La3+/La(OH)3 loaded magnetic cationic hydrogel composites for phosphate removal: Effect of lanthanum species and mechanistic study.

In this study, La 3+ (ion)/La(OH) 3 -W/La(OH) 3 -EW-loaded magnetic cationic hydrogel (MCH) composites were fabricated in situ and characterized to investigate the effects of lanthanum species on phosphate adsorption. The corresponding maximum P adsorption capacities of MCH-loaded La 3+ (ion) (MCH-La 3+ (ion)), La(OH) 3 -W (MCH-La(OH) 3 -W), and La(OH) 3 -EW (MCH-La(OH) 3 -EW) were 70.5 ± 2.67, 69.2 ± 3.5, and 90.2 ± 2.9 mg P/g, respectively. Furthermore, for MCH-La(OH) 3 -EW, the P adsorption capacity was maintained relatively stable and high at pH 4.5–11 because of the ligand exchange, electrostatic interactions, and Lewis acid–base interactions. The enhanced adsorption of P was achieved over a wide pH range, as well as in the presence of competing anions (including Cl − , NO 3 − , SO 4 2− , HCO 3 − and SiO 4 4− ). Moreover, the exhausted MCH-La(OH) 3 -EW could be easily regenerated by a NaOH-NaCl desorption agent with above 72% adsorption capacity remained during five recycles. The column adsorption capacity of MCH-La(OH) 3 -EW reached ∼3500 bed volumes (BV) (∼67.7 mg P/g) as the concentration of P decreased from 5 mg/L to 0.1 mg/L. The ATR-IR, Raman, and XPS deconvolution results revealed that both MCH and lanthanum compounds, including La 3+ (ion), La(OH) 3 -W and La(OH) 3 -EW, contributed to the phosphate adsorption because of the electrostatic interactions between –N + (CH 3 ) 3 and phosphate, as well as the formation of LaPO 4 · x H 2 O. [ABSTRACT FROM AUTHOR]