Bi-functional resin for removal of contaminants from groundwater

Abstract

groundwater used for processing uranium or plutonium at US DOE sites is frequently contaminated with the technetium radionuclide 99Tc, with half-life of 213,000 yrs. At DOE's Paducah and Portsmouth sites, contaminated solutions were poured into lagoons and burial pits, creating a plume that has seeped into the sandy aquifers below the vadose zone. Technetium is the principal radioactive contaminant in Paducah site groundwater where it is present at a concentration of 170 to 250 ng/L (~2.5nM) in a plume that covers 2 square miles and extends several miles off site. Concentrations as high as 400ng/L have been reported at the Portsmouth site, with the average concentration being 26 ng/L in a 14-acre plume. The chemical form of the technetium in oxygen-rich groundwater is the pertechnetate anion, TcO4-. This water-soluble species is highly mobile, and transport of the 99Tc into the biosphere is of great concern. Removal by sorption onto strong-base ion exchange resins has become the accepted method of treatment, but enhanced selectivity for the pertechnetate anion is needed over other anions commonly found in groundwater such as chloride, sulfate, and nitrate. New biofunctional anion-exchange resins that were designed to be highly selective for pertechnetate have been prepared and tested as part of this research project at ORNL and the U of Tennessee. Features that enhance selectivity while maintaining favourable exchange kinetics and good capacity were identified in a testing program involving more that 90 new resins. The optimum resin identified in this program in turn has been compared with the commercial Purolite A-520E resin in current use at the Paducah Gaseous Diffusion Plant (PGDP).