One-Pot Preparation of NaA Zeolite Microspheres for Highly Selective and Continuous Removal of Sr(II) from Aqueous Solution

This paper describes a synthesis method and adsorption properties of geopolymer microspheres toward strontium ions; first, it was prepared by a dispersion–pelletizing–solidification (DPS) method followed by transformation into NaA zeolite microspheres (about 100 μm) through an in situ heat curing process. The adsorption experiments were investigated and the experimental data were fitted well by the pseudo-second-order kinetic model and Freundlich isotherm model. Loading experiments were performed by batch and column process techniques. The maximum adsorption capacity in the batch process was assigned to be 106.28 mg/g, the zeolite microspheres’ adsorption of strontium ions reached adsorption equilibrium in approximately 15 min. In the dynamic column, the most suitable flow rate was found to be 4 mL/min; this was higher compared with other sorbents with the same particle size. Moreover, the zeolite microspheres have a good dynamic separation effect, the concentration of the outlet Sr(II) ions from the column began to rise after 18 h with a bed height of 1.5 cm. The competitive adsorption capabilities are investigated and have the following order Na + < Mg 2+ < K + < Ca 2+, indicating that this adsorbent has a good adsorption effect in real seawater. Through the analysis of the solution after adsorption, the process is not only chemical adsorption but also ion exchange. The used adsorbents could be easily regenerated using 0.05 mol/L EDTA-2Na solution. This result showed that NaA zeolite microspheres are convenient and low-cost adsorbents for the removal of Sr(II) from liquid wastes.