Method for Recovering Lithium and Method for Producing Lithium Carbonate

Abstract

A method for recovering lithium, wherein after obtaining a molten metal that contains a valuable metal and a molten slag that contains at least aluminum and lithium by melting a lithium ion secondary battery to be discarded, lithium is recovered from the slag that contains at least aluminum and lithium, said slag having been separated from the molten metal that contains a valuable metal. With respect to this method for recovering lithium, the melting conditions of the lithium ion secondary battery are adjusted so that the mass ratio of aluminum to lithium contained in the slag, namely the value of aluminum / lithium is 6 or less; a leachate, into which lithium contained in the slag has leached, is obtained by bringing the slag and an aqueous liquid into contact with each other; and a purified solution, in which lithium is dissolved, is obtained by means of solid-liquid separation by bringing the leachate and a basic substance into contact with each other, thereby having unwanted metals contained in the leachate precipitate in the form of a poorly soluble substance.

Description

Technical Field

[0001] The present invention relates to a method for recovering lithium and a method for producing lithium carbonate.

Background Art

[0002] Lithium-ion secondary batteries are mounted on relatively small devices such as smartphones, notebook computers, electric tools, and radio repeaters, as well as large devices such as hybrid vehicles, electric vehicles, household storage batteries, solar power storage facilities, and emergency storage batteries.

[0003] A lithium-ion secondary battery has a structure in which a metal can body made of aluminum, iron, stainless steel, etc., or a laminate film made of polypropylene, aluminum foil, etc. is used as an exterior material, and a copper foil is used as a negative electrode current collector inside, and a negative electrode active material such as graphite is fixed on the surface. A negative electrode material, a positive electrode material in which a positive electrode active material such as lithium nickelate or lithium cobaltate is fixed on a positive electrode current collector made of aluminum foil, and a separator made of a porous resin film of polypropylene, etc. are enclosed together, and an organic solvent containing a lithium salt electrolyte is sealed as an electrolytic solution.

[0004] The performance of the lithium-ion secondary battery mounted on the above equipment deteriorates due to repeated charging and discharging or overcharging, and it is disposed of as a waste lithium-ion secondary battery. Even in equipment where the deterioration of the lithium-ion secondary battery has not been confirmed, it may be disposed of due to replacement by the user. In addition, in the manufacturing process of lithium-ion secondary batteries, they may be discarded as defective products before being used due to defects in the process.

[0005] These waste lithium-ion secondary batteries contain valuable components such as nickel, cobalt, copper, and lithium, and it has been studied to recover and reuse the valuable components as a measure for effective utilization of resources and environmental pollution control.

[0006] Generally, when efficiently recovering valuable components from materials, members made of metal, or devices composed of multiple structures, a dry process of charging into a heating furnace or the like and roasting or melting at a high temperature is used.

[0007] Conventionally, most of the lithium recovery from lithium-ion secondary batteries has been limited to the recovery from crushed powders of roasted lithium-ion secondary batteries (Patent Documents 1 and 2). In Patent Document 1, as a means for recovering lithium from roasted lithium-ion secondary battery scraps, attempts have been made to recover it by leaching and neutral separation. In Patent Document 2, lithium recovery is performed through a number of processes such as multi-stage extraction of lithium from roasted lithium-ion secondary battery scraps using a solvent and an extractant, and separation and removal of each impurity. On the other hand, Patent Document 3 describes recovering lithium from slag obtained by a dry melting process for waste lithium-ion secondary batteries. In the dry melting process, the lithium-ion secondary battery is heated at a high temperature, for example, at 1100 °C or higher together with a flux (fluxing agent), and the waste lithium-ion secondary battery is separated into a metal containing valuable metals such as cobalt, nickel, and copper, and slag to be disposed of.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0009] In the method described in Patent Document 1, a large amount of chemicals are required to melt nickel, cobalt, and copper in the roasted lithium-ion secondary battery scrap. In addition, since nickel, cobalt, and copper, which are valuable metals, are incorporated into the neutralization residue, the labor and loss for redissolving and separating and recovering them increase. The complicated process described in Patent Document 2 not only reduces the recovery efficiency of lithium, but also has problems such as the chemicals, solvents, etc. used generate a large amount of waste liquid and waste, so that the cost and labor for reducing environmental impact are high. In addition, the quality of the obtained lithium compound is deteriorated due to the influence of the chemicals used, so it is difficult to say that it is an efficient method. Using the slag generated in the dry melting process as in the method described in Patent Document 3 is advantageous in that the slag with poor economic value from which nickel, cobalt, and copper have been removed can be effectively utilized. However, the inventor has found that the lithium recovery rate is not sufficient by simply using a leaching process in which the slag is brought into contact with an aqueous liquid as in Patent Document 3. Therefore, an object of the present invention is to solve the problems not solved by the above prior art.

[0010] The inventor has intensively studied a technique for increasing the recovery efficiency of lithium from slag obtained by subjecting a lithium-ion secondary battery to be disposed of to a melting process. As a result, it has been found that the lithium recovery rate improves dramatically when the mass ratio of aluminum to lithium in the slag is below a specific value.

