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THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA 1
Citation:
IMPELLITTERI, CHRISTOPHER AND K. G. SCHECKEL. THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA 1. CHEMOSPHERE. Elsevier Science Ltd, New York, NY, 64(6):875-880, (2006).
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Arsenic concentrations (Total Recoverable As by EPA Method 3051, soluble, Toxicity Characteristic Leaching Procedure extractable) 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-H2O) concentrations of As equilibrated with the Fe-media in an anoxic environment at 4� C. These conditions (anoxic, 4� 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 (GFH media 9620 mg/kg As, E33 Media 5246 mg/kg). Arsenic concentrations decreased with bed depth. For the E33 media, XANES results showed that As(V) was the dominant species. For the GFH media, As(III) was detected and the proportion (relative to As(V)) of As(III) increased with bed depth. Arsenic concentrations in DI-H2O equilibrated with the media were low ( μg/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 bound by surface exchange sites. Kinetic desorption experiments carried out at different pH values (3, 5, 7, 8, and 9) show that the media exhibit some acid/base neutralization capacity and tend to bind As sufficiently. Concentrations of As in the pH desorption experiments were in the same order of magnitude as the TCLP extractions (tens of μg/L) except at low pH values. For the GFH media tested at a pH of 3, As increases in solution and is mainly associated with colloidal (operationally defined as between 0.1 and 1.0 μm) iron.
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THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA 1