Immobilization Mechanisms of Arsenate in Iron Hydroxide Sludge Stabilized with Cement

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Abstract

Leaching tests, Fourier transform infrared spectroscopy (FTIR), extended X-ray absorption fine structure (EXAFS) spectroscopy, and thermodynamic modeling were performed to investigate arsenate [As(V)] immobilization mechanisms in iron hydroxide sludge stabilized with cement. The sludge from a groundwater remediation site in Tacoma, WA was mixed and immobilized with premixed cement to reach cement-to-sludge ratios of 2.5, 3.3, 5, 10, and 20 (wt premixed cement/wt dry sludge). The EXAFS analysis determined that As(V) formed bidentate mononuclear complexes on the iron hydroxide surface in the sludge. The adsorbed As(V) had a characteristic FTIR band at 830 cm-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 in an adsorption triple layer model (TLM) to describe the leaching behavior of As(V) in a pH range between 3 and 12. Cement treatment significantly reduced arsenic mobility because of the formation of the sparingly soluble calcium arsenate.

Original languageEnglish
Pages (from-to)5050-5056
Number of pages7
JournalEnvironmental Science and Technology
Volume37
Issue number21
DOIs
StatePublished - 1 Nov 2003

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