Optimization of Elemental Sulphur Recovery during an Acid Mine Water Treatment

Abstract

The South African mining industry is a major contributor to South Africa’s Gross Domestic product (GDP). The negative consequences of mining include toxic effluents from mineral processing and decanting streams, even after mine closure. Large volumes of Acid Mine Drainage (AMD) are expected to increase as the mining industry grows. Currently, biological treatment of mine waters are preferred to chemical methods, due to various advantages offered such as low operational cost and small environmental footprint. Biological treatment of AMD primarily rely on the activity of sulphate reducing bacteria which reduce sulphate to sulphide in the presence of organic matter thus allowing the precipitation of the metals and increase in pH. However, excess of sulphide remains in the system and if not removed, can be oxidized to sulphate. A sustainable AMD management plan could entail development of treatment technologies to remove total sulphur (sum of sulphur species) from the system. Production of elemental sulphur, which involves partial oxidation of sulphide, has been a recent subject of interest. The use of colourless sulphide oxidizing bacteria, especially Thiobacillus species has been widely reported. Six isolates of sulphide oxidizing microorganisms, of which 4 bacterial and 2 filamentous fungal species from a gold mine (Johannesburg, South Africa) were tested in this study to achieve partial oxidation of sulphide to sulphur. The microbial species were selected for high sulphide oxidation in the presence of carbon sources (glucose and lactate). Lysinicibacillus fusiformis was observed to be the most suitable microorganism for sulphide oxidation. In iiorder to investigate optimal conditions for sulphur recovery, L. fusiformis bacterial activity was tested under different conditions of pH and redox potential. It resulted that at a pH of 8 and Eh of -80mV up to 95% of sulphur was recovered.