How to recover lithium

Abstract

A method for recovering lithium from a material that contains fluorine and lithium, wherein: the material is mixed with an aqueous sulfuric acid solution or water, thereby obtaining a mixed solution in which fluorine and lithium in the material have been dissolved; and a purified solution, in which lithium is dissolved, is obtained by means of solid-liquid separation after forming a sediment that contains fluorine and calcium by mixing the mixed solution with a poorly soluble or slightly soluble calcium-containing alkaline agent. It is preferable that, when the mixed solution is obtained, the material that contains fluorine and lithium is mixed with an aqueous sulfuric acid solution or water, and heated at a temperature within the temperature range of from 60°C to 90°C.

Description

[Technical Field]

[0001] The present invention relates to a method for recovering lithium from a material containing fluorine and lithium. [Background technology]

[0002] Lithium compounds are used in a wide range of applications, including as additives for glass, fluxes for steel casting, refrigerant absorbents for large-scale air conditioners, and catalysts for the production of synthetic rubber.

[0003] In recent years, there has been a particularly strong demand for lithium-ion secondary batteries, which have high energy density and excellent rapid charge / discharge characteristics.

[0004] Lithium-ion secondary batteries are used in a wide range of applications, including relatively small electronic and electrical devices such as small communication terminals like smartphones, laptops, power tools, and radio wave repeaters, as well as in larger devices such as hybrid cars, electric cars, home storage batteries, solar power storage equipment, and emergency storage batteries.

[0005] To meet these demands, a wide variety of lithium compounds are produced, and a wide variety of lithium-containing waste products are produced.

[0006] The lithium-containing waste materials include waste materials, wastewater, and defective products discharged in processes ranging from the production of lithium compounds as raw materials to the production of lithium-containing product equipment, and also includes waste materials disposed of due to deterioration of lithium-containing product equipment over time or replacement.

[0007] The waste and wastewater generated during the production and replacement of these products are a cause of environmental pollution. In recent years, recovery of valuable components from various materials such as waste and wastewater has been studied from the viewpoints of effective utilization of resources and prevention of environmental pollution.

[0008] Generally, when recovering lithium from the above waste, a method is used in which lithium is extracted using water or acid, and then impurities are reduced by extraction treatment with an organic solvent, neutralization treatment, salt exchange, or the like.

[0009] However, when recovering lithium from waste containing fluorine, there is a problem that the recovery of lithium is hindered by the generation of water-insoluble lithium fluoride in various treatment steps.

[0010] As a method for recovering lithium from waste in the presence of fluorine, Patent Document 1 describes a lithium recovery method including an extraction step in which an alkali is added to a discharge solution and / or a cleaning solution containing lithium discharged in a step of recovering valuable metals from lithium ion batteries, and the solution is brought into contact with an acidic solvent extractant at a pH of 9 or less and a temperature of 0 to 25°C to extract lithium ions, and a stripping step in which the acidic solvent extractant from which lithium ions have been extracted in the extraction step is brought into contact with an acidic solution at a pH of 3 or less to strip-extract lithium ions.

[0011] Patent Document 2 describes a lithium recovery method including a step a of stirring unpurified lithium fluoride into a gel state and adding an acid to prepare a purified lithium fluoride gel-like feed, and a step of adding the unpurified lithium fluoride gel-like feed obtained in step a to a boiling calcium chloride solution, adding a basic substance, and obtaining a lithium chloride solution.