[0011] The present invention is based on the above findings, and after melting a lithium-ion secondary battery to be disposed of to obtain a molten metal containing valuable metals and a molten slag containing at least aluminum and lithium, lithium is recovered from the slag containing at least aluminum and lithium separated from the molten metal containing the valuable metals, and the melting conditions of the lithium-ion secondary battery are adjusted so that the value of aluminum / lithium, which is the mass ratio of aluminum to lithium contained in the slag, is 6 or less. A lithium leaching step is included, in which the slag and an aqueous liquid are brought into contact with each other to obtain a leachate in which lithium contained in the slag has leached out. A method for recovering lithium is provided, which includes a purification step of bringing the leachate into contact with a basic substance to precipitate unnecessary metals contained in the leachate in the form of hardly soluble substances, and obtaining a purified liquid in which lithium is dissolved by solid-liquid separation.

[0012] The present invention also relates to a method for producing lithium carbonate from slag containing at least aluminum and lithium, which is separated from molten metal containing valuable metals, after melting a lithium ion secondary battery to be disposed of to obtain the molten metal containing valuable metals and the molten slag containing at least aluminum and lithium, and adjusting the melting conditions of the lithium ion secondary battery so that the value of aluminum / lithium, which is the mass ratio of aluminum to lithium contained in the slag, is 6 or less, bringing the slag into contact with an aqueous liquid to obtain a leachate in which lithium contained in the slag has leached out, bringing the leachate into contact with a basic substance to precipitate unnecessary metals contained in the leachate in the form of hardly soluble substances, and obtaining a purified liquid in which lithium is dissolved by solid-liquid separation, A method for producing lithium carbonate is provided, in which the purified liquid in which lithium is dissolved is brought into contact with a carbonate or carbon dioxide gas to precipitate lithium carbonate in the liquid.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the method for recovering lithium and the method for producing lithium carbonate according to the present invention will be described based on their preferred embodiments.

[0014] In the present invention, a slag generated when a lithium ion secondary battery to be disposed of is melted and valuable metals are recovered is used as a raw material.

[0015] Here, the lithium-ion secondary battery to be disposed of refers to a used lithium-ion secondary battery or an object with a concept that includes waste materials in the manufacturing process of a lithium-ion secondary battery. Examples of waste materials in the manufacturing process of a lithium-ion secondary battery include defective products generated in the manufacturing process of the positive electrode material and the like that constitute the lithium-ion secondary battery, residues inside the manufacturing process, generated chips, and the like. For used lithium-ion secondary batteries and waste materials in the manufacturing process of lithium-ion secondary batteries that contain electrolyte inside, direct treatment is dangerous as there is a risk of explosion, and although the specific method is not particularly limited, for example, after discharging, the battery needs to be physically perforated with a needle-like blade tip to remove the electrolyte, or the used lithium-ion secondary battery needs to be heated as it is to burn the electrolyte for harmless treatment. Examples of the melting process for generating slag include the following processes. Specifically, the lithium-ion secondary battery to be treated is melted and separated at a high temperature in a reducing atmosphere. The lithium-ion secondary battery is put into a melting furnace and melted at a temperature of about 1100°C to 1500°C, for example, in the presence of at least carbon or carbon monoxide. Through such a dry melting treatment based on reduction roasting, molten metal containing valuable metals and molten slag containing at least aluminum and lithium are generated. Valuable metals such as copper, nickel, and cobalt contained in the used lithium-ion battery are distributed into the molten metal (metal). On the other hand, lithium and aluminum contained in the used lithium-ion battery are basically distributed into the melt of the slag, which is an oxide. The molten metal and the slag melt in the molten state can be separated by the difference in specific gravity. The heavier metal with a higher specific gravity sinks to the lower layer, and the lighter slag with a lower specific gravity is naturally separated to the upper layer. In this way, the molten metal and the slag melt obtained from the melt can be separated, and by cooling each of them, valuable metals (crude metal) mainly composed of nickel, cobalt, and copper, and slag containing impurity elements such as lithium, aluminum, manganese, and phosphorus are obtained. In the melting treatment, it is preferable to adjust the degree of oxidation-reduction. To adjust the degree of oxidation-reduction, it is possible to use, for example, an increase or decrease in the amount of carbon, a gas containing oxygen such as air, pure oxygen, or oxygen-enriched gas. In this specification, basically, the slag in a molten state is referred to as "molten" or "melt". When simply referred to as "slag" without these words, it refers to the solid slag after separation from the metal, unless otherwise specified.

[0016] In the present invention, the value of aluminum / lithium, which is the mass ratio of aluminum to lithium contained in the slag, is 6 or less, preferably 5.0 or less, more preferably 4.0 or less, and particularly preferably 3.5 or less. The value of aluminum / lithium, which is the mass ratio of aluminum to lithium contained in the slag, is preferably 0.5 or more, particularly preferably 1.0 or more, in terms of the availability of the slag and the separation of aluminum. The value of aluminum / lithium contained in the slag can be determined by ICP emission spectrometry, fluorescent X-ray analysis, etc., and specifically can be determined by the method described in the examples below.

