The possibility of reducing the chemical losses of alkali during the reduction of nickel directly from the sulfide compounds that form part of the nickel concentrate of converter matte separation is considered. It was proved that at temperatures of 350-650 ° C the disproportionation of elemental sulfur in an alkaline medium is accompanied by the polymerization of sulfide and elemental sulfur to give the compound Na₂S_n, (where n = 1 ÷ 4). It was ascertained that under increasing the degree of polymerization the nickel reduction rate decreases. Titrimetric, gravimetric, x-ray spectral and x-ray phase analysis methods were used for the work.