Method for producing lithium carbonate

Abstract

This method for producing lithium carbonate (S04) comprises: a first carbonation reaction step (S41) for adding a soluble carbonate compound to a lithium-containing liquid in which calcium ions are also present and heating to produce calcium carbonate; a first solid-liquid separation step (S42) for separating the calcium carbonate generated in the first carbonation reaction step (S41) and the lithium-containing liquid; a second carbonation reaction step (S43) for adding a soluble carbonate compound to the lithium-containing liquid separated in the first solid-liquid separation step (S42) and heating to produce lithium carbonate; and a second solid-liquid separation step (S44) for separating the lithium carbonate generated in the second carbonation reaction step (S43) and the mother liquor.

Description

Lithium carbonate manufacturing method

[0001] The present invention relates to a method for producing lithium carbonate using a lithium-containing liquid as a raw material. This application claims priority based on Japanese Patent Application No. 2024-006655 filed on January 19, 2024, Japanese Patent Application No. 2024-006659 filed on January 19, 2024, and Japanese Patent Application No. 2024-006790 filed on January 19, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, lithium has been recovered and reused from lithium-containing materials such as crushed lithium-ion battery waste. A known method for recovering lithium from lithium-containing materials involves roasting lithium-ion battery waste, immersing the resulting battery dregs in an acidic solution, thereby leaching the lithium into the acidic solution, and recovering lithium 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. Therefore, as shown in Patent Document 1, for example, calcium salt is added to the lithium leachate to neutralize it, thereby precipitating mainly metals other than lithium, and solid-liquid separation is then performed to separate the lithium solution from other substances. Carbonate is then added to the lithium solution to recover lithium as lithium carbonate.

[0004] Japanese Patent Application Laid-Open No. 2019-011518

[0005] Incidentally, as shown in Patent Document 1, when calcium coexists in a lithium solution, calcium carbonate is preferentially produced when carbon dioxide is added, and there is a risk that calcium carbonate will be mixed into lithium carbonate as an impurity.

[0006] 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 lithium carbonate that can suppress the presence of calcium carbonate when producing lithium carbonate from a lithium-containing liquid and thereby obtain lithium carbonate with high purity.

[0007] In order to solve the above-mentioned problems, a method for producing lithium carbonate according to Aspect 1 of the present invention is characterized by comprising: a first carbonation reaction step of adding a soluble carbonate compound to a lithium-containing liquid in which calcium ions coexist and heating the mixture to produce calcium carbonate; a first solid-liquid separation step of separating the calcium carbonate produced in the first carbonation reaction step from the lithium-containing liquid; a second carbonation reaction step of adding a soluble carbonate compound to the lithium-containing liquid separated in the first solid-liquid separation step and heating the mixture to produce lithium carbonate; and a second solid-liquid separation step of separating the lithium carbonate produced in the second carbonation reaction step from a mother liquor.

[0008] The method for producing lithium carbonate according to Aspect 1 of the present invention includes a first carbonation reaction step of producing calcium carbonate by adding a soluble carbonate compound (a water-soluble carbonate compound) and heating, and a first solid-liquid separation step of separating the calcium carbonate produced in the first carbonation reaction step from the lithium-containing liquid, so that calcium contained in the lithium-containing liquid can be removed as calcium carbonate in the first carbonation reaction step and the first solid-liquid separation step. Therefore, in the subsequent second carbonation reaction step, production of calcium carbonate is suppressed, and high-purity lithium carbonate can be produced.

[0009] A method for producing lithium carbonate according to Aspect 2 of the present invention is the method for producing lithium carbonate according to Aspect 1, wherein the amount of substance of the soluble carbonate compound added in the first carbonation reaction step and the amount of substance of calcium in the lithium-containing solution supplied to the first carbonation reaction step are in a stoichiometric ratio (CO ３ ２－ / Ca ２＋ According to the method for producing lithium carbonate of Aspect 2 of the present invention, the amount of substance (number of moles) of the soluble carbonate compound added in the first carbonation reaction step and the amount of substance (number of moles) of calcium in the lithium-containing solution supplied to the first carbonation reaction step are in a stoichiometric ratio (CO ３ ２－ / Ca ２＋) (molar ratio) is within the range of 1.0 or more and 10.0 or less, so that calcium can be sufficiently removed as calcium carbonate, and production of lithium carbonate in this first carbonation reaction step can be suppressed, thereby making it possible to increase the recovery efficiency of lithium.

[0010] A method for producing lithium carbonate according to Aspect 3 of the present invention is characterized in that, in the method for producing lithium carbonate according to Aspect 1 or Aspect 2, the pH in the first carbonation reaction step is 9.0 or more and 11.0 or less. According to the method for producing lithium carbonate according to Aspect 3 of the present invention, the pH in the first carbonation reaction step is 9.0 or more and 11.0 or less, so that the production of calcium carbonate can be promoted and calcium can be sufficiently removed by the first carbonation reaction step and the first solid-liquid separation step.

