In Situ LanthanumGrowth in Magnetic Chitosan Microgelfor 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.