Direct elemental sulphur recovery from gold acid mine drainage streams

The metal precipitates resulting from the neutralization and desalination processes of acid mine water with lime, limestone and barium carbonate are wastes identified as sludge. The composition of these sludges generally comprises hydrated manganese, magnesium hydroxides, gypsum and large amount of barite. Legislation requires that these sludges be disposed in an environmentally acceptable manner to prevent metals from leaching and entering the environment. However; the enormous volumes of sludge produced and the limited disposal spaces present major environmental and economic concerns for the development of a viable technology for acid mine water treatment. This paper assesses the conversion of CaSO4/Mg(OH)2 and BaSO4/CaCO3 generated in the water stage of the Alkali Barium Calcium desalination process into sulphur. Africa is a major importer of large tonnages of sulphur at high cost often inflated by the cost of transportation whilst sulphur itself remains a relatively cheap product. This paper investigates a) the reduction of BaSO4/CaCO3 and CaSO4/Mg(OH)2 sludges to barium and calcium sulphide; b) the stripping of the sulphide with CO2 gas and the production of sulphur. Thermal reduction study shows that BaSO4/CaCO3 and CaSO4/Mg(OH)2 sludges can be reduced to BaS/CaS with duff carbon in a muffle furnace operating at about 1100 °C with BaS/CaS yield between 70 and 76%. The BaS/CaS formed was slurried in water and CO2 was used for the stripping of sulphide to form H2S gas and BaCO3/CaCO3 precipitate. The H2S generated was reacted with ferric sulphate to form elemental sulphur. Sulphur with purity between 95.2% and 99.1% was recovered from the sulphate rich wastes.