LEAD AND CADMIUM REMOVAL BY ION-EXCHANGE

The ion exchange properties of the zeolites can be used to remove certain ions from the effluents. In this work a natural clinoptilolite has been examined systematically in order to evaluate whether this low cost mineral can be employed for the removal of the metals lead and cadmium which are very toxic, even at very low concentrations. Studies were performed under various conditions such as presence of different cations (Pb, Cd, Na), zeolite grain size, solution temperature. The results obtained indicate that the size of the zeolite does not affect the actual metal uptake at the equilibrium point, but the metal removal is greatly affected when the contact of the solid/liquid phases is short, a very essential parameter for the waste water treatment. For a short contact time the metal quantities removed using small grain size is nearly doubled. The same pattern is followed at higher temperatures, though a slight increase is observed for both zeolite grain sizes and both metals, lead and cadmium. At equilibrium half of the theoretical exchange capacity of the zeolite is used, approximately 1.4 meq/g for lead and 1.1 meq/g for cadmium. The kinetic curves show very clearly the selectivity of the zeolite for the Pb ions but also significant amounts of cadmium are removed as well.