Micellar-enhanced ultrafiltration of cadmium ions with anionic–nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF), a surfactant-based separation process, is promising in removing multivalent metal ions from aqueous solutions. The micellar-enhanced ultrafiltration of cadmium from aqueous solution was studied in systems of anionic surfactant and mixed anionic/nonionic surfactants. The micelle sizes and zeta potentials were investigated by dynamic light scattering measurements. The effects of feed surfactant concentration, cadmium concentration and the molar ratio of nonionic surfactants to sodium dodecyl sulfate (SDS) on the cadmium removal efficiency, the rejection of SDS and nonionic surfactants and the permeate flux were investigated. The rejection efficiencies of cadmium in the MEUF operation were enhanced with higher SDS concentration and moderate Cd concentration. When SDS concentration was fixed at 3 mM, the optimal ranges of the molar ratios of nonionic surfactants to SDS for the removal of cadmium were 0.4–0.7 for Brij 35 and 0.5–0.7 for Triton X-100, respectively. With the addition of nonionic surfactants, the SDS dosage and the SDS concentration in the permeate were reduced efficiently.