Acid mine drainage generation potential of waste rocks using weathering cell test in gold mine, Thailand

In gold mine, tons of waste rocks produced and left under atmospheric condition may consequently generate acid mine drainage (AMD). The aims of this study was to predict the AMD generation potential and estimate the concentrations of potentially toxic metals elements of three dump sites of waste rocks from a gold mine in Thailand. Twenty-Five waste rock samples from three dump sites, 9, 11, and 5 samples from oxide dump site, transition dump site and sulfide dump site, respectively, were determined the AMD generation potential by used the weathering cell test. The kinetic test composes with seven-day cycle (experiment run ~21 cycles), the effluent from each cycle were measured pH, conductivity, redox potential, sulfate and major and trace metals (i.e., As, Ca, Co, Cu, Fe, Mg, Mn, Pb, Zn).The results showed that some samples generate significant amount of AMD, especially samples collected from transition and sulfide dump sites. The pH of effluent water in oxide dump site had neutral to slightly alkalinity (pH ~6-9) while those in transition and sulfide dump sites had neutral to acid pH (pH ~ 3-7). The samples in transition and sulfide dump sites significantly generate higher acidity and sulfate than those in oxide dump site. Futhermore, the result revealed that some waste rock samples released relativly high concentration of heavy metal. Especially, As which was toxic heavy metal found in oxide dump site, transition dump site and sulfide dump site (maximum 0.748, 0.725 ,0.851 mg/L, respectively). Theses toxic elements may contaminate in surface or ground water and affect to living health. The long term acid generation interpreted by using oxidation-neutralization curve, indicating that after 144 days of leaching waste rock samples from all dump sites continue to generate acid for long period.