Active Treatment of Polluted Mine Waters

Abstract

The impact of large quantities of sulphate-polluted water, by-products of various mining and mineral industries, can be disastrous on ecosystems and water resources. The social and economic benefits of reducing the salt content in the effluent to acceptable levels, to produce potable water, could be spectacular, if an economically viable solution to the problem is obtained. Mintek, Savannah Mining and the Wren Group are developing a solution to this problem. It entails the precipitation of metal hydroxides, calcium sulphate and ettringite. The key to the viability of the new technology lies in the correct use, regeneration and recycling of the compound used to precipitate the ettringite. The water produced by this process is suitable for disposal to watercourses or for agricultural, domestic or industrial consumption. The salts in the acid mine drainage are converted to solid hydroxides, gypsum and calcium carbonate. The technology has been tested on several waters in the laboratory, on a mini plant, and in two pilot plants. Preliminary results obtained from the mini-plant indicate that potable water can be produced (containing less than 200 mg/l sulphate and no heavy metals) as long as the monovalent ions (Na+, Cl-, etc.) are within limits. In this paper, an overview of the process is presented, along with the results obtained in the laboratory, mini-plant and pilot-plant tests on specific samples of polluted mine drainage.