[0017] In order to make the value of aluminum / lithium contained in the slag within the above range, the following methods (1) to (3) for controlling the amount of aluminum present in the melting process can be mentioned. Particularly, it is preferable to perform (1), more preferably to perform (1) and (2), and most preferably to perform all of (1) to (3).

[0018] The method of (1) is to separate at least part of the aluminum from the lithium-ion secondary battery before the melting process by selectively removing aluminum by melting or selectively removing aluminum by crushing and separation. Specifically, it is to perform separation of at least part of the aluminum from the scrap of the lithium-ion secondary battery to be melted before the melting process by selectively removing aluminum by melting or selectively removing aluminum by crushing and separation. The exterior materials of lithium-ion secondary batteries are often made of metallic aluminum films, aluminum cans, iron cans, or stainless steel cans. In particular, when preferentially removing aluminum from lithium-ion secondary batteries using aluminum films or aluminum cans, it is preferable to perform a method of selectively melting and removing the aluminum film or aluminum can as a pretreatment for the melting process that generates slag. The pretreatment may be performed simultaneously with the detoxification treatment described above or may be performed later. When separating the aluminum foil coated with the positive electrode active material from a lithium-ion secondary battery containing the aluminum foil coated with the positive electrode active material or waste materials (defective products generated in the manufacturing process of the positive electrode material, etc., residues inside the manufacturing process, generated chips, etc.) in the manufacturing process of the lithium-ion secondary battery, it is preferable to perform a method of removing aluminum by crushing and separation. Also, for lithium-ion secondary batteries using aluminum films or aluminum cans that have not undergone aluminum melting and removal, aluminum can also be selectively removed by crushing and separation. Note that a combination of melting and removal and removal by crushing and separation may be used. As a process for selectively melting and removing aluminum, for example, before the melting treatment described above, a method of heating the lithium-ion secondary battery to be disposed of at a predetermined temperature exceeding the melting point of aluminum to selectively melt and remove aluminum can be mentioned. In order to be used for selective melting and removal of aluminum, the heating temperature is preferably 660°C or higher and less than 1100°C, and more preferably 700°C or higher and 800°C or lower. The atmosphere for selective melting and removal of aluminum is not particularly limited, but a low-oxygen atmosphere is preferable from the viewpoint of preventing oxidation of aluminum, and high-temperature exhaust gas from an incinerator or the like can also be used. By heating at such a temperature before roasting at a high temperature of 1100°C or higher described above, aluminum can be selectively melted. Selective melting and removal of aluminum may be performed in the same heat treatment furnace as the above melting treatment or may be performed in a different furnace. The melted aluminum is not particularly limited in terms of specific method, but for example, after cooling, it can be removed from the lithium-ion secondary battery to be disposed of by a method of selectively manually removing only the melted and solidified aluminum from the lithium-ion secondary battery to be disposed of.

[0019] On the one hand, crushing is carried out to break the lithium-ion secondary battery or the iron outer can of the lithium-ion secondary battery from which the aluminum film or aluminum can has been melted and removed, or the aluminum film (positive electrode current collector) or aluminum can (outer can) that has not been subjected to melting and removal in advance, and to selectively separate the aluminum outer can that has not been removed due to reasons such as not having been subjected to melting and removal from the waste materials (defective products generated in the manufacturing process of the positive electrode material, etc., residues inside the manufacturing process, generated scraps, etc.) in the manufacturing process of the lithium-ion secondary battery or the lithium-ion secondary battery. Also, it is carried out to selectively separate the aluminum foil from the lithium-ion secondary battery containing the aluminum foil coated with the positive electrode active material or the waste materials in the manufacturing process of the lithium-ion secondary battery.

[0020] For crushing, an impact type crusher that can apply impact while cutting the lithium-ion secondary battery scrap to be disposed of can be used, such as a sample mill, hammer mill, cutter mill, pin mill, wing mill, tornado mill, hammer crusher, etc. After crushing the lithium-ion secondary battery scrap to be disposed of, the lithium-ion secondary battery scrap is sieved using a sieve with a predetermined mesh size. As a result, on the sieve, for example, aluminum foil, aluminum can, and copper foil remain, and below the sieve, a powdered lithium-ion secondary battery scrap with aluminum removed to a certain extent can be obtained. For efficient aluminum removal, it is preferable to use a sieve with a mesh size of 1 mm to 10 mm, and more preferably a sieve with a mesh size of 2 mm to 5 mm. Also, when removing the aluminum film or aluminum can from above the sieve, only the aluminum film or aluminum can can be selectively removed by a pneumatic separator using the specific gravity difference or an electromagnetic induction separator.

