Method for producing lithium concentrate

Abstract

This lithium-concentrated liquid production method (S03) is characterized by comprising: a carbonation reaction step (S31) in which a soluble carbonic acid compound is added to a lithium-containing liquid having calcium ions coexisting therein to produce calcium carbonate; a solid-liquid separation step (S32) in which the calcium carbonate produced in the carbonation reaction step (S31) and the lithium-containing liquid are separated; a decarbonation step (S33) in which an inorganic acid is added to the lithium-containing liquid separated in the solid-liquid separation step (S32) and the dissolved carbonic acid compound is removed from the lithium-containing liquid as carbon dioxide gas; and a membrane separation step (S34) in which, after the decarbonation step (S33), a reverse osmosis membrane is used to obtain a lithium-concentrated liquid in which lithium ions in the lithium-containing liquid are concentrated.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a lithium concentrate, which is obtained by concentrating lithium ions contained in a lithium-containing solution. This application claims priority based on Japanese Patent Application No. 2024-006655, filed in Japan on January 19, 2024, Japanese Patent Application No. 2024-006659, filed in Japan on January 19, 2024, and Japanese Patent Application No. 2024-006790, filed in Japan on January 19, 2024, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, lithium has been recovered and reused from lithium-containing materials such as crushed lithium-ion batteries. As a method for recovering lithium from lithium-containing materials, as shown in Patent Documents 1 and 2, for example, there is known a method in which lithium ion battery waste is roasted to obtain battery slag, which is then immersed in an acidic solution to leach lithium into the acidic solution, and lithium is recovered from the resulting lithium leachate.

[0003] The lithium leachate from which lithium has been leached also contains metals other than lithium, such as cobalt and aluminum, but by adding calcium hydroxide or the like and neutralizing it, mainly the metals other than lithium are precipitated, and further solid-liquid separation is performed to separate the lithium-containing solution from the other substances. Carbonate is then added to the lithium-containing solution to recover lithium as lithium carbonate.

[0004] Here, Patent Document 1 proposes a technical method for concentrating lithium in a lithium-containing solution using a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane. Furthermore, Patent Document 2 proposes a method for concentrating lithium in a lithium-containing solution using an electrodialysis device having an ion exchange membrane.

[0005] However, when calcium is contained in the lithium-containing liquid, calcium precipitates on ion exchange membranes, nanofiltration (NF) membranes, and reverse osmosis (RO) membranes, resulting in a problem of reduced permeation flow rate through the membranes. Therefore, Patent Document 2 proposes reducing the calcium content to 10 mg / L or less by precipitating and separating calcium as calcium carbonate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-164547 [Patent Document 2] Japanese Patent Application Publication No. 2023-106309 Summary of the Invention [Problem to be solved by the invention]

[0007] However, as shown in Patent Document 2, it is not easy to reduce the calcium content to 10 mg / L or less without precipitating lithium, and it has been difficult to sufficiently suppress the decrease in the membrane permeation flow rate due to calcium precipitation. Furthermore, if carbonate ions remain in the lithium-containing liquid, carbon dioxide gas may be generated in the permeable membrane module, which may reduce the permeation flow rate through the membrane.Furthermore, when the lithium-containing liquid is concentrated, calcium carbonate may be precipitated, which may reduce the permeation flow rate through the membrane.

[0008] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a lithium concentrated solution that can suppress a decrease in the permeation flow rate of a membrane and efficiently and stably concentrate lithium ions contained in a lithium-containing solution. [Means for solving the problem]

[0009] In order to solve the above problems, a method for producing a lithium concentrated solution according to a first aspect of the present invention is characterized by comprising: a carbonation reaction step of adding a soluble carbonate compound to a lithium-containing solution coexisting with calcium ions to produce calcium carbonate; a solid-liquid separation step of separating the calcium carbonate produced in the carbonation reaction step from the lithium-containing solution; a decarbonation step of adding an inorganic acid to the lithium-containing solution separated in the solid-liquid separation step to remove the dissolved carbonate compound as carbon dioxide from the lithium-containing solution; and a membrane separation step of obtaining a lithium concentrated solution in which lithium ions in the lithium-containing solution are concentrated using a reverse osmosis membrane after the decarbonation step.

[0010] According to the method for producing a lithium concentrated solution of aspect 1 of the present invention, a decarbonation step is provided before the membrane separation step, in which an inorganic acid is added to the lithium-containing solution separated in the solid-liquid separation step to remove dissolved carbonate compounds as carbon dioxide from the lithium-containing solution. Therefore, the amount of carbonate compounds contained in the lithium-containing solution supplied to the membrane separation step is sufficiently reduced, generation of carbon dioxide gas in the permeable membrane module is suppressed, and precipitation of calcium carbonate is suppressed even when the lithium-containing solution is concentrated. As a result, the permeation flow rate of the reverse osmosis membrane is ensured in the membrane separation step, and it becomes possible to efficiently and stably concentrate lithium ions contained in the lithium-containing solution.

[0011] A method for producing a lithium concentrated solution according to a second aspect of the present invention is characterized in that, in the method for producing a lithium concentrated solution according to the first aspect, the lithium-containing solution supplied to the carbonation reaction step has a lithium concentration of 1 g / L or more and 15 g / L or less, and a calcium concentration of 10 mg / L or more. According to the method for producing a lithium concentrated solution of the second aspect of the present invention, the lithium concentration in the lithium-containing solution supplied to the carbonation reaction step is 1 g / L or more and 15 g / L or less, so that lithium can be efficiently concentrated. Also, the calcium concentration supplied to the carbonation reaction step is 10 mg / L or more, so that the effect of calcium removal can be obtained by the carbonation reaction step and the solid-liquid separation step, and the amount of carbonate compounds can be sufficiently reduced by the decarbonation step, so that precipitation of calcium carbonate can be reliably suppressed when the lithium-containing solution is concentrated.

