Strong adsorption of phosphate from aqueous solution by zirconium-loaded Ca-montmorillonite

Achieving ultralow levels of phosphorus (P) concentrations to prevent eutrophication is an important goal of surface water management. Hence, a highly efficient and economical adsorbent for phosphate removal is urgently required to meet the increasingly stringent water quality standards. This study investigated the phosphate adsorption performance of zirconium (Zr)-modified calcium-montmorillonite (Zr-CaMs). Batch experiments were conducted to obtain the adsorption isotherms, kinetics, and the influences of dosage, solution pH, and coexisting anions. The results demonstrated that Zr was successfully introduced to the surface and interlayer of raw CaM in the presence of the [Si-O]center dot center dot center dot[HO-Zr ] hydrogen bond and that it increased the specific surface area. The adsorption isotherms obeyed the Langmuir nonlinear model. The calculated maximum phosphate adsorption capacity was 22.37 mg/g, which was more than twice that of Phoslock. The Elovich model fit the kinetics data well, which was indicative of chemical adsorption. An optimum dosage of 100/1-150/1 and wide pH range (4-8.5) are recommended for practical applications. The coexistence of HCO3- slightly inhibited the adsorption capacity, whereas Cl- and SO42- had a positive impact. The adsorption mechanism was primarily the ligand exchange between the surface hydroxyl groups and phosphate resulting from the formation of innersphere coordination complexes. This study demonstrated that Zr-CaMs can serve as a prospective adsorbent for phosphate removal from contaminated surface water.