the powdered lithium compound is large, the reactivity with hydrochloric acid is not significantly improved, resulting in a low yield of lithium carbonate. Therefore, by forming the powder into an average particle size of 500 μm or less, the yield of lithium chloride obtained in the next step can be significantly improved. This also increases the amount of lithium carbonate recovered, which is easy to handle.

[0011] <Anode reaction vessel> The cathode reaction vessel used in the present invention is not particularly limited as long as it is a cathode reaction vessel used in the production of a cathode material for a lithium secondary battery. Generally, a ceramic vessel mainly composed of Al2O3-SiO2-MgO can be used.

[0012] <Pretreatment of used cathode reaction vessel> High concentrations of cathode material powder precursors containing nickel, cobalt, manganese, and lithium are deposited on the surface of used cathode reaction vessels, and these are collected and reused. The collected used cathode reaction vessels contain a large amount of lithium as a metal. It is sufficient to remove as much of the cathode material powder and cathode material powder precursor as possible from the used cathode reaction vessels, and a small amount may remain.

[0013] <Process for crushing used cathode reaction vessels> The process of crushing the used cathode reaction vessel is not particularly limited and can be appropriately selected depending on the purpose. The process of crushing the used cathode reaction vessel can include, for example, a primary crushing process for roughly crushing the used cathode reaction vessel and a secondary crushing process for crushing the used cathode reaction vessel to a particle size of a certain level or less through a screen (a metal plate with holes) or the like. In the primary pulverization step, the positive electrode reaction vessel is roughly pulverized in a crusher or a shredder to a size that can be fed into a fine pulverizer or an ultrafine pulverizer. In the secondary pulverization step, the coarsely pulverized material is preferably pulverized in a fine pulverizer or an ultrafine pulverizer to a size of 0.5 mm or less. Examples of the crusher used in the primary crushing step include an impact crusher, a compression crusher, a cutting / shearing crusher, etc. Examples of the compression crusher include a jaw crusher, a gyratory crusher, a cone crusher, and an impact crusher. Examples of the crusher used in the primary crushing step include a single-shaft crusher, a double-shaft crusher, a hammer crusher, and a mobile crusher.

[0014] Examples of the fine pulverizer used in the secondary pulverization step include a roller mill, a jet mill, a high-speed rotary pulverizer, a container-driven mill, etc. Examples of the high-speed rotary pulverizer include a hammer mill and a pin mill, and examples of the container-driven mill include a rotary mill, a vibration mill, a planetary mill, etc. The secondary pulverization step can be performed using an ultrafine pulverizer, such as a media agitation mill, or an attritor or a bead mill.

[0015] A screen (a metal plate with holes) can be used to remove particles from the crusher used in the secondary crushing process. Only materials smaller than the size of the holes in the screen are ejected. There are no particular restrictions on the size of the screen's openings, and they can be selected appropriately depending on the purpose. However, by selecting a screen of 0.5 mm or less, the particle size of the particles crushed from the cathode reaction vessel (hereafter referred to as crushed particles) can be controlled to 0.5 mm or less. This allows the crushed particles to be sorted into particles that pass through a 0.5 mm mesh. When the crushed particles are 0.5 mm or less, the extraction rate of lithium compounds in water improves.

[0016] <Process of stirring crushed particles in water> Water is added to the pulverized particles. The lithium compound is then extracted into the aqueous layer by heating and stirring. The weight of water used is preferably 3 times or more by mass, more preferably 5 to 20 times by mass, in consideration of the extraction efficiency of lithium. When the mass of water is 3 times or more by mass of the pulverized particles, the extraction efficiency of the lithium compound improves. Similarly, when the mass of water is 20 times or less by mass, the separation efficiency by filtration improves.

[0017] The extraction temperature is preferably 30°C or higher, more preferably 60°C or higher, and even more preferably 80°C or higher. The efficiency of extraction of lithium compounds into the aqueous layer improves in proportion to the increase in temperature. The extraction time is preferably 10 minutes or longer, more preferably 30 minutes or longer, and even more preferably 1 hour or longer. The longer the extraction time, the higher the extraction rate of lithium compounds. However, the conditions will vary depending on the extraction equipment, etc.

