Zirconium-loaded zeolite composites for selective sorption of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) from water: Performance and mechanism

Three zirconium-loaded zeolite (Zr-Z) composites—namely, Zr 4+ -Z, ZrO 2 -Z, and ZrMo 2 O 8 -Z—were prepared by co-precipitation of Zr 4+ , ZrO 2 , and ZrMo 2 O 8 , respectively, with artificial zeolite, and these composites were used for the efficient removal of a representative phosphonate, i.e., 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). The adsorption efficiency of the three composites for HEDP at an initial concentration of 2 mg/L was more than double that of artificial zeolite. Pseudo-second-order kinetics could fit the adsorption process of the three composites well. The heterogeneous adsorption by Zr 4+ -Z, ZrO 2 -Z, and ZrMo 2 O 8 -Z was determined by using the Sips model. And the theoretical maximum HEDP-adsorption capacities of Zr 4+ -Z, ZrO 2 -Z and ZrMo 2 O 8 -Z were 3.52 mg P/g, 3.38 mg P/g and 3.77 mg P/g, respectively, at 308 K. At pH 4–9, the three Zr-Z composites could achieve efficient and stable HEDP adsorption. Among Co-existing ions (Cl − , HCO 3 − , NO 3 − , SO 4 2− , Ca 2+ , Mg 2+ ), 50 mM HCO 3 − hindered adsorption due to its competition with HEDP. The characterization results show that the adsorption mechanism involved hydrogen bonds, electrostatic attraction, and ligand exchange. In addition, the reusability and column adsorption performance of the Zr-Z composites were explored for the efficient removal of the organic phosphonate HEDP from wastewater in practical applications.