Effects of co-existed anions on retention characteristics of chromate by MEUF

Abstract

Micellar enhanced ultrafiltration (MEUF) process was proposed to evaluate effects of anions (nitrate and sulfate) in single- and multi-component aqueous solutions for chromate removal with cationic surfactant (cetyltrimethylammonium bromide, CTAB) under constant transmembrane pressure drop (40 psi), temperature (25°C), and surfactant/chromium (S/M) molar ratio of 3 (S/M = 3 mM/1 mM). First of all, in the single-component anion (only one anion was used) solutions, the order of removal efficiency was: chromate 99.9% > sulfate 96.1% > nitrate 94.0%. These results indicate that chromate preferentially binds on the CTAB micelles but sulfate and nitrate bind less. On the other hand, in the multi-component anions (chromium together with co-existed anions) solution, the removal efficiency of chromate decreased (99.4–98.4%) with the increase of sulfate and nitrate. The retention of surfactant was enhanced by the addition of electrolytes into solution due to the counterion dissolved from electrolyte reduced the repulsive electrostatic force between the head groups of cationic surfactant molecule. In addition, the effect of temperature in multi-component on MEUF was evaluated simultaneously.