Method for producing purified lithium carbonate

Abstract

This method (S05) for producing purified lithium carbonate comprises: a slurrying step (S51) in which water is added to lithium carbonate that contains 400 mass ppm or more of calcium so as to produce a lithium carbonate slurry; a bicarbonation step (S52) in which a CO2 gas is blown into the lithium carbonate slurry so as to produce lithium bicarbonate, thereby obtaining a lithium bicarbonate solution; a first solid-liquid separation step (S53) in which calcium carbonate suspended in the lithium bicarbonate solution is separated; a purified lithium carbonate crystallization step (S54) in which the lithium bicarbonate solution after the removal of the calcium carbonate is warmed so as to decompose the lithium bicarbonate, thereby precipitating purified lithium carbonate; a second solid-liquid separation step (S55) in which the precipitated purified lithium carbonate is separated from the mother liquid; and a mother liquid returning step (S56) in which the mother liquid obtained in the second solid-liquid separation step (S55) is returned to the slurrying step (S51).

Description

Method for producing purified lithium carbonate

[0001] The present invention relates to a method for producing purified lithium carbonate, which enables obtaining purified lithium carbonate with higher purity from lithium carbonate containing impurities such as calcium. 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] Here, when the purity of lithium in the recovered lithium carbonate is insufficient, the lithium carbonate may be purified in order to improve the purity of lithium. For example, Patent Document 1 proposes a method for purifying lithium carbonate, which includes a step of bringing lithium carbonate into contact with water or an acidic solution, supplying carbonate ions to the water or the acidic solution, and reacting the produced carbonic acid with the lithium carbonate to dissolve it as soluble lithium hydrogen carbonate, and a step of heating the obtained lithium hydrogen carbonate solution to remove the carbonic acid, thereby precipitating and recovering purified lithium carbonate of high purity.

[0005] Japanese Patent Application Laid-Open No. 2019-026531

[0006] However, as shown in Patent Document 1, when a lithium bicarbonate solution is heat-treated to remove carbonic acid and precipitate lithium carbonate, lithium remains in the mother liquor after solid-liquid separation of the lithium carbonate, and there is a problem that lithium cannot be sufficiently recovered. Furthermore, when purifying lithium carbonate containing calcium as an impurity, there is a risk that calcium may be mixed in as an impurity even after the lithium carbonate is purified.

[0007] 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 purified lithium carbonate that can efficiently recover lithium and can obtain purified lithium carbonate having a sufficiently high purity.

[0008] In order to solve the above problems, a method for producing purified lithium carbonate according to aspect 1 of the present invention includes a slurrying step of adding water to lithium carbonate containing 400 mass ppm or more of calcium to produce a lithium carbonate slurry, and a CO ２ The method is characterized by comprising: a bicarbonation step of blowing in a gas to generate soluble lithium bicarbonate and obtain a lithium bicarbonate solution; a first solid-liquid separation step of separating calcium carbonate suspended in the lithium bicarbonate solution; a purified lithium carbonate crystallization step of heating the lithium bicarbonate solution from which the calcium carbonate has been removed to decompose the lithium bicarbonate and precipitate purified lithium carbonate; a second solid-liquid separation step of separating the precipitated purified lithium carbonate from a mother liquor; and a mother liquor return step of returning the mother liquor obtained in the second solid-liquid separation step to the slurrying step.

[0009] The method for producing purified lithium carbonate according to the first aspect of the present invention includes a purified lithium carbonate crystallization step of heating the lithium bicarbonate solution from which the calcium carbonate has been removed to decompose the lithium bicarbonate and precipitate purified lithium carbonate, a second solid-liquid separation step of separating the precipitated purified lithium carbonate from a mother liquor, and a mother liquor return step of returning the mother liquor obtained in the second solid-liquid separation step to the slurrying step. Therefore, the lithium remaining in the mother liquor can be incorporated into the lithium carbonate slurry as a raw material, thereby improving the lithium recovery efficiency. In addition, the lithium carbonate slurry can be treated by adding CO ２ The method includes a bicarbonation step of injecting a gas to generate soluble lithium bicarbonate and obtain a lithium bicarbonate solution, and a first solid-liquid separation step of separating calcium carbonate suspended in the lithium bicarbonate solution. This allows calcium to be removed efficiently, and highly purified lithium carbonate to be produced.

[0010] A method for producing purified lithium carbonate according to Aspect 2 of the present invention is characterized in that, in the method for producing purified lithium carbonate according to Aspect 1, the liquid temperature in the purified lithium carbonate crystallization step is within a range of 85° C. or higher and 98° C. or lower. According to the method for producing purified lithium carbonate according to Aspect 2 of the present invention, the liquid temperature in the purified lithium carbonate crystallization step is within a range of 85° C. or higher and 98° C. or lower, and therefore it becomes possible to efficiently decompose the lithium bicarbonate and precipitate purified lithium carbonate.

