Excessive internal phosphate presented in sediments is the essential problem causing eutrophication of lake for decades, as a consequence of iron reduction under anaerobic conditions. Recent studies reported that the rare-earth element lanthanum has a strong binding ability towards phosphate ions, while the underlying mechanisms are still not fully understood. Herein, this work systematically investigated the mechanisms of phosphate removal using La(OH)3 by employing extended X-ray absorption spectroscopy (EXAFS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), density functional theory (DFT) and chemical equilibrium modelling. The results showed that surface complexation was the primary mechanism for phosphate removal and in binary phosphate configurations, namely diprotonated bidentate mononuclear (BM-H2) and bidentate binuclear (BB-H2), coexisting on La(OH)3 in acidic conditions. By increasing the pH to 7, BM-H1 and BB-H2 were the two major configurations governing phosphate adsorption on La(OH)3, whereas BB-H1 was the dominant configuration of phosphate adsorption at pH 9. With increasing phosphate loading, the phosphate configuration of on La(OH)3 transforms from binary BM-H1 and BB-H2 to BB-H1. Amorphous Ca3(PO4)2 forms in the presence of Ca, leading to enhanced phosphate removal at alkaline conditions. The contributions of different mechanisms to the overall phosphate removal were successfully simulated by a chemical equilibrium model that was consistent with the spectroscopic results. Taking the great advantage of the strong complexation ability of La with P, novel magnetically recoverable magnetite/lanthanum hydroxide [M-La(OH)3] hybrids have been further developed. Results show that M-La(OH)3 exhibits a strong sorption towards phosphate with sorption capacities of up to 52.7 mg-P/g at pH 7.0 in water, and also demonstrate that sediment suspensions mixed with a M-La(OH)3 content of 1-3% exhibit a capability of up to 1.2 mg-P/g for sequestering external phosphate compared with that of 0.2 mg-P/g for pristine sediment at pH 7.3. M-La(OH)3-mixed sediment suspensions appear to effectively sequester phosphate over an environmentally relevant pH range from 4 to 8.5. These findings shed light on understanding the surface complexes of La with P at the molecular level, and guiding to develop new technologies for phosphate sequestration and recovery from lake.