Adsorptive separation of Ce Co Ru Sb and Sr ions using inorganic ion exchangers

Abstract

Ion exchange and adsorption (can both be referred to as ‘sorption’) are widely used as purification and concentration methods in the nuclear industry. Various mathematic models have been developed to describe the mechanisms of sorption using the kinetics and equilibrium data. In this study, the ion exchange and adsorption capability and efficacy of various inorganic sorbent materials to remove contaminants were investigated with the intent of applying the process in the purification of post reactor uranium for reuse and cleaning of research reactors pool water. The contaminants studied are Ce, Co, Ru, Sb and Sr ions. The sorbent materials candidates investigated are antimony pentoxide, CoTreat®, IONSIV R9120B, activated carbons, alumina, titania, manganese oxide and SrTreat®. The sorption of Ce and Sr on antimony pentoxide was determined to be a slow sorption process. The sorption kinetics data obtained for Sr removal by antimony pentoxide conformed to the pseudo-second order kinetic model, with the sorption process reaching completion after 78 hours contact time. The considerably slow kinetics makes the sorbent material a less suitable candidate. At fixed solid/aqueous ratio, various parameters affecting sorption of Co on CoTreat® were studied which include initial Co concentration, contact time, solution pH and temperature. The sorption capacity of CoTreat® for Co ions was identified to increase with increasing contact time and with increasing initial Co concentration. The Co sorption was halted at pH < 2. The sorption of Co on CoTreat® reaction can be approximated to first order reversible kinetics at high initial concentrations of Co while the sorption kinetics followed the pseudo-second order kinetics at low initial concentrations of Co. The examination of the thermodynamic parameters revealed that the sorption of Co on CoTreat® is an endothermic process and is spontaneous in the studied temperature range. The equilibrium isotherm data was analysed using the Langmuir, Freundlich and Dubinin-Radushkevich equations. The sorption of Co on CoTreat® followed the Langmuir isotherm model. The Dubinin-Radushkevich parameters revealed that the sorption process is driven by ion exchange. Slow kinetics were obtained for the Co removal by IONSIV R9120B sorption process, therefore making the sorbent material not a good candidate for practical application. The sorption capacities of manganese oxide for Ru removal from aqueous solutions was investigated at different initial concentrations of Ru. The fitting of the Langmuir and Freundlich sorption models to the equilibrium data was investigated. The equilibrium data for the Ru sorption on manganese oxide followed the Freundlich isotherm. The monolayer sorption capacity was determined to be 0.90 mg/g at 30 °C. The pseudo-first order and the pseudo-second order kinetic models were used to fit the kinetic experimental data. The sorption of Ru on manganese oxide follows the pseudo-second order kinetic model. The temperature dependent data revealed that the sorption process is an endothermic and spontaneous ion exchange process. Poor sorption capacities were determined for Ru removal by activated carbons. The maximum sorption of Sb on titania was obtained at 0.1 M nitric acid medium. Kinetics studies revealed that the sorption process followed pseudo-second order kinetics. The equilibrium data was evaluated using the Langmuir and Freundlich isotherm models, and well fitted the Freundlich isotherm. The obtained negative values of ΔG° and positive value of ΔH° advocate that Sb sorption on titania is a spontaneous and endothermic process. The effect of the experimental parameters: contact time, initial concentration of metal ion and solution pH were investigated for Sb removal by alumina. The sorption capacity increased with increasing contact time and initial Sb concentration. The sorption data could be explained by the pseudo-first order kinetic model and the Langmuir isotherm. The sorption data on Sr removal by SrTreat® revealed that the sorption capacity increases with increasing initial Sr concentration. The sorption of Sr ions on SrTreat® was halted at pH < 2, and the kinetics data obtained at high initial Sr concentration can be approximated to the pseudosecond order kinetics. The dynamic sorption studies revealed that efficacy of the studied sorbent materials to remove the target contaminants drastically declined in the presence of uranium ions.