[0011] A method for producing purified lithium carbonate according to Aspect 3 of the present invention is characterized in that, in the method for producing purified lithium carbonate according to Aspect 1 or Aspect 2, the concentration of lithium carbonate in the lithium carbonate slurry produced in the slurrying step is within the range of 30 g / L or more and 45 g / L or less. According to the method for producing purified lithium carbonate according to Aspect 3 of the present invention, the concentration of lithium carbonate in the lithium carbonate slurry is within the range of 30 g / L or more and 45 g / L or less, so that in the bicarbonation step, lithium bicarbonate can be sufficiently produced and residual lithium carbonate can be suppressed, making it possible to produce purified lithium carbonate more efficiently.

[0012] A method for producing purified lithium carbonate according to Aspect 4 of the present invention is characterized in that, in the method for producing purified lithium carbonate according to any one of Aspects 1 to 3, the pH in the bicarbonation step is 7.5 or higher. According to the method for producing purified lithium carbonate according to Aspect 4 of the present invention, the pH in the bicarbonation step is 7.5 or higher, so that calcium contamination in the bicarbonation step can be suppressed, and it becomes possible to produce purified lithium carbonate with even higher purity. ２ As the gas is blown in, the pH decreases, so when the pH reaches 7.5, CO ２ The gas injection will be stopped, and CO ２ Gas consumption can be reduced.

[0013] A method for producing purified lithium carbonate according to Aspect 5 of the present invention is characterized in that, in the method for producing purified lithium carbonate according to any one of Aspects 1 to 4, the liquid temperature in the bicarbonation step is 30° C. or lower. According to the method for producing purified lithium carbonate according to Aspect 5 of the present invention, the liquid temperature in the bicarbonation step is 30° C. or lower, so that scale generation in the bicarbonation step can be suppressed and a lithium bicarbonate solution can be stably obtained.

[0014] A method for producing purified lithium carbonate according to a sixth aspect of the present invention is the method for producing purified lithium carbonate according to any one of the first to fifth aspects, further comprising the step of crystallizing the purified lithium carbonate, wherein CO liberated from the lithium bicarbonate in the crystallization step is ２ According to the method for producing purified lithium carbonate of Aspect 6 of the present invention, CO released from the lithium bicarbonate in the purified lithium carbonate crystallization step is used in the bicarbonation step. ２ CO gas is used in the bicarbonation step. ２ This reduces the amount of gas used and reduces operating costs.

[0015] According to an aspect of the present invention, it is possible to provide a method for producing purified lithium carbonate that can efficiently recover lithium and can obtain purified lithium carbonate with sufficiently high purity.

[0016] Fig. 1 is a flow chart showing a lithium recovery method using a method for producing purified lithium carbonate 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 step in Fig. 1. Fig. 5 is a flow chart showing a method for producing purified lithium carbonate according to one embodiment of the present invention, which is applied as 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.

[0017] Hereinafter, a method for producing purified 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 purified lithium carbonate of the present embodiment is applied to a process for recovering lithium from lithium-containing materials such as pulverized waste lithium-ion batteries, for example. First, a lithium recovery method to which the method for producing purified 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] In addition, 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. In addition, 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 concentrated solution containing lithium 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 .

[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, lithium carbonate is purified. A method for producing purified lithium carbonate according to one embodiment of the present invention is applied to this lithium carbonate purification step S05. The method for producing purified lithium carbonate according to this embodiment (lithium carbonate purification step S05) includes, as shown in FIG. 5 , 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 the gas, soluble lithium bicarbonate is generated, and a 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 a lithium bicarbonate solution is produced. 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 purified lithium carbonate according to this embodiment, which is applied as the lithium carbonate purification step S05, includes a purified lithium carbonate crystallization step S54 in which the lithium bicarbonate solution from which calcium carbonate has been removed is heated to decompose the lithium bicarbonate and precipitate purified lithium carbonate, a second solid-liquid separation step S55 in which the precipitated purified lithium carbonate is separated from the mother liquor, and a mother liquor return step S56 in which the mother liquor obtained in the second solid-liquid separation step S55 is returned to the slurrying step S51. Therefore, the lithium remaining in the mother liquor can be contained in the lithium carbonate slurry as a raw material, thereby improving the lithium recovery efficiency. In addition, the lithium carbonate slurry can be cooled by adding CO ２ This process includes a bicarbonation step S52 in which soluble lithium bicarbonate is produced by injecting a gas to obtain a lithium bicarbonate solution, and a first solid-liquid separation step S53 in which calcium carbonate suspended in the lithium bicarbonate solution is separated. Therefore, calcium can be efficiently removed, and highly purified lithium carbonate can be produced.