[0018] <First Separation> The pulverized particles are stirred in water, and then the particles and the aqueous solution are separated (first separation) to obtain an aqueous solution from which the pulverized particles have been removed. The separation method is not limited, and examples include filtration, centrifugal filtration, and centrifugation. Among these, filtration is preferred. In the separation, it is preferable to remove as many pulverized products as possible that are 0.2 mm or larger. This separates the extracted crucible fragments and increases the recovery rate of the lithium compound. Therefore, for example, a filter material such as a filter cloth can be used to remove crucible fragments that are 0.2 mm or larger. As the filter material, various known filter materials can be used. Filter media can be broadly classified by material, structure, shape, and mesh size (also known as filtration accuracy).

[0019] Filter media materials can be broadly divided into inorganic compounds and organic compounds. Examples of inorganic compounds include metals such as titanium; alloys such as stainless steel and Hastelloy; metal oxides (ceramics) such as alumina, zirconia, and titanium oxide; silicon dioxide (glass) such as glass fiber, activated carbon, and diatomaceous earth. Examples of organic compounds include polyethylene, polypropylene, polyester, polyolefin, polyethylene terephthalate, polytetrafluoroethylene, polyurethane, polyacrylonitrile, polyvinylidene fluoride, perfluoroalkoxyalkane, cellulose phenol resin, nylon, nylon 66, rayon, acetate, polyphenylene sulfide, polyethersulfone, polysulfone, cotton, wool, and silk.

[0020] The structure of the filter material can be mesh, powder (particles), fiber, etc. The mesh is made by processing the filter material into fibers and weaving them in a regular pattern. The gaps between the fibers are used to capture coarse particles. Examples of weaving methods include plain weave, twill weave, tatami weave, and twill tatami weave. Powder is a form of filter media processed into fine particles. The fine particles are packed together and the gaps between them are used to capture coarse particles. Fiber is a filter material that has been processed into fibers and irregularly intertwined. The gaps between the fibers are used to capture coarse particles. In addition to the above, other methods include a structure in which a void-free resin containing a solvent is made into a thin film and then the solvent is evaporated to create tiny voids in the resin (phase inversion method), and a structure in which a void-free resin is made into a thin film and then stretched to create tiny voids (stretching method).

[0021] Examples of the shape of the filter medium include a disc filter, a membrane filter, a cartridge filter, etc. Examples of the cartridge filter include a depth filter, a pleated filter, a depth-pleated filter, and a thread-wound filter. A depth filter is a filter that uses a thick filter material placed on the outside of the cartridge core to perform filtration. A pleated filter has a thin filter material folded into pleats around the outside of the cartridge core, and utilizes the large surface area of the filter material to perform filtration. Depth-pleated filters have a thick filter material folded into pleats around the outside of the cartridge core, and utilize the thickness and large surface area of the filter material to perform filtration. Depth filters have thick filter media with many voids that can capture coarse particles, making them suitable for filtering low-viscosity liquids with many coarse particles. Pleated filters have thin filter media with few voids that can capture coarse particles, making them suitable for filtering high-viscosity liquids with few coarse particles. Depth pleated filters combine the properties of both.

[0022] The mesh size (filtration accuracy) of the filter medium can be selected from the range of 1 nm to 1 mm depending on the size of the target object. In the first filtration, the mesh size is preferably about 0.1 mm to 0.5 mm.

[0023] The mesh size (filtration accuracy) of the filter material can be measured using the following method. If the filter media's mesh size is less than 50 μm, add ACFTD (natural particles with a particle size distribution of 50 μm or less, as specified in ISO 4402) as dust to the purified water, begin filtration at a flow rate of 10 liters / minute, and continue filtration until the manufacturer's specified exchange differential pressure is reached, at which point the filtrate is collected. The number of particles in the solution before and after filtration is counted using a particle counter (Beckman Coulter HIAC9703+, measurement range 0.5 to 600 μm), and the β value (filtration ratio) is calculated using the following formula (1). The particle size at which the β value is 1,000 or greater (meaning that 99.9% or more of the particles have been removed) is considered to be the filter media's mesh size (filtration accuracy).

