Micellar-enhanced ultrafiltration of chromate and nitrate: binding competition between chromate and nitrate

Simultaneous removal of chromate and nitrate, major anionic pollutants in subsurface water system, was investigated using micellar-enhanced ultrafiltration (MEUF) with cetylpyridinium chloride as a cationic surfactant. Rejection of nitrate and chromate was expressed as a function of molar ratio of surfactant to pollutants. With the molar ratio of 1:1:10 (chromate: nitrate: surfactant), rejection of nitrate and chromate reached 80% and 98%, respectively. Rejection of surfactant was observed to be >95% under the same conditions. The rejection of nitrate was inhibited by co-existence of chromate. It was due to the differences in binding power between ionic micelles and counter ions, which is proportional to the valence of counter ions; the valence of chromate was higher than that of nitrate.