Dependences of the cobalt recovery into the carbonyl gas phase on the content of sulfur and carbon in sulfidized copper-nickel metallurgical half-products subjected to carbonylation were studied at a medium pressure of the reaction gas (70 gage atm). The behavior of cobalt was examined by means of metallographic analysis of the residue formed in carbonylation. A mechanism of solid-phase interaction of cobalt with copper sulfide and a method for calculation of the volume self-diffusion coefficient of cobalt in the crystal lattice of metallic copper deformed after removal of nickel were suggested.