The removal of cadmium and lead from aqueous solution by ion exchange with NaY zeolite

Abstract

Lead and cadmium removal from aqueous solution by batch ion exchange with a solid NaY zeolite has been studied under competitive and non-competitive conditions. The extent of heavy metal (HM) removal is found to be inlependent of the nature of the anion, and equilibrium exchange isotherms are presented for NaY treatment of lead and cadmium nitrate and chloride solutions at 293 K. An increase in solution phase HM concentration lowers the affinity of the zeolite for the in-going HM ion, but lead was preferred to the indigenous sodium ion over the entire range of initial metal concentration to zeolite weight ratios (0.3–13 × 10−2 mol dm−3 gz−1) that were studied. Lead removal was much greater than that of cadmium under identical experimental conditions and NaY exchange efficiency is shown to increase in the order Ni2+ < Cu2+ < Cd2+ < Pb2+. Exchange selectivity is discussed in terms of metal ion hydration and siting within the zeolite framework. A Pb/Cd/NaY ternary exchange isotherm was constructed from 38 pairs of experimental points, and is treated quantitatively in terms of ternary and pseudo-binary separation factors. Treatment of the lead/cadmium solutions resulted in a greater depletion (by a factor of 2) of the lead component.