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, TcO 4 −) from contaminated groundwater. Activated carbon was used in both batch adsorption and column leaching studies. The adsorption experiments indicated that activated carbon adsorbs TcO 4 − 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 TcO 4 − exceeded 27 000 ml/g when actual groundwater was used, and exceeded 12000 ml/g when background solutions of 0.01 M CaCl 2 and Na 2SO 4 were used. TcO 4 − removal efficiency was > 99% under these conditions, except in a 0.01 M NaNO 3 background solution. Column studies confirmed a high adsorption capacity and selectivity of activated carbon for TcO 4 −. 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 TcO 4 − from activated carbon was studied using various chemical reagents such as salicylate, phthalate, NaNO 3, NaCl, and Na 2SO 4. Salicylate was found to be the most effective in desorbing and recovering the adsorbed TcO 4 − (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.