This paper characterizes two natural zeolites, chabazite and clinoptilolite, and investigates the effects of treatment and conditioning on the removal of Pb and Cd from effluent wastewaters. The results demonstrated that the as-received zeolites contained a complement of exchangeable K, Ca, and Na ions but exposing them to concentrated NaCl solutions converts them to a homoionic state in the Na form, which improves significantly their exchange capacity. Particle size was found to have no effect on the exchange, suggesting that the mechanism is not surface controlled. Pb and Cd removal results using as-received, conditioned, and treated zeolites showed that conditioning and treatment improved both the exchange capacity and the removal efficiency when operating at metal concentrations greater than 250 mg/L. NaOH-treated chabazite and clinoptilolite performed best with optimum Pd and Cd exchange capacities exceeding 200 mg/g. The chabazite exchange capacity performance was superior to the clinoptilolite's for both Pd and Cd. This result was expected as chabazite characterization showed that it had a higher Al substitution of Si, which in turn will produce a negative framework favorable to higher cation exchange capability. Overall, metal removal efficiencies exceeding 99 % were achieved, revealing the natural zeolites potential in treating effluent contaminated with high levels of Pb and Cd.
