Non-competitive and competitive adsorption of Pb2+, Cd2+ and Zn2+ ions onto SDS in process of micellar-enhanced ultrafiltration

Abstract

Competitive adsorption of Pb2+, Cd2+ and Zn2+ ions on sodium dodecyl sulfate (SDS) in binary mixtures were investigated compared with non-competitive adsorption in the unitary metal solution in micellar-enhanced ultrafiltration at a temperature of 25 °C. Mutual interference effects were investigated based on the removal rate, the Langmuir Competitive Model (LCM) and equilibrium adsorption capacity ratios, qe/qm, which indicated the presence of other metal ions. The results indicated that the removal rate and adsorption capacity of Pb2+ were higher than that of the other metal ions in unitary and binary systems. The effects on SDS micelles for Cd-Pb and Zn-Pb combinations were found to be antagonistic. However, it was a favorable effect for the Cd-Zn combination, and the metal ions sorption followed the order: Pb2+ > Cd2+ > Zn2+. The behavior of non-competitive and competitive adsorption for Cd2+ and Zn2+ in a single system and in the presence of Pb2+ were well described by LCM. Moreover, the LCM showed poor fitting to non-competitive and competitive adsorption of Pb2+ in a single solution and in the presence of Cd2+ or Zn2+. In conclusion, the removal of Pb2+ in the presence of Zn2+ or Cd2+ showed greater efficacy than that of Cd2+ or Zn2+ in the presence of Pb2+.