Removal of lead, copper and cadmium ions from aqueous streams using lecithin enhanced microfiltration

The removal of lead, copper and cadmium ions from aqueous streams using lecithin enhanced micro filtration with 0.2μm pore size tubular ceramic membranes has been investigated. Measurements of the surface tension at varying lecithin concentrations were carried out to determine the critical micelle concentration (CMC) of lecithin and the effects of lead ions, mixtures of lead and copper ions, and mixtures of lead, copper and cadmium ions in solutions on the CMC of lecithin. The zeta potential and the effects of the single and multiple metal ions on the zeta potential of lecithin were also investigated. The influence of lecithin concentrations, cross flow velocity and transmembrane pressure on the rejections and steady state permeate flux behaviours were examined. The CMC of lecithin was found to be 9 grl. An increase in metal ion concentration caused a decrease in the CMC and an increase in the zeta potential of lecithin solutions, suggesting the binding of the metal ions onto the lecithin. An increase in lecithin concentration was found to improve metal ions removal. Lecithin showed preference for the metal ions in the order Pb2+ > Cd 2+ > Cu 2+. Metal ion removal was influenced more by lecithin concentration and less by transmembrane pressure and cross flow velocity. The steady state permeate flux and rejection behaviours have been explained by microscopic phenomena and a mathematical model has been developed to predict the steady state permeate flux. The lecithin concentration that remains in the permeate was less than 9% of the feed solution. The study has shown that lecithin enhanced micro filtration is a technically suitable technique for removal of lead, copper and cadmium ions in aqueous solution.