Column leaching test to study effect of cover of fly ash for preventing acid mine drainage from coal waste

Coal waste that releases highly acidic, sulfate and metals rich drainage is a serious environmental problem which causes the contamination of surface and ground water as well as soils in coal mining areas in China. In order to study the effect of using fly ash for preventing acid-mine drainage and controlling heavy metals contamination from coal waste, two column leaching tests were conducted to determine if a cover of fly ash could be used for the control of acid-mine drainage from coal waste. We investigated the effect of the cover of fly ash on controlling acid, sulfate and heavy metals contamination from coal waste. The results from the experimental data analyses show that the cover of fly ash can effectively immobilize cadmium, copper, iron, lead and zinc in acid-mine drainage from coal waste, increase the pH value from 2.0 to 7.5 and decrease Eh from 249 mV to 148 mV, EC from 5.22 mS/cm to 1.05 mS/cm and SO42- concentrations from 12911.7 mg/L to 881.4 mg/L of acid-mine drainage from coal waste. The immobilization rate of heavy metals reached 99%. The oxidation of sulfide minerals in coal waste was prevented by the cover of fly ash, which favors the generation of alkalinity, the decrease of the population of Thiobacillus ferrooxidans, the heavy metals immobilization by precipitation inside the column, and the halt of the oxidation process of sulfide through iron coating on the surface of sulfide minerals in coal waste. The cover of fly ash can effectively control acid-mine drainage and heavy metals contamination from coal waste in situ treatment systems.