[0011] A method for producing lithium carbonate according to Aspect 4 of the present invention is characterized in that, in the method for producing lithium carbonate according to any one of Aspects 1 to 3, the soluble carbonate compound added in the first carbonation reaction step and the second carbonation reaction step is sodium carbonate. According to the method for producing lithium carbonate according to Aspect 4 of the present invention, the soluble carbonate compound added in the first carbonation reaction step and the second carbonation reaction step is sodium carbonate, so that calcium carbonate and lithium carbonate can be efficiently precipitated.

[0012] A method for producing lithium carbonate according to Aspect 5 of the present invention is characterized in that, in the method for producing lithium carbonate according to any one of Aspects 1 to 4, the heating temperature in the first carbonation reaction step is within the range of 40° C. or higher and 95° C. or lower. According to the method for producing lithium carbonate according to Aspect 5 of the present invention, the heating temperature in the first carbonation reaction step is within the range of 40° C. or higher and 95° C. or lower, and therefore, the production of calcium carbonate can be promoted in the first carbonation reaction step.

[0013] A method for producing lithium carbonate according to Aspect 6 of the present invention is characterized in that, in the method for producing lithium carbonate according to any one of Aspects 1 to 5, the heating temperature in the second carbonation reaction step is within the range of 80° C. or higher and 95° C. or lower. According to the method for producing lithium carbonate according to Aspect 6 of the present invention, the heating temperature in the second carbonation reaction step is within the range of 80° C. or higher and 95° C. or lower, and therefore, the production of lithium carbonate in the second carbonation reaction step can be promoted.

[0014] A method for producing lithium carbonate according to Aspect 7 of the present invention is characterized in that, in the method for producing lithium carbonate according to any one of Aspects 1 to 6, the carbonate compound containing calcium carbonate recovered in the first solid-liquid separation step is returned to the first carbonation reaction step. According to the method for producing lithium carbonate according to Aspect 7 of the present invention, the carbonate compound containing calcium carbonate recovered in the first solid-liquid separation step is returned to the first carbonation reaction step, and the returned calcium carbonate can be used as seed crystals to promote the production of calcium carbonate in the first carbonation reaction step. Furthermore, lithium carbonate can be returned to the first carbonation reaction step, thereby improving the recovery efficiency of lithium.

[0015] According to an aspect of the present invention, it is possible to provide a method for producing lithium carbonate that can suppress the contamination of calcium carbonate when producing lithium carbonate from a lithium-containing liquid and thereby obtain lithium carbonate with high purity.

[0016] FIG. 1 is a flow chart showing a lithium recovery method using a lithium carbonate production method according to one embodiment of the present invention. FIG. 2 is a flow chart showing an impurity removal step in FIG. 1. FIG. 3 is a flow chart showing a lithium-containing liquid concentration step in FIG. 1. FIG. 4 is a flow chart showing a lithium carbonate production method according to one embodiment of the present invention, which is applied as the lithium carbonate production step in FIG. 1. FIG. 5 is a flow chart showing the lithium carbonate purification step in FIG. 1. FIG. 6 is a graph showing the relationship between the pH of the liquid and the lithium concentration in the liquid in the bicarbonation step. FIG. 7 is a graph showing the relationship between the Li concentration in the simulated liquid and the reaction time in the second carbonation reaction step in Test Example A of Example 2. FIG. 8 is a graph showing the relationship between the Li concentration in the simulated liquid and the reaction time in the second carbonation reaction step in Test Example B of Example 2.

[0017] Hereinafter, a method for producing lithium carbonate according to one embodiment of the present invention will be described with reference to the drawings. Note that each embodiment shown below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the "solution" described in the specification is an aqueous solution.

[0018] The method for producing lithium carbonate of the present embodiment is applied to a process for recovering lithium from lithium-containing materials such as crushed waste lithium-ion batteries, etc. First, a lithium recovery method to which the method for producing lithium carbonate of the present embodiment is applied will be described with reference to FIG.

[0019] As shown in FIG. 1, the method for recovering lithium includes a leaching step S01, an impurity removal step S02, a lithium-containing solution concentrating step S03, a lithium carbonate production step S04, and a lithium carbonate purification step S05.

[0020] (Leaching Step S01) In the leaching step S01, a lithium-containing material such as pulverized lithium-ion battery material is 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), and the lithium in the lithium-containing material is dissolved to obtain a lithium leachate.

[0021] The pH of the lithium leaching solution is not particularly limited and is, for example, 1.0 or more and 2.0 or less. Note that metals other than lithium, fluorine, etc., are also leached into the leaching solution. The metals contained in the leaching solution 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.

[0022] (Impurity Removal Step S02) Next, impurities contained in the lithium leachate are removed. As shown in Fig. 2, 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.

[0023] 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. These metal hydroxide and calcium fluoride precipitate as solid phases in the solution. 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 the metal hydroxide and calcium fluoride is adjusted to be 8.0 or higher and 12.0 or lower.

[0024] 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 leaching solution. 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.

