Removal of metal ions at low concentration by micellar-enhanced ultrafiltration (MEUF) using sodium dodecyl sulfate (SDS) and linear alkylbenzene sulfonate (LAS)

Micellar-enhanced ultrafiltration (MEUF) has been used to remove dissolved metals including Cd2+, Cu2+, Ni2+, Pb2+, and Zn2+ from synthetic water using two anionic surfactants: sodium dodecyl sulfate (SDS), and linear alkylbenzene sulfonate (LAS) in a lab-scale membrane system. The effect of surfactant concentration, pH and conductivity on metal retention was studied. The molar concentration ratio of the surfactant to metal (S/M ratio) is higher than 5 in all experiments. When the initial SDS concentration was below the critical micelle concentration (CMC), metal retention higher than 90% was unexpectedly obtained (at conditions used in these experiments), except for Ni2+. Moreover, it was shown that complete removal of metal ions, except for Ni2+, could be achieved at an LAS concentration below CMC. The addition of NaCl provokes the complexation of metal cations with chloride ions and the adsorption competition of sodium cations with metal ions, therefore increasing conductivity decreases metal retention. The presence of the NaCl in the feed surfactant solution had a drastic adverse effect on metal retention by SDS and LAS.