A STUDY ON THE MEASURES TO TREAT THE MINE DRAINAGE FROM THE SAMTAN COAL MINE, KOREA

An experimental program was undertaken for establishing cost effective measures to prevent pollution of the creek near the Samtan coal mine. The Samtan mine, located at about 200 km southeast of Seoul, was one of the largest coal mines in Korea until September 2001. The slant chute block caving method was employed and, after closure of the mine, large underground voids and waste rock dumps have been left over. About 10 million tones of the waste rock dump with drainage channels have been left uncovered. All water passing through underground voids was collected and pumped to a central treatment plant. A flocculent was added to accelerate the precipitation of suspended solids before the closure of mine. The pumping of mine water is still being continued, to prevent water from overflowing into the nearby active coal mines. Water samples have been collected periodically for chemical analysis, and the pH, Eh, TDS were measured. Blending tests of pumping water with leachate and neutralization experiment with sludge recycling steps (HDS) were also performed. The chemical quality of the underground water before and after the closure of mine seems to be satisfactory, and neither chemical treatment for metals nor pH control was required. The pH of the mine water prior to its shut down was 7.63 and the iron content was 0.03 ppm. However, the iron content of Fe in underground water is increased to 2 ppm recently. The waste rock dump is releasing acidic leachate with high contents of metals. The pH of the leachate is about 3.0, and the Fe content ranges from 51 to 90 ppm. Average flow rate of pumping water and leachate are about 20,000 t/day and 1,000t/d, respectively. Under these circumstances, various measures for effective treatment of the mine drainage are being investigated. The pumping of underground water should be continued to prevent highly contaminated water from flooding nearby mines. Also, if pumping is stopped, water quality will be quickly deteriorated. The dilution settlement method seems to be another promising measure for effective treatment. Results of the mixture test of underground water with acidic leachate (20:1) showed that a lot of sludge was removed by dilution only.