Radioactive Iodine Removal From Water By An Integrated Precipitation Reactor And Membrane Separator System And Preparation Of The Membranes

With the rapid development of nuclear power and the wide application of radionuclides,the risk of radioactive contamination of water is increasing.Radioactive iodine produced during nuclear fission reactions is one of the most important radioactivity elements in the nuclear industry wastewater under the safe operation and nuclear accidents conditions.In this work,inactive I^-was used as a target pollutant instead of radioactive I^-based on the carrying mechanism.Studies on I^-removal methods and mechanism were conducted and further a novel water treatment process was developed in order to remove radioactive I^-from the nuclear industry wastewater whether what is produced under normal operation or sudden nuclear accidents.Some innovative findings have been made as follows:（1）Cuprous chloride（CuCl）was examined as a precipitant to remove I^-from aqueous solutions.The results show the efficient I^-removal with a low dosage and short reaction time using CuCl was obtained in comparation with other precipitants for removing I^-such as silver-,bismuth-and copper-based compounds.The dissociation of CuCl,the disproportionation reaction of Cu⁺,the precipitation of cuprous iodide（CuI）and cuprous oxide（Cu₂O）,and the formations of copper sulfide（Cu_xS,1≤x<2）were identified as the primary reactions using the PHREEQC software,the measurements of water quality parameters and XPS analysis under various conditions.In addition,the removal I^-efficiency and effluent quality were affected to some extent by the dosage of CuCl,reaction time,initial concentrations of I^-,Cl^-and HCO₃^-.（2）A novel integrated precipitation reactor（PR）and membrane separator（MS）system was developed for the removal of radioactive I^-from water,and main chemical reactions were identified and elucidated during deoxygenation phase,precipitation reaction and membrane separation process.The PR-MS system was evaluated at the lab-scale,the I^-removal efficiency reached approximately 97.0%and the concentration factor（CF）value was 1050 when the concentration of added Na₂SO₃ was 40 mg/L and the CuCl dosage was 260 mg/L.（3）Combined with graphene oxide membrane（GO）as a next-generation separation membrane and the characteristics of radionuclide emissions,GO-polyelectrolyte membranes were assembled via Layer-by-layer（Lb L）technique.The effects of salt（Na Cl）concentration and p H values on the formation of GO-polyethyleneimine（PEI）layers were investigated in details.Salt concentration greatly affected the charge/size of GO and PEI and their interactions thus changed the deposition mechanism from intrinsic to extrinsic charge compensation with increasing salt concentration.The ionization degree of-COOH and-NH₂ was highly dependent on a p H value,which had an important influence on the membrane structure and separation performance of GO-PEI membranes.The results demonstrate that GO-PEI membranes as nanofiltration membrane could remove radioactive I^-and Sr²⁺from water,which provides a promising method to address radioactive contamination in water.