[0025] 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 to precipitate dissolved fluorine. The second calcium compound is not particularly limited as long as it is a basic calcium compound capable of controlling the pH to 5.0 or higher and 9.0 or lower. For example, solid calcium compounds such as calcium carbonate, calcium hydroxide, calcium oxide, or mixtures thereof can be used. To produce a dissolved fluorine precipitate (e.g., calcium fluoride), the pH of the lithium leachate is adjusted to 5.0 or lower by first adding aluminum sulfate, and then adding the second calcium compound to adjust the pH to 5.0 or higher and 9.0 or lower. 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 precipitate as a dissolved fluorine precipitate. Note that a portion of the unreacted second calcium compound precipitates together with the dissolved fluorine precipitate. 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, and more preferably 8.0 or lower, and even more preferably 7.5 or lower.

[0026] 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.

[0027] 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 the precipitate of dissolved fluorine separated and recovered in the second solid-liquid separation step S24 and the unreacted second calcium compound. Furthermore, the second calcium compound added in the second calcium compound addition step S23 may be calcium carbonate obtained in the solid-liquid separation step S32 after the carbonation reaction step S31 (described later) or calcium carbonate obtained in the first solid-liquid separation step S42 after the first carbonation reaction step S41 (described later). Furthermore, in the second calcium compound addition step S23, the solid content removed in the second solid-liquid separation step S24 may be used as seed crystals.

[0028] 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.

[0029] (Lithium-containing liquid concentrating step S03) Next, the lithium ions contained in the obtained lithium-containing liquid are concentrated to obtain a lithium-concentrated liquid. As shown in Fig. 3 , the lithium-containing liquid concentrating step S03 includes a carbonation reaction step S31, a solid-liquid separation step S32, a decarbonation step S33, and a membrane separation step S34.

[0030] 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. As the soluble carbonate compound, for example, sodium carbonate or sodium bicarbonate can be used in the form of a solution or powder. Carbon dioxide gas may also 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.

[0031] 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 ３ ２－ / Ca ２＋ ) (molar ratio) is preferably in the range of 1.0 to 10.0. ３ ２－ / Ca ２＋ When the stoichiometric ratio (CO ) is 1.0 or more, calcium ions can be sufficiently precipitated as calcium carbonate. ３ ２－ / Ca ２＋ ) is 10.0 or less, it is possible to suppress the precipitation of lithium as lithium carbonate.

[0032] In addition, the stoichiometric ratio (CO ３ ２－ / Ca ２＋ ) is more preferably 2.0 or more, and even more preferably 3.0 or more. ３ 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 adding the soluble carbonate compound. Furthermore, aluminum sulfate may be added as a flocculant together with a polymer flocculant. Adding aluminum sulfate can aggregate the precipitated calcium carbonate into larger flocs, preventing them from remaining in the supernatant liquid. This enables more reliable solid-liquid separation, even when performing solid-liquid separation using a gravity settling 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 more. An aluminum sulfate concentration of less than 27 mg / L is undesirable because coagulation is insufficient. An aluminum sulfate concentration of more than 110 mg / L is undesirable because the volume of solids, including precipitated calcium carbonate, increases, necessitating the use of large-scale settling equipment to achieve sufficient solid-liquid separation using a gravity settling method. Examples of polymer flocculants include Diaflock AP825 manufactured by MT Aquapolymer Co., Ltd. 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.

[0033] Here, 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 setting the pH of the lithium-containing liquid within a range of 8.0 to 12.0, the production of calcium carbonate can be promoted. Note that 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. Furthermore, the pH of the lithium-containing liquid in the carbonation reaction step S31 is more preferably 11.0 or lower.

[0034] 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 liquid to be treated is more preferably 1 g / L or more, and even more preferably 5 g / L or more. The lithium concentration in the lithium-containing liquid to be treated is more preferably 15 g / L or less, and even more preferably 13 g / L or less. 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. The calcium concentration in the lithium-containing liquid to be treated is preferably 100 mg / L or less, and even more preferably 50 mg / L or less.

[0035] 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.

[0036] 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. As the inorganic acid to be added, for example, sulfuric acid, nitric acid, hydrochloric acid, or a mixed acid of two or more selected from these can be used.

[0037] Here, in the decarbonation step S33, it is preferable to set the pH of the lithium-containing liquid within 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 more, 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 less, 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. Note that the pH of the lithium-containing liquid in the decarbonation step S33 is more preferably 3.0 or more, and even more preferably 6.0 or more. Furthermore, the pH of the lithium-containing liquid in the decarbonation step S33 is more preferably 7.0 or less, and even more preferably 6.5 or less.

[0038] 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. Examples of the reverse osmosis membrane that can be used include hollow fiber, spiral, and tubular types of reverse osmosis membranes made of materials such as cellulose acetate. The lithium-concentrated solution obtained in the membrane separation step S34 preferably has a lithium concentration of 18 g / L or more. Furthermore, 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.

[0039] 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.

[0040] (Lithium carbonate production step S04) Next, lithium carbonate is produced using the lithium-containing lithium concentrated solution as a raw material. A lithium carbonate production method according to one embodiment of the present invention is applied to this lithium carbonate production step S04. The lithium carbonate production method according to this embodiment (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 .