[0024]

number

[0025] The filter medium preferably has a structure with a filtration gradient. A filtration gradient is a structure in which the mesh size of the filter medium gradually decreases. By adopting a structure in which the mesh size of the filter medium on the side that comes into contact with the solution before filtration is the largest and the mesh size of the filter medium on the side from which the solution after filtration is discharged is the smallest, coarse particles are removed in stages from large particles to small particles, which is preferable because coarse particles are efficiently removed and the life of the filter medium is extended.

[0026] The material of the filter medium used in the present invention is preferably, for example, polyethylene, polypropylene, polytetrafluoroethylene, or glass fiber. The filter material preferably has a structure of fiber, a structure obtained by a phase inversion method, or a structure obtained by a drawing method. The filter medium is preferably in the form of a depth filter or a depth pleat filter. The mesh size (filtration accuracy) of the filter medium is preferably 1 to 500 μm, more preferably 10 to 300 μm, and even more preferably 50 to 150 μm. By selecting the above filter media, coarse particles can be removed more efficiently.

[0027] Commercially available filter media include, for example, ROKI TECHNO's SLS series depth filters (material: polypropylene, structure: fiber, shape: depth, with filtration gradient), MPX series (material: polypropylene, structure: fiber, shape: pleated), CTY series (material: polytetrafluoroethylene, structure: structure that generates tiny voids by pulling, shape: membrane), SLP series (material: polypropylene, structure: fiber, shape: depth pleated), DIA-CS series (material: cotton, structure: fiber, shape: spool), SNN series (material: nylon, structure: fiber, shape: depth, with filtration gradient), and MPS series (material: polyester, structure: fiber, shape: pleated);

[0028] The temperature during filtration is preferably 5 to 80° C., more preferably 15 to 60° C., and even more preferably 20 to 45° C. The pressure during filtration is preferably 0.01 to 2.00 MPa, more preferably 0.02 to 1.00 MPa, and even more preferably 0.03 to 0.5 MPa.

[0029] <Addition of flocculant and second separation> The resulting aqueous solution contains not only lithium compounds but also silicon compounds and aluminum compounds originating from the positive electrode reaction vessel. When a flocculant is added to the resulting aqueous solution and stirred, the flocculant reacts with the charged fine particles in the aqueous solution to form flocculants. A second separation is then performed to separate the flocculants from the aqueous solution, yielding an aqueous solution containing lithium compounds. Particles of silicon compounds and aluminum compounds often have a negative charge and form flocculants upon reaction with the flocculant, so they can be removed by the separation. Most metal compounds other than lithium can be removed by the separation, allowing for efficient recovery of lithium compounds. The lithium concentration of the second aqueous solution after this second separation is preferably 50% or more by ICP analysis. A lithium concentration of 50% or more further improves the recovery rate of lithium carbonate.

[0030] Examples of the flocculant include cationic flocculants, anionic flocculants, nonionic flocculants, etc. Among these, cationic flocculants are preferred. Examples of cationic flocculants include inorganic flocculants and polymer flocculants. Examples of inorganic flocculants include aluminum sulfate, polyaluminum chloride (PAC), ferric chloride, polyferric chloride, polyferric sulfate, ferrous sulfate, calcium hydroxide, calcium carbonate, calcium acetate, sodium hydroxide, sodium bicarbonate, sodium chloride, sodium sulfate, sodium carbonate, ammonium sulfate, barium sulfate, barium carbonate, barium nitrate, and seawater. Among these, polyaluminum chloride is preferred in terms of flocculation efficiency. The polymer flocculant may be, for example, a cationic polymer flocculant. If a polymer flocculant is further added to the flocculants to which an inorganic flocculant has been added, larger flocculants are produced, which make them easier to separate in the subsequent filtration step. The polymer flocculant is preferably, for example, a cationic flocculant, but an anionic flocculant or a nonionic flocculant can be appropriately selected and used instead or in combination.

[0031] The amount of the flocculant used is preferably 0.01 to 5.0 parts by mass, more preferably 0.02 to 3.0 parts by mass, per 100 parts by mass of the aqueous solution. Using an appropriate amount improves the flocculation efficiency of silicon compounds and aluminum compounds, making separation easier.