[0021] The method of (2) is to use a furnace material that does not contain aluminum in the part that contacts the molten slag in the furnace used in the melting process, and to perform the melting process. For example, in the melting process of generating slag, a melting method is performed using a melting furnace that uses a furnace material that does not contain aluminum. Alumina is generally a refractory material widely used in melting furnaces, but it is preferable to perform the above-mentioned melting using a melting furnace or furnace material that does not contain it. Examples of furnace materials that do not contain aluminum include furnace materials that constitute the furnace bottom and furnace wall parts that come into contact with the melt. On the other hand, alumina can be used limited to parts that do not come into contact with the melt. For example, it can be used in the gas zone, furnace lid, etc. Examples of the material of the furnace material that constitutes the furnace bottom and furnace wall parts include magnesia, magnesia carbon, magnesia chrome, etc.

[0022] When adding a flux that promotes the generation of slag in the melting process, as the flux used in the melting process, a flux is added in which the content of the aluminum-containing component is such that the aluminum / lithium value of the slag does not exceed 6 based on the aluminum and lithium contents in the raw material. In the melting process, it can be carried out by charging a flux that promotes the generation of slag together with the melt. As such a flux, it is preferable to use one that does not contain aluminum. For example, calcium oxide, magnesium oxide, silicon oxide, etc. can be mentioned. In addition, the addition amount of the aluminum-free flux is not particularly limited, and can be arbitrarily changed within a range where the lithium content in the slag does not become too low from the viewpoint of lithium recovery, depending on the temperature of the obtained slag, impurities in the crude metal, etc. Also, a flux containing aluminum can be used. The content of aluminum in the aluminum-containing flux and the amount of the flux used are adjusted so that the aluminum / lithium value, which is the mass ratio of aluminum to lithium contained in the obtained slag, is 6 or less, preferably 0.5 or more and 5.0 or less, particularly preferably 1.0 or more and 4.0 or less.

[0023] As described above, the crude metal and slag can be separated from the melt obtained by the above melting step. Thereby, a crude metal mainly composed of copper, nickel, and cobalt and a slag containing lithium and impurity elements are obtained.

[0024] As the slag, those usually having aluminum, magnesium, silicon, lithium, fluorine, manganese, etc. in the form of oxides are used. From the viewpoint of efficiently recovering lithium from the obtained slag, the lithium content in the slag is preferably 1.0 to 25.0% by mass, more preferably 5.0 to 15.0% by mass. The lithium content in the slag can be measured by the method described in the examples below.

[0025] [Lithium Leaching Step] Next, the separated slag and the aqueous liquid are brought into contact to obtain a leachate in which lithium contained in the slag is leached (lithium leaching step). As the aqueous liquid used in this step, water or an aqueous acid solution can be used. Examples of the acid include mineral acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, and carbonic acid, and organic acids such as citric acid, glycine, oxalic acid, and acetic acid. Sulfuric acid and hydrochloric acid are preferred in terms of high lithium leaching efficiency, low cost, and less labor for impurity separation.

[0026] The pH of the leachate is preferably pH 7 or less, more preferably pH 5 or less. Also, the pH of the leachate being 5 or less is preferable in terms of enhancing the leaching efficiency of lithium. Here, the pH of the leachate is the pH at the temperature of the mixture of the aqueous liquid and the slag.

[0027] In the lithium leaching step, the amount of the aqueous liquid mixed with 100 parts by mass of the slag is preferably 100 parts by mass or more and 2000 parts by mass or less, more preferably 200 parts by mass or more and 1500 parts by mass or less, in terms of cost suppression and increasing the lithium concentration.

[0028] The temperature of the leachate (the liquid temperature during leaching) in this process is not particularly limited, but from the viewpoint of lithium leaching efficiency, it can be from room temperature to 300°C. From the viewpoint of energy cost, it is preferably from 30°C to 150°C, more preferably from 60°C to 100°C, and particularly preferably from 70°C to 90°C. The leaching process can be carried out under atmospheric pressure, but it may also be carried out under pressure from the viewpoint of lithium leaching efficiency. In this case, the pressure conditions are, for example, an absolute pressure of 8.0 MPa or less, and more preferably from 2.0 MPa to 4.5 MPa.

[0029] The slag used in this process is preferably a granular material with an average particle size of 5 mm or less, more preferably a granular material with an average particle size of 3 mm or less, and particularly preferably a granular material with an average particle size of 1 mm or less, from the viewpoint of lithium leaching efficiency. The smaller the particle size of the slag, the more efficiently lithium can be recovered. However, if it is fine powder, it becomes difficult to handle, and the cost required for processing such as pulverization also increases. Therefore, from the viewpoints of handleability and economy, the average particle size of the granular material is preferably 0.5 mm or more. The adjustment of the particle size of the slag can be carried out by recovering the slag obtained by separating from the metal through a dry process, subjecting the slag to known pulverization, crushing treatment, etc., and also performing a sieving treatment. The average particle size can be analyzed by a known method, for example, the volume cumulative particle size at a cumulative volume of 50% measured by the laser diffraction scattering method. For example, sodium hexametaphosphate can be used as the dispersion medium of the slag when using the laser diffraction scattering method.

