Method of producing high-purity lithium carbonate and barium sulfate from discarded lithium secondary batteries

A method of producing high-purity lithium carbonate and barium sulfate from discarded lithium secondary batteries, the method comprising:

• (I) providing high-purity lithium phosphate from a discarded lithium secondary battery;
• and
• (II) producing high-purity lithium sulfate from the high-purity lithium phosphate and producing high-purity lithium carbonate and barium sulfate from the high-purity lithium sulfate,
• wherein step (II) comprises
• (a) mixing high-purity lithium phosphate from step (I) and a sulfuric acid aqueous solution to produce a liquid mixture,
• (b) condensing the liquid mixture of step (a) and performing solid-liquid separation on the liquid mixture to obtain high purity lithium sulfate solid,
• (c) dissolving the high-purity lithium sulfate solid in water or a sodium hydroxide aqueous solution having a pH value of 12 or higher, and performing solid-liquid separation to obtain a lithium sulfate aqueous solution and a solid-phase lithium phosphate,
• (d) adding carbonate, carbonate aqueous solution, or a carbonic acid gas to the lithium sulfate aqueous solution and performing solid-liquid separation to obtain solid-phase lithium carbonate,
• (e) finely grinding the solid-phase lithium carbonate and classifying lithium carbonate particles having a particle size of 1 to 5 μm to produce lithium carbonate slurry,
• (f) blowing a carbonic acid gas to the lithium carbonate slurry and dissolving edges of lithium carbonate particles or dissolving and removing minute particles of the lithium carbonate,
• (g) performing solid-liquid separation for the lithium carbonate slurry obtained by step (f) to obtain high-purity lithium carbonate having a solid phase, and
• (h) adding a soluble barium salt aqueous solution to a filtrate obtained from the solid-liquid separation of step (g) and performing solid-liquid separation to obtain high-purity barium sulfate having a solid phase,
• wherein the solid-phase lithium phosphate obtained through the solid-liquid separation of step (c) is used as the liquid mixture of lithium phosphate and sulfuric acid of step (a),
• wherein the lithium carbonate particles having a size larger than 5 μm in the classification of step (e) are additionally grinded until the particle size becomes 1 to 5 μm, and
• wherein the filtrate of step (h), which is formed after performing solid-liquid separation to obtain high purity barium sulfate having a solid phase, is added to the fine grinding of step (e).