[0012] Patent Document 3 describes a method for preparing a lithium-containing solution, including the following: a calcium acid solution containing lithium chloride or lithium sulfate containing a solid lithium raw material is subjected to multistage countercurrent leaching using trisodium phosphate to obtain a lithium-containing solution and leached slag. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-41621 [Patent Document 2] US2019 / 0152793A1 [Patent Document 3] China Publication No. 110498433 Summary of the Invention

[0014] The technology described in Patent Document 1 involves a multi-stage solvent extraction method under low temperature conditions to recover lithium from a hexafluorophosphate solution. However, this method does not recover lithium fluoride produced by hydrolysis, and the multi-stage extraction process not only reduces the lithium recovery efficiency, but also generates large amounts of the organic solvents and other materials used as waste liquids and waste, resulting in high waste disposal costs and high lithium recovery costs. The method for recovering lithium from crude lithium fluoride described in Patent Document 2 requires numerous chemicals, including acid, calcium chloride, and a neutralizing agent, to dissolve the lithium fluoride. Because the calcium chloride used here is highly soluble, the resulting lithium contains a large amount of calcium, necessitating re-purification. In the method described in Patent Document 3, leaching is performed using a lithium salt and a calcium-containing acid, and recovery is performed using trisodium phosphate, but the preparation of the calcium-containing acid is time-consuming. Therefore, an object of the present invention is to provide a method for recovering lithium that does not require the use of an extraction organic solvent and therefore has a low environmental impact, can use inexpensive materials, and can recover lithium with a small number of steps and high efficiency.

[0015] The present inventors have found that lithium can be recovered simply and efficiently by mixing a material containing fluorine and lithium with an aqueous sulfuric acid solution or water, and then reacting the mixture with a poorly soluble or slightly soluble calcium-containing alkaline agent.

[0016] The present invention is based on the above findings and provides a method for recovering lithium from a material containing fluorine and lithium, which comprises preparing a mixed solution of the material containing fluorine and lithium with an aqueous sulfuric acid solution or water, mixing the mixed solution with a poorly soluble or slightly soluble calcium-containing alkaline agent to form a precipitate containing fluorine and calcium, and performing solid-liquid separation to obtain a purified solution in which lithium is dissolved. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described below based on preferred embodiments thereof. The present invention is a method for recovering lithium from a material containing fluorine and lithium, comprising the steps of: a first step of mixing the material with an aqueous sulfuric acid solution or water to prepare a mixed solution; and a second step of mixing the mixed solution with a poorly soluble or slightly soluble calcium-containing alkaline agent to form a precipitate containing fluorine and calcium, followed by solid-liquid separation to obtain a purified solution in which lithium is dissolved.

[0018] In the present invention, the material containing fluorine and lithium may be either a solid or a liquid, and these solids may be dispersed in a solvent such as water.

[0019] Examples of materials containing fluorine and lithium include waste lithium ion secondary battery scrap and roasted products of such scrap, solid industrial waste, and liquid industrial waste such as factory wastewater.

[0020] The form of fluorine and lithium in the above material is not particularly limited, but examples include salts consisting of both fluorine and lithium elements and mixtures containing both elements in separate substances.

[0021] Salts composed of both fluorine and lithium include, but are not limited to, lithium fluorides, fluorophosphates, fluorosulfonates, fluoroborates, and fluorosulfonylimides. An example of a lithium fluoride salt is lithium fluoride. Examples of lithium fluorophosphates include lithium monofluorophosphate, lithium difluorophosphate, lithium methyl monofluorophosphate, and lithium hexafluorophosphate. Examples of lithium fluorosulfonates include lithium trifluoromethanesulfonate and lithium nonafluorobutanesulfonate. Examples of lithium fluoroborates include lithium tetrafluoroborate. Examples of lithium fluorosulfonylimides include lithium bis(fluorosulfonyl)imide. These substances may be used alone or in the form of a mixture of two or more.

[0022] The mixture containing both fluorine and lithium as separate substances is not particularly limited, and examples of the fluorine-containing compound in the mixture include alkali metal fluorides, alkaline earth metal fluorides, hydrofluoric acid, etc. Examples of the lithium-containing compound in the mixture include lithium halide, lithium oxide, lithium hydroxide, lithium phosphate, lithium borate, lithium sulfate, lithium nitrate, etc.

[0023] In the present invention, the fluorine- and lithium-containing material to be mixed with the sulfuric acid aqueous solution or water may have been previously subjected to a chemical or physical treatment, but is preferably obtained without a step of removing a precipitate. If the precipitate is removed before the hardly soluble or slightly soluble calcium-containing alkaline agent is applied, lithium may be present in the precipitate, which reduces the recovery efficiency of lithium.