[0030] [Purification process] Next, the leachate is brought into contact with a basic substance to precipitate the unwanted metals contained in the leachate in the form of insoluble substances. The method of adding the basic substance is not particularly limited, and it may be added to the above-mentioned leachate, or may be added to the liquid fraction obtained by solid-liquid separation of the insoluble matter from the leachate. By raising the pH of the leachate by contacting with the basic substance, unwanted metals other than lithium in the leachate form precipitates. The unwanted metals are not particularly limited, and examples include calcium, magnesium, manganese, silicon, aluminum, etc.

[0031] The contact between the leachate and the basic substance is preferably carried out such that the pH of the mixture of the leachate and the basic substance is 5 or more and 14 or less, particularly preferably such that the pH is 10 or more and 12 or less, and most preferably such that the pH is 10 or more and 11 or less. In particular, carrying out the contact such that the pH of the mixture of the leachate and the basic substance is 10 or more is preferable in terms of effectively precipitating unnecessary metals such as manganese and magnesium. Also, the fact that the pH of the mixture of the leachate and the basic substance is 12 or less is preferable in terms of preventing the redissolution of aluminum, which is an amphoteric metal. In the present invention, since the aluminum / lithium ratio in the slag is small, even when the pH of the aqueous solution is within the above range, the formation of the composite hydroxide of lithium and aluminum in the leachate is small, and the lithium recovery efficiency can be effectively increased. The pH of the mixture of the leachate and the basic substance is the pH at the temperature at the start of solid-liquid separation.

[0032] The contact between the leachate and the basic substance is preferably carried out under atmospheric pressure conditions in terms of simplicity. The contact between the leachate and the basic substance may be carried out at room temperature or may be heated. When heating, from the viewpoint of the lithium recovery efficiency and the effect of reducing the viscosity of the mixed solution, the temperature of the mixture of the leachate and the basic substance is preferably room temperature or higher and 100°C or lower, and more preferably 60°C or higher and 90°C or lower.

[0033] Examples of the type of basic substance include hydroxides such as sodium hydroxide solution, magnesium hydroxide, calcium hydroxide, and lithium hydroxide, which are alkali metal hydroxides or alkaline earth metal hydroxides; carbonates such as sodium carbonate, potassium carbonate, calcium carbonate, and lithium carbonate, which are alkali metal carbonates or alkaline earth metal carbonates; oxides such as sodium oxide, potassium oxide, calcium oxide, and lithium oxide, which are alkali metal oxides or alkaline earth metal oxides; and amines such as methylamine, dimethylamine, and trimethylamine.

[0034] Next, as a method for solid-liquid separation of the mixture of the basic substance and the leachate, it is not particularly limited and can be carried out by a known method. By solid-liquid separation, a poorly soluble substance containing unnecessary metals and a lithium-containing liquid purified by reducing the unnecessary metals are separated.

[0035] [Carbonate formation step] In the present invention, a carbonate or carbon dioxide gas is brought into contact with the purified liquid containing lithium obtained in the above purification step to form a carbonate of lithium in the purified liquid. As the carbonate, an alkali metal carbonate is preferable from the viewpoint of reactivity, and among them, sodium carbonate and potassium carbonate are preferable. Further, the purified liquid may be concentrated before reacting with the carbonate or carbon dioxide gas. In this case, the concentration ratio is preferably 1.1 to 30 times, more preferably 1.5 to 20 times.

[0036] In the formation of the carbonate, the temperature of the purified liquid is preferably 60°C to 100°C from the viewpoints of reaction efficiency and impurity removal.

Examples

[0037] The present invention will be described based on the following examples, but the present invention is not limited to the following examples. In addition, all the fluxes used below had the effect of promoting the formation of slag. (Composition analysis) In the following examples, the component amounts of each metal element in the slag were determined by compositional analysis using ICP emission spectrometry on a dissolution solution obtained by adding 60 mass% nitric acid at 10 times the mass of the slag, 35 mass% hydrochloric acid at 10 times the mass of the slag, and 30 times the mass of ultrapure water, and mixing and dissolving at 110°C for 2 hours. In the dissolution treatment, insoluble matter may have occurred. Therefore, as the lithium and aluminum amounts in the slag, the weight of the substance insoluble in the dissolution treatment was separately measured, and the lithium amount calculated using the weight obtained by subtracting the amount of insoluble matter from the charged amount of the slag is described in Tables 1 and 2. In addition, the mass ratio of aluminum to lithium was determined from the aluminum concentration and lithium concentration in the solution obtained by the dissolution treatment and is described in Tables 1 and 2. The insoluble matter was separated from the liquid by a membrane filter, then dried on a glass petri dish at 50°C for 2 hours using an electric dryer, and the weight was measured to obtain the value. Similarly, the amounts of metal elements in the leachate and the neutralized solution were also determined by compositional analysis using ICP emission spectrometry. Also, the amount of lithium in lithium carbonate was determined by compositional analysis using ICP emission spectrometry in the same manner after dissolving lithium carbonate.

