Facile preparation of bentonite/nano-gamma alumina composite as a cost-effective adsorbent for Ca2+ removal from aqueous solutions

Abstract

Desalination and removing elements such as calcium from aqueous solutions is very important to improve water quality. In this study, bentonite/nano γ-alumina composites were utilized as a low-cost adsorbent for calcium removal from aqueous solutions. To investigate the adsorption process, several experiments were conducted, including initial calcium concentration, adsorbent dosage, pH, contact time, and the γ-alumina content in the composite. Increasing γ-alumina amounts in the composite by more than 1% had the reverse effect due to agglomeration. The increase in specific surface area for bentonite-1wt% γ-alumina compared to bentonite is mainly due to the addition of γ-alumina. The calcium adsorption capasity increased from 0.5 mg/g to 1.15 mg/g when the initial ion concentration was raised from 60 ppm to 100 ppm. The adsorption capacity of 1.15 mg/g and removal % of 23 with were obtained for optimal initial concentration of 100 ppm, adsorbent dosage of 20 g.l−1, and composite percentage of bentonite/1 wt% γ-alumina. The adsorption mechanism was studied by the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models, and the adsorption data was fitted better by the Freundlich model. The Dubinin-Radushkevich isotherm revealed the physical nature of the adsorption. Conclusively, the bentonite-1wt% γ-alumina nanocomposite had better results than the raw bentonite.