Abstract: Provided is a method for producing lithium carbonate from lithium ion battery waste, the lithium ion battery waste including battery positive material components containing Li and at least one metal selected from the group consisting of Co, Ni and Mn, wherein, after subjecting the lithium ion battery waste to a wet process, thereby separating the at least one metal of the battery positive material components from the lithium ion battery waste to obtain crude lithium carbonate, the method includes: a dissolution step of dissolving the crude lithium carbonate in a liquid while feeding a carbon dioxide gas; and a decarbonization step of heating a lithium dissolved solution obtained in the dissolution step to release carbonic acid, and wherein when dissolving the crude lithium carbonate in the liquid in the dissolution step, the liquid is stirred in a reaction vessel using a stirrer, and a ratio of a diameter (d) of a stirring blade of the stirrer to an inner diameter (D) of the reaction vessel (d/D) is from 0.

Abstract: A method for dissolving a lithium compound according to the present invention includes bringing a lithium compound into contact with water or an acidic solution, and feeding, separately from the lithium compound, a carbonate ion to the water or the acidic solution to produce carbonic acid, and allowing the carbonic acid to react with the lithium compound to produce lithium hydrogen carbonate.

Abstract: A method for dissolving a lithium compound according to the present invention includes bringing a lithium compound into contact with water or an acidic solution, and feeding, separately from the lithium compound, a carbonate ion to the water or the acidic solution to produce carbonic acid, and allowing the carbonic acid to react with the lithium compound to produce lithium hydrogen carbonate.

Abstract: Provided is a method for producing lithium hydroxide, which can obtain lithium hydroxide from lithium sulfate with a relatively low cost. A method for producing lithium hydroxide from lithium sulfate includes: a hydroxylation step of allowing the lithium sulfate to react with barium hydroxide in a liquid to provide a lithium hydroxide solution; a barium removal step of removing barium ions in the lithium hydroxide solution using a cation exchange resin and/or a chelate resin; and a crystallization step of precipitating lithium hydroxide in the lithium hydroxide solution that has undergone the barium removal step.

Abstract: Provided is a method for producing lithium carbonate from lithium ion battery waste, the lithium ion battery waste including battery positive material components containing Li and at least one metal selected from the group consisting of Co, Ni and Mn, wherein, after subjecting the lithium ion battery waste to a wet process, thereby separating the at least one metal of the battery positive material components from the lithium ion battery waste to obtain crude lithium carbonate, the method includes: a dissolution step of dissolving the crude lithium carbonate in a liquid while feeding a carbon dioxide gas; and a decarbonization step of heating a lithium dissolved solution obtained in the dissolution step to release carbonic acid, and wherein when dissolving the crude lithium carbonate in the liquid in the dissolution step, the liquid is stirred in a reaction vessel using a stirrer, and a ratio of a diameter (d) of a stirring blade of the stirrer to an inner diameter (D) of the reaction vessel (d/D) is from 0.

Abstract: A method for dissolving a lithium compound according to the present invention includes bringing a lithium compound into contact with water or an acidic solution, and feeding, separately from the lithium compound, a carbonate ion to the water or the acidic solution to produce carbonic acid, and allowing the carbonic acid to react with the lithium compound to produce lithium hydrogen carbonate.

Abstract: A sodium removal method according to the present invention is a method for removing sodium from a sodium-containing solution by precipitating a sodium ion in the sodium-containing solution as a sodium salt, the method including: a sodium precipitating step of precipitating the sodium salt by decreasing a temperature of the sodium-containing solution so that a sodium concentration of the sodium-containing solution exceeds solubility of the sodium salt at said temperature; and a solid-liquid separation step of removing the precipitated sodium salt by solid-liquid separation.