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THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED TREATMENT MEDIA
Citation:
Impellitteri**, C A. AND K G. Scheckel*. THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED TREATMENT MEDIA. Presented at 32nd Annual Water Quality Technology Conference and Exposition, San Antonio, TX, November 14 - 18, 2004.
Impact/Purpose:
To inform the public.
Description:
Arsenic concentrations (Total Recoverable As by EPA Method 3051) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two commercially available products from pilot-scale field tests. These results were compared with data from solution (de-ionized water-DI-H20) concentrations of As equilibrated with the Fe-media in an anoxic environment at 4o C. These conditions (anoxic, 4o C) were employed in order to minimize variation (especially microbial effects) and lay a foundation for future studies on As desorption tests with more variables (e.g. temperature, oxygen, different leachate constituents, etc.). Both of the commercially available media had a high capacity for As (US Filter media 9620 mg/kg As, Severn Trent Media 5246 mg/kg). Arsenic concentrations decreased with bed depth. For the US Filter media, XANES results showed that As (V) was the dominant species. For the Severn Trent media, As (III) increased with bed depth. Arsenic concentrations in DI-H2O equilibrated with the media were very low (approximately 35 mug/L) over a period of 50 days. Arsenic concentrations in the equilibrated solutions also decreased with depth. Assessment of the solution As speciation (via ion exchange resin) suggests that As in solution consists of As (V) that was probably weakly held by surface exchange sites. This research lays the foundation for future studies on the desorption/dissolution of arsenic from Fe-based media which will aid in future decisions concerning the proper disposal of As contaminated Fe-based water treatment media.