Characteristics of calcium adsorption by Ca-Selectivity zeolite in fixed-pH and in a range of pH

Ca-Selectivity zeolite was synthesized and the structure morphology, the physical and chemical performances were characterized by SEM, XRD and FT-IR. It was used as adsorbents of calcium in batch system for this study. The Ca2+ adsorption performances in the fixed-pH 9.18 and in pH ranges from 2 to 12.5 were tested. The Langmuir and Freundlich isotherms were adopted to evaluate the experimental data in fixed-pH and the competitive adsorption models were fitted to data in the condition which the pH values are without any control during adsorption process, respectively. The results noted that the Ca-Selectivity zeolite presented good adsorption capacity with about 105 mg/g and electrostatic adsorption, ion-exchange and hydroxyl complex are major mechanism of calcium adsorption. It indicated that the Ca-Selectivity zeolite has potential application value in zero discharge of seawater desalination.