Acid mine drainage mitigation using bulk blended fly ash/coal refuse mixtures: Column study results

Many Appalachian coal refuse materials contain significant amounts of pyritic-S and are likely to produce acid mine drainage (AMD). A column technique was designed and implemented to evaluate the effects of various AMD mitigation treatments including fly ash, topsoil, lime, and rock-P. Two types of fly ash were tested, one at four rates of application, the other at two rates. Conventional lime plus topsoil, lime without topsoil, topsoil only, topsoil with fly ash, rock-P, rock-P plus topsoil, and rock-P plus fly ash were also evaluated and compared with pure refuse controls. The drainage from the unamended columns rapidly dropped to pH 2 with very high levels of Fe and Mn. Alkaline fly ash dramatically reduced drainage Fe concentrations as well as Mn when compared with untreated refuse. The rock-P treatment also improved drainage but eventually lost its mitigation capability. Leachate B concentrations were initially high for some of the ash columns, but decreased over time, while the unamended refuse B levels increased with time. Combined treatments of phosphate/ash, ash/topsoil, and pure refuse with topsoil were intermediate between the alkaline ash/lime treatments and unamended refuse in drainage quality. With further analysis, fly ash may prove to be a viable alternative to conventional topsoiling/lime treatments to control AMD if adequate alkalinity is present in the ash/refuse mixture. If fly ash alkalinity is inadequate to balance potential acidity, accelerated leaching of ash bound metals may occur. Therefore, the uncontrolled disposal of fly ash within coal refuse disposal facilities should be discouraged unless acid/base balance concerns are met