REHABILITATION WORKS OF MINE WASTES IN ABANDONED METAL MINES IN KOREA

About 900 abandoned metal mines are distributed in Korea, and the waste materials, mainly tailings, in most of these abandoned mines have been left uncovered. Under these circumstances, it is possible that the mine wastes will quickly be oxidized, and eventually be eroded away. In fact, many tailings impoundments were failed during rainy seasons, and contaminated nearby streams and rivers. According to the acid-base accounting for 50 tailings taken from several abandoned mines, the average neutralization potential (NP) and the acid potential (AP) were 20.71 kgCaCO₃/t and 163.86 kgCaCO₃/t, respectively. These results indicate that lots of tailings have a strong potential to release acid leachate. The paste pH of tailings ranged from 1.73 to 8.11. Speciation of some metals, such as Fe, Mn, Al, Zn, As, Cd, Cu and Pb in some tailings was in soluble state with high level of concentration. Some tailings have actually released acidic leachate with heavy metals and contaminated the environment around. Due to these reasons, abandoned metal mines have been treated as a pollution source and, in order to prevent further mine pollution, the Korean government and local autonomous entities have carried out rehabilitation works for mine wastes from the middle of 1990's. The total budget for prevention of environmental pollution in 20 abandoned metal mines reached up to 25million dollars from 1995 to 2002, and this project will presumably be continued. The major methods for rehabilitation works include capping, vertical grouting and encapsulation, varied for different situation of abandoned mines. The gross volume of rehabilitated mine wastes ranged mostly from 30,000m³ to 200,000m³. It is acknowledged that systematic guidelines for restoration works based on characteristics of mine wastes should be provided for more efficient and safer rehabilitation.