Influence of Ca2+ on phosphate removal from water using a non-core-shell Fe3O4@ZIF-67 composites

Excessive phosphate in surface water can spur the growth of organism, which put a threat on the bio-safety of drinking water. Different from previous study, sodium acetate (NaAc) was used as modification agent of Fe3O4, then the magnetic Fe3O4@ZIF-67 composites with a non-core-shell sturture were synthesized. According to ZIF67 loading and phosphate adsorption of synthesized Fe3O4@ZIF-67, the Fe3O4@ZIF-67 composites with a Co2+/Fe3O4 molar ratio of 1:2 was taken into further evaluation. Fe3O4@ZIF-67 composites exhibited satisfactory adsorption performance and easy magnetic recovery, and the sorption capacity reached 116.59 mg P/g within 180 min (C-0 = 20 mg P/L, 298 K). The maximum adsorption capacity of phosphate was obtained at the neutral pH, and not significantly interfered with ions of K+, Mg2+, NO3- and SO42-. Remarkably, Fe3O4@ZIF-67 described enhanced phosphate adsorption ability in the presence of Ca2+. To investigate the role of Ca2+, two modes (preloading and addition) of Ca2+ dosing were examined and the improved adsorptive performance could be owing to the synergistic eff ;ect of adsorption and Ca-P micro-precipitation on the surface of Fe3O4@ZIF-67. During the regeneration process, the performance of desorbent was evaluated by phosphate releasing and secondary adsorption, and the absence or presence of Ca2+ would have a significant impact on the selection of desorption solution.