Binding of heavy metals to derivatives of cholesterol and sodium dodecyl sulfate

The binding behaviors of five metals (cadmium, copper, nickel, lead, and zinc), individually at pH 6 and collectively at pHs 6 and 3, to deoxycholic acid (DCA) and taurocholic acid (TCA) were compared with those of sodium dodecyl sulfate (SDS) using a continuous diafiltration method. DCA and SDS have been successfully applied in micellar-enhanced ultrafiltration (MEUF) for metal removal from water. In this study, SDS exhibits the strongest binding in the single-component experiments while DCA binds the most in the multicomponent trials. TCA does not show any significant binding compared with DCA and SDS. Overall the molar binding ratios of the mixture at pH 3 were well below those of the other two solutions. This diafiltration technique quantifies the binding characteristics of a surfactant by generating sorption isotherms and determining the intrinsic association constants with corresponding number of binding sites. These parameters can be useful in designing an efficient MEUF system.