Provided is a method for producing nickel powder from a nickel ammine sulfate complex solution, comprising treatment steps of: (1) a seed crystal production step of producing nickel powder having an average particle size of 0.1 to 5 m; (2) a seed crystal addition step of adding the nickel powder obtained in the step (1) as seed crystals to form a mixed slurry; (3) a reduction step of forming a reduced slurry containing nickel powder formed by precipitation of a nickel component in the mixed slurry on the seed crystals; and (4) a growth step of performing solid-liquid separation to separate and recover the nickel powder as a solid phase component and then blowing hydrogen gas into a solution prepared by adding the nickel ammine sulfate complex solution to the recovered nickel powder to grow the nickel powder to form high purity nickel powder.

Provided is a production method for producing coarse particles of high purity Co powder from a cobalt ammine sulfate complex solution using fine Co powder and using industrially inexpensive H.sub.2 gas.

Provided is a method for producing nickel powder from a nickel ammine sulfate complex solution, comprising treatment steps of: (1) a seed crystal production step of producing nickel powder having an average particle size of 0.1 to 5 m; (2) a seed crystal addition step of adding the nickel powder obtained in the step (1) as seed crystals to form a mixed slurry; (3) a reduction step of forming a reduced slurry containing nickel powder formed by precipitation of a nickel component in the mixed slurry on the seed crystals; and (4) a growth step of performing solid-liquid separation to separate and recover the nickel powder as a solid phase component and then blowing hydrogen gas into a solution prepared by adding the nickel ammine sulfate complex solution to the recovered nickel powder to grow the nickel powder to form high purity nickel powder.

In a method of selectively recovering a valuable metal from lithium secondary battery waste, a complex oxide is separated from a lithium secondary battery waste powder. The powder is dissolved in sulfuric acid. The solution is separated into a solution and a residue by solid-liquid separation. The solution is subjected to solid-liquid separation to produce a solution and a solid. Valuable metal manganese is extracted from the solution by solvent extraction, and the remaining valuable metals including cobalt, nickel, and lithium are separated into a first raffinate. Valuable metal cobalt is extracted from the first raffinate by solvent extraction, and the remaining valuable metals are separated into a second raffinate. Valuable metal nickel is extracted from the second raffinate by solvent extraction, and the remaining valuable metal lithium is separated into a third raffinate. Valuable metal lithium is extracted and concentrated from the third raffinate.