Evaluation of Leachate Quality from Codisposed Coal Fly Ash and Coal Refuse
1997
Stewart, Barry R. | Daniels, W Lee | Jackson, Meral L.
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 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.
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