[0024] The lithium content in the above-mentioned fluorine- and lithium-containing material is not particularly limited, but the lithium content in the material is preferably 100 ppm or more by mass, and more preferably 1000 ppm or more from the viewpoint of productivity. The upper limit of the lithium content is not particularly limited, but is usually 30 mass% or less.

[0025] The amount of lithium in a material containing fluorine and lithium can be determined by dissolving the solid or dispersion in a mineral acid and analyzing the composition of the obtained sample by inductively coupled plasma atomic emission spectroscopy (ICP-AES) when the material is a solid or dispersion. When the material is a liquid, the amount of lithium can be determined by subjecting the liquid to ICP atomic emission spectroscopy (ICP-AES).

[0026] The fluorine content in the above-mentioned materials containing fluorine and lithium is not particularly limited, but the value of fluorine / lithium, which is the mass ratio of fluorine to lithium contained in the material, is preferably 0.1 or more, because this is highly significant in applying the present invention, and the value of fluorine / lithium is preferably 30 or less, particularly 20 or less, from the viewpoint of productivity.

[0027] The fluorine content can be measured by known analytical methods, such as ion chromatography, lanthanum-alizarin complexone absorptiometry, and energy dispersive X-ray spectroscopy, depending on the form of the material.

[0028] (1st step) In the present invention, a material containing fluorine and lithium is mixed with an aqueous sulfuric acid solution or water. From the viewpoints of increasing lithium recovery efficiency and productivity, the amount of the aqueous sulfuric acid solution or water is preferably 20 to 10,000 times by mass, more preferably 30 to 2,000 times by mass, and even more preferably 50 to 300 times by mass, relative to the mass of lithium in the material containing fluorine and lithium.

[0029] The acid concentration of the aqueous sulfuric acid solution is not particularly limited, but from the viewpoints of productivity and ease of handling, the sulfuric acid concentration in the aqueous sulfuric acid solution is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0030] In terms of lithium recovery efficiency, it is preferable to contact the fluorine- and lithium-containing material with the aqueous sulfuric acid solution or water in a heated state. From this viewpoint, the temperature of the mixture of the fluorine- and lithium-containing material and the aqueous sulfuric acid solution or water is preferably room temperature or higher and 300°C or lower, and from the viewpoint of energy cost, it is more preferably 30°C or higher and 150°C or lower, and particularly preferably 60°C or higher and 90°C or lower. The mixture of the fluorine- and lithium-containing material and the aqueous sulfuric acid solution or water may be mixed under pressure or atmospheric pressure.

[0031] The time for which the material containing fluorine and lithium is mixed with the aqueous sulfuric acid solution or water and brought into contact with the aqueous sulfuric acid solution or water is preferably 10 minutes or more and 5 hours or less, from the viewpoint of work efficiency and lithium recovery efficiency, provided that the temperature is within the above-mentioned range, and more preferably 10 minutes or more and 3 hours or less.

[0032] The mixed liquid obtained by mixing a material containing fluorine and lithium with an aqueous sulfuric acid solution or water has at least a portion of the fluorine and lithium dissolved in the material. The mixed liquid may contain solids or may consist of only liquid. From the viewpoint of extraction efficiency, the solid content of the mixed liquid is preferably 30% by mass or less, more preferably 10% by mass or less. The solid content here refers to the amount at 25°C and atmospheric pressure. In the second step, the mixed liquid can be directly mixed with a poorly soluble or slightly soluble calcium-containing alkaline agent. However, if necessary, the material containing fluorine and lithium may be mixed with an aqueous sulfuric acid solution or water, followed by solid-liquid separation, and the liquid content may be subjected to the second step.

