The oxidation of the sulphide ion at very low concentrations in aqueous solutions

Abstract

The oxidation, by oxygen, of the sulphide ion at very low concentrations in aqueous solutions has been studied at various temperatures and hydrogen ion concentrations. Under all conditions the reaction was close to first order with respect to the sulphide ion when other variables were constant. The rate of oxidation was enhanced by an increase of pH and temperature, and by increasing the oxygen:nitrogen ratio in the gas mixture. The overall reaction is summarized as follows HS–+ O2→ SO32–+ H+, SO32–+½ O2→ SO42–, SO32–+ HS–+½ O2→ S2O32–+ OH–, S2O32–+½ O2→ SO42–+ S. The first reaction is the initial rate-determining step, followed by the rapid removal of SO32– ion from solution as SO42– and S2O32–, and finally the slow oxidation of the S2O32– ion and elementary sulphur to SO42–.