Evaluation of leachate quality from codisposed coal fly ash and coal refuse

The 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 SO(4)(2-)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), SO42-(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 ny ash and coal refuse, at high blending rates (>20%), appears to be an effective codisposal option that also provides Long-term AMI) control. Only B and SO42- 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.