[0033] (2nd process) The mixed solution obtained in the first step is mixed with a poorly soluble or slightly soluble calcium-containing alkaline agent. A poorly soluble or slightly soluble calcium-containing alkaline agent preferably means one having a solubility of 5 g or less, more preferably 1 g or less, in 100 ml of water at, for example, 25°C and atmospheric pressure. Specific examples include calcium oxide, calcium hydroxide, and calcium carbonate, with calcium hydroxide being particularly preferred in terms of ease of handling and fluoride removal efficiency. Mixing the mixed solution with the poorly soluble or slightly soluble calcium-containing alkaline agent forms a precipitate containing fluoride and calcium.

[0034] The particle size of the poorly soluble or slightly soluble calcium-containing alkaline agent can be, for example, an average particle size of 1 μm to 1400 μm, more preferably 1 to 50 μm, and particularly preferably 5 μm to 20 μm. Measurement methods include laser diffraction / scattering (volume-based D50) and image analysis (maximum Feret diameter) using SEM or the like, and it is preferable that the particle size be within the range determined by laser diffraction / scattering.

[0035] In the present invention, a poorly soluble or slightly soluble calcium-containing alkaline agent is actively mixed with the mixed solution. Therefore, even if calcium hydroxide is produced in a mixture obtained by mixing calcium chloride with a strong base such as sodium hydroxide, this is not included in the present invention. Note that, in the present invention, it is preferable not to mix calcium chloride with the mixed solution obtained in the first step, even if a poorly soluble or slightly soluble calcium-containing alkaline agent is present. This is because calcium chloride is water-soluble and would be mixed into the purified solution obtained in the second step. For example, when lithium carbonate is produced from the purified solution, calcium would be mixed into the resulting lithium carbonate, lowering the purity of the lithium carbonate.

[0036] The poorly soluble or slightly soluble calcium-containing alkaline agent may be mixed with the mixed liquid as it is, or may be added to water and mixed to form a suspension, which may then be mixed with the mixed liquid.

[0037] In the present invention, the amount of the hardly soluble or slightly soluble calcium-containing alkaline agent used varies depending on the amount of fluorine in the mixed solution. For example, from the standpoint of reaction efficiency and handleability, it is preferable that the amount of calcium element in the hardly soluble or slightly soluble calcium-containing alkaline agent be 0.1 mol to 20 mol, and more preferably 0.3 mol to 15 mol, per 1 mol of fluorine element contained in the mixed solution.

[0038] The mixture of the hardly soluble or slightly soluble calcium-containing alkaline agent and the mixture obtained in the first step may be carried out at room temperature. mix The mixture with the liquid can be heated mix This is preferable in terms of the reaction efficiency between the fluorine in the liquid and the poorly or slightly soluble calcium-containing alkaline agent. When the mixture is heated, a temperature of 30°C or higher is preferable in terms of reaction efficiency, and a temperature of 300°C or lower is preferable in terms of energy efficiency, since heating above this temperature does not improve the reaction efficiency. From these points of view, a temperature of 50°C or higher and 200°C or lower is more preferable, and a temperature of 60°C or higher and 90°C or lower is particularly preferable. The poorly soluble or slightly soluble calcium-containing alkaline agent and the mixed liquid may be mixed under atmospheric pressure or under pressure.

[0039] The pH of the mixture of the hardly soluble or slightly soluble calcium-containing alkaline agent and the mixed solution at the temperature of the mixture is preferably 3 or higher in order to promote the formation of a precipitate containing fluorine and calcium, and is preferably 14 or lower in order to prevent the precipitation of lithium. From this point of view, the pH is particularly preferably 5 or higher and 12 or lower, and most preferably 10 or higher and 12 or lower.

[0040] The precipitate formed in the second step is removed by solid-liquid separation, and the liquid portion is recovered to obtain a purified solution in which the lithium compound is dissolved.

[0041] The purified liquid obtained above can be used for various purposes, for example, by contacting it with carbonate or carbon dioxide gas to produce lithium carbonate in the purified liquid.

