LONG-TERM BEHAVIOR OF TOXIC METALS IN STABILIZED STEEL FOUNDRY DUSTS

A study of the long-term behaviour of stabilized steel foundry dust (SFD) wastes has been performed using a dynamic leaching test (DLT). Two stabilized/solidified forms were produced by solidifying the SFD (containing Pb, Cr, Cd and Zn) using either cement or cement and anhydrite (waste material) as binders. The results of the dynamic leaching test were fitted to a semi-empirical mathematical model based on simple leaching rate mechanism, which permitted the evaluation of an apparent diffusion coefficient and a leachability index, thus providing a measure of the contaminants' mobility in the solidified waste. In the case of Pb and Zn, the rate of leaching was controlled by either an initial resistance or an initial washoff, followed by diffusion of the metallic contaminants. The leaching indexes obtained in both cases were higher than 12, suggesting that both solidification/stabilization processes are acceptable.