In Situ Lanthanum Growth in Magnetic Chitosan Microgel for Accelerated Phosphate Separation from Water: Metal Efficiency, Specific Hydrogel Swelling, and Mechanistic Insights

In this work, lanthanum was in situ incubated in magnetic chitosan microgel (LCS) for phosphate separation from surface water. Compared to commercial La(OH)₃ and its direct encapsulation into CS, in situ La incubation in CS structure could render an La efficiency (Γ_La) 3.3 times higher than that of commercial La(OH)₃, harvesting the highest P capacity (95.25 mg P/g) at the lowest La content. LCS microgel can be easily extracted by magnetic separation, regenerated by NaOH, and thus reused for cyclic phosphate removal. Compared to monovalent anions, divalent SO₄^2– could largely accelerate P capture on LCS microgel within the first several hours. The effect of SO₄^2– was comparatively analyzed in batch modes and then verified by stirred-flow reactors using practical lake water as the feed. Under continuous operation, the presence of SO₄^2– could increase the dynamic P capacity and help suppress effluent P to a low concentration level, with the system breakthrough time nearly doubled. Further characterization analysis clarified the specific swelling behavior of LCS hydrogel network in the presence of SO₄^2–, which could increase the specific surface area and pore size for phosphate diffusion and uptake. Overall, our work highlighted a promising option for the fabrication of inorganic/polymer composites and provided useful insights for water treatment.