Synthesis, optimization and characterization of zeolite A and its ion-exchange properties

Zeolite A was synthesized from fumed silica and sodium aluminate precursors. The optimum conditions for synthesis of zeolite A were studied to obtain a high ion-exchange capacity and an affinity for heavy metal ions. The findings revealed that the optimum conditions for synthesis of zeolite A were SiO2:Al2O3:H2O:Na2O molar ratios = 1:0.83:150:1.15 at 110 °C with 4 days crystallization time. As synthesized, zeolite A had a specific surface area of 497 m2/g and pore volume of 0.16 cm3/g. SEM images demonstrated that the produced zeolites A are highly ordered cubic crystals. Significant data were obtained through studying the main parameters affecting the adsorption of heavy metals on the optimized zeolite A during the removal of Cu, Cr, Ni, and Cd. The findings indicate that the pH, zeolite dose and ion concentration are significant but the shaking time and reaction temperature are insignificant. Maximum removal of heavy metals ∼100% onto zeolite was achieved at pH 4. Heavy metal ion uptake decreased for non-zeolite crystalline material or the amorphous synthesis products and mixtures of amorphous material and zeolite 4A due to decreased specific surface area and pore volume that resulted in lower accessibility and possibly less sites for ion exchange. The larger pore size of zeolite A provides more facile intraparticle diffusion for metal ions and increases the ion-exchange rate.