EXPERIMENTAL AND THEORETICAL DIFFUSIVITIES OF CD AND SR IN HYDROUS FERRIC-OXIDE

Oxides of manganese, aluminum, and especially iron are important sorbe nts for inorganic contaminants. The sorption process can be characteri zed by two steps. The first step is a rapid, reversible reaction betwe en the bulk aqueous phase and external surfaces. The slow, second step is the rate limiting mechanism wherein the contaminant diffuses throu gh small pores along surface sites. Isotherm and constant boundary con dition studies were conducted to evaluate the sorption process. Best f it experimental surface diffusivities ranged from 10(-14) to 6 X 10(-1 3) cm(2)/s. Using site activation theory and assuming a sinusoidal pot ential field along the pore surface, theoretical surface diffusion coe fficients were estimated from the adsorption enthalpy. (C) 1997 Academ ic Press