Removal of technetium-99 from contaminated groundwater with sorbents and reductive materials

Abstract

Pertechnetate oxyanion (TcO₄⁻), which is highly soluble in water and readily mobile in the environment, can be immobilized through an ion exchange /adsorption process and chemical reduction followed by adsorption and/or precipitation. Previous studies have focused on the separation and removal of ⁹⁹TcO₄⁻ from high-level waste streams; however, little information is available for ⁹⁹TcO₄⁻ removal from only slightly contaminated groundwater. This paper describes treatment of ⁹⁹TcO₄⁻-contaminated groundwater with both batch and column flowthrough experiments. Synthetic resins and sponges, and zero-valence iron filings were used to evaluate their capacities and the rates of ⁹⁹TcO₄⁻ removal. The toxicity characteristic leaching procedure (TCLP) was applied to evaluate the leachability of ⁹⁹Tc adsorbed or co-precipitated on iron. Results suggest that both iron and synthetic resins remove ⁹⁹TcO₄⁻ from groundwater and that at a high flow rate (with residence time of less than 1 min), ⁹⁹TcO₄⁻ removal capacity is greater for iron filings than for the synthetic resins on a volume basis. Additionally, the rate of ⁹⁹TcO₄⁻ sorption on the sponge is slow (approximately 3 days), and the capacity is relatively low. No appreciable amount of ⁹⁹Tc can be leached out from the spent iron filings by the TCLP test. Overall, zero-valence iron filings provide fast reaction and high removal capacity for ⁹⁹TcO₄⁻ in groundwater. The high removal efficiency, low cost, and the small waste production of zero-valence iron are attractive for remediation of ⁹⁹TcO₄⁻-contaminated groundwater.