Evaluation of Leachate Quality from Codisposed Coal Fly Ash and Coal Refuse

Abstract

AbstractThe exclusion of coal fly ash from regulation as a hazardous waste has led to increased interest in returning ash to the coal fields for disposal. Bulk blending alkaline fly ash with acid forming coal refuse may present a disposal option that also aids in the control of acid mine drainage (AMD). A column leaching study was initiated to examine the leachate quality from acid forming coal refuse‐fly ash blends. Coal refuse alone (2.2% total S), and bulk blended coal refuse and alkaline fly ash (20 and 33% ash, w/w) were packed into 20‐cm diameter leaching columns and run under unsaturated conditions for over 4 yr. Leachates were analyzed for pH, electrical conductivity, Fe, Mn, and SO2−4 content. The coal refuse columns acidified quickly and produced leachates that, at peak levels, contained high contents of acidity (pH 1.6), Fe (10 000 mg L−1), SO2−4 (30 000 mg L−1), and Mn (300 mg L−1). The high levels of metals in these leachates decreased over time. The ash‐treated columns maintained leachate pH values near 8.0 with very low metal levels. The bulk mixing of alkaline fly ash and coal refuse, at high blending rates (>20%), appears to an effective codisposal option that also provides long‐term AMD control. Only B and SO2−4 appeared to leach at any significant level and the quality of leachates from the ash‐treated columns was significantly improved with respect to the untreated coal refuse.