Tuesday, November 6, 2007
231-2
Modeling Arsenate Adsorption by Drinking-Water Treatment Residuals.
Dibyendu Sarkar1, Rachana Nagar1, Konstantinos C. Makris2, and Rupali Datta1. (1) University of Texas at San Antonio, Earth & Environmental Science Dept., San Antonio, TX 78249-0663, (2) Univ. Of Texas, 15801 Chase Hill Blvd. Apt. 612, San Antonio, TX 78256-1039
Use of drinking-water treatment residuals (WTRs), as a soil amendment is a promising alternative to remediate arsenic from contaminated sites. Binding of arsenate to WTR is typically attributed to surface complexation with metal oxides. Previous work in our laboratory has shown the adequacy of a double layer model (DLM) in predicting arsenate adsorption onto the surface of an Al-based water treatment residual (Al-WTR) as a function of solution properties, such as pH and presence of a competing ion, phosphate. The current study aims to model surface complexation of arsenate by both Al and Fe-based WTRs as a function of solution pH, ionic strength, competing ligands (phosphate and sulfate), and a complexing metal (calcium). The model predictions are compared to both macroscopic as well as microscopic data on arsenate adsorption obtained from the Extended X-ray Absorption Fine Structure (EXAFS) studies. The EXAFS data shows that arsenate forms inner-sphere complexes with a mixture of monodentate mononuclear, monodentate binuclear, and bidentate binuclear surface configurations. The surface complexation modeling approach using the Triple Layer Model (TLM) predicts formation of both mononuclear monodentate and mononuclear bidentate complexes of arsenate.
Key Words: Arsenic, drinking-water treatment residuals (WTRs), surface complexation modeling, EXAFS, solution properties.