Synthesis of Zeolite A and Its Application as a High-Capacity Cadmium Ion Exchanger

A facile method comprised of alkali fusion activation and hydrothermal reaction was developed to synthesize high-quality crystallized zeolite A from cost-effective low-grade bauxite. Using sodium aluminate powder as an extra aluminum source and sodium carbonate as an activator, the reactant molar ratios of SiO2/Al2O3, Na2O/SiO2, and H2O/Na2O, the hydrothermal reaction time are optimized in detail. Highly crystallized phase-pure zeolite A is successfully synthesized from low-grade bauxite under the optimized experimental conditions of 1.5 Na2O:0.5 Al2O3:1 SiO2:128 H2O after hydrothermal reaction at 90 degrees C for 12 h. The cadmium ion removal from aqueous solutions using the as-synthesized zeolite A powders as an adsorbent was studied. The effects of contact time, solution concentration, solution pH value, and adsorbent amount on adsorption was investigated. The adsorption equilibrium could be reached very fast within 90 min. The adsorption followed a pseudo-second-order kinetic adsorption mode well. Both Langmuir and Freundlich models could fit the experimental data well at pH = 6. The maximum adsorption capacity was estimated to be 161.3 mg/g. The optimal adsorbent dosage is about 1.00 g/L.