Magnetite/hydrated cerium(III) carbonate for efficient phosphate elimination from aqueous solutions and the mechanistic investigation

Recently, to mitigate eutrophication nuisance, the use of cerium(Ce)-based materials for effectively eliminating phosphate from waters and wastewaters has garnered increasing attention. However, insufficient sorption capacities as well as difficulty for spent sorbents separation still restrict their development and utilization. Herein, magnetic Ce 2 (CO 3 ) 3 ·xH 2 O/Fe 3 O 4 (M−HCC) sorbent was firstly synthesized via a facile co-precipitation method and employed for removing phosphate from aqueous solutions. It was showed that M−HCC displays a fast sorption kinetic, notable sorption capacity of 98.3 mg-P/g, wide pH applicable range (pH 3–9) and strong selectivity for phosphate in the co-existence of common anions (i.e. Cl − , NO 3 − , SO 4 2− , HCO 3 − and F − ) and cations (i.e. Ca 2+ and Mg 2+ ). Moreover, the uptake of phosphate by M−HCC was independent of the ionic strength of solution. The application of as-prepared sorbent in eutrophic water and wastewaters evidenced that, M−HCC performs very well in the real water bodies, and the phosphate level of outflow could be reduced from 0.55 mg-P/L to ≤ 0.03 mg-P/L at a low dosage of 0.1 g/L. As the spent M−HCC could be easily recovered from treated liquids and regenerated satisfactorily, M−HCC also exhibits a good reusability. Mechanistic investigation revealed that the formation of inner-sphere complexation via ligand exchange between phosphate and carbonate/surface hydroxyls of M−HCC as well as electrostatic attraction are answerable for the superior uptake of phosphate by M−HCC. Overall, M−HCC sorbent with the novel species of Ce 2 (CO 3 ) 3 ·xH 2 O as active site could be considered as a promising alternative for phosphate removal from waters or wastewaters.