SORPTIVE REMOVAL OF CESIUM-137 AND SR-90 FROM WATER BY UNCONVENTIONALSORBENTS .1. USAGE OF BAUXITE WASTES (RED MUDS)

Bauxite wastes of alumina manufacture, i.e., red muds, have been teste d for radiocesium and strontium removal from water. The red muds were water-washed, acid-, and heat-treated before usage to produce hydrous oxide like sorbents. Surface treatment of the sorbent was benefical fo r Cs-137 uptake, while heat-treatment was detrimental to the -SOH surf ace sites responsible for high Sr-90 affinity. Fractionation of the so rbent with respect to apparent grain size did not produce significant differences in the sorption efficiency. The distribution coefficients vs. equilibrium activity in solution showed a maximum with Cs, and a g radual decrease trend with Sr. The solution activity vs. adsorption da ta were fitted to B.E.T. (essentially types IV-V) isotherms for Cs and B. E. T.-Langmuir isotherms for Sr. Desorption, temperature, pH-, and ionic strength-dependence tests revealed that the primary mode of sor ption for both cations is specific adsorption while the secondary mode is ion exchange. A rise in pH favours the ion-exchange sorption of Sr while the specific adsorption of Cs is negatively affected. Competiti ve adsorption of an inert electrolyte, i.e., NaCl, severely hinders Cs sorption, while Sr sorption on water-washed red mud is not significan tly affected.