[0012] A method for producing a lithium concentrate according to a third aspect of the present invention is characterized in that, in the method for producing a lithium concentrate according to the first or second aspect, the pH in the carbonation reaction step is 8.0 or more and 12.0 or less. According to the method for producing a lithium concentrated solution of the third aspect of the present invention, the pH in the carbonation reaction step is set to 8.0 or more and 12.0 or less, so that the production of calcium carbonate can be promoted and the amount of calcium in the lithium-containing solution can be efficiently reduced.

[0013] A fourth aspect of the present invention is a method for producing a lithium concentrate according to any one of the first to third aspects, characterized in that the pH in the decarbonation step is 3.0 or higher and 7.0 or lower. According to the method for producing a lithium concentrate of the fourth aspect of the present invention, the pH in the decarbonation step is set to 3.0 or more and 7.0 or less, which makes it possible to suppress damage to the reverse osmosis membrane in the membrane separation step and further promote the generation of carbon dioxide gas.

[0014] A fifth aspect of the present invention is a method for producing a lithium concentrated solution according to any one of the first to fourth aspects, characterized in that the lithium concentrated solution obtained by the membrane separation step has a lithium concentration of 18 g / L or more. According to the method for producing a lithium concentrated solution of aspect 5 of the present invention, the lithium concentration in the lithium concentrated solution obtained by the membrane separation step is set to 18 g / L or more, so that a lithium concentrated solution in which lithium is sufficiently concentrated can be obtained, and lithium can be efficiently recovered.

[0015] A sixth aspect of the present invention is a method for producing a lithium concentrated solution according to any one of the first to fifth aspects, characterized in that the calcium carbonate recovered in the solid-liquid separation step is returned to the carbonation reaction step and utilized as seed crystals for calcium carbonate to be produced. According to the method for producing a lithium concentrated solution of aspect 6 of the present invention, the calcium carbonate recovered in the solid-liquid separation step is returned to the carbonation reaction step to be used as seed crystals for calcium carbonate to be produced, thereby promoting the production of calcium carbonate in the carbonation reaction step and enabling efficient removal of calcium.

[0016] A method for producing a lithium concentrate according to a seventh aspect of the present invention is characterized in that, in the method for producing a lithium concentrate according to any one of the first to sixth aspects, sulfuric acid, hydrochloric acid, nitric acid, or a mixed solution thereof is used as the inorganic acid used in the decarbonation step. According to the method for producing a lithium concentrate of the seventh aspect of the present invention, sulfuric acid, hydrochloric acid, nitric acid, or a mixed solution of two or more selected from these is used as the inorganic acid used in the decarbonation step, so that carbonate compounds can be efficiently removed as carbon dioxide gas in the decarbonation step. [Effects of the Invention]

[0017] According to an aspect of the present invention, it is possible to provide a method for producing a lithium concentrated solution that can suppress a decrease in the permeation flow rate of a membrane and efficiently and stably concentrate lithium ions contained in a lithium-containing solution. [Brief explanation of the drawings]

[0018] [Figure 1]FIG. 1 is a flow diagram showing a method for recovering lithium using a method for producing a lithium concentrate according to one embodiment of the present invention. [Figure 2] FIG. 2 is a flow chart showing an impurity removal step in FIG. [Figure 3] FIG. 2 is a flow chart showing a method for producing a lithium-concentrated solution according to one embodiment of the present invention, which is applied as the lithium-containing solution concentrating step in FIG. 1. [Figure 4] FIG. 2 is a flow chart showing a lithium carbonate production step in FIG. 1. [Figure 5] FIG. 2 is a flow chart showing a lithium carbonate purification step in FIG. 1. [Figure 6] 1 is a graph showing the relationship between the pH of the liquid and the lithium concentration in the liquid in the bicarbonation step. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a method for producing a lithium concentrate according to one embodiment of the present invention will be described with reference to the drawings. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the present invention. Furthermore, the "solution" described in the specification is an aqueous solution.

[0020] The method for producing a lithium concentrate according to this embodiment is applied to a process for recovering lithium from lithium-containing materials such as crushed waste lithium-ion batteries. First, a lithium recovery method to which the method for producing a lithium concentrate according to the present embodiment is applied will be described with reference to FIG.

[0021] As shown in FIG. 1, the lithium recovery method includes a leaching step S01, an impurity removal step S02, a lithium-containing solution concentration step S03, a lithium carbonate production step S04, and a lithium carbonate purification step S05.

[0022] (Leaching process S01) In the leaching step S01, lithium-containing materials such as crushed lithium-ion batteries are immersed in an acidic solution to leach lithium into the acidic solution, thereby obtaining a lithium leachate. As the acidic solution, for example, an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid can be used alone, or a mixture of two or more inorganic acids can be used. In this embodiment, sulfuric acid is used as the acid. In this embodiment, the lithium-containing material and sulfuric acid are mixed and stirred (stirring time: 30 minutes to 20 hours) to dissolve the lithium in the lithium-containing material, thereby obtaining a lithium leachate.

[0023] The pH of the lithium leachate is not particularly limited, and can be, for example, between 1.0 and 2.0. The leachate also contains metals other than lithium, such as fluorine. The metals contained in the leachate vary depending on the lithium-containing material used, but examples include cobalt, nickel, and manganese, which are used as positive electrode active materials, and copper, aluminum, and iron, which are used as battery current collectors and exterior materials.

