LEACHING BEHAVIOR AND MECHANISMS CONTROLLING THE RELEASE OF ELEMENTS FROM SOIL STABILIZED WITH FLY ASH

摘要

In situ soil stabilized with fly ash has become a practical and economicalsolution for soil stabilization. Understanding the pH-dependent leaching behavior andmechanisms controlling release of major and trace elements from soil-fly ash mixtureis important for assessing the environmental impacts associated with using fly ash insoil stabilization. A pH-dependent leaching test was used to investigate the leachingbehavior of soil-fly ash mixtures used in roadway construction. Three broad leachingbehaviors as a function of pH were observed from the soils, the fly ashes and the soilflyash mixtures: (i) leaching of Ca, Cd, Mg, and Sr follows a cationic pattern wherethe concentration decreases monotonically as pH increases; (ii) leaching of Al, Fe, Cr,Cu, and Zn follow an amphoteric pattern where the concentration increases at acidicand alkaline pH; and (iii) leaching of As and Se shows both the behaviors followingoxyanionic pattern where concentration increases at acidic and alkaline pH and thoseshow anomalous leaching behavior. Consistency in leaching behavior for manyelements was observed, which is believed to be due to solubility-controlled. Thedifference and inconsistency for As and Se are likely due to different controllingmechanism, such as sorption, or solid-solution formation.