AN EQUILIBRIUM-MODEL FOR LIGAND-MODIFIED MICELLAR-ENHANCED ULTRAFILTRATION USING A WATER-INSOLUBLE LIGAND

The semiequilibrium dialysis method has been used to investigate the ionic equilibria occurring in a ligand-modified micellar-enhanced ultrafiltration (LM-MEUF) process. With attachment of a C12-hydrocarbon group to an iminodiacetic acid group and incorporation of this ligand in a cationic micelle, it is possible to bind Cu2+ selectively to the ligand in the retentate and expel Ca2+ into the permeate. An ion equilibrium model has been developed to predict the concentrations of the divalent ions in the permeate from known concentrations in the retentate and known experimental parameters, including the binding constants of the divalent metal ion/ligand complexes. In contrast with other micellar-enhanced ultrafiltration processes, addition of salt increases the retention of the bound metal ion. The model explains both the enhanced retention of Cu2+ and variations in the extent of expulsion of Ca2+ caused by changing the added salt concentration.