Recovery of Drinking Water and By-products from Gold Mine Effluents

Abstract

South Africa is a water constrained country with a large mining industry. Effluents from the mining industry, which is rich in calcium sulphate, resulted in salination of the limited amount of surface water. South Africa is also a large importer of sulphur because it is required for the manufacture of sulphuric acid. It is argued that importation of sulphur can be replaced by recovering it as a by-product during treatment of sulphate-rich effluents. The removal of acid, metals and sulphate from mine water was assessed using the CSIR ABC (Alkali-Barium-Calcium) Desalination process. The CSIR ABC Desalination process was used for neutralization and removal of the total dissolved solids content from 7600 to 400 mg/l. Metals were removed effectively through precipitation with CaS or Ca(HS)₂. The latter compound had a high solubility with higher metal removal rates compared to CaS. Sulphate remained in solution during metals precipitation with sulphide. The rate of sulphate removal during gypsum crystallization was influenced by the gypsum seed crystal content. The rate of sulphate removal during BaCO₃ treatment was influenced by pH, CaCO₃ solids and BaCO₃ solid concentration. Ca(HS)₂ was produced from CaS by passing CO₂ through a CaS slurry. Further CO₂ additions resulted in H₂S-stripping. BaSO₄ and CaCO₃ were converted simultaneously to BaS and CaO, respectively. The optimum temperature was 1050°C. The cost of raw materials for the treatment of water with a TDS content of 7 600 mg/l amounted to R2.21/cubic metre (m³). The potential value of the water and by-products amounted to R11.10/m³ (US$1.00 = ZAR7.60).

Acknowledgements

The authors wish to thank the following organizations: CSIR, the National Research Foundation, which provided funding for CSIR projects on neutralization and sulphate removal through their Technology and Human Resources for Industry Programme (THRIP); and Tshwane University of Technology.