[0065] In the present embodiment, when the liquid temperature in the purified lithium carbonate crystallization step S54 is set within the range of 85°C or higher and 98°C or lower, it becomes possible to efficiently decompose lithium bicarbonate and promote precipitation of purified lithium carbonate.

[0066] In the present embodiment, when the concentration of lithium carbonate 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, lithium bicarbonate can be sufficiently produced in the bicarbonation step, and residual lithium carbonate can be suppressed, making it possible to produce purified lithium carbonate more efficiently.

[0067] In the present embodiment, when the pH in the bicarbonation step S52 is 7.5 or higher, it is possible to suppress the incorporation of calcium in the bicarbonation step S52, and it is possible to produce purified lithium carbonate with even higher purity. ２ Gas consumption can be reduced.

[0068] In the present embodiment, when the liquid temperature in the bicarbonation step S52 is 30°C or lower, the generation of scale in the bicarbonation step S52 can be suppressed, and a lithium bicarbonate liquid can be stably obtained.

[0069] In this embodiment, CO liberated from lithium bicarbonate in the purified lithium carbonate crystallization step S54 ２ When the gas is used in the bicarbonation step S52, CO ２ This reduces the amount of gas used and reduces operating costs.

[0070] Although the present invention has been described above as an embodiment, it is not limited thereto and can be appropriately modified within the scope of the technical requirements of the invention. In the present embodiment, as described above, the present invention has been described as being applied to the lithium carbonate purification step S05 of the lithium recovery method including the leaching step S01, the impurity removal step S02, the lithium-containing liquid concentration 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 it is used to purify lithium carbonate containing 400 ppm by mass or more of calcium.

[0071] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0072] Example 1 45 g of crude lithium carbonate having the chemical composition shown in Table 1 was added to 1 L of water to form a slurry. ２ The mixture was stirred while gas was blown in at a rate (amount) of 0.5 L / min, and lithium carbonate was leached as lithium bicarbonate. When the hydrogen ion concentration in the solution decreased from pH > 8 at the start of leaching to pH = 7.5, CO ２ The gas blowing was stopped. The remaining solid was subjected to solid-liquid separation using a suction filter to obtain an undissolved residue and a lithium bicarbonate solution. The undissolved residue was dried for 12 hours in a thermostatic dryer at 105°C. The chemical composition of the undissolved residue obtained is shown in Table 2, and the chemical composition of the lithium bicarbonate solution is shown in Table 3. The chemical composition was measured by ICP atomic emission spectroscopy (ICAP7600 DUO, manufactured by THERMO SCIENTIFIC).

[0073] One liter of the obtained lithium bicarbonate solution was maintained at 85-90°C for 30 minutes, and a highly purified lithium carbonate slurry was produced from the lithium bicarbonate solution. During this process, preheated water was appropriately added to compensate for the water content lost due to evaporation, maintaining the original liquid volume. The obtained purified lithium carbonate slurry was filtered using a suction filter to obtain purified lithium carbonate and a decarbonation filtrate. The purified lithium carbonate was dried for 12 hours in a thermostatic oven at 105°C, and its dried weight was 33.1 g. The purified 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 decarbonation filtrate was also measured by ICP atomic emission spectroscopy. The chemical compositions of the obtained purified lithium carbonate and the decarbonation filtrate are shown in Table 4 and Table 5, respectively.

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] Tables 2 and 3 show that Li was mainly leached from the crude lithium carbonate as lithium bicarbonate, with Ca remaining in the undissolved residue. Tables 3 to 5 also show that high-quality purified lithium carbonate was produced from the lithium bicarbonate solution, with impurities remaining in the post-decarbonation solution. It can be seen that the above-described method enables the production of purified lithium carbonate with fewer impurities from crude lithium carbonate containing impurities.

[0080] <Comparative Example 1> When lithium carbonate is leached as lithium bicarbonate, CO ２ The same procedure as in Example 1 was carried out except that the hydrogen ion concentration at which the blowing was stopped was set to pH = 7.0.

[0081] <Comparative Example 2> When lithium carbonate is leached as lithium bicarbonate, CO ２ The same procedure as in Example 1 was carried out except that the hydrogen ion concentration at which the blowing was stopped was set to pH = 8.0.

