Application of indigenous inorganic sorbents in combination with membrane technology for treatment of radioactive liquid waste from decontamination processes

The purpose of the work was to improve the process for treatment of liquid radioactive waste containing complexing agents, which are generated during the decontamination operations. We performed some experiments using simulated waste solutions like secondary waste from the modified CANDEREM process (Canadian Decontamination and Remediation Process) and secondary waste from the modified CANDECON process (Canadian Decontamination Process). To improve efficiency and economics of the process it was proposed to treat the waste by combining the sorption of radionuclides on natural inorganic sorbents (zeolites) with membrane filtration. Standard procedures are applied to compare the sorption of radionuclides on different sorbent forms-determination of the ion exchange capacity, construction of sorption isotherms, determination of the distribution coefficients, and kinetics experiments. To check the influence of converting the sorbents to various cationic forms on their sorption properties, distribution coefficients of Cs-137 and Co-57 on natural zeolites from local deposits converted to NH4+, Na+ or H+ forms were determined. The results obtained show that the distribution coefficients of Cs-137 on the materials converted to Na+ form are higher than for the remaining forms studied [1]. The parameters of Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms have been determined using sorption data. The Dubinin-Radushkevich model shows better correlation between the theoretical and experimental data for Cs-137 sorption on natural zeolites from local deposits converted to NH4+ and H+ forms than Langmuir and Freundlich equations. Kinetic studies were carried out with various zeolite forms. The sorbents studied are natural zeolites from local deposits (Marsid-Romania). The batch sorption kinetics has been tested for pseudo-second order reaction. The pseudo-second order model fits the experimental data well for all of the systems studied.