[0041] In the first carbonation reaction step S41, a first soluble carbonate compound (first water-soluble carbonate compound) is added to a lithium concentrate solution in which lithium ions and calcium ions coexist, and the solution is heated to produce calcium carbonate. In the first carbonation reaction step S41, the lithium concentrate solution may be heated after the addition of the first soluble carbonate compound, or the first soluble carbonate compound may be added while the lithium concentrate solution is being heated. As the first soluble carbonate compound, for example, sodium carbonate or sodium bicarbonate may be used in the form of a solution or powder. Alternatively, carbon dioxide gas may be blown in to solubilize the carbonate compound, thereby allowing it to react with the dissolved calcium.

[0042] 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 ３ ２－ / Ca ２＋ ) (molar ratio) is preferably in the range of 1.0 to 10.0. ３ ２－ / Ca ２＋ When the stoichiometric ratio (CO ) is 1.0 or more, calcium ions can be sufficiently precipitated as calcium carbonate. ３ ２－ / Ca ２＋ When the stoichiometric ratio (CO ) in the first carbonation reaction step S41 is 10.0 or less, it is possible to suppress the precipitation of lithium as lithium carbonate. ３ ２－ / Ca ２＋) is more preferably 2.0 or more, and even more preferably 3.0 or more. ３ ２－ / Ca ２＋ ) is more preferably 7.0 or less, and even more preferably 5.0 or less.

[0043] The pH of the lithium concentrated solution in the first carbonation reaction step S41 is preferably 9.0 or higher and 11.0 or lower. By adjusting the pH of the lithium concentrated solution in the first carbonation reaction step S41 to 9.0 or higher and 11.0 or lower, the production of calcium carbonate can be promoted. The pH of the lithium concentrated solution in the first carbonation reaction step S41 is more preferably 9.5 or higher, and even more preferably 10.0 or higher.

[0044] 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, the production of calcium carbonate can be promoted. 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 within 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.

[0045] 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 a gravity settling separation method, a centrifugal separation method, or a filter cloth filtration method using a filter press or the like can be appropriately selected and used.

[0046] 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. As the second soluble carbonate compound, for example, sodium carbonate or sodium bicarbonate can be used. 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 is in a state in which more particles of the second soluble carbonate compound than the solubility are not dissolved in the aqueous solution. Alternatively, the second soluble carbonate compound can be solubilized by injecting carbon dioxide gas, thereby causing it to react with the dissolved calcium. The second soluble carbonate compound is preferably in the form of a powder. This allows impurities (SO ) contained in the produced lithium carbonate to be removed. ４ 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.

[0047] Regarding the amount of the second soluble carbonate compound added, the amount of carbonate ions (CO ) in the second soluble carbonate compound is twice the amount (number of moles) of lithium ions contained in the lithium concentrate. ３ ２－ ) ratio (CO ３ ２－ / 2Li ＋ It is preferable to adjust the amount of the second soluble carbonate compound added so that the ratio (%) of the soluble carbonate compound added to the lithium carbonate solution 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.

[0048] The addition rate of the second soluble carbonate compound (the amount added per second relative to 8 g of Li in the lithium concentrate) is preferably 0.05 to 1 g / s. This allows the impurities (SO ４ ２－When the second soluble carbonate compound is in the form of a slurry or a 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 the solution, and can also be referred to as the addition rate of the second soluble carbonate compound contained in the slurry or the solution.

[0049] In the second carbonation reaction step S43, the lithium concentrated solution may be heated after the addition of the second soluble carbonate compound, or the second soluble carbonate compound may be added while heating the lithium concentrated solution. However, 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, the production of lithium carbonate can be promoted. 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 within the reaction tank can be suppressed, enabling the second carbonation reaction step S43 to 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. A lower temperature of the lithium concentrated solution when sodium carbonate is added slows the crystal growth of the lithium carbonate produced, thereby reducing the amount of impurities contained therein. However, in order to produce lithium carbonate at a high recovery rate, it is necessary to heat the lithium concentrate. Therefore, in the step 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°C to 95°C. This prevents impurities (SO ) contained in the produced lithium carbonate from being easily removed. ４ ２－ , Zn, Na, etc.) contained in the produced lithium carbonate. ４ ２－ The amount of ) is preferably 1% by mass or less.

[0050] 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.

[0051] 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. The lithium carbonate can be separated from an existing solid-liquid separation method, such as gravity settling, centrifugal separation, or filter cloth filtration using a filter press or the like, by appropriately selecting the method. Through the above steps, lithium carbonate is produced. This lithium carbonate may contain calcium at a concentration of 400 ppm by mass or more.

[0052] (Lithium carbonate purification step 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.

[0053] 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 ppm by mass or more of calcium. The amount of calcium contained in the lithium carbonate is preferably 5000 ppm by mass or less. If the amount of calcium exceeds 5000 ppm by mass, a large amount of calcium remains, which is likely to cause clogging when separating the solid content (calcium carbonate) by filtration in the first solid-liquid separation step S53 described below. Here, the lithium carbonate concentration in the lithium carbonate slurry produced in the slurrying step S51 is preferably within the range of 30 g / L or more and 45 g / L or less. By setting the lithium carbonate concentration in the lithium carbonate slurry within the above range, lithium bicarbonate can be sufficiently produced in the bicarbonation step S52 described below, while lithium carbonate residue can be suppressed, enabling more efficient production of purified lithium carbonate. The lithium carbonate concentration in the lithium carbonate slurry is more preferably 35 g / L or more, and even more preferably 38 g / L or more. The concentration of lithium carbonate in the lithium carbonate slurry is more preferably 44 g / L or less, and even more preferably 43 g / L or less.

