Thermal treatment of leaching residue from hydrometallurgical zinc production

A method of treating residual material from the hydrometallurgical production of zinc which material consists of the leaching residue, iron precipitates from the leaching solution or mixtures of both from such production and which material contains zinc, lead and iron which method comprises heating and melting said residual material in a reactor under oxidation conditions at partial oxygen pressure to form lead oxide from the lead present in said residual material by supplying air to said material during such heating;

• said partial oxygen pressure being at least sufficient to prevent formation of lead sulphide;
• thereafter heating the oxidized material to fume off zinc in its elemental form by the addition of a reducing agent in a quantity sufficient to provide a partial oxygen pressure low enough to substantially reduce the lead and zinc yet high enough to avoid the simultaneous reduction of iron present;
• thereafter recovering at least the zinc from the fume and the lead as a melt;
• and the iron remaining in a slag.