Thermodynamics of salt roasting of sulphide ores

Abstract

Thermodynamic analysis of a non-polluting process for the effective treatment of lean multimetallic sulphide ores is presented. The sulphide ore is roasted with sodium chloride in air. Metal sulphides are converted to chlorides that can be separated from the unaffected gangue material. At a temperature of 1100 K the chlorides are present both in gaseous and in condensed states. Volatile chlorides can be easily removed and subsequently condensed. The chlorides present in the condensed state can be leached to separate them from the gangue. The sulphur is trapped as Na₂SO₄ and thus SO₂ emission is minimized. Ellingham diagrams are used to compare data for a large number of elements. The major thermodynamic driving force is provided by the higher stability of Na₂SO₄ relative to NaCl.