Rapid and selective harvest of low-concentration phosphate by La(OH)3 loaded magnetic cationic hydrogel from aqueous solution: Surface migration of phosphate from –N+(CH3)3 to La(OH)3
2021
Li, Xiaolin | Wang, Yili | Li, Junyi | Dong, Shuoxun | Hao, Haotian | Liu, Chenyang | Tong, Yao | Zhou, Yanqing
Phosphate is an important factor for the occurrence of surface water eutrophication, and is also a non-renewable resource which faces a potential depletion crisis. In this study, La(OH)₃ loaded magnetic cationic hydrogel composite MCH-La(OH)₃-EW was used to absorb low strength phosphate in simulated water and real water. The adsorption amount of MCH-La(OH)₃-EW was 39.14 ± 0.31 mg P/g and the equilibrium time was 120 min at the initial phosphate concentration of 2.0 mg P/L. The adsorption process was a spontaneous endothermic reaction. MCH-La(OH)₃-EW exhibited a high selectivity towards phosphate within pH of 4.0–10.0 or in the presence of co-existing ions (including Cl⁻, SO₄²⁻, NO₃⁻, HCO₃⁻, SiO₃²⁻) and humic acid. After 10 cycles of adsorption-desorption, the adsorption amount of regenerated MCH-La(OH)₃-EW still remained at 63.4% of its maximum value. For the real water sample with phosphate concentration of 2.0 mg P/L, the phosphate removal efficiency could achieve 97.65–98.90% and the effluent turbidity was 2.10–4.27 NTU at the MCH-La(OH)₃-EW dosage of 0.04 g/L. The adsorption mechanism analysis showed that both quaternary amine groups (–N⁺(CH₃)₃) and La(OH)₃ of MCH-La(OH)₃-EW were involved in the process of phosphate adsorption. The electrostatic interaction between phosphate and –N⁺(CH₃)₃ rapidly occurred at the initial stage of adsorption process, then the electrostatic absorbed phosphate migrated to La(OH)₃ on the surface of MCH-La(OH)₃-EW via ligand exchange to form inner-sphere complex. This phenomenon was conducive to phosphate adsorption kinetics by MCH-La(OH)₃-EW.
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