X-ray absorption spectroscopy as a tool investigating arsenic(III) and arsenic(V) sorption by an aluminum-based drinking-water treatment residual
Journal
Journal of Hazardous Materials
Date Issued
November 15, 2009
Abstract
Historic applications of arsenical pesticides to agricultural land have resulted in accumulation of residual arsenic (As) in such soils. In situ immobilization represents a cost-effective and least ecological disrupting treatment technology for soil As. Earlier work in our laboratory showed that drinking-water treatment residuals (WTRs), a low-cost, waste by-product of the drinking-water treatment process exhibit a high affinity for As. Wet chemical experiments (sorption kinetics and desorption) were coupled with X-ray absorption spectroscopy measurements to elucidate the bonding strength and type of As(V) and As(III) sorption by an aluminum-based WTR. A fast (1 h), followed by a slower sorption stage resulted in As(V) and As(III) sorption capacities of 96% and 77%, respectively. Arsenic desorption with a 5 mM oxalate from the WTR was minimal, being always <4%. X-ray absorption spectroscopy data showed inner-sphere complexation between As and surface hydroxyls. Reaction time (up to 48 h) had no effect on the initial As oxidation state for sorbed As(V) and As(III). A combination of inner-sphere bonding types occurred between As and Al on the WTR surface because mixed surface geometries and interatomic distances were observed.