Abstract: A process for substantially reducing the presence of impurities from a sulfur-containing feed material such as dust and hydrometallurgical wastes that result from smelting and refining operations. Pelletized feed materials are heated to 800.degree. to 1150.degree. C and reacted with a gas stream containing chlorine and oxygen. In the presence of sulfur dioxide formed in situ and due to the presence of residual sulfur, the order of volatilization of the elements contained in the feed material is changed from that known for conventional chloridization processes to a more advantageous order. The elements Cd, Bi, Re, Pb, Mo, Sn, Sb, Zn, and As are volatilized and thereby separated from the solid feed material which is consequently enriched in Cu, Ag, Co, Fe, Ni, Au, and precious metals. The feed material is subsequently refined conventionally.