[0082] The chemical compositions of the undissolved residues obtained by the methods of Comparative Examples 1 and 2 are shown in Table 6, the chemical compositions of the lithium bicarbonate solutions are shown in Table 7, and the chemical compositions of the purified lithium carbonate finally obtained from the solutions are shown in Table 8.

[0083]

[0084]

[0085]

[0086] From Tables 7 and 8, when the end point pH was 7.0 (<7.5), a large amount of Ca was leached into the lithium bicarbonate solution, and the Ca concentration in the obtained purified lithium carbonate increased. ２ On the other hand, Tables 6 and 7 show that when the end point pH is 8.0 (>7.5), the amount of Li remaining in the undissolved residue increases, leading to a decrease in yield.

[0087] Example 2 The same procedure as in Example 1 was carried out except that 1 L of the decarboxylation filtrate obtained by the method shown in Example 1 was used as a mother liquor, and 33 g of crude lithium carbonate was added to form a slurry.

[0088] Example 3 1 L of the decarbonation filtrate obtained in Example 2 was used as a mother liquor, and 33 g of crude lithium carbonate was added to form a slurry. Then, purified lithium carbonate was produced by the same operation as in Example 2. 1 L of the obtained decarbonation filtrate was used as a mother liquor, and 33 g of crude lithium carbonate was added to form a slurry. Then, purified lithium carbonate was produced by the same operation as in Example 2. The process from the step of slurrying the mother liquor to the step of producing purified lithium carbonate was repeated five times in total.

[0089] The chemical compositions of the decarbonation filtrates obtained in Examples 1 to 3 are shown in Table 9, and the chemical compositions of the purified lithium carbonate finally obtained from the decarbonation filtrates are shown in Table 10. The Li recovery rates shown in Table 10 were calculated using the following formula: {(total amount of purified lithium carbonate recovered (g)) / (total amount of crude lithium carbonate added (g))}×100

[0090]

[0091]

[0092] Tables 9 and 10 show that the Li recovery rate improved as the number of repetitions of the decarbonation filtrate increased. Specifically, when the number of repetitions was 0, the amount of purified lithium carbonate was 33.1 g relative to the amount of crude lithium carbonate of 45 g, resulting in a recovery rate of 74%. A component equivalent to approximately 12 g of crude lithium carbonate remained in the solution. From the first repetition onwards, an amount of purified lithium carbonate obtained was approximately equal to the amount of newly added crude lithium carbonate (33 g). Therefore, the ratio of the total amount of recovered purified lithium carbonate to the total amount of crude lithium carbonate (Li recovery rate) increased with an increase in the number of repetitions. These results confirm that, according to the present invention, purified lithium carbonate can be obtained with a high recovery rate without significantly reducing the quality of the lithium carbonate obtained by repeatedly using the mother liquor.

[0093] The method for producing purified 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.

[0094] S05 Lithium carbonate purification step S51 Slurrying step S52 Bicarbonation step S53 First solid-liquid separation step S54 Purified lithium carbonate crystallization step S55 Second solid-liquid separation step S56 Mother liquor return step.

Claims

1. A slurrying step of adding water to lithium carbonate containing 400 mass ppm or more of calcium to produce a lithium carbonate slurry, and blowing CO ２ gas into the lithium carbonate slurry to produce soluble lithium bicarbonate and obtain a lithium bicarbonate solution; a first solid-liquid separation step of separating calcium carbonate suspended in the lithium bicarbonate solution; a purified lithium carbonate crystallization step of heating the lithium bicarbonate solution after removing the calcium carbonate to decompose the lithium bicarbonate and precipitate purified lithium carbonate; a second solid-liquid separation step of separating the precipitated purified lithium carbonate from the mother liquor; and a mother liquor return step of returning the mother liquor obtained in the second solid-liquid separation step to the slurrying step. A method for producing purified lithium carbonate, characterized by comprising the above steps.

2. The method for producing purified lithium carbonate according to claim 1, wherein the liquid temperature in the step of crystallizing the purified lithium carbonate is in the range of 85°C or higher and 98°C or lower.

3. The method for producing purified lithium carbonate according to claim 1 or 2, wherein the concentration of lithium carbonate in the lithium carbonate slurry produced in the slurrying step is in the range of 30 g / L or higher and 45 g / L or lower.

4. The method for producing purified lithium carbonate according to claim 1 or 2, wherein the pH in the bicarbonation step is 7.5 or higher.

5. The method for producing purified lithium carbonate according to claim 1 or 2, wherein the liquid temperature in the bicarbonation step is 30°C or lower.

6. In the step of crystallizing the purified lithium carbonate, the CO ２ gas released from the lithium bicarbonate is used in the bicarbonation step. The method for producing purified lithium carbonate according to claim 1 or claim 2, characterized in that.