Technical Evaluation of Fly Ash and Bottom Ash (FABA) Utilization for Acid Mine Drainage Mitigation in Coal Mining Operations

Abstract

Acid mine drainage (AMD) continues to represent a long-term, technically complex environmental risk in coal mining operations, especially where waste streams are dominated by sulfide-rich, Potentially Acid Forming (PAF) materials. This study critically evaluates fly ash and bottom ash (FABA), a widely available by-product of coal-fired power plants, as an integrated geochemical–geotechnical amendment for AMD control. A multi-tier analytical approach is applied, combining static geochemical characterization, extended kinetic leaching tests, and decadal-scale hydrogeochemical modeling to capture both short-term reactivity and long-term system behavior. The results show that the relatively high CaO content in FABA (18–25%) generates persistent alkalinity via Ca(OH)₂ dissolution, enabling rapid neutralization of acidic leachates and promoting the precipitation of Fe, Mn, and Al as thermodynamically stable hydroxide phases. Incorporating 20–30% FABA into PAF material produced near-neutral pH conditions within 10–20 weeks and yielded more than 80% reductions in dissolved metal concentrations. Hydrogeochemical simulations further indicate that FABA-based cover layers with thicknesses of 0.5–1.0 m can maintain hydrogeochemical stability over a 10-year period, whereas untreated PAF dumps remain acidic. Overall, the findings demonstrate that FABA operates through coupled geochemical and geotechnical mechanisms that suppress pyrite oxidation and reduce water and oxygen fluxes. In addition, FABA reuse supports circular-economy principles by transforming industrial residues into a cost-effective, scalable, and environmentally beneficial material for AMD mitigation.