[0024] (Impurity removal process S02) Next, impurities contained in the lithium leachate are removed. The impurity removal step S02 includes a first calcium compound addition step S21, a first solid-liquid separation step S22, a second calcium compound addition step S23, and a second solid-liquid separation step S24, as shown in Fig. 2.

[0025] In the first calcium compound addition step S21, the first calcium compound is added to the lithium leachate to produce metal hydroxide and calcium fluoride, which are separated out and precipitated in the solution as solid phases. The first calcium compound is added, for example, while stirring the lithium leachate. The first calcium compound is not particularly limited as long as it is basic, and solid calcium compounds such as calcium carbonate, calcium hydroxide, calcium oxide, or mixtures thereof can be used. The pH of the lithium leachate during production of metal hydroxide and calcium fluoride is adjusted to be 8.0 or higher and 12.0 or lower.

[0026] In the first solid-liquid separation step S22, the metal hydroxide and calcium fluoride produced in the first calcium compound addition step S21 are removed from the lithium leachate. The method for removing the metal hydroxide and calcium fluoride can be appropriately selected from existing solid-liquid separation methods such as gravity settling, centrifugation, or filter cloth filtration using a filter press or the like.

[0027] In the second calcium compound addition step S23, a second calcium compound is added to the lithium leachate from which the precipitate has been removed in the first solid-liquid separation step S22, thereby precipitating dissolved fluorine. The second calcium compound is not particularly limited as long as it is a basic calcium compound that can control the pH to 5.0 or more and 9.0 or less, and for example, solid calcium compounds such as calcium carbonate, calcium hydroxide, calcium oxide, or mixtures thereof can be used. The pH of the lithium leachate when producing a precipitate of dissolved fluorine (e.g., calcium fluoride) is adjusted by first adding aluminum sulfate to adjust the pH to 5.0 or less, and then adding a second calcium compound to adjust the pH to 5.0 or more and 9.0 or less. This allows dissolved fluorine that was not completely removed in the first calcium compound addition step S21 and the first solid-liquid separation step S22 to be precipitated as a precipitate of dissolved fluorine. Note that a portion of the unreacted second calcium compound precipitates together with the precipitate of dissolved fluorine. The pH of the lithium leaching solution in the second calcium compound addition step S23 is preferably 6.5 or higher, and more preferably 7.0 or higher. The pH of the lithium leaching solution in the second calcium compound addition step S23 is more preferably 8.0 or lower, and even more preferably 7.5 or lower.

[0028] In the second solid-liquid separation step S24, the precipitate of dissolved fluorine precipitated in the second calcium compound addition step S23 and the unreacted second calcium compound are removed from the lithium leaching solution to obtain a lithium-containing solution. The method for removing the precipitate can be appropriately selected from existing solid-liquid separation methods such as gravity settling, centrifugation, or filter cloth filtration using a filter press or the like.

[0029] In the impurity removal step S02, in order to reduce chemical costs and the amount of sludge generated, the first calcium compound added in the first calcium compound addition step S21 may be a precipitate of dissolved fluorine separated and recovered in the second solid-liquid separation step S24 and an unreacted portion of the second calcium compound. Furthermore, the second calcium compound added in the second calcium compound addition step S23 may be calcium carbonate obtained in a solid-liquid separation step S32 after a carbonation reaction step S31 (described later) or calcium carbonate obtained in a first solid-liquid separation step S42 after a first carbonation reaction step S41. Furthermore, the solid content removed in the second solid-liquid separation step S24 may be used as seed crystals in the second calcium compound addition step S23.

[0030] By the above-mentioned steps, it is possible to obtain a lithium-containing solution containing lithium from a lithium-containing material. Here, calcium remains in the lithium-containing solution obtained by the above-mentioned impurity removal step S02. That is, lithium ions and calcium ions coexist in the lithium-containing solution.

[0031] (Lithium-containing liquid concentration step S03) Next, the lithium ions contained in the obtained lithium-containing solution are concentrated to obtain a lithium-concentrated solution. The method for producing a lithium-concentrated solution according to one embodiment of the present invention is applied to this lithium-containing solution concentration step S03. The method for producing a lithium concentrated solution of this embodiment (lithium-containing solution concentrating step S03) includes, as shown in FIG. 3, a carbonation reaction step S31, a solid-liquid separation step S32, a decarbonation step S33, and a membrane separation step S34.

[0032] In the carbonation reaction step S31, a soluble carbonate compound (water-soluble carbonate compound) is added to the lithium-containing solution to precipitate dissolved calcium as calcium carbonate. Examples of the soluble carbonate compound that can be used include sodium carbonate and sodium bicarbonate in the form of a solution or powder. Alternatively, carbon dioxide gas may be directly blown in. This reaction is preferably carried out at a temperature of 5°C or higher and 50°C or lower, and particularly preferably at a temperature of 10°C or higher and 30°C or lower. Setting the solution temperature below 5°C is undesirable because it reduces the reaction efficiency. Setting the solution temperature above 50°C is also undesirable because it accelerates the precipitation of lithium carbonate, resulting in a loss of lithium.

[0033] Here, in the carbonation reaction step S31, the amount of substance (number of moles) of the soluble carbonate compound to be added and the amount of substance (number of moles) of calcium in the lithium concentrated solution are in the stoichiometric ratio (CO 2- / Ca 2+ ) (molar ratio) is preferably within the range of 1.0 or more and 10.0 or less. Stoichiometric ratio (CO3 2- / Ca 2+ ) is 1.0 or more, calcium ions can be sufficiently precipitated as calcium carbonate. 2- / Ca 2+ ) is 10.0 or less, it is possible to suppress the precipitation of lithium as lithium carbonate.

