Selenium-Water Treatment Residual Adsorption and Characterization.

Aluminum-based water treatment residuals (WTR) have the ability to adsorb tremendous quantities of soil-borne P, and have been shown to adsorb other anions such as As(V), As(III), and ClO₄^-.  Environmental issues associated with Se in the Western US lead us to study WTR sorption of Se(VI) and Se(IV).  The WTR were mixed with either Na₂SeO₄ (Se(VI)) or Na₂SeO₃ (Se(IV)) at a Se concentration of 60 mg L^-1.  Solution pH was varied from 5 to 9, and triplicate samples of WTR-Se(VI) (exposed to atmospheric conditions) and WTR-Se(IV) (exposed to an N₂ atmosphere to control redox) were shaken for 24 hr.  All samples were centrifuged, the solution discarded, and the WTR-Se(VI) mixtures were allowed to dry under atmospheric conditions while the WTR-SE(IV) mixtures were dried in an anaerobic glove bag.  An additional set of WTR-Se(IV) redox controlled treatments were reacted for 24 hr at pH 7, exposed to compressed air for 1, 2, 4, 7, 14, and 28 d, then centrifuged and allowed to dry under atmospheric conditions.  All samples were analyzed using XAS to determine Se speciation.  Results will be discussed.