Enhanced Phosphorus Locking by Novel Lanthanum/Aluminum–Hydroxide Composite: Implications for Eutrophication Control

Lanthanum (La) bearing materials have been widely used to remove phosphorus (P) in water treatment. However, it remains a challenge to enhance phosphate (PO 4 ) adsorption capacity and La usage efficiency. In this study, La was coprecipitated with aluminum (Al) to obtain a La/Al–hydroxide composite (LAH) for P adsorption. The maximum PO 4 adsorption capacities of LAH (5.3% La) were 76.3 and 45.3 mg P g –1 at pH 4.0 and 8.5, which were 8.5 and 5.3 times higher than those of commercially available La-modified bentonite (Phoslock, 5.6% La), respectively. P K-edge X-ray absorption near edge structure analysis showed that PO 4 was preferentially bonded with Al under weakly acid conditions (pH 4.0), while tended to associate with La under alkaline conditions (pH 8.5). La L III -edge extended X-ray absorption fine structure analysis indicated that PO 4 was bonded on La sites by forming inner sphere bidentate-binuclear complexes and oxygen defects exhibited on LAH surfaces, which could be active adsorption sites for PO 4 . The electrostatic interaction, ligand exchange, and oxygen defects on LAH surfaces jointly facilitated PO 4 adsorption but with varied contribution under different pH conditions. The combined contribution of two-component of La and Al may be an important direction for the next generation of commercial products for eutrophication mitigation.