[0054] In the bicarbonation step S52, CO is added to the lithium carbonate slurry. ２ By blowing in gas, soluble lithium bicarbonate is generated, and lithium bicarbonate solution is obtained. That is, as shown in formula (1), solid lithium carbonate reacts with carbon dioxide gas to become lithium bicarbonate, which dissolves in water as a solvent, and lithium bicarbonate solution is generated. Li ２ CO ３ +H ２ O+CO ２ →2LiHCO ３ ...(1)

[0055] Here, the pH in the bicarbonation step S52 is preferably 7.5 or more and 12 or less. ２As the gas is blown in, the lithium bicarbonate dissolves in the liquid, and the pH of the lithium bicarbonate solution decreases. Figure 6 shows the relationship between the pH of the lithium bicarbonate solution and the lithium concentration in the solution. ２ As the pH of the lithium bicarbonate solution decreases due to the gas injection, the lithium concentration in the solution increases. However, if the pH is less than 7.5, no increase in the lithium concentration is observed. Therefore, by setting the pH to 7.5 or higher in the bicarbonation step S52, ２ The amount of gas used can be reduced, and the incorporation of calcium as calcium bicarbonate in the bicarbonation step S52 can be suppressed, making it possible to produce purified lithium carbonate with even higher purity. ２ The pH at the time when gas blowing is stopped is preferably 7.5 or more and less than 8.0.

[0056] In the bicarbonation step S52, the liquid temperature is preferably set to 5° C. or higher and 30° C. or lower. ２ When the gas reacts with lithium carbonate to produce lithium bicarbonate, the liquid temperature rises due to the heat of reaction. Because lithium carbonate dissolved in the solution has the property of decreasing in solubility as the liquid temperature increases, an increase in the liquid temperature can result in the precipitation of lithium carbonate. 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 stirring blades. By keeping the liquid temperature at 30°C or less in the bicarbonation step S52, the generation of scale can be suppressed in the bicarbonation step S52, and lithium bicarbonate liquid can be stably obtained. In consideration of energy costs and the capacity of the cooling device, it is preferable to keep the liquid temperature at 5°C or higher.

[0057] 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, centrifugal separation, or filter cloth filtration using a filter press or the like can be appropriately selected and used.

[0058] 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. 2LiHCO ３ →Li ２ CO ３ +H ２ O+CO ２ ... (2)

[0059] 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, 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. Note that 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. Furthermore, the liquid temperature in the purified lithium carbonate crystallization step S54 is more preferably 97°C or lower, even more preferably 96°C or lower, and even more preferably 95°C or lower.

[0060] In addition, the carbon dioxide gas (CO ２ It is preferable to use CO 2 in the bicarbonation step S52. ２ This reduces the amount of gas used and reduces operating costs.

[0061] 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.

[0062] 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. Since lithium remains in the mother liquor from which purified lithium carbonate has been separated in the second solid-liquid separation step S55, by returning this mother liquor to the slurrying step S51, the remaining lithium can be contained in the lithium carbonate slurry that serves as a raw material, and it becomes possible to improve the recovery efficiency of lithium.

[0063] 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.

[0064] The method for producing a lithium carbonate solution of the present embodiment, which is applied as the lithium carbonate production step S04, includes a first carbonation reaction step S41 in which a soluble carbonate compound is added and heating is performed to produce calcium carbonate, and a first solid-liquid separation step S42 in which the calcium carbonate produced in the first carbonation reaction step S41 is separated from the lithium-containing solution, so that calcium contained in the lithium-containing solution can be removed as calcium carbonate in the first carbonation reaction step S41 and the first solid-liquid separation step S42. Therefore, in the subsequent second carbonation reaction step S43, production of calcium carbonate is suppressed, and high-purity lithium carbonate can be produced.

[0065] In this embodiment, the amount of substance (number of moles) of the first soluble carbonate compound added in the first carbonation reaction step S41 and the amount of substance (number of moles) of calcium in the lithium-containing solution supplied to the first carbonation reaction step S41 are in a stoichiometric ratio (CO ３ ２－ / Ca ２＋ ) (molar ratio) is within the range of 1.0 or more and 10.0 or less, calcium in the lithium-containing liquid can be sufficiently removed as calcium carbonate, and production of lithium carbonate in this first carbonation reaction step S41 can be suppressed, thereby making it possible to increase the recovery efficiency of lithium.

[0066] In the present embodiment, when the pH in the first carbonation reaction step S41 is 9.0 or higher and 11.0 or lower, the production of calcium carbonate can be promoted in the first carbonation reaction step S41, and calcium can be sufficiently removed by the subsequent first solid-liquid separation step S42.