[0038] (Average particle size) For the measurement of the average particle size of the slag, a Horiba-made device was used as the measuring apparatus by the laser diffraction scattering method.

[0039] (Example 1) As the raw material slag, one containing 13.0 mass% aluminum and 8.8 mass% lithium was used. This slag was obtained as follows. In the above melting process, as (1), the scrap of the aluminum can-made lithium-ion secondary battery after the above-mentioned detoxification treatment was heated to 750°C in a low-oxygen atmosphere with an oxygen concentration of 10% by volume or less and the balance being nitrogen and carbon dioxide to selectively melt aluminum. The obtained molten aluminum was removed from the scrap by hand sorting. Next, the scrap after aluminum removal was pulverized with a hammer mill, and after sieving using a sieve with an opening of 2 mm, the obtained undersize and a flux (such as a calcium compound) containing no aluminum were subjected to a melting treatment by heating at 1400°C in a reducing atmosphere in the presence of carbon. All of the furnace materials constituting the furnace wall of the melting furnace were made of magnesia. By the above process, slag having an aluminum / lithium mass ratio of 1.5 was obtained. The slag was pulverized so that the average particle size was 0.5 mm or more and 1 mm or less. To 10 g of the above slag, 77 g of sulfuric acid diluted to 40% by mass with water was added, heated to 70°C under atmospheric pressure, and the pH was adjusted to less than 1. To the leachate containing the obtained slag, 64 g of calcium hydroxide diluted to 25% by mass with water as a basic substance was added at 70°C under atmospheric pressure, and the pH at 70°C was adjusted to 11. After the precipitate was subjected to solid-liquid separation by filtration, the residue of the filtration was washed with running water with 100 g of water to obtain a purified liquid including the washing liquid. The amount of lithium in the purified liquid was measured by the above method. The lithium recovery rate from the slag was as shown in Table 1.

[0040] (Example 2) As the raw material slag, one having 13.9% by mass of aluminum and 5.2% by mass of lithium was used. In Example 1, this slag was obtained by selectively melting and removing aluminum from the scrap of a lithium-ion secondary battery, pulverizing the scrap after aluminum removal with a hammer mill, screening it using a sieve with an aperture of 2 mm, removing the aluminum remaining on the sieve by a pneumatic separator from the obtained oversize fraction, and then performing the same operations as in Example 1 except that the oversize fraction after removing the residual aluminum, the undersize fraction, and a flux (such as a calcium compound) containing no aluminum were subjected to a melting treatment. By the above steps, a slag having an aluminum / lithium mass ratio of 2.7 was obtained. The slag used was pulverized to an average particle size of 0.5 mm or more and 1 mm or less. To 10 g of the above slag, 41 g of sulfuric acid diluted with water to 40 mass% was added, heated to 70 °C under atmospheric pressure, and the pH was adjusted to 2.3. To the leachate containing the obtained slag, 90 g of calcium hydroxide diluted with water to 5 mass% as a basic substance was added at 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to 11. After the precipitate was separated by filtration into solid and liquid, the filter residue was washed with pure water passed through 100 g of water, and a purified solution including the washing liquid was obtained. The amount of lithium in the purified solution was measured by the above method. The lithium recovery rate from the slag was as shown in Table 1.

[0041] (Example 3) As the raw material slag, one containing 19.1 mass% of aluminum and 5.5 mass% of lithium was used. In Example 1, this slag was obtained in the same manner as in Example 1 except that the crushed material pulverized with a hammer mill and a flux (such as a calcium compound) containing no aluminum were subjected to a melting treatment. By the above steps, a slag having an aluminum / lithium mass ratio of 3.5 was obtained. The slag used was pulverized to an average particle size of 0.5 mm or more and 1 mm or less. To 10 g of the above slag, 58 g of sulfuric acid diluted with water to 40% by mass was added, and the mixture was heated to 70 °C under atmospheric pressure to adjust the pH to 1.1. To the leachate containing the obtained slag, 83 g of calcium hydroxide diluted with water to 15% by mass as a basic substance was added at 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to 11. After the precipitate was separated by filtration into solid and liquid, the filter residue was washed with water passing through 170 g of water, and a purified liquid including the washing liquid was obtained. The lithium amount in the purified liquid was measured by the above method. The lithium recovery rate from the slag was as shown in Table 1.

[0042] (Example 4) As the raw material slag, one containing 27.9% by mass of aluminum and 4.9% by mass of lithium was used. This slag was obtained in the same manner as in Example 1, except that in Example 1, melting treatment was carried out together using alumina as a flux in the melting step. By the above steps, a slag having an aluminum / lithium mass ratio of 5.7 was obtained. The slag used was one pulverized to have an average particle size of 0.5 mm or more and 1 mm or less. To 10 g of the above slag, 140 g of sulfuric acid diluted with water to 30% by mass was added, and the mixture was heated to 70 °C under atmospheric pressure to adjust the pH at 70 °C to less than 1. To the leachate containing the obtained slag, 209 g of calcium hydroxide diluted with water to 15% by mass as a basic substance was added at 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to 11. After the precipitate was separated by filtration into solid and liquid, the filter residue was washed with water passing through 100 g of water, and a purified liquid including the washing liquid was obtained. The lithium amount in the purified liquid was measured by the above method. The lithium recovery rate from the slag was as shown in Table 1.

