Functional Magnetic Nanoparticles and Mill Scale for Phosphorus Extraction from Contaminated Water

Phosphorus (P) