Oxidation of Thiosulfate with Oxygen Using Copper (II) as a Catalyst

Thiosulfate effluents are generated in the photography and radiography industrial sectors, and in a plant in which thiosulfates are used to recover the gold and silver contained in ores. Similar effluents also containing thiosulfate are those generated from the petrochemical, pharmaceutical and pigment sectors. In the future, the amounts of these effluents may increase, particularly if the cyanides used in the extraction of gold and silver from ores are substituted by thiosulfates, or if the same happens to electronic scrap or in metallic coating processes. This paper reports a study of the oxidation of thiosulfate, with oxygen using copper (II) as a catalyst, at a pH between 4 and 5. The basic idea is to avoid the formation of tetrathionate and polythionate, transforming the thiosulfate into sulfate. The nature of the reaction and a kinetic study of thiosulfate transformation, by reaction with oxygen and Cu2+ at a ppm level, are determined and reported. The best conditions were obtained at 60 degrees C, pH 5, with an initial concentration of copper of 53 ppm and an oxygen pressure of 1 atm. Under these conditions, the thiosulfate concentration was reduced from 1 gL(-1) to less than 20 ppm in less than three hours.