| Abstract
| - Leaching tests, Fourier transform infrared spectroscopy(FTIR), extended X-ray absorption fine structure (EXAFS)spectroscopy, and thermodynamic modeling were performedto investigate arsenate [As(V)] immobilization mechanismsin iron hydroxide sludge stabilized with cement. Thesludge from a groundwater remediation site in Tacoma,WA was mixed and immobilized with premixed cement toreach cement-to-sludge ratios of 2.5, 3.3, 5, 10, and 20(wt premixed cement/wt dry sludge). The EXAFS analysisdetermined that As(V) formed bidentate mononuclearcomplexes on the iron hydroxide surface in the sludge.The adsorbed As(V) had a characteristic FTIR band at 830cm-1. Cement treatment converted the adsorbed As(V)to calcium arsenate precipitate with a FTIR peak at 860 cm-1.The chemical forms of the As(V) were incorporated inan adsorption triple layer model (TLM) to describe theleaching behavior of As(V) in a pH range between 3 and12. Cement treatment significantly reduced arsenic mobilitybecause of the formation of the sparingly soluble calciumarsenate.
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