Abstract: Substantially pure copper is produced from impure cupriferous materials by leaching the cupriferous material with an ammonium sulfate-containing ammoniacal solution in the presence of oxygen, followed by separating the copper-containing aqueous liquor from the insoluble leach residue and contacting the thus separated leach liquor with an organic extractant of the metal ion exchange type to extract the copper from the leach liquor. The organic phase comprising the copper-bearing organic extractant is separated from the aqueous phase comprising the leach liquor of reduced copper content, and the resulting copper-bearing organic extractant is contacted with an aqueous solution of sulfuric acid to strip the copper from the copper-bearing extractant.