PURPOSE: To efficiently remove copper from copper-contg. high carbon molten iron by bringing a copper-contg. scrap steel into contact with Na2S series flux, executing decoppering treatment to subject the copper-contg. flux to molten salt electrolysis and to reutilize the flux.

CONSTITUTION: Copper-contg. high carbon steel scrap 1c melted by using the energy of a carbonaceous material is brought into contact with Na2S series flux by stirring and mixing in a reaction vessel 2a to remove away copper components in the molten iron into the flux as copper sulfide. The CuS-contg. Na2S series flux 2f is fed to a molten salt electrolytic cell 3a, and the decopperized high carbon molten iron 2g is fed to a steel making furnace or the like. In the molten salt electrolytic cell 3, metallic copper 3e precipitated in the cathode is formed into molten copper, is piled up on the cell bottom 3f and is recovered via an exhaust port 3g. The Na2S series flux 4a is separated and recovered via an exhaust port 3h and is recycled for the following decopperizing operation.