Abstract
FeS leaching was carried out in aqueous sulfur dioxide solution at low temperature and pressure ( T = 60° CC; P SO 2 = 51.7 kPa) using both a constant-pressure gas-uptake apparatus and conventional glass-leaching equipment. In the initial stages of the leaching reaction the ratio [SO 2]/[Fe 2+] was found equal to 1.3. This suggests a stoichiometry given by the following sequence of equations FeS + SO 2·H 2O ⇌ FeS + H + FeS · HSO 3 − + H + → Fe 2+ + H 2S + SO 3 2− ▪ As the reactions progressed a build up of various oxy-sulfur species was observed. The leaching process appears to proceed by two concurrent dissolution paths, namely acid dissolution and aquated sulfur dioxide dissolution. In both cases the rate determining step (r.d.s.) involves a surface desorption reaction. In the constant leaching region, the kinetics can be represented by the following rate expression: ▪ At low [H+] relative to [SO 2-H 2O], path I predominates. This can be represented by: | sFeS +SO 2 · H 2O ⇌ | 2FeS SO 2 · H 2O | sFeS SO 2 · H 2O ⇌ | s FeS HSO 3 − + H + | s FeS HSO 3 − → Fe 2+ (aq) r.d.s. At high [H +] relative to [SO 2·H 2O], path II predominates. This can be represented by: | sFeS + H + ⇌ | s FeS H + | sFeS H + → Fe 2+ (aq) r.d.s. The apparent activation energy was found to be 41.6 kJ per mole.
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