Enhanced rejection of cations by low-level cationic surfactant during ultrafiltration of low-level radioactive wastewater

Abstract

Abstract The influence of cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) on the rejection of metal salts was investigated during ultrafiltration of low-level radioactive wastewater (LLRW). In the presence of CTAB below the critical micelle concentration (CMC), the rejection of nuclides significantly increased from 24%–33% to 50% for Cs(I) and above 90% for Sr(II), Co(II), and Ag(I). These increased rejections are attributed to CTAB fouling layer, which led to a more hydrophilicity and more positively-charged membrane surface. The nuclide content on the fouling layer increased with increasing CTAB concentration, and 55–80% of Co(II), Sr(II), and Ag(I) were adsorbed on the membrane at 400 mg/L CTAB. The high deposition of Ag(I) is partially due to the formation of AgBr. Based on these results, low-levels of cationic surfactant can significantly enhance the UF rejections of cations, but membrane fouling and nuclide deposition should not be ignored.