[0032] The second separation is not limited as long as it can remove the aggregates. As with the first separation, the second separation can be performed by, for example, filtration, centrifugal filtration, or centrifugation. In the case of filtration, it is preferable to use a filter with a pore size of 5 μm or less. This can prevent cationic flocculants and metal compounds other than lithium from being mixed into the aqueous solution (filtrate). Filtration can be performed multiple times, for example, by using a filter with a smaller pore size or an even smaller pore size. The filter may be one of the filter media already described above. Preferred examples of the filter include membrane filters, such as a membrane filter, a cellulose mixed ester type membrane filter, a cellulose acetate type membrane filter, a PTFE type membrane filter, a hydrophilic PTFE type membrane filter, a polycarbonate type membrane filter, and a coated type filter.

[0033] The pore size of the filter is preferably 100 μm or less, more preferably 0.1 μm or less. It is also preferable to perform pretreatment before filtering with the filter. The pretreatment is performed to remove large aggregates using a filter medium with a large filtration size in order to prevent clogging of the filter. Pretreatment can be performed multiple times by preparing multiple filter mediums with large, medium, and small filtration sizes.

[0034] Examples of filter media used in pretreatment include ROKI TECHNO's SLS series depth filters (material: polypropylene, structure: fiber, shape: depth, with filtration gradient), MPX series (material: polypropylene, structure: fiber, shape: pleated), CTY series (material: polytetrafluoroethylene, structure: structure that generates tiny voids by pulling, shape: membrane), SLP series (material: polypropylene, structure: fiber, shape: depth pleated), DIA-CS series (material: cotton, structure: fiber, shape: spool), SNN series (material: nylon, structure: fiber, shape: depth, with filtration gradient), and MPS series (material: polyester, structure: fiber, shape: pleated).

[0035] <The process of drying the extract to obtain powder with an average particle size of 500 μm or less> The aqueous solution (extract) obtained in the second separation is dried to obtain a powder having an average particle size of 500 μm or less. The obtained powder is a lithium compound. The average particle size of the powder is preferably 0.1 to 500 μm, more preferably 0.1 to 300 μm, and even more preferably 0.1 to 200 μm. Adjusting the average particle size of the powder to an appropriate range improves the reactivity of the lithium compound with hydrochloric acid in the next step, thereby improving the yield of lithium chloride.The average particle size is determined by averaging the long axis length of approximately 10 powder particles from enlarged images (magnification 1,000 to 50,000 times) taken using a scanning electron microscope (SEM) or scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX).

[0036] By recovering the lithium compound in powder form, its reactivity with hydrochloric acid in the next step is improved, which reduces the amount of hydrochloric acid used, and thus reduces the amount of waste liquid containing hydrochloric acid generated.

[0037] The drying method is not limited as long as it can produce a powder with an average particle size of 500 μm or less. The drying method is preferably carried out using an apparatus that combines a means for atomizing the extract and a means for instantaneously removing moisture with high-temperature hot air, such as a spray dryer, flash dryer, or fluidized bed dryer. Examples of spray dryers include spray dryers. Examples of flash dryers include attritors, cage mills, Elofol mills, roller mills, and Roesche mills. Examples of fluidized bed dryers include micron dryers and spin flash dryers. Among these, spray dryers are preferred because they are easy to use to obtain fine powders.

[0038] The drying temperature is preferably 100 to 400° C., more preferably 180 to 300° C. The drying time is about 1 second to 30 minutes.

[0039] Using a spray dryer for drying allows for quick removal of moisture. Furthermore, powders with particle sizes of approximately 10 nm to 100 μm are obtained, improving reactivity with hydrochloric acid in the next step. The preferred drying conditions are an inlet temperature of the extract of approximately 200 to 350°C and an outlet temperature of approximately 100 to 200°C. The average particle size of the powder can be adjusted appropriately by changing the amount of feed to the spray dryer, the atomizer rotation speed, the inlet temperature, and the outlet temperature.

[0040] The moisture content of the resulting powder is preferably 5% by mass or less, more preferably 3% by mass or less. Reducing the moisture content improves the reactivity of the lithium compound with hydrochloric acid, and reduces the amount of unreacted material. The reaction is uniform, and the generation of unreacted material is reduced. Furthermore, if water remains during the lithium chloride production reaction, the amount of hydrochloric acid waste liquid generated increases, so it is preferable to remove water before the reaction with hydrochloric acid.

