Removal of some radionuclides from contaminated solution using natural clay: bentonite

Clays and specially bentonite are widely used as natural adsorbents for wastewater treatment and as a barrier in landfills to prevent the contamination of subsoil and groundwater by leachates containing radioactive materials. The adsorption of four radionuclides, Cs-134(I), Sr-90(II), Ba-133(II) and Eu-152(III) by an Egyptian bentonite (Bent) and its modified Na+ form (Na-Bent) collected from a deposit within Alexandria governorate was investigated as a function of different parameters. The batch equilibrium technique was used and the kinetic results showed that the equilibrium was mostly reached within 10 min and the kinetic data fit well to the pseudo-second order model. The Langmuir model fits well the experimental data of all metals adsorption on Bent and Na-Bent except for adsorption of Ba-133 on Bent, while Eu-152 adsorption on Na-Bent fits better to the Freundlich model rather than to the Langmuir. Both Bent and Na-Bent fit well to the D-R model with adsorption energy of E > 8 kJ mol(-1) that means that the adsorption reaction is expected to be controlled by both cation exchange and surface complexation reactions. At lower concentrations, the values of distribution coefficient (K (d)), follow the order of Eu-152 > Sr-90 > Cs-134 > Ba-133 for Bent and Na-Bent. The K (d) of Eu-152 is higher than that of Cs-134 in Bent up to 150 mg L-1. This order changes at higher concentration where the K (d) of Cs-134 becomes higher than Eu-152 after 150 mg L-1 for Bent and after 200 mg L-1 for Na-Bent. Na-Bent is preferred than Bent for the uptake of Sr-90 and Cs-134 especially at high concentration.