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

摘要

The purpose of the work was to improve theprocess for treatment of liquid radioactive waste contain-ing complexing agents, which are generated during thedecontamination operations. We performed some experiments using simulated waste so-lutions like secondary waste from the modified CANDEREMprocess (Canadian Decontamination and Remediation Process)and secondary waste from the modified CANDECON process(Canadian Decontamination Process). To improve efficiency and economics of the process itwas proposed to treat the waste by combining the sorptionof radionuclides on natural inorganic sorbents (zeolites) withmembrane filtration. Standard procedures are applied to compare the sorptionof radionuclides on different sorbent forms-determination ofthe ion exchange capacity, construction of sorption isotherms,determination of the distribution coefficients, and kineticsexperiments. To check the influence of converting the sorbents to variouscationic forms on their sorption properties, distribution coeffi-cients of ~(137)Csand ~(57)Co on natural zeolites from local depositsconverted to NН_4~+, Na~+or H~+forms were determined. Theresults obtained show that the distribution coefficients of ~(1З7)Cson the materials converted to Na+ form are higher than forthe remaining forms studied [1]. The parameters of Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms have been determinedusing sorption data. The Dubinin—Radushkevich model showsbetter correlation between the theoretical and experimentaldata for ~(1З7)Cssorption on natural zeolites from local de-posits converted to NН_4~+and H~+forms than Langmuir andFreundlich 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 fitsthe experimental data well for all of the systems studied.