[0042] The treatment method of the present invention described above enables highly efficient recovery of lithium with fewer steps from materials containing fluorine and lithium, such as water-insoluble lithium fluoride, from which lithium recovery has been difficult in the past. Compounds containing fluorine and lithium, such as lithium hexafluorophosphate, that are easily hydrolyzed to produce lithium fluoride are present in waste materials from lithium-ion secondary batteries, etc. Furthermore, mixtures of lithium-containing compounds and fluorine-containing compounds may also produce lithium fluoride through reaction. The present invention enables simple and highly efficient recovery of lithium from these compounds and mixtures, making it highly applicable to industry.

[0043] In the present invention, no organic solvent is required in the first and second steps, and it is preferable not to actively add an organic solvent to either the mixture of the fluorine- and lithium-containing material and aqueous sulfuric acid solution or water obtained in the first step, or to the mixture of the mixture and the poorly soluble or slightly soluble calcium-containing alkaline agent in the second step, because adding an organic solvent increases the cost of waste liquid treatment. [Example]

[0044] The present invention will be described below based on examples, but the present invention is not limited to the following examples. In each of the following examples, calcium hydroxide having an average particle size in the range of 5 μm to 10 μm was used. Example 1 Lithium fluoride powder was used as a material containing fluorine and lithium. 3.7 g of lithium fluoride powder was added to 68.6 g of a 30 mass % aqueous solution of sulfuric acid, and the mixture was heated at 70°C under atmospheric pressure for 3 hours to obtain a mixed solution. The resulting mixture was maintained at atmospheric pressure and 70° C. In this state, 200 g of a 5% by mass aqueous suspension of calcium hydroxide was added and mixed, and the pH of the mixture at 70° C. was adjusted to 12. The insoluble impurities precipitated in the mixed solution were separated by filtration to obtain a purified solution as the liquid fraction. The amount of lithium in the purified solution was determined by composition analysis using ICP atomic emission spectrometry. The lithium recovery rate was calculated from the above results, and the results are shown in Table 1.

[0045] Example 2 Lithium hexafluorophosphate powder was used as the material containing fluorine and lithium. 22 g of the lithium hexafluorophosphate powder was added to 59.2 g of a 15% by mass aqueous solution of sulfuric acid, and the mixture was heated at 70°C under atmospheric pressure for 3 hours to obtain a mixed solution. The resulting mixture was maintained at 70°C under atmospheric pressure conditions. In this state, 191 g of a 45% by mass aqueous suspension of calcium hydroxide was added and mixed, and the pH of the mixture at 70°C was adjusted to 12. The insoluble impurities precipitated in the mixed solution were separated by filtration to obtain a purified solution as the liquid fraction. The amount of lithium in the purified solution was determined by composition analysis using ICP atomic emission spectrometry. The lithium recovery rate was calculated from the above results, and the results are shown in Table 1.

[0046] Example 3 Lithium difluorophosphate powder was used as the material containing fluorine and lithium. 15.5 g of lithium difluorophosphate powder was added to 49.9 g of water, and the mixture was heated at 70°C under atmospheric pressure for 10 minutes to obtain a mixed solution. The resulting mixture was maintained at atmospheric pressure and 70° C. In this state, 154 g of a 10 mass % aqueous suspension of calcium hydroxide was added to the mixture and mixed, and the pH of the mixture at 70° C. was adjusted to 11. The insoluble impurities precipitated in the mixed solution were separated by filtration to obtain a purified solution as the liquid fraction. The amount of lithium in the purified solution was determined by composition analysis using ICP atomic emission spectrometry. The lithium recovery rate was calculated from the above results, and the results are shown in Table 1.

