Sorption behavior studies of Cs and its migration in soil samples around Visakhapatnam, India

Meeting the requirement of high specific activity of radioisotopes and carrying out comprehensive research and development activities in the nuclear field, different nuclear facilities, including their waste disposal facilities, are going to be operational at Visakhapatnam, India. Due to environmental processes, the engineered disposal modules may lose their structural integrity and may release some radioactivity to the geo-environment. The subsequent migration of radionuclides reaching the geological environment will be governed by the distribution coefficient (K_d). Cs was chosen for the sorption study in two soil samples (soil-29 and 31) and to estimate the K_d in all the 40 soil samples through the laboratory batch method at the new campus of DAE, Visakhapatnam, India. Different soil chemical parameters like pH, organic matter, CaCO₃, and cation exchange capacity were determined in 40 soil samples and their effect on Cs sorption was investigated. The effect of solution pH and initial concentration of Cs on sorption was also studied. The results show that the sorption of Cs increases with increasing pH. The Cs sorption was well explained by Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Site-specific distribution coefficients (K_d) were also estimated and the values were found to vary from 75 ± 1 to 540 ± 12 L kg^-1. The observed wide variation in K_d could be due to large variations in the physico-chemical properties of collected soil. The competitive ions effect study suggests that K⁺ has higher interference for Cs⁺ sorption as compared to Na⁺. The present study results will help assess the environmental impact due to Cs release in any unforeseen scenario and in planning effective remediation strategies.