Removal of hexavalent chromium by mixed micelles of cetyl trimethyl ammonium bromide using micellar enhanced ultrafiltration

Abstract

Our study includes removal of Cr(VI) by using mixed surfactants (Non-ionic: Cationic). A common cationic surfactant Cetyl trimethyl ammonium bromide(CTAB) with two different nonionic surfactant Triton X-100 and Tween-80 were used to remove Cr(VI) by micellar enhanced ultrafiltration technique.The effect of parameters such as initial feed metal ion concentration, pH and filtration time on % Rejection of Cr(VI) were analysed. Low pH favoured the removal of Cr(VI) and exhibited maximum rejection percentage(>90%) at pH 2 for both systems. The optimum feed Cr(VI) ion concentration and filtration time can be suggested as 20 mgL-1 and 60 minutes respectively. It was found that CTAB+Triton X-100 and CTAB+Tween-80 gave Cr(VI) percentage removal upto 97% and 93% respectively. The adsorption data were studied using Langmuir, Freundlich and Dubinin-Radushkevick (DRK) adsorption Isotherms. The data fitted well in Langmuir model (R2=0.99). From DRK isotherm, mean free energy EDR, was much lower than 8 kJ.mol-1 suggesting the Cr(VI) adsorption onto mixed micelles is physisorption. Thermodynamic parameters ∆G°, ∆H° and ∆S° were evaluated revealing the process to be spontaneous and exothermic accompanied by increased randomness at the interface.