Removal of copper ions and dissolved phenol from water using micellar-enhanced ultrafiltration with mixed surfactants

A laboratory study was conducted to evaluate the effects of composition and concentration of mixed anionic/nonionic surfactants on the efficiency of a micellar-enhanced ultrafiltration (MEUF) operation in removing metal ions/organic solutes from aqueous solutions. Based on the analysis of surface tensions and micelle sizes, it was found that for mixed sodium dodecylsulfate (SDS)/Triton X-100 surfactants, the critical micelle concentration (cmc) was significantly lower than that of SDS and mixed micelles formed. The mixed surfactant system was then applied in a cross-flow mode of MEUF, in which the concentration polarization can be neglected, to remove Cu²⁺ from aqueous solutions. With a surfactant concentration of 10 mM, the Cu²⁺ rejection was negligible by using pure Triton X-100 and increased with increasing SDS mole fraction with a value as high as 85%, which suggests that the rejection of Cu²⁺ was due to the electrostatic attraction between Cu²⁺ and SDS. Furthermore, pronounced Cu²⁺ rejection was obtained for a 5 mM SDS solution, which was attributable to a decrease in the cmc of SDS by the existence of Cu²⁺. When the MEUF technique was applied to remove Cu²⁺ and phenol simultaneously from aqueous solutions, the Cu²⁺ rejection was slightly enhanced in the presence of phenol. However, the rejection of phenol was comparatively low, ∼27%, which may be caused by its relatively hydrophilic characteristic.