[0041] <Step of Reacting a Lithium Compound with Hydrochloric Acid to Obtain Lithium Chloride> The resulting lithium compound is a mixture containing the lithium compound. This lithium compound is reacted with hydrochloric acid to obtain lithium chloride. The mass of hydrochloric acid used is preferably about 100 to 500 parts by weight, more preferably 150 to 300 parts by weight, per 100 parts by weight of the lithium compound in the case of 35% by weight hydrochloric acid. Using an appropriate amount of hydrochloric acid can highly efficiently achieve both high reaction efficiency and suppression of the amount of hydrochloric acid-containing waste liquid produced.

[0042] <Step of isolating lithium carbonate from the obtained lithium chloride compound> The method for recovering lithium carbonate of the present invention is a method for obtaining lithium carbonate by reacting the lithium chloride compound obtained by the above-mentioned recovery method with sodium carbonate. When the resulting lithium chloride compound is added to an aqueous solution of sodium carbonate in an amount equal to or greater than the amount of hydrochloric acid added, crystals precipitate. These crystals are collected by filtration and the water is removed to obtain lithium carbonate.

[0043] Another method for recovering lithium carbonate according to the present invention is a method for obtaining lithium carbonate by reacting the lithium chloride compound obtained by the above-mentioned recovery method with carbon dioxide. When carbon dioxide is added to the obtained lithium chloride compound in an amount equivalent to or greater than the amount of hydrochloric acid added, crystals are precipitated. These crystals are collected by filtration, and lithium carbonate is obtained by removing water. The carbon dioxide is preferably introduced by bubbling it into the extract, and the reaction temperature is preferably 25°C to 100°C, more preferably 60°C to 100°C. If the temperature is below 25°C, the reaction proceeds slowly. [Example]

[0044] The present invention will be specifically described below with reference to examples. However, the present invention is not particularly limited to the examples. In the examples, "parts" means "parts by mass" and "%" means "% by mass."

[0045] Example 1 A used cathode reaction vessel (main component: Al2O3-SiO2-MgO) that had been used for 30 days in the production of nickel, cobalt, and manganese-based cathode materials was tapped, and then the surface was washed with water to remove the cathode material powder and cathode material powder precursor, thereby preparing a used cathode reaction vessel. The used cathode reaction vessel was subjected to primary pulverization using a jaw crusher to obtain a coarsely crushed product. The obtained coarsely crushed product was subjected to secondary pulverization using a Makino type pulverizer (model name: DD-2-3.7, manufactured by Makino Sangyo Co., Ltd.) at a rotation speed of 3500 rpm to obtain a pulverized product. The obtained pulverized product was passed through a stainless steel screen with a mesh size of 0.5 mm to obtain pulverized particles with a particle diameter of 0.5 mm or less. A reaction vessel equipped with a thermometer, a condenser, and a stirrer was charged with 400 parts of the obtained pulverized particles and 4,000 parts of distilled water, and the mixture was stirred for 6 hours at 100° C. The obtained slurry was filtered through a filter cloth (nylon 66, mesh size 108 μm) while being washed with 400 parts of distilled water, to obtain 4,350 parts of a first filtrate. Next, 17.4 parts of polyaluminum chloride (manufactured by Taiyo Sha) was added to the resulting filtrate while stirring, and the mixture was stirred for 1 hour. This solution was filtered under reduced pressure through a membrane filter (cellulose mixed ester type, pore size 5 μm, manufactured by ADVANTEC) to remove the cationic flocculant aggregates, thereby obtaining a second filtrate containing the lithium compound.

[0046] <Lithium concentration evaluation> The obtained second filtrate was subjected to ICP analysis (apparatus name: ICP-OES (inductively coupled plasma optical emission spectroscopy) manufactured by Agilent 720-ES). As a result of the analysis, the ratio of lithium atoms in the nonvolatile matter was found to be 92.7%. The content of lithium atoms in the second filtrate was evaluated in terms of recovery efficiency according to the following criteria.

[0047] <Lithium purity> In order to efficiently extract lithium compounds from the second filtrate, it is preferable that the lithium atom concentration is at least a certain level. From this perspective, the evaluation was made according to the following criteria. The ratio of lithium atoms is 90% or more. ◎Excellent The ratio of lithium atoms is between 70% and 90%. Good Lithium atom ratio is between 60% and 70% △ Practical range Lithium atom ratio less than 60% × Impossible to use

[0048] <Drying process> The second filtrate was spray-dried in a mini spray dryer ("B-290" manufactured by Nippon Buchi Co., Ltd.) in an atmosphere of 180°C, to obtain 5.8 g of powder having an average particle size of 50 µm.

