Calcined Dolomite: Alternative to Lime for Minimizing Undesirable Element Leachability from Fly Ash

A comparison of the effectiveness of totally and partially calcined dolomite additives (TCD and PCD) on the leachability of elemental constituents from three fly ashes was performed. Both additives were found effective in reducing the concentrations of several undesirable oxyanion constituents in fly ash leachates, although enhanced leaching of fly ashes was also detected as a result of calcined dolomite treatment. As compared to the straight water/ash runs, the extra leached fraction of fly ashes range approximately from 4 to 13% for the PCD-added runs and 25 to 31% for the TCD-added runs, respectively. The principal mechanism for oxyanion removal is through the formation of hydrocalumite and hydrotalcite. Although PCD is not quite as efficient as TCD in reducing oxyanion concentrations, it produces a less caustic leachate composition characterized by lower pHs, alkalinities, and calcium concentrations. PCD is a viable alternative to lime as fly ash additive.