[0067] In the present embodiment, when the first and second soluble carbonate compounds added in the first carbonation reaction step S41 and the second carbonation reaction step S43 are sodium carbonate, calcium and lithium in the lithium-containing liquid can be efficiently precipitated as calcium carbonate and lithium carbonate.

[0068] In this embodiment, when the heating temperature in the first carbonation reaction step S41 is within the range of 40° C. or higher and 95° C. or lower, the production of calcium carbonate in the first carbonation reaction step S41 can be promoted.

[0069] In the present embodiment, when the heating temperature in the second carbonation reaction step S43 is within the range of 80° C. or higher and 95° C. or lower, the production of lithium carbonate in the second carbonation reaction step S43 can be promoted.

[0070] In the present embodiment, when the carbonate compound containing calcium carbonate recovered in the first solid-liquid separation step S42 is returned to the first carbonation reaction step S41, the returned calcium carbonate can be used as seed crystals to promote the production of calcium carbonate in the first carbonation reaction step S41. Furthermore, lithium carbonate can be returned to the first carbonation reaction step S41, thereby improving the recovery efficiency of lithium.

[0071] While the present invention has been described above as an embodiment, it is not limited thereto and can be modified as appropriate within the scope of the technical requirements of the invention. As described above, the present embodiment has been described as being applied to the lithium carbonate production step S04 of the lithium recovery method including the leaching step S01, the impurity removal step S02, the lithium-containing liquid concentrating step S03, the lithium carbonate production step S04, and the lithium carbonate purification step S05. However, the present invention is not limited thereto and is not particularly limited as long as lithium carbonate is produced from a lithium-containing liquid containing lithium.

[0072] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0073] Example 1 (Invention Example 1) Used lithium-ion batteries were roasted in a non-oxidizing atmosphere, then crushed and sorted to obtain black mass powder (BM). This BM was added to a sulfuric acid solution and stirred, allowing the lithium contained in the BM to be leached into the sulfuric acid solution. Calcium hydroxide was then added to the sulfuric acid solution containing the BM to adjust the pH of the solution to an alkaline range, thereby precipitating metals other than lithium leached during the lithium leaching process as solids. Solid-liquid separation was performed using a suction filter to obtain a lithium leachate. The chemical composition of the metal components contained in the lithium leachate is shown in Table 1. This chemical composition was measured using ICP atomic emission spectroscopy (ICAP7600 DUO, manufactured by THERMO SCIENTIFIC).

[0074]

[0075] (First carbonation reaction step) 5.8 g of sodium carbonate (molar ratio CO ３ ２－ / Ca ２＋= 5.0) was added and reacted at a liquid temperature of 90°C for 30 minutes. The pH in this first carbonation reaction step was 9.0 to 10.0. After 30 minutes had elapsed, the resulting precipitate was subjected to solid-liquid separation using a suction filter to obtain a post-Ca-removal liquid (process discharge after removing Ca) and a Ca precipitate. The Ca precipitate was dried for 12 hours in a constant temperature dryer at 105°C. The chemical composition of the obtained post-Ca-removal liquid is shown in Table 2, and the chemical composition of the Ca precipitate after drying is shown in Table 3.

[0076]

[0077]

[0078] (Second Carbonation Reaction Step) 500 mL of the obtained decahydrated liquid was heated, and when the liquid temperature reached 80°C, 25.6 g of sodium carbonate (molar ratio CO ３ ２－ / 2Li ＋ = 1.2) was added. Then, the mixture was allowed to react at a liquid temperature of 90°C for 30 minutes. After 30 minutes had elapsed, the resulting precipitate (lithium carbonate) was subjected to solid-liquid separation using a suction filter to obtain a post-Li discharge liquid (process discharge after removing Li) and lithium carbonate. The obtained lithium carbonate was dried for 12 hours in a constant temperature dryer at 105°C. The chemical composition of the obtained lithium carbonate is shown in Table 4. Lithium carbonate was dissolved in a 50% nitric acid aqueous solution, and its chemical composition was measured by ICP atomic emission spectroscopy (ICAP7600 DUO, manufactured by THERMO SCIENTIFIC).

[0079]

[0080] According to Inventive Example 1, it was found that even if the lithium leachate contained a high concentration of Ca, high-quality lithium carbonate with a low Ca content could be obtained.

[0081] (Invention Example 2) In the first carbonation reaction step, 1.16 g of sodium carbonate was added to 1 L of the lithium leaching solution (molar ratio CO ３ ２－ / Ca ２＋ The same procedure as in Example 1 of the present invention was carried out except that HCl was added.

[0082] (Invention Example 3) The same procedure as in Invention Example 1 was carried out except that in the first carbonation reaction step, the reaction was carried out at a liquid temperature of 40°C for 30 minutes.

[0083] (Invention Example 4) In the first carbonation reaction step, 0.58 g of sodium carbonate was added to 1 L of the lithium leaching solution (molar ratio CO ３ ２－ / Ca ２＋ The same procedure as in Example 1 of the present invention was carried out except that HCl was added.

[0084] (Invention Example 5) In the first carbonation reaction step, 11.6 g of sodium carbonate was added to 1 L of the lithium leaching solution (molar ratio CO ３ ２－ / Ca ２＋ The same procedure as in Example 1 of the present invention was carried out except that HCl was added.

