Efficient separation and recovery of technetium-99 from contaminated groundwater

Abstract

This work reports a new approach that can effectively separate and recover Tc (as pertechnetate, TcO₄⁻) from contaminated groundwater. Activated carbon was used in both batch adsorption and column leaching studies. The adsorption experiments indicated that activated carbon adsorbs TcO₄⁻ selectively and effectivele over a wide range of pH values and from various dilute electrolyte solutions (< 0.01 M). The partitioning coefficient (K_d) of TcO₄⁻ exceeded 27 000 ml/g when actual groundwater was used, and exceeded 12000 ml/g when background solutions of 0.01 M CaCl₂ and Na₂SO₄ were used. TcO₄⁻ removal efficiency was > 99% under these conditions, except in a 0.01 M NaNO₃ background solution. Column studies confirmed a high adsorption capacity and selectivity of activated carbon for TcO₄⁻. Within the detection limit, no Tc breakthrough was observed when more than 14000 pore volumes of contaminated groundwater (containing ∼3000 pCi Tc/1) were passed through a small column (6.6 × 30 mm) with 0.5 g activated carbon. Recovery of TcO₄⁻ from activated carbon was studied using various chemical reagents such as salicylate, phthalate, NaNO₃, NaCl, and Na₂SO₄. Salicylate was found to be the most effective in desorbing and recovering the adsorbed TcO₄⁻ (as high as 100%). Therefore, the spent carbon can be disposed as low-level radioactive wastes or may be regenerated. Results of this work suggest that the use of activated carbon to remediate Tc-contaminated groundwater can be a promising technology — it is cost-effective and requires minimal installation and maintenance during the pump-and-treat processes.