Residence Time Effects on Arsenate Surface Speciation at the Aluminum Oxide-water Interface

SOILS and sediments are nearly always at disequilibrium with respect to ion transformations (Sparks, 1987). The rate of bioavailability of contaminants in the environment can be reduced with increasing time (Pignatello and Xing, 1995). The observation that less sorbate is released with increasing contact time between the sorbent and sorbate is referred to as a residence time/aging effect (Pignatello and Xing, 1995; Sparks, 1995). Even in the absence of a residence time effect, one often observes biphasic reaction processes for both sorption and desorption of metals, metalloids, and organic chemicals (Sparks, 1989). The biphasic behavior is characterized by a relatively rapid reaction followed by a slow reaction(s).The slow reactions have been ascribed to diffusion phenomena, differing sites of reactivity, and surface precipitation (Scheidegger et al., 1996); howTECHNICAL ARTICLES