[0047] Example 4 A 50% by mass aqueous solution of lithium bis(fluorosulfonyl)imide was used as a material containing fluorine and lithium. 10 g of the lithium bis(fluorosulfonyl)imide solution was added to 6.9 g of a 30% by mass aqueous solution of sulfuric acid, and the mixture was heated at 70°C under atmospheric pressure for 3 hours to obtain a mixed solution. The resulting mixed solution was maintained at 70°C under atmospheric pressure conditions. In this state, 41 g of a 5% by mass aqueous suspension of calcium hydroxide was added to the mixed solution and mixed, and the pH of the resulting mixed solution at 70°C was adjusted to 12. The insoluble impurities precipitated in the mixed solution were separated by filtration to obtain a purified solution as the liquid fraction. The amount of lithium in the purified solution was determined by composition analysis using ICP atomic emission spectrometry. The lithium recovery rate was calculated from the above results, and the results are shown in Table 1.

[0048] Example 5 The fluorine- and lithium-containing material used was lithium-ion battery roasted scrap containing 2.7 mass% lithium, primarily composed of lithium oxide, based on Li metal, and 5.7 mass% fluorine, primarily composed of calcium fluoride, based on elemental fluorine. 6 g of the lithium-ion secondary battery roasted scrap was added to 24.9 g of a 40 mass% aqueous sulfuric acid solution, and the mixture was heated at 70°C under atmospheric pressure for 3 hours to obtain a mixed solution. The resulting mixed solution was maintained at 70°C under atmospheric pressure conditions. In this state, 260 g of a 5 mass % aqueous suspension of calcium hydroxide was added to the mixed solution and mixed, and the pH of the resulting mixed solution at 70°C was adjusted to 10. The insoluble impurities precipitated in the mixed solution were separated by filtration to obtain a purified solution as the liquid fraction. The amount of lithium in the purified solution was determined by composition analysis using ICP atomic emission spectrometry. The lithium recovery rate was calculated from the above results, and the results are shown in Table 1.

[0049] [Table 1]

[0050] As shown in Table 1, the present invention achieves a high lithium recovery rate with fewer steps and inexpensive materials. [Industrial Applicability]

[0051] According to the present invention, lithium can be recovered with high efficiency and fewer steps from materials containing fluorine and lithium, from which lithium recovery has been difficult in the past. The method of the present invention does not require the use of an organic solvent for extraction, so it has a low environmental impact and can use inexpensive materials.

Claims

1. 1. A method for recovering lithium from a material containing fluorine and lithium, comprising: The material is mixed with an aqueous sulfuric acid solution or water to obtain a mixed solution, The method for recovering lithium includes mixing the mixed solution with a hardly soluble or slightly soluble calcium-containing alkaline agent so that the pH of the mixture is 10 or more and 14 or less, forming a precipitate containing fluorine and calcium, and then performing solid-liquid separation to obtain a purified solution in which lithium is dissolved.

2. 2. The method for recovering lithium according to claim 1, wherein, when obtaining the mixed solution, the material containing fluorine and lithium is mixed with an aqueous sulfuric acid solution or water, and the mixture is heated at a temperature in the range of 60°C to 90°C.

3. 3. The method for recovering lithium according to claim 1, wherein the material containing fluorine and lithium includes a solid that is a roasted product of lithium ion secondary battery scrap, or wastewater containing fluorine and lithium.

4. 4. The method for recovering lithium according to claim 1, wherein the material containing fluorine and lithium includes at least one of a lithium fluoride salt, a fluorophosphate salt, a fluorosulfonate salt, a fluoroborate salt, and a fluorosulfonylimide salt.

5. 5. The method for recovering lithium according to claim 1, wherein the hardly soluble or slightly soluble calcium-containing alkaline agent is calcium oxide, calcium hydroxide, or calcium carbonate.

6. 6. The method for recovering lithium according to claim 1, wherein the mixed solution and a poorly soluble or slightly soluble calcium-containing alkaline agent are mixed so that the pH of the mixture is 10 or more and 12 or less, thereby forming a precipitate containing fluorine and calcium.

7. 7. The method for recovering lithium according to claim 6, wherein the mixed solution and the poorly soluble or slightly soluble calcium-containing alkaline agent are mixed so that the mixture is heated to 60° C. or higher and 90° C. or lower and has a pH of 10 or higher and 12 or lower.

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