Investigation into the sustainable use of mine waste to treat or prevent acid mine drainage

Abstract

Mine waste rock or tailings generate acid when sulphide minerals such as Pyrite (FeS2) oxidise in the presents of oxygen and water. The acid not neutralised by acid neutralising minerals such as calcite is leached into nearby water bodies such as lakes, rivers and underground water reservoirs and is referred to as Acid Mine Drainage (AMD). AMD is usually highly acidic, containing elevated concentrations of toxic dissolved metals. AMD is the second most significant threat to sustainable life after global warming. The primary aim of this study is to determine the feasibility of using alkaline gold mine tailings as a pH neutralising cover to mitigate AMD generated by gold mine tailings that have become acidic located in the Sabie-Pilgrim's Rest Goldfields, Mpumalanga province, South Africa. The study assessed the acid generating and acid neutralising capabilities of the alkaline (AN), acidic (AG) gold mine tailings and blends (MIX25 and MIX50) using Acid-Base Accounting (ABA), Net Acid Generation (NAG), Acid Buffering Characteristic Curve (ABCC) and leach column test procedures. The results found that the acidic gold mine tailings have become acidic and would continue to produce an acidic effluent. The alkaline gold mine tailing has a high acid neutralising capacity due to the high dolomite content. Results found that blends MIX50 and MIX25 consisting of a 1:1 and 1:3 weight ratio of alkaline and acidic gold mine tailings contained sufficient acid neutralising capacity (due to high Dolomite content) to neutralise acid generated by the acidic gold mine tailing portion of the blend. The leach column tests found that during the first few weeks of the experiment, the columns containing the alkaline gold mine tailing (top layer) used as a pH or acid neutralising cover material could not neutralise the acid generated by the acidic gold mine tailings (bottom layer). However, after prolonged exposure, the alkaline gold mine tailings effectively neutralise the acid generated by the acid-generating gold mine tailings, producing an alkaline effluent.