Lime Treatment of Mine Drainage at the Sarcheshmeh Porphyry Copper Mine, Iran

Abstract

Laboratory and field treatment tests were performed to evaluate the effectiveness of lime treatment for mitigation of environmental effects of acid mine drainage (AMD) at the Sarcheshmeh porphyry copper mine. AMD associated with the rock waste dumps is contaminated with Al (>36,215 μg/L), Cd (>105 μg/L), Co (>522 μg/L), Cu (>53,250 μg/L), Mn (>42,365 μg/L), Ni (>629 μg/L), and Zn (>12,470 μg/L). The concentrations of other metals (Fe, Mo, Pb, and Se) are low or below detection limits (As, Cr, and Sb). Due to the very high Al and Mn content and the low concentration of Fe, a two-stage lime treatment method was chosen for the laboratory tests. In the first stage, the AMD was treated at four pH set points: 7.5, 8.9, 9, and 10. In the second stage, after removing the sludge at pH 9, treatment was continued at pH 10 and 11. The results indicated that a two-stage treatment method was not necessary because elements such as Al, Cu, Co, and Zn were easily treated at pH 7.5, while complete removal of Cd, Mn, and Ni only required a pH of 10. Increasing pH during the treatment process only caused a slight increase in Al. Field treatment tests support the laboratory results. Lime treatment of highly contaminated AMD from dump 11, using simple low density sludge pilot scale equipment, show that contaminant metals are treatable using this method. The mean treatment efficiency for contaminant metals was 99.4% for Al, % for Cd, 99.6% for Co, 99.7% for Cu, 98.5% for Mn, 99.7% for Ni, 99% for U, and 99.5% for Zn. The optimum pH for AMD treatment by lime was in the range of 9–10. The produced sludge in the treatment process was highly enriched in the contaminant metals, especially Cu (>7.34%), Al (>4.76%), Mn (>2.94%), and Zn (>1.25%). A correlation coefficient matrix indicates that the distribution pattern of the contaminant metals between soluble and precipitated phases is consistent with the hydrochemical behavior of the metals during the lime treatment process.