Lime Treatment of Acid Mine Drainage in Canada

Although many different biological and chemical technologies exist for treatment of acid mine drainage, lime neutralisation remains by far the most widely applied method. This is largely due to the high efficiency in removing dissolved metals through neutralisation, combined with the fact that lime costs are low in comparison to alternatives. Lime treatment essentially consists in bringing the pH of the AMD to a point where the metals of concern are insoluble. These metals therefore precipitate to form minuscule particles. A subsequent separation of these precipitates is then required to produce a clear effluent which meets regional discharge criteria. The solid/liquid separation forms a sludge which, depending on the applied process, can contain 1 to 30% solids by weight. The different types of lime neutralisation processes, including their respective strengths and weaknesses, are discussed in this paper. The evaluated processes are linked to concrete examples of existing treatment systems throughout Canada.