EFFICIENT SEPARATION AND RECOVERY OF TC-99 FROM CONTAMINATED GROUNDWATER

This work reports a new approach that can effectively separate and rec over Tc (as pertechnetate, TcO4-) from contaminated groundwater. Activ ated carbon was used in both batch adsorption and column leaching stud ies. The adsorption experiments indicated that activated carbon adsorb s TcO4- selectively and effectively over a wide range of pH values and from various dilute electrolyte solutions (< 0.01 M). The partitionin g coefficient (K-d) of TcO4- exceeded 27 000 ml/g when actual groundwa ter was used, and exceeded 12 000 ml/g when background solutions of 0. 01 M CaCl2 and Na2SO4 were used. TcO4- removal efficiency was > 99% un der these conditions, except in a 0.01 M NaNO3 background solution. Co lumn studies confirmed a high adsorption capacity and selectivity of a ctivated carbon for TcO4-. Within the detection limit, no Tc breakthro ugh was observed when more than 14 000 pore volumes of contaminated gr oundwater (containing similar to 3000 pCi Tc/l) were passed through a small column (6.6 x 30 mm) with 0.5 g activated carbon. Recovery of Tc O4- 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 adsorb ed TcO4- (as high as 100%). Therefore, the spent carbon can be dispose d as low-level radioactive wastes or may be regenerated. Results of th is work suggest that the use of activated carbon to remediate Tc-conta minated groundwater can be a promising technology - it is cost-effecti ve and requires minimal installation and maintenance during the pump-a nd-treat processes.