[0049] <Lithium carbonate recovery process> 13.4 parts of 35% hydrochloric acid was added to 5.8 parts of the obtained powder and stirred for 30 minutes. Then, 13.6 parts of sodium carbonate dissolved in 40.9 parts of distilled water was added, and the resulting slurry was filtered under reduced pressure through a membrane filter (cellulose mixed ester type, pore size 5 μm, manufactured by ADVANTEC) to obtain 4.6 parts of lithium carbonate.

[0050] <Lithium carbonate recovery efficiency> The crushed particles in the positive electrode reaction vessel were extracted with 500 times the amount of water, and ICP analysis (instrument name: ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy, Agilent 720-ES)) measured 3636 ppm of Li. If this value is taken as 100%, the amount of lithium carbonate obtained from 400 parts of crushed particles is as follows: 400×3636÷1000000÷6.941÷2×73.891=7.74 parts That is, 4.6 parts of lithium carbonate obtained in Example 1 is 59% of the theoretical value. The lithium carbonate recovery efficiency was evaluated according to the following criteria. Lithium carbonate yield is 50% or more of the theoretical value. ◎Excellent Lithium carbonate yield is 30% or more but less than 50% of the theoretical value. Good Lithium carbonate yield is less than 30% of the theoretical value × Impossible to use

[0051] (Examples 2, 5 to 9) The same procedure as in Example 1 was carried out except that the recovery method in Example 1 was changed to the conditions shown in Table 1, and lithium carbonate was recovered by the methods of Examples 2 and 5 to 9, respectively.

[0052] Example 4 The same procedure as in Example 1 was carried out except that the drying step was carried out under the conditions shown below, and lithium carbonate was recovered by the method of Example 4. <Drying method> The second filtrate was dried at 200°C using a spin flash dryer (manufactured by Matsubo) to obtain a powder having an average particle size of 350 µm.

[0053] (Examples 3 and 10) The same procedures as in Example 1 were carried out except that the drying step was carried out under the conditions shown below, and lithium carbonate was recovered by the methods of Examples 3 and 10. <Drying method> The second filtrate was dried at 200° C. using a micron dryer (manufactured by Hosokawa Micron Corporation) to obtain a powder having an average particle size of 320 μm.

[0054] (Comparative Example 1) 9.8 parts of 35% hydrochloric acid was added to 3915 parts of the second filtrate and stirred for 30 minutes. Then, 9.9 parts of sodium carbonate dissolved in 29.8 parts of distilled water was added, and the resulting slurry was filtered under reduced pressure through a membrane filter (cellulose mixed ester type, pore size 5 μm, manufactured by ADVANTEC) to obtain 0.6 parts of lithium carbonate.

[0055] [Table 1] JPEG2025114218000003.jpg132162

[0056] As can be seen from the results in Table 1, in Examples 1 to 10, a method of instantly removing moisture with high-temperature hot air was used in the drying step, and therefore the drying time was short and powder with a particle size of 500 μm or less was obtained, and the subsequent extraction yield of lithium carbonate was also good.

Claims

1. A method for recovering a lithium compound, comprising: pulverizing a used cathode reaction vessel from which the cathode material powder and cathode material powder precursor have been removed, stirring the resulting particles in water, separating the particles from the aqueous solution, adding a flocculant to the resulting aqueous solution and stirring, further separating the flocculates from the aqueous solution, and removing water from the resulting aqueous solution to obtain a powder having an average particle size of 500 μm or less.

2. 2. The method for recovering a lithium compound according to claim 1, wherein the powder has an average particle size of 300 μm or less.

3. 3. A method for recovering lithium chloride, which is obtained by reacting the lithium compound obtained by the recovery method of claim 1 or 2 with hydrochloric acid.

4. A method for recovering lithium carbonate, which comprises reacting the lithium chloride compound obtained by the recovery method of claim 3 with sodium carbonate.

5. A method for recovering lithium carbonate, which comprises reacting the lithium chloride compound obtained by the recovery method of claim 3 with carbon dioxide.

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