Leaching Kinetics of As, Mo, and Se from Acidic Coal Fly Ash Samples

Annually, coal-fired electric power plants produce large volumes of potentially hazardous coal combustion products (CCPs) including fly ash. Since majority of the coal fly ash and other CCPs deposited in dry land fills or wet lagoons, they pose risk of contamination to local environment. In this study, we present results of leaching kinetics for As, Mo, and Se from three acidic fly ash samples collected from coal-fired power plants in the southeastern United States. This study shows that the leachate concentrations of As, Mo, and Se increase over time. Three kinetics equations, pseudo-second order, Elovich, and power-function, are able to adequately describe the experimental leaching kinetics data. Experimental leaching data and modeling results indicate that the rate limiting leaching of As, Mo, and Se is controlled by the diffusional process responsible for transferring these elements from interior to the surface of the particles as well as the dissolution of the fly ash particles. Therefore, it is important to adopt effective containment/treatment schemes to avoid potential and persistent dispersion of trace elements from ash disposal facilities to surrounding environment for a long time.