A new thiosalt depuration bioprocess for water- recycling in metallic sulphide mineral processing

Abstract

Economic and environmental imperatives force the metallic sulphide processing industry to re-use liquors that normally contain thiosalts; this processing entails difficulties in operation control and losses in metal-extraction performance. Bio-oxidation presents a promising option for thiosalt removal. Hitherto, this method has been tested to treat synthetic liquors containing only one thiosalt, either tetrathionate or thiosulphate, usually at low concentration (<1 g/L). In this article, bio-oxidation is studied of synthetic and real liquors containing mixtures of these thiosalts at concentrations close to 4.5 g/L. Coexistence of thiosulphate and tetrathionate in an acidic medium leads to strong and irreversible inhibition phenomena (performance losses close to 80%). In order to solve this problem, a previous treatment is proposed consisting of the 8-hour aeration of inlet solution after adding up to 20 mg/L and pH 1.5 of Cu2+ and sulphuric acid, respectively, resulting in the complete removal of thiosulphate and sulphite. Pre-treated real liquors were fed into a 1 L discontinuous stirred tank bioreactor and a 1 L continuous flooded packed-bed bioreactor, which were successfully started up and operated, thereby obtaining bio-oxidation rates close to the highest rates found in the literature with synthetic liquors.