Heavy metals and acid generation potentials of solid mining wastes from Akara gold mine, Phichit province

Abstract

Gold mining wastes were chemically characterized particularly in aspects of acid drainage formation and heavy metal leaching. Solid mining wastes contain waste rocks and tailings that were taken from the largest gold mine in Thailand, Akara gold mine in Phichit Province. Waste rock samples from C-H pit and tailing samples from tailing storage facility were collected to be representatives of waste material. All samples were tested for geochemical characteristics including leaching of heavy metal and acid generating potentials. All information gained from this study can provide such good idea for environmental management. Two particular types of waste rocks (i.e., silicified lapilli tuff and sheared tuff) appear to have potential to generate acid mine drainage; therefore, good management plan must be taken with great care. Other rock types and tailing samples did not show signature to generate acidic drainage. From metal analyses of tailing, most toxic elements (e.g., Co, Cu, Cd, Cr, Pb, Ni and Zn) were found falling within the standard of Thailand Soil Quality Standards for Habitat and Agriculture. Only Mn appears to have higher content than the standard. However both Mn and Pb can leach out exceeding the surface water standard for agricultural at all pH condition, based on experiment leaching test. Ni can leach out exceeding the surface water standard at below pH 4. Thus, these 3 metals are needed to be monitor even at neutral pH condition. For waste rocks, most metals (e.g. As, Ag, Cd, Co, Cu, Mn, Ni and Pb) were found exceeding the average in igneous rocks. However, leaching experiment indicate the most metals have potential to leach out only at lower pH (pH2); besides, many metals show just little difference of leaching at pH 4 and 6.5. Mn, Pb and Cu appear to be the most concern in the leachate because these metals in all rock types yielded high concentration in the leachates at all pH conditions which are over the standards in most cases. These results lead to management and monitoring plan.