PVA-stabilized La(OH)3-Fe2O3 composites with unparalleled cycling stability for sustainable phosphate recovery

Enriching low-concentration phosphorus in water is prerequisite for phosphorus recovery. In this study, a polyvinyl alcohol (PVA)-assisted high-temperature stabilization method was developed to synthesize a magnetically recoverable La(OH) 3 -Fe 2 O 3 composite, designated as PMLH, via stable crosslinking. Compared with MLH-1, a conventionally synthesized La(OH) 3 /Fe 2 O 3 composite, PMLH-1 (La/Fe molar ratio = 1:1) exhibited 31.77 % more La(OH) 3 adsorption sites and maintained 2.32 times higher phosphate adsorption capacity after 10 reuse cycles. The optimal synthesis conditions were determined as calcination temperature of 150 °C, PVA dosage of 0.375 %, and La-to-Fe molar ratio of 1.5. Structural characterization revealed that PMLH-1.5 consisted of rod-like La(OH) 3 and irregular γ-Fe 2 O 3 tightly bonded via PVA bridging. The composite demonstrated a maximum phosphate adsorption capacity of 79.51 mg P/g, reaching equilibrium within 16 h at 0.5 g/L dosage. The saturated adsorption remained stable across pH 3–9. While coexisting NO 3 − and humic acid showed negligible effects, Mg 2+ , Cl − , SO 4 2− and HCO 3 − reduced adsorption by 10–20 %, whereas Ca 2+ significantly enhanced phosphate uptake. Notably, PMLH-1.5 exhibited exceptional practical performance, exceeding its theoretical saturation capacity by 20 % with prolonged adsorption in real water matrices. Efficient desorption (4 h) was achieved using 2.5 M NaOH/1.875 M NaCl mixed solution. The PMLH-1.5 demonstrated remarkable stability across 40 consecutive adsorption-desorption cycles using actual water samples, consistently meeting discharge standards for 13–14 full cycles. This performance established a new reference point for cyclic durability assessments in water treatment research. Sequential desorption in the same desorbent progressively concentrated phosphorus from 0 to 26.69 mg/L, enabling effective low-concentration phosphate enrichment. Economic analysis confirmed that PMLH-1.5 exhibits a competitive chemical cost, ranging from 3.28 to 5.26 CNY/mol P (0.46 to 0.74 US $/mol P).