| According to Long-term National Development Plan of Nuclear Power, Chinese nuclear installed capacity will achieve 40 000 000 kilowatt-hour. Nuclear power industry has developed rapidly in recent years in China. Medium and low-level radioactive liquid waste generated during the operation of nuclear power plant needs to treat in the urgent. Cobalt ion is very common in the outflow of nuclear power plant which causes radioactivity and has long half life enough to eliminate storage as a method to remove the radioactivity in effluent. Theγray and theβray radiated from cobalt decay in the nuclear liquid waste, would have an impact on the genetic material of creatures. Mutation will be induced by the radiation which might alter the health status of human being. The ultimate method to treat the nuclear liquid waste is to reserve until the decay of the nuclide is accomplished. Since the volume of medium and low-level liquid waste is large in quantity, compression in volume is the key strategy to treat large quantity liquid waste.Polymer enhanced ultrafiltration (PEUF) is studied in this research. Complexation efficiency comparison among chitosan, polyacrylate sodium(PAANa) and polyethylineimine (PEI) are carried out. To choose the most suitable polymer for the PEUF process evaluation indexes such as retention, polymer complexation capacity and membrane fouling, are introduced during the research. Optimizing the operation parameters and analysis of flux discrepancy and the consist of membrane resistance are involved in the paper. Meanwhile the study also includes the effect of non-radioactive cation such as Na+and Ca2+to the PEUF process and investigates the complexation reaction through Langmuir binding equation.Removal of cobalt (Co2+) in medium and low level radioactive liquid waste was realized by polymer enhanced ultrafiltration (PEUF) in this study. PEI was chosen based on the efficiency of cobalt removal between PEI and chitosan and PAANa at Co2+concentration of 1 mg/l and solution pH from 3 to 9 giving the excellent performance in removal and less membrane fouling causing flux decrease. PEUF experiments were performed as a function of aqueous pH, PEI/Co2+ratio, and background electrolyte concentration. Two local maximum retentions are reached when pH is 4 and 7 indicating that two binding group exist in each polymer unit. Results of further research support the indication. The best cobalt removal rate was obtained at 100% when pH value of 7.0, and PEI/Co2+ratio of 4 without any background electrolytes added. The coablt removal rate was found to decrease as the adding electrolytes concentrations of Na+ and Ca2+ increases. Our further investigations show the probable mechanism is the compression of the electric double layer and not the competitive complexation. Finally, Langmuir-type binding isotherm equation was employed to evaluate the extent of cobalt binding to PEI. 2.08 Co2+ions were found to be bound to one PEI unit, which is consistent with the result obtained from studying the effect of P/M on the cobalt removal rate. The results indicate that PEUF could be a promising method for cobalt removal and limiting medium and low radioactive liquid waste with Co2+in nuclear power industry. |
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