Project Summary (2000-2005)

The deleterious health effects associated with ingestion of arsenic and chromium require that they be removed to levels below 50 ug/L in potable water supplies. This project is investigating two removal methods which involve reduction of highly water soluble As(III), As(V) and chromium (Cr)(VI) compounds to lower valence states which are less water soluble. Although laboratory investigations have demonstrated the short-term effectiveness of zero-valent iron for mediating the reductive precipitation of chromium and arsenic compounds, the long-term effectiveness of the process has not been established, and the conditions favoring arsenic and chromium removal are not well understood. Researchers are investigating the effects of water chemistry, surface precipitate buildup and iron surface aging on arsenic and chromium removal from contaminated waters by zero-valent iron. Additionally, this project is investigating arsenic and chromium removal via electrosorption and reduction by anodically polarized magnetite. The research objectives are: 1) to determine if zero-valent iron is effective for arsenic and chromium removal in above ground canister remedial systems; 2) to determine the long-term effectiveness of zero-valent for arsenic and chromium removal in in-situ permeable barrier configurations; 3) to determine the effectiveness of anodically polarized magnetite for removing arsenic and chromium oxyanions from contaminated waters; and 4) to develop a flow-through treatment process which removes dissolved arsenic compounds to levels below 1 ug/L for a variety of source waters. Both batch and column studies are being performed to measure arsenic and chromium removal kinetics by zero-valent iron and by anodically polarized magnetite. The morphology and oxidation state of the arsenic and chromium precipitates, as well as the iron corrosion products, will be determined using electron microscopy and X-ray absorption spectroscopy. Thermodynamic solution modeling using the U.S. EPA model MINTEQA2 will be performed to determine the agreement between predictions based on equilibrium behavior and the observed results.