[0043] (Comparative Example 1) As the raw material slag, one containing 29.4% by mass of aluminum and 3.9% by mass of lithium was used. This slag was obtained in the same manner as in Example 1, except that in Example 1, the crushed material pulverized with a hammer mill without performing the above-described aluminum melting removal in (1) was used for melting. The slag used was one pulverized to have an average particle size of 0.5 mm or more and 1 mm or less. To 10 g of the above slag, 75 g of sulfuric acid diluted with water to 40 mass% was added, and the mixture was heated to 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to less than 1. To the leachate containing the obtained slag, 110 g of calcium hydroxide diluted with water to 15 mass% as a basic substance was added at 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to 11. After the precipitate was separated by filtration into solid and liquid, the filter residue was washed with 120 g of water by passing water through it, and a purified liquid containing the washing liquid was obtained. The lithium amount in the purified liquid was measured by the above method. The lithium recovery rate from the slag was as shown in Table 1.

[0044] (Comparative Example 2) As the raw material slag, one containing 28.6 mass% of aluminum and 3.6 mass% of lithium was used. This slag was obtained in the same manner as in Example 1 except that in Example 1, the crushed product pulverized with a hammer mill without performing the aluminum melting removal described in (1) was subjected to melting, and alumina was used as the furnace material. The slag used was pulverized to an average particle size of 0.5 mm or more and 1 mm or less. To 10 g of the above slag, 75 g of sulfuric acid diluted with water to 40 mass% was added, and the mixture was heated to 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to less than 1. To the leachate containing the obtained slag, 111 g of calcium hydroxide diluted with water to 15 mass% as a basic substance was added at 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to 11. After the precipitate was separated by filtration into solid and liquid, the filter residue was washed with 120 g of water by passing water through it, and a purified liquid was obtained. The lithium amount in the purified liquid was measured by the above method. The lithium recovery rate from the slag was as shown in Table 1.

[0045] [Table 1]

[0046] As shown in Table 1, by setting the aluminum / lithium mass ratio to 6 or less, the lithium recovery rate can be significantly increased.

[0047] (Examples 5 to 8) As the raw material slag, one containing 19.1% by mass of aluminum and 5.5% by mass of lithium was used. This slag was obtained in the same manner as in Example 1, except that in Example 1, it was subjected to a melting treatment together with the crushed material pulverized by a hammer mill and a flux (such as a calcium compound) not containing aluminum. By the above process, a slag with an aluminum / lithium mass ratio of 3.5 was obtained. The slag was pulverized so that the average particle size became the value shown in Table 2. To 15 g of the above slag, 113 g of sulfuric acid diluted with water to 40% by mass was added, heated to 70 °C under atmospheric pressure, and the pH at 70 °C was adjusted to less than 1. The amount of lithium and the lithium recovery rate in the obtained leachate were as shown in Table 2.

[0048]

Table 2

[0049] As shown in Table 2, when the slag particle size was 5 mm or less, the lithium recovery rate was 59% or more, resulting in good results.

[0050] (Example 9) As the raw material slag, one containing 13.9% by mass of aluminum, 5.2% by mass of lithium, 3.7% by mass of magnesium, and 2.9% by mass of manganese was used. This slag was obtained in the same manner as in Example 1, except that in Example 1, after selectively melting aluminum from the scrap of a lithium-ion secondary battery, it was pulverized by a hammer mill, then sieved using a sieve with an aperture of 2 mm, the aluminum remaining on the sieve after sieving was removed by a pneumatic separator, and then the material on the sieve and under the sieve after removing the remaining aluminum and a flux (such as a calcium compound) not containing aluminum were subjected to a melting treatment. By the above process, a slag with an aluminum / lithium mass ratio of 2.7 was obtained. The slag used was pulverized so that the average particle size was 0.5 mm or more and 1 mm or less. To 18 g of the above slag, 68 g of sulfuric acid diluted with water to 40% by mass was added, and the mixture was heated to 70°C under atmospheric pressure, and the pH at 70°C was adjusted to 1.8. To the leachate containing the obtained slag, calcium hydroxide diluted with water to 5% by mass as a basic substance was added at 70°C under atmospheric pressure, and the pH at 70°C was adjusted to the value described in Table 3. After the precipitate was separated by filtration into solid and liquid, the filter residue was washed with running water with 180 g of water to obtain a purified solution. The amounts of lithium, magnesium, and manganese in the purified solution were measured by the above method. The results are shown in Table 3.

[0051] (Examples 10 and 11) The pH at 70°C prepared by adding a basic substance to the leachate was changed to the value described in Table 3. Otherwise, in the same manner as in Example 9, a purified solution was obtained. The amounts of lithium, magnesium, and manganese in the purified solution were measured by the above method. The results are shown in Table 3.

