A novel La(OH)3 decorated co-graft tannin and polyethyleneimine co-coating magnetic adsorbent for effective and selective phosphate removal from natural water and real wastewater

Abstract

Our study synthesized La(OH)3 decorated co-graft tannin and polyethyleneimine (PEI) co-coating magnetic composites (La@TP@Fe3O4). Dual organic modification with co-grafted tannin and PEI can significantly enhance the material's charge density, allowing La@TP@Fe3O4 to maintain a high phosphate adsorbability at a wide pH range (3.0–11.0). La@TP@Fe3O4 achieved a maximum theoretical phosphate adsorption capacity of 363.64 mg/g at 25 °C under pH 3.0 and was consistent with the Langmuir model, reaching adsorption equilibrium in 20 min. Phosphate adsorption was less affected by various coexisting ions with >90% of phosphate removal maintained after five cycles. La@TP@Fe3O4 could be quickly separated by magnetic force with negligible La and Fe leakages. Besides electrostatic attraction, inner-sphere complexation and weak precipitation contributed to phosphate uptake on La@TP@Fe3O4, as demonstrated by X-ray absorption near edge structure (XANES) analysis. Importantly, low La@TP@Fe3O4 doses could quickly decrease phosphate concentrations in natural water and wastewater to meet regulatory requirements, thus highlighting the potential applicability of La@TP@Fe3O4 for phosphate removal.