Evaluation of Leachate Chemistry from Coal Refuse Blended and Layered with Fly Ash

Alkaline fly ash has been studied as a liming agent within coal refuse fills to reclaim acid-forming refuse. Previous studies focused on bulk blending ash with acid-forming (pyritic) refuse. A better representation of field conditions is a "pancake layer" of ash above the refuse. A column study was initiated to evaluate the leachate chemistry from acid-forming refuse-ash bulk blends vs. ash over refuse layers. An acidic and an alkaline ash were blended with, or layered over, acid-forming refuse and sandstone and packed into columns which were leached with deionized water twice a week for 24 weeks under unsaturated conditions. Leachates were analyzed for pH, electrical conductivity, and a suite of elements with a focus on the oxyanions of As, Cr, Mo, and Se. A sequential extraction procedure revealed a significant portion of the elements in the residual fraction for the refuse/spoil substrates and in metal-oxide bound fractions for the ashes prior to leaching, and a general trend for a greater proportion of oxyanion elements to be associated with metal oxide fractions after leaching. Bulk-blended treatments maintained higher leachate pH than corresponding layered treatments. The acidic ash and refuse pancaked treatments exhibited relatively high initial concentrations of most elements analyzed. Pancake layers of ash over refuse are an inadequate co-disposal method to prevent and mitigate acid mine drainage. Blending alkaline ash with refuse to acid-base accounting specifications should improve leachate quality overall, but there may be water quality concerns for loss of Se and other soluble ions during initial leaching events.