Uptake of Radiostrontium from Aqueous Solutions by Biomass and Natural Zeolites: Implications in the Treatment of Contaminated Waters by Aecl’s Chemictm Process

AECL’s CHEMIC process has effectively treated in excess of 4 million gallons of radiostrontiumcontaminated water since 1993. One aspect of the ongoing effort to expand the application of the process involves the use of powdered sorbents such as biomass in addition to natural zeolites in conjunction with precipitation for the removal of different contaminants including radiostrontium from waste solutions. In this paper, laboratory-scale test results are presented on removal performance of radiostrontium from synthetic and actual waste solutions by different natural zeolites and biomass. The natural zeolites included calcium-chabazite, sodium-chabazite, sodium-clinoptilolite, mordenite, potassium-clinoptilolite, zeobrite and zeobrite 100. The biomass used in the tests included S. faccium, B. subtilis, L. plantarum, L. acidophillos, P. cerevisial and M. luteus. Results showed that strontium was preferentially removed by chabazite with high removal efficiencies even in the presence of the competing calcium ion. Clinoptilolite performed similar to chabazite, but only at low concentrations of the competing ion. The initial sorption rates of strontium by powdered zeolites were generally rapid at low concentrations of the competing calcium ion, and removal efficiencies in excess of 90% occurred within 30 minutes of contact between the solution and zeolite. The behaviour of different biomass sorbents for radiostrontium removal was found to be similar in many respects to that of the natural zeolites. Among the biomass tested, L. plantarum and P. cerevisial gave the highest removal efficiencies for radiostrontium when the concentration of the competing calcium ion was low. It appears that contaminant binding to specific regions on the cell surface is a key mechanism for cation removal by the biomass. The majority of the cation removal by biosorption was found to occur within a 20-minute exposure of the biomass to the contaminated solution.