[0034] In addition, the stoichiometric ratio (CO3 2- / Ca 2+ ) is more preferably 2.0 or more, and even more preferably 3.0 or more. In addition, the stoichiometric ratio (CO3 2- / Ca 2+ ) is more preferably 7.0 or less, and even more preferably 5.0 or less. Furthermore, calcium carbonate may be added as seed crystals before the addition of the soluble carbonate compound. Furthermore, aluminum sulfate may be added as a flocculant together with the polymer flocculant. By adding aluminum sulfate, the precipitated calcium carbonate can be aggregated into larger flocs so that they do not remain in the supernatant liquid, and solid-liquid separation can be performed more reliably even when solid-liquid separation is performed by a gravity settling separation method such as a thickener. The concentration of aluminum sulfate in the lithium-containing solution is preferably 0 mg / L or more and 110 mg / L or less, and more preferably 27 mg / L or more and 83 mg / L or less. An aluminum sulfate concentration of less than 27 mg / L is not preferred because coagulation does not occur sufficiently. An aluminum sulfate concentration of more than 110 mg / L is not preferred because the volume of the precipitated solids, including calcium carbonate, increases, and in order to perform sufficient solid-liquid separation by gravity settling, the settling equipment must be large-scale. Examples of polymer flocculants include Diaflock AP825 and Diaflock NP500 manufactured by MT Aquapolymer Co., Ltd. The concentration of the polymer flocculant in the lithium-containing liquid is preferably 1 to 10 ppm. For example, 2 mL of a 0.05% AP825 solution is added per 1 L of lithium-containing liquid. Also, 1 mL of a 0.1% NP500 solution is added per 1 L of lithium-containing liquid.

[0035] In the carbonation reaction step S31, the pH of the lithium-containing liquid is preferably set within a range of 8.0 to 12.0. By adjusting the pH of the lithium-containing solution to a range of 8.0 to 12.0, the production of calcium carbonate can be promoted. The pH of the lithium-containing liquid in the carbonation reaction step S31 is more preferably 9.0 or higher, and even more preferably 10.0 or higher. The pH of the lithium-containing liquid in the carbonation reaction step S31 is more preferably 11.0 or lower.

[0036] Furthermore, it is preferable that the lithium concentration in the lithium-containing liquid to be treated is 1 g / L or more and 15 g / L or less, and the calcium concentration is 10 mg / L or more and 100 mg / L or less. The lithium concentration in the lithium-containing solution to be treated is more preferably 1 g / L or more, and even more preferably 5 g / L or more, and more preferably 15 g / L or less, and even more preferably 13 g / L or less. Furthermore, the calcium concentration in the lithium-containing liquid to be treated is more preferably 10 mg / L or more, and even more preferably 20 mg / L or more, and preferably 100 mg / L or less, and even more preferably 50 mg / L or less.

[0037] In the solid-liquid separation step S32, the calcium carbonate produced in the carbonation reaction step S31 is separated from the lithium-containing liquid. As a method for separating the calcium carbonate from the lithium-containing liquid, an existing solid-liquid separation method such as a gravity settling separation method, a centrifugal separation method, or a filter cloth filtration method such as a filter press can be appropriately selected and used.

[0038] In the decarbonation step S33, an inorganic acid is added to the lithium-containing liquid separated in the solid-liquid separation step S32, and the dissolved carbonate compounds are removed from the lithium-containing liquid as carbon dioxide gas. The inorganic acid to be added may be, for example, sulfuric acid, nitric acid, hydrochloric acid, or a mixed acid of two or more selected from these.

[0039] Here, in the decarbonation step S33, it is preferable to adjust the pH of the lithium-containing liquid to a range of 3.0 or more and 7.0 or less. By setting the pH of the lithium-containing liquid to 3.0 or higher, it is possible to suppress damage to the reverse osmosis membrane caused by acid in the membrane separation step S34 described below. On the other hand, by setting the pH of the lithium-containing liquid to 7.0 or lower, it is possible to promote the generation of carbon dioxide gas. This allows carbonate compounds to be sufficiently removed from the lithium-containing liquid as carbon dioxide gas in the decarbonation step S33, thereby suppressing damage to the reverse osmosis membrane caused by precipitation of calcium carbonate in the membrane separation step S34. The pH of the lithium-containing liquid in the decarboxylation step S33 is more preferably 3.0 or higher, and even more preferably 6.0 or higher. The pH of the lithium-containing liquid in the decarboxylation step S33 is more preferably 7.0 or lower, and even more preferably 6.5 or lower.

[0040] In the membrane separation step S34, after the decarbonation step S33, lithium ions in the lithium-containing solution are concentrated using a reverse osmosis membrane. As the reverse osmosis membrane, for example, a reverse osmosis membrane having a hollow fiber type, spiral type, tubular type, or the like structure made of a material such as cellulose acetate can be used. Here, the lithium concentration in the lithium concentrated solution obtained in the membrane separation step S34 is preferably 18 g / L or more. In addition, the upper limit of the lithium concentration in this lithium concentrated solution is preferably 35 g / L or less, taking into account the solubility of lithium sulfate.

[0041] By the above steps, a lithium-concentrated solution is produced in which the lithium ions in the lithium-containing solution are concentrated. Note that calcium ions may remain in this lithium-concentrated solution.

[0042] (Lithium carbonate production process S04) Next, lithium carbonate is produced using the lithium-containing concentrated lithium solution as a raw material. The lithium carbonate production step S04 includes a first carbonation reaction step S41, a first solid-liquid separation step S42, a second carbonation reaction step S43, and a second solid-liquid separation step S44, as shown in Fig. 4.

