Selective removal of cobalt species using nanofiltration membranes.
Selective removal of cobalt species from simulated nuclear liquid waste was investigated with different nanofiltration (NF) membranes at various solution pH levels, initial cobalt concentrations, and background ion concentrations. This study provides insight into the understanding of the relationships between rejections of a target compound (cobalt) and chemical equilibria of various species in the feed solution during NF. Particularly, the ratio of electrostatic rejection to steric rejection for different membranes used was quantitatively evaluated to find outthe relative significance in NF. Substantial cobalt rejection by NF was achieved along with partial separation of monovalent ionic species, although it depended on the level of liquid pH and the presence of background species. Greater cobalt rejection at increased pH was attributed to the precipitation of CoCO3(s) associated with natural carbonates originating from atmospheric CO2 gas rather than that of Co(OH)2(s). A loose NF membrane (e.g., NTR7410) gave as high a rejection as other tighter ones due to the stronger influence of electrostatic rejection, particularly at low pH where no cobalt precipitation was occurring. The decrease of cobalt rejection with the addition of boric acid was found to occur due to the formation of complexes between cobalt and boric acid, which was verified by the analyses of solution turbidity and near-infrared spectroscopy.
Choo
Kwang-Ho
KH
Department of Architectural, Civil, and Environmental Engineering, Daegu University, Gyeongsan, Gyeongbuk, Korea.
Kwon
Dae-Joong
DJ
Lee
Kwang-Won
KW
Choi
Sang-June
SJ
D001888:Boric Acids; D003035:Cobalt / Q000737:chemistry*; D005374:Filtration; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D011850:Radioactive Waste; D013057:Spectrum Analysis; D014875:Water Pollutants, Radioactive / Q000032:analysis*
D001888:Boric Acids; D008567:Membranes, Artificial; D011850:Radioactive Waste; D014875:Water Pollutants, Radioactive; D003035:Cobalt; C032688:boric acid