[0085] (Invention Example 6) The same procedure as in Invention Example 1 was carried out, except that in the first carbonation reaction step, the reaction was carried out at a liquid temperature of 25°C for 30 minutes.

[0086] Comparative Example The first carbonation reaction step was not carried out, and lithium carbonate was precipitated directly from the lithium leaching solution (stock solution).

[0087] In Examples 1 to 6 of the present invention and the comparative example, the chemical compositions of the post-Ca decalysis solutions (lithium-containing solutions) obtained in the first carbonation reaction step and the chemical compositions of the finally obtained lithium carbonate are shown in Table 5. The chemical compositions of the post-Ca decalysis solutions were measured by ICP atomic emission spectroscopy (ICAP7600 DUO, manufactured by THERMO SCIENTIFIC). The finally obtained lithium carbonate was dissolved in a 50% nitric acid aqueous solution, and the chemical composition thereof was measured by ICP atomic emission spectroscopy (ICAP7600 DUO, manufactured by THERMO SCIENTIFIC).

[0088]

[0089] In the comparative examples, the first carbonation reaction step was not carried out, and the obtained lithium carbonate contained calcium at a high concentration. In contrast, in invention examples 1 to 6 in which the first carbonation reaction step was carried out, the first carbonation reaction step was carried out, and therefore the calcium concentration in the obtained lithium carbonate was lower than in the comparative examples.

[0090] In addition, the heating temperature in the first carbonation reaction step was the same (90°C) and the molar ratio CO ３ ２－ / Ca ２＋ When comparing Examples 1, 2, 4, and 5 of the present invention in which the molar ratio CO ３ ２－ / Ca ２＋ Inventive Examples 1, 2, and 5, the molar ratio CO ３ ２－ / Ca ２＋ It was confirmed that the calcium concentration in the obtained lithium carbonate was even lower than in Inventive Example 4 in which the saturation temperature was set to 0.5.

[0091] Furthermore, the molar ratio CO ３ ２－ / Ca ２＋ Comparing Inventive Examples 1, 3, and 6 in which the heating temperature was changed while the pH was the same (5.0), it was confirmed that Inventive Examples 1 and 3 in which the heating temperature was 40°C or higher and 95°C or lower had a lower calcium concentration contained in the obtained lithium carbonate than Inventive Example 6 in which the heating temperature was 25°C.

[0092] Example 2 A simulant liquid having the same composition as the Ca-depleted liquid obtained in Example 1 of the present invention (Table 2) was prepared. ３ ２－ / 2Li ＋ A second carbonation reaction step S43 was carried out by adding sodium carbonate in an amount such that the RI=1.2. Test Example A: 137.3 g of sodium carbonate was added to 2 L of the simulated liquid. When adding the sodium carbonate, the temperature of the simulated liquid was set to 15 to 25°C (room temperature). After adding the sodium carbonate, the simulated liquid was heated to 80°C. Test Example B: 68.7 g of sodium carbonate was added to 1 L of the simulated liquid. After heating the temperature of the simulated liquid to 80°C, sodium carbonate was added. The Li concentration in the simulated liquid at each reaction time was measured. The results are shown in Tables 6 and 7 and Figures 7 and 8.

[0093]

[0094]

[0095] Table 6 and Figure 7 show the relationship between the Li concentration in the simulated solution (filtrate) and reaction time in Test Example A, and Table 7 and Figure 8 show the relationship between the Li concentration in the simulated solution (filtrate) and reaction time in Test Example B. In Test Example B, the Li concentration rapidly decreased from the start of the addition of sodium carbonate, indicating the formation of lithium carbonate. After the entire amount of sodium carbonate was added, the Li concentration reached approximately 2 g / L, and it is estimated that most of the Li in the simulated solution had become lithium carbonate. In Test Example A, the Li concentration barely changed at the stage when sodium carbonate was added, indicating that almost no lithium carbonate had been formed at this stage. However, when the simulated solution was heated after the entire amount of sodium carbonate was added, the Li concentration decreased. This indicates that the Li concentration decreased especially at low solution temperatures, indicating the formation of lithium carbonate. After 50 minutes of reaction time, the Li concentration reached approximately 2 g / L, indicating that most of the Li in the simulated solution had become lithium carbonate. In Test Example A, it was found that the Li concentration decreased and lithium carbonate was produced at a stage when the liquid temperature was low, compared to Test Example B.

[0096] (Example 3) Solutions and Ca-depleted solutions having the compositions shown in Tables 8 and 9 were prepared. Table 8 shows the compositions of the solutions used in Test Examples 1 to 4 and 8 to 11. The solutions in Table 8 were prepared by dissolving commercially available lithium sulfate in sulfuric acid so as to have the same Li concentration as the lithium concentrated solution obtained in the lithium-containing solution concentration step S03. The Li and SO ４ The elements other than were impurities contained in commercially available lithium sulfate. Table 9 shows the compositions of the post-Ca depletion solutions used in Test Examples 5 to 7. In Test Examples 1 to 4 and 8 to 11, solutions having the compositions shown in Table 8 were used to investigate the effects of the form of sodium carbonate added, the temperature at which sodium carbonate was added, and the rate at which sodium carbonate was added on the amount of impurities in the lithium carbonate produced.

