Bottom ash and fly ash wastes as alkalinising reagents for neutralising acid mine drainage

Preliminary investigation was conducted to evaluate the utilization of bottom ash and fly ash by-products on a study limited to their role as alkalizing reagents, with the ultimate objective of examining their potential use for insitu treatment of acid mine drainage (AMD) in South African mines. Bottom ash (BA) and fly ash (FA) obtained from a coal-powered electricity generation station were used in varied combined proportions of 100/0, 90/10, 70/30 BA:FA reagent mixtures and used to conduct neutralization tests done at mix proportions varied from 20:1 to 1:1 AMD to reagent mixtures. Three types of acid mine drainage water from an underground gold mine (AMD-Wz), gold tailings dam (AMD-Lc) and a coal mine (AMD-MpK) were used in the investigation. Water quality tests were carried out before and after the neutralisation treatment. It was found that both bottom ash and fly ash are effective alkalinising reagents for neutralising AMD. The materials were found to be most effective when mixed at a ratio no greater than 5:1 of mine water to reagent. Use of the coal ash wastes effectively removed up to 99% of iron from the AMD. The sulphate concentration was also reduced by the treatment but it remained fairly elevated. Manganese concentration reduced as the pH of the treated water increased, reaching a negliglible concentration of < 1.0 mg/l at pH ≥ 11. Further investigations are underway to examine leaching and weathering characteristics of the reagents