[0043] In the first carbonation reaction step S41, a first soluble carbonate compound (first water-soluble carbonate compound) is added to a lithium concentrate in which lithium ions and calcium ions coexist, and the mixture is heated to produce calcium carbonate. Note that in the first carbonation reaction step S41, the lithium concentrate may be heated after the addition of the first soluble carbonate compound, or the first soluble carbonate compound may be added while heating the lithium concentrate. The first soluble carbonate compound can be, for example, sodium carbonate or sodium bicarbonate in the form of a solution or powder. Alternatively, carbon dioxide gas can be blown in to solubilize the carbonate and cause it to react with the dissolved calcium.

[0044] Here, in the first carbonation reaction step S41, the amount of substance (number of moles) of the first soluble carbonate compound to be added and the amount of substance (number of moles) of calcium in the lithium concentrated solution are in a stoichiometric ratio (CO 2- / Ca 2+ ) (molar ratio) is preferably within the range of 1.0 or more and 10.0 or less. Stoichiometric ratio (CO3 2- / Ca 2+ ) is 1.0 or more, calcium ions can be sufficiently precipitated as calcium carbonate. 2- / Ca 2+ ) is 10.0 or less, it is possible to suppress the precipitation of lithium as lithium carbonate. In addition, the stoichiometric ratio (CO3 2- / Ca 2+ ) is more preferably 2.0 or more, and even more preferably 3.0 or more. In addition, the stoichiometric ratio (CO3 2- / Ca 2+ ) is more preferably 7.0 or less, and even more preferably 5.0 or less.

[0045] The pH of the lithium concentrate in the first carbonation reaction step S41 is preferably 9.0 or more and 11.0 or less. By adjusting the pH of the lithium concentrate in the first carbonation reaction step S41 to 9.0 or more and 11.0 or less, it is possible to promote the production of calcium carbonate. The pH of the lithium concentrate in the first carbonation reaction step S41 is more preferably 9.5 or higher, and even more preferably 10.0 or higher.

[0046] The heating temperature in the first carbonation reaction step S41 is preferably within the range of 40°C or higher and 95°C or lower. By setting the heating temperature in the first carbonation reaction step S41 to 40°C or higher, it is possible to promote the production of calcium carbonate. On the other hand, by setting the heating temperature in the first carbonation reaction step S41 to 95°C or lower, an increase in pressure inside the reaction tank is suppressed, and the first carbonation reaction step S41 can be carried out stably. The heating temperature in the first carbonation reaction step S41 is more preferably 60°C or higher, and even more preferably 90°C or higher.

[0047] In the first solid-liquid separation step S42, the calcium carbonate produced in the first carbonation reaction step S41 is separated from the lithium concentrated solution. As a method for separating the calcium carbonate from the lithium concentrated solution, an existing solid-liquid separation method such as gravity settling separation, centrifugation, or filter cloth filtration using a filter press or the like can be appropriately selected and used.

[0048] In the second carbonation reaction step S43, a second soluble carbonate compound (second water-soluble carbonate compound) is added to the lithium concentrate from which calcium carbonate has been separated, and the mixture is heated to produce lithium carbonate. The second soluble carbonate compound can be, for example, sodium carbonate or sodium bicarbonate. The second soluble carbonate compound can be in the form of a powder, a slurry, or a solution. A slurry is composed of an aqueous solution and particles of the second soluble carbonate compound, and more particles of the second soluble carbonate compound than the solubility of the second soluble carbonate compound are not dissolved in the aqueous solution. Carbon dioxide gas can also be blown into the solution to solubilize the second soluble carbonate compound, allowing it to react with the dissolved calcium. The second soluble carbonate compound is preferably in the form of a powder. This allows the impurities (SO4 2- The amount of Zn, Na, etc. can be reduced. When the second soluble carbonate compound is in the form of a powder, the average particle size is preferably 10 to 100 μm. The average particle size is the volume-based D50 (median diameter) measured by a laser diffraction scattering method.

[0049] Regarding the amount of the second soluble carbonate compound added, the amount of carbonate ions (CO3 2- ) ratio (moles) of CO3 2- / 2Li + It is preferable to adjust the amount of the second soluble carbonate compound added so that the ratio (%) is 1.0 or more and 5.0 or less. This makes it possible to reduce the amounts of Ca and Al contained in the produced lithium carbonate.

[0050] The addition rate of the second soluble carbonate compound (the amount added per second per 8 g of Li in the lithium concentrate) is preferably 0.05 to 1 g / s. This allows the impurities (SO4 2- , Zn, Na, etc.) can be reduced. When the second soluble carbonate compound is in the form of a slurry or solution, the addition rate of the second soluble carbonate compound is a value converted into the amount of the second soluble carbonate compound contained in the slurry or solution, and can also be referred to as the addition rate of the second soluble carbonate compound contained in the slurry or solution.

[0051] In the second carbonation reaction step S43, the lithium concentrated solution may be heated after the second soluble carbonate compound is added, or the second soluble carbonate compound may be added while heating the lithium concentrated solution, but as described below, it is preferable to add the second soluble carbonate compound at 15 to 25°C (room temperature) and then heat the lithium concentrated solution. The heating temperature in the second carbonation reaction step S43 is preferably within the range of 80°C or higher and 95°C or lower. By setting the heating temperature in the second carbonation reaction step S43 to 80°C or higher, it is possible to promote the production of lithium carbonate. On the other hand, by setting the heating temperature in the second carbonation reaction step S43 to 95°C or lower, an increase in pressure inside the reaction tank is suppressed, and the second carbonation reaction step S43 can be carried out stably. The heating temperature in the second carbonation reaction step S43 is more preferably 85°C or higher, and even more preferably 90°C or higher. If the temperature of the lithium concentrate is low when sodium carbonate is added, the crystal growth of the lithium carbonate produced will be slower, and the amount of impurities contained therein can be reduced. However, in order to produce lithium carbonate at a high recovery rate, it is necessary to heat the lithium concentrate. Therefore, at the stage of adding the second soluble carbonate compound to the lithium concentrate, it is preferable to set the temperature of the lithium concentrate to 15 to 25°C. Then, after adding the second soluble carbonate compound to the lithium concentrate, it is preferable to set the temperature of the lithium concentrate within a range of 80 to 95°C. This will reduce the amount of impurities (SO4 2- , Zn, Na, etc.) can be reduced. The sulfate ions (SO4 2- ) is preferably 1% by mass or less.

[0052] Here, in the lithium carbonate production step S04, it is preferable to return the carbonate compound containing calcium carbonate recovered in the first solid-liquid separation step S42 to the first carbonation reaction step S41. In the first carbonation reaction step S41, the production of calcium carbonate can be promoted by using the returned calcium carbonate as seed crystals. In addition, lithium carbonate produced together with calcium carbonate can be returned to the first carbonation reaction step S41, which makes it possible to improve the recovery efficiency of lithium.

[0053] In the second solid-liquid separation step S44, the lithium carbonate produced in the second carbonation reaction step S43 is separated from the mother liquor. As a method for separating lithium carbonate, an existing solid-liquid separation method such as gravity settling separation, centrifugation, or filter cloth filtration using a filter press or the like can be appropriately selected and used. The above process produces lithium carbonate, which may contain more than 400 mass ppm of calcium.

[0054] (Lithium carbonate refining process S05) Next, in order to further improve the purity of the lithium carbonate obtained in the lithium carbonate production step S04, the lithium carbonate is purified. As shown in FIG. 5, the lithium carbonate purification step S05 includes a slurrying step S51, a bicarbonation step S52, a first solid-liquid separation step S53, a purified lithium carbonate crystallization step S54, a second solid-liquid separation step S55, and a mother liquor returning step S56.

[0055] In the slurrying step S51, water is added to the lithium carbonate to produce a lithium carbonate slurry. The lithium carbonate contains, for example, 400 mass ppm or more of calcium. The amount of calcium contained in the lithium carbonate is preferably 5000 mass ppm or less. If the amount of calcium exceeds 5000 mass ppm, a large amount of calcium remains, which is likely to cause clogging when the solid content (calcium carbonate) is separated by filtration in the first solid-liquid separation step S53 described below. Here, it is preferable that the lithium carbonate concentration in the lithium carbonate slurry produced in the slurrying step S51 is within the range of 30 g / L or more and 45 g / L or less. By setting the concentration of lithium carbonate in the lithium carbonate slurry within the above-described range, lithium bicarbonate can be sufficiently produced in the bicarbonation step S52 described below, and residual lithium carbonate can be suppressed, making it possible to more efficiently produce purified lithium carbonate. The lithium carbonate concentration in the lithium carbonate slurry is more preferably 35 g / L or more, and more preferably 38 g / L or more, and more preferably 44 g / L or less, and more preferably 43 g / L or less.

[0056] In the bicarbonation step S52, CO2 gas is blown into the lithium carbonate slurry to produce soluble lithium bicarbonate, thereby obtaining a lithium bicarbonate solution. That is, as shown in formula (1), solid-phase lithium carbonate reacts with carbon dioxide gas to become lithium bicarbonate, which dissolves in water as a solvent, thereby producing a lithium bicarbonate solution. Li2CO3+H2O+CO2→2LiHCO3···(1)

[0057] Here, the pH in the bicarbonation step S52 is preferably 7.5 or higher and 12 or lower. In the bicarbonation step S52, as CO2 gas is blown in, lithium bicarbonate dissolves in the liquid, and the pH of the lithium bicarbonate liquid decreases. The relationship between the pH of the lithium bicarbonate solution and the lithium concentration in the solution is shown in Figure 6. As the pH of the lithium bicarbonate solution decreases due to the injection of CO2 gas, the lithium concentration in the solution increases, but when the pH is below 7.5, no increase in the lithium concentration is observed. Therefore, by setting the pH to 7.5 or more in the bicarbonation step S52, it is possible to reduce the amount of CO2 gas used and also to suppress the incorporation of calcium as calcium bicarbonate in the bicarbonation step S52, thereby making it possible to produce purified lithium carbonate with even higher purity. In the bicarbonation step S52, the pH at the time when the blowing of CO2 gas is stopped is preferably 7.5 or more and less than 8.0.

[0058] In addition, in the bicarbonation step S52, the liquid temperature is preferably set to 5°C or higher and 30°C or lower. In the bicarbonation step, when CO2 gas reacts with lithium carbonate to produce lithium bicarbonate, the liquid temperature rises due to the heat of reaction. Because the solubility of lithium carbonate dissolved in the solution decreases as the liquid temperature rises, an increase in the liquid temperature can cause lithium carbonate to precipitate. In this case, calcium carbonate in the lithium carbonate slurry is also entrained and co-precipitated, forming a deposit called scale (calcium carbonate, lithium carbonate) on the surface of the tank and the agitator blades. By keeping the liquid temperature at 30°C or below in the bicarbonation step S52, the generation of scale can be suppressed in the bicarbonation step S52, enabling a stable production of lithium bicarbonate liquid. Considering the energy cost and the capacity of the cooling device, it is preferable to set the liquid temperature to 5°C or higher.

[0059] In the first solid-liquid separation step S53, the lithium bicarbonate liquid produced in the bicarbonation step S52 is separated from the remaining solid content (calcium carbonate). As a method for separating the lithium bicarbonate liquid from the remaining solid content, an existing solid-liquid separation method such as gravity settling separation, centrifugation, or filter cloth filtration using a filter press or the like can be appropriately selected and used.

[0060] In the purified lithium carbonate crystallization step S54, the lithium bicarbonate solution from which calcium carbonate has been removed is heated to decompose the lithium bicarbonate and precipitate purified lithium carbonate. That is, as shown in formula (2), lithium carbonate is precipitated by releasing carbon dioxide gas from the lithium bicarbonate upon heating. 2LiHCO3→Li2CO3+H2O+CO2···(2)

[0061] Here, in the purified lithium carbonate crystallization step S54, the liquid temperature is preferably set within a range of 85°C or higher and 98°C or lower. By setting the liquid temperature to 85°C or higher, the decomposition of lithium bicarbonate is promoted, and purified lithium carbonate can be efficiently precipitated. Furthermore, by setting the liquid temperature to 98°C or lower, an increase in pressure inside the reaction tank is suppressed, and the purified lithium carbonate crystallization step S54 can be stably carried out. The liquid temperature in the purified lithium carbonate crystallization step S54 is more preferably 87° C. or higher, and even more preferably 90° C. or higher. The liquid temperature in the purified lithium carbonate crystallization step S54 is more preferably 97° C. or lower, more preferably 96° C. or lower, and even more preferably 95° C. or lower.

[0062] It is also preferable to use the carbon dioxide gas (CO2 gas) generated in the purified lithium carbonate crystallization step S54 in the bicarbonation step S52, which makes it possible to reduce the amount of CO2 gas used and reduce operation costs.

[0063] In the second solid-liquid separation step S55, the purified lithium carbonate produced in the purified lithium carbonate crystallization step S54 is separated from the mother liquor. As a method for separating the purified lithium carbonate from the mother liquor, an existing solid-liquid separation method such as a gravity settling separation method, a centrifugal separation method, or a filter cloth filtration method such as a filter press can be appropriately selected and used.

[0064] In the mother liquor returning step S56, the mother liquor from which purified lithium carbonate has been separated in the second solid-liquid separation step S55 is returned to the slurrying step S51. Lithium remains in the mother liquor from which purified lithium carbonate has been separated in the second solid-liquid separation step S55. Therefore, by returning this mother liquor to the slurrying step S51, the remaining lithium can be contained in the lithium carbonate slurry that serves as the raw material, thereby making it possible to improve the recovery efficiency of lithium.

[0065] Through the above-described steps, it becomes possible to recover highly purified lithium carbonate from lithium-containing materials such as crushed waste lithium-ion batteries.

[0066] According to the method for producing a lithium-concentrated liquid of this embodiment, which is applied as the lithium-containing-liquid concentrating step S03, a decarbonation step S33 is provided before the membrane separation step S34. In the decarbonation step S33, an inorganic acid is added to the lithium-containing liquid separated in the solid-liquid separation step S32 to remove dissolved carbonate compounds from the lithium-containing liquid as carbon dioxide. Therefore, the amount of carbonate compounds contained in the lithium-containing liquid supplied to the membrane separation step S34 is sufficiently reduced, suppressing the generation of carbon dioxide gas in the permeable membrane module and suppressing the precipitation of calcium carbonate even when the lithium-containing liquid is concentrated. This ensures a sufficient permeation flow rate through the reverse osmosis membrane in the membrane separation step S34, making it possible to efficiently and stably concentrate lithium ions contained in the lithium-containing liquid.

[0067] In this embodiment, when the lithium concentration in the lithium-containing liquid supplied to the carbonation reaction step S31 is set to 1 g / L or more and 15 g / L or less, it is possible to efficiently concentrate lithium. Furthermore, when the calcium concentration in the lithium-containing liquid supplied to the carbonation reaction step S31 is 10 mg / L or more, the amount of carbonate compounds can be sufficiently reduced by the decarbonation step S33, thereby reliably suppressing the generation of carbon dioxide gas in the permeable membrane module and reliably suppressing the precipitation of calcium carbonate even when the lithium-containing liquid is concentrated.

[0068] In this embodiment, when the pH in the carbonation reaction step S31 is set to 8.0 or more and 12.0 or less, the production of calcium carbonate can be promoted, and the amount of calcium in the lithium-containing liquid can be efficiently reduced.

[0069] In this embodiment, when the pH in the decarbonation step S33 is set to 3.0 or more and 7.0 or less, damage to the reverse osmosis membrane in the membrane separation step S34 can be suppressed and the generation of carbon dioxide gas can be further promoted.

[0070] In this embodiment, when the lithium concentration in the lithium concentrated solution obtained by the membrane separation step S34 is 18 g / L or more, a lithium concentrated solution in which lithium is sufficiently concentrated can be obtained, making it possible to efficiently recover lithium.

[0071] In the present embodiment, when the calcium carbonate recovered in the solid-liquid separation step S32 is returned to the carbonation reaction step S31 and used as seed crystals for the calcium carbonate to be produced, the production of calcium carbonate in the carbonation reaction step S31 can be promoted and calcium can be efficiently removed.

[0072] In this embodiment, when sulfuric acid, hydrochloric acid, nitric acid, or a mixed solution of two or more selected from these is used as the inorganic acid used in the decarbonation step S33, carbonate compounds can be efficiently removed as carbon dioxide gas in the decarbonation step S33.

[0073] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical requirements of the invention. In the present embodiment, as described above, among the lithium recovery method including the leaching step S01, the impurity removing step S02, the lithium-containing-liquid concentrating step S03, the lithium carbonate production step S04, and the lithium carbonate purification step S05, the method has been described as being applied to the lithium-containing-liquid concentrating step S03, but the present invention is not limited thereto, and there is no particular limitation as long as the method is for concentrating lithium ions in a lithium-containing liquid that contains lithium. [Example]

[0074] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0075] First, 20 L of the lithium-containing liquid to be tested was prepared, with a lithium concentration of 6 g / L, a calcium concentration of 400 mg / L, and a pH of 7.0. In the carbonation reaction step, sodium carbonate in the amount shown in Table 1 was added to the lithium-containing liquid, and the pH was adjusted to 10.0 with caustic soda (sodium hydroxide) or sulfuric acid, followed by stirring for 60 minutes. Note that in Comparative Examples 1 and 2, sodium carbonate was not added, and the carbonation reaction step was not carried out.

[0076] In the solid-liquid separation step, the solid matter was filtered using a membrane filter with a pore size of 0.45 μm. The calcium concentration in the lithium-containing liquid after filtration is shown in Table 1. In the decarbonation step, sulfuric acid was added to adjust the pH of the lithium-containing liquid to the value shown in Table 1. In Comparative Examples 1 and 3, sulfuric acid was not added, and the pH of the lithium-containing liquid was not adjusted. In the membrane separation step, the lithium-containing liquid was passed through a reverse osmosis membrane module (HOLLOSEP® BC membrane, manufactured by Toyobo MC Co., Ltd.) to obtain a lithium-enriched liquid.

[0077] The permeation flow rate in the membrane separation step and the lithium concentration of the obtained lithium concentrated solution were evaluated. The evaluation results are shown in Table 1. The lithium and calcium concentrations were measured by ICP atomic emission spectroscopy (Thermo Fisher Scientific, iCAP7600Duo). The permeation flow rate was calculated from the measured volume of the lithium-enriched solution that passed through the reverse osmosis membrane module over a certain period of time.

[0078] [Table 1]

[0079] In Comparative Example 1, the carbonation reaction step was not performed, and the pH adjustment by adding sulfuric acid was not performed, so the calcium concentration and pH in the lithium-containing solution were high, and the permeation flow rate in the membrane separation step was slow. In addition, the lithium concentration in the obtained lithium-concentrated solution was low, and lithium could not be concentrated efficiently.

[0080] In Comparative Example 2, the carbonation reaction step was not performed, so the calcium concentration in the lithium-containing solution was high, and the permeation flow rate in the membrane separation step was slow. In addition, the lithium concentration in the obtained lithium-concentrated solution was low, and lithium could not be concentrated efficiently.

[0081] In Comparative Example 3, since pH adjustment by addition of sulfuric acid was not performed, the calcium concentration and pH in the lithium-containing solution were high, and the permeation flow rate in the membrane separation step was slow. In addition, the lithium concentration in the obtained lithium-concentrated solution was low, and lithium could not be concentrated efficiently.

[0082] In contrast, in Examples 1 to 3 of the present invention, the carbonation reaction step, solid-liquid separation step, decarbonation step, and membrane separation step were performed, and therefore the permeation flow rate in the membrane separation step was increased. In addition, the lithium concentration in the obtained lithium concentrated solution was high, and lithium could be efficiently concentrated.

[0083] As a result of the above-mentioned confirmatory experiments, it was confirmed that the present invention can provide a method for producing a lithium concentrated solution that can suppress a decrease in the permeation flow rate of the membrane and efficiently and stably concentrate lithium ions contained in a lithium-containing solution. [Industrial Applicability]

[0084] The method for producing a lithium concentrate of the present embodiment is suitably applied to a process for recovering lithium from lithium-containing materials such as pulverized lithium-ion battery material. [Explanation of symbols]

[0085] S03 Lithium-containing liquid concentration process S31 Carbonation reaction process S32 Solid-liquid separation process S33 Decarboxylation process S34 Membrane separation process.

Claims

1. a carbonation reaction step of adding a soluble carbonate compound to a lithium-containing solution in which calcium ions coexist to produce calcium carbonate; a solid-liquid separation step of separating the calcium carbonate produced in the carbonation reaction step from the lithium-containing liquid; a decarbonation step of adding an inorganic acid to the lithium-containing liquid separated in the solid-liquid separation step to remove dissolved carbonate compounds from the lithium-containing liquid as carbon dioxide gas; a membrane separation step of concentrating lithium ions in the lithium-containing solution using a reverse osmosis membrane after the decarbonation step to obtain a lithium-concentrated solution; A method for producing a lithium concentrate, comprising:

2. 2. The method for producing a lithium concentrated solution according to claim 1, wherein the lithium-containing solution supplied to the carbonation reaction step has a lithium concentration of 1 g / L or more and 15 g / L or less and a calcium concentration of 10 mg / L or more.

3. 3. The method for producing a lithium concentrate according to claim 1, wherein the pH in the carbonation reaction step is 8.0 or more and 12.0 or less.

4. 3. The method for producing a lithium concentrate according to claim 1, wherein the pH in the decarbonation step is 3.0 or more and 7.0 or less.

5. 3. The method for producing a lithium concentrate according to claim 1, wherein the lithium concentrate obtained by the membrane separation step has a lithium concentration of 18 g / L or more.

6. 3. The method for producing a lithium concentrated solution according to claim 1, wherein the calcium carbonate recovered in the solid-liquid separation step is returned to the carbonation reaction step and used as seed crystals for calcium carbonate to be produced.

7. 3. The method for producing a lithium concentrate according to claim 1, wherein the inorganic acid used in the decarbonation step is sulfuric acid, hydrochloric acid, nitric acid, or a mixture thereof.

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