Abstract: In a method for preparing a cobalt sulfate salt, a feeding solution comprising cobalt sulfate and a sulfuric acid aqueous solution is prepared. A first solution is produced by evaporation-crystallizing the feeding solution. A first cobalt sulfate salt is produced by filtering the first solution together with first purging. A second solution is produced by cooling-crystallizing an aqueous solution comprising the first cobalt sulfate salt. A second cobalt sulfate salt is produced by filtering the second solution together with second purging.

Abstract: A method for recovering an active metal of a lithium secondary battery according to an embodiment of the present application whereby a used lithium-containing mixture is prepared, and the used lithium-containing mixture is treated with a hydrogen reduction to prepare a preliminary precursor mixture. The preliminary precursor mixture is washed with water to generate a lithium precursor including lithium hydroxide. Lithium hydroxide can be obtained by the washing treatment with high purity.