[0097]

[0098]

[0099] Sodium carbonate was added to 1 L of the solution and the deca-dehydrated liquid under the conditions shown in Table 10 below, and a second carbonation reaction step was carried out. The sodium carbonate was in the form of a powder or a slurry. In Test Examples 5 to 8, 10, and 11, the temperature of the solution or the deca-dehydrated liquid was set to 15 to 25°C (room temperature) in the step of adding sodium carbonate, and after adding sodium carbonate, the solution or the deca-dehydrated liquid was heated to 80°C. In Test Examples 1 to 4 and 9, the solution or the deca-dehydrated liquid was heated to 80°C, and then sodium carbonate was added. The rate of addition of sodium carbonate (amount added per second relative to 8 g of Li in the lithium concentrated liquid) and the amount of sodium carbonate added (ratio of the number of moles of sodium carbonate added to twice the number of moles of Li (CO ３ ２－ / 2Li ＋ )) were adjusted to the values ​​shown in Table 10. The produced precipitate (lithium carbonate) was subjected to solid-liquid separation using a suction filter to obtain a Li-depleted solution and lithium carbonate. The obtained lithium carbonate was dried for 12 hours in a constant temperature dryer at 105°C. Lithium carbonate was dissolved in a 50% nitric acid aqueous solution, and its chemical composition was measured by ICP atomic emission spectroscopy (ICAP7600 DUO, manufactured by THERMO SCIENTIFIC). The chemical composition of the obtained lithium carbonate is shown in Table 10. In Table 10, "-" means that the concentration of the corresponding element was not measured.

[0100] From the results of Test Examples 1 to 4, when the addition rate of sodium carbonate is 1 g / s or less, the amount of Na, SO in lithium carbonate is reduced compared to when the addition rate of sodium carbonate is more than 1 g / s. ４ ２－ The results of Test Examples 5 to 7 show that the amount of carbonate ions (CO ３ ２－ ) ratio (CO ３ ２－ / 2Li ＋) is increased, the amounts of Ca and Al in lithium carbonate are reduced. From the results of Test Examples 8 and 9, it was found that the amounts of Na and SO in lithium carbonate are reduced more when the temperature of the solution is kept at 15 to 25°C (room temperature) at the stage of adding sodium carbonate than when the temperature of the solution is heated to 80°C and then sodium carbonate is added. ４ ２－ Test Examples 10 and 11 show that the amount of Na, SO in lithium carbonate is smaller when the sodium carbonate is added in the form of powder than when the sodium carbonate is added in the form of slurry. ４ ２－ The amount was small.

[0101]

[0102] As a result of the above-described confirmatory experiments, it was confirmed that the present invention can provide a method for producing lithium carbonate that can suppress the contamination of calcium carbonate when producing lithium carbonate from a lithium-containing liquid and thereby obtain lithium carbonate with high purity.

[0103] The method for producing lithium carbonate of the present embodiment is suitably applied to a step of recovering lithium from a lithium-containing material such as pulverized lithium-ion battery material.

[0104] S04 Lithium carbonate production step S41 First carbonation reaction step S42 First solid-liquid separation step S43 Second carbonation reaction step S44 Second solid-liquid separation step.

Claims

1. A method for producing lithium carbonate, comprising: a first carbonation reaction step of generating calcium carbonate by adding a soluble carbonate compound to a lithium-containing solution in which calcium ions coexist and heating; a first solid-liquid separation step of separating the calcium carbonate generated in the first carbonation reaction step from the lithium-containing solution; a second carbonation reaction step of generating lithium carbonate by adding a soluble carbonate compound to the lithium-containing solution separated in the first solid-liquid separation step and heating; and a second solid-liquid separation step of separating the lithium carbonate generated in the second carbonation reaction step from the mother liquor.

2. The amount of substance of the soluble carbonate compound added in the first carbonation reaction step and the amount of substance of calcium in the lithium-containing liquid supplied to the first carbonation reaction step are in a stoichiometric ratio (CO ３ ２－ / Ca ２＋ ) in the range of 1.0 or more and 10.0 or less. The method for producing lithium carbonate according to claim 1, characterized in that.

3. The method for producing lithium carbonate according to claim 1 or 2, wherein the pH in the first carbonation reaction step is 9.0 or more and 11.0 or less.

4. The method for producing lithium carbonate according to claim 1 or 2, wherein the soluble carbonate compound added in the first carbonation reaction step and the second carbonation reaction step is sodium carbonate.

5. The method for producing lithium carbonate according to claim 1 or 2, wherein the heating temperature in the first carbonation reaction step is in the range of 40°C or more and 95°C or less.

6. The method for producing lithium carbonate according to claim 1 or 2, wherein the heating temperature in the second carbonation reaction step is in the range of 80°C or more and 95°C or less.

7. The method for producing lithium carbonate according to claim 1 or 2, wherein the carbonate compound containing calcium carbonate recovered in the first solid-liquid separation step is returned to the first carbonation reaction step.

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