[0052] [Table 3]

[0053] (Example 12) The purified solution obtained in Example 9 was concentrated 10-fold by vacuum concentration, and then 2.5 g of sulfuric acid diluted with water to 10% by mass was added to adjust the pH at 70°C to 7. Sodium carbonate was added to this solution and reacted at 80°C. Then, the precipitated lithium carbonate was separated by filtration under heating conditions and recovered, and dried at 100°C. The amount of lithium in the lithium carbonate was measured, and the lithium recovery rate from the slag was determined to be 52%. From the analytical values of the impurity metals, the lithium carbonate purity was 98% by mass. [Industrial Applicability]

[0054] The present invention can recover lithium more efficiently from the slag generated when a lithium-ion secondary battery to be disposed of is melted and valuable metals are recovered. The method of the present invention can effectively utilize the above slag, which has been limited in applications such as building materials in the past, with fewer steps and has a low environmental impact.

Claims

1. A method for recovering lithium from slag containing at least aluminum and lithium separated from molten metal containing valuable metals after melting a lithium-ion secondary battery to be disposed of to obtain the molten metal containing valuable metals and the molten slag containing at least aluminum and lithium, comprising: adjusting the melting conditions of the lithium-ion secondary battery so that the value of aluminum / lithium, which is the mass ratio of aluminum to lithium contained in the slag, is 6 or less; bringing the slag into contact with an aqueous solution to obtain a leachate having a pH of 7 or less in which lithium contained in the slag is leached; bringing the leachate into contact with a basic substance to precipitate unwanted metals contained in the leachate in the form of a hardly soluble substance, and obtaining a purified solution in which lithium is dissolved by solid-liquid separation.

2. The recovery method according to claim 1, wherein when melting the lithium-ion secondary battery, the amount of aluminum present in the melting step is controlled so that the value of aluminum / lithium, which is the mass ratio of aluminum to lithium contained in the slag, is 6 or less.

3. The recovery method according to claim 2, wherein the amount of aluminum present in the melting step is controlled by any one of the following methods (1) to (3). (1) Separating at least part of the aluminum from the lithium-ion secondary battery before the melting step by selectively removing aluminum by melting or selectively removing aluminum by crushing and separation. (2) Using a furnace material that does not contain aluminum in a portion in contact with the molten slag in the furnace used in the melting step, and performing the melting step. (3) Not adding a flux that promotes the formation of slag in the melting step, or using, as the flux to be used, a flux having an aluminum content such that the aluminum / lithium value of the slag does not exceed 6 based on the contents of aluminum and lithium in the raw material.

4. The recovery method according to any one of claims 1 to 3, wherein the slag pulverized into granules having an average particle size of 5 mm or less is brought into contact with an aqueous solution to obtain a leachate in which lithium contained in the slag is leached.

5. The recovery method according to any one of claims 1 to 4, wherein the contact between the leachate and the basic substance is performed so that the pH of the mixture of the leachate and the basic substance is 10 or more and 12 or less.

6. The recovery method according to any one of claims 1 to 5, wherein the purified liquid in which lithium is dissolved is brought into contact with a carbonate or carbon dioxide gas to precipitate a carbonate of lithium in the liquid.

7. The recovery method according to any one of claims 1 to 6, wherein the slag is brought into contact with an aqueous liquid to obtain a leachate having a pH of 5 or less in which lithium contained in the slag has leached out.

8. The recovery method according to any one of claims 1 to 6, wherein the slag is brought into contact with an aqueous liquid to obtain a leachate having a pH of 2.3 or less in which lithium contained in the slag has leached out.

9. A method for producing lithium carbonate from a slag containing at least aluminum and lithium, which is separated from a molten metal containing a valuable metal, after melting a lithium-ion secondary battery to be subjected to waste treatment to obtain a molten metal containing a valuable metal and a molten slag containing at least aluminum and lithium, comprising: adjusting the melting conditions of the lithium-ion secondary battery so that the value of aluminum / lithium, which is the mass ratio of aluminum to lithium contained in the slag, is 6 or less; bringing the slag into contact with an aqueous liquid to obtain a leachate having a pH of 7 or less in which lithium contained in the slag has leached out; bringing the leachate into contact with a basic substance to precipitate unnecessary metals contained in the leachate in the form of a poorly soluble substance, and obtaining a purified liquid in which lithium is dissolved by solid-liquid separation; A method for producing lithium carbonate, wherein the purified liquid in which lithium is dissolved is brought into contact with a carbonate or carbon dioxide gas to precipitate a carbonate of lithium in the liquid.

10. The method for producing lithium carbonate according to claim 9, wherein the slag is brought into contact with an aqueous liquid to obtain a leachate having a pH of 5 or less in which lithium contained in the slag has leached out.

11. The method for producing lithium carbonate according to claim 9, wherein the slag is brought into contact with an aqueous liquid to obtain a leachate having a pH of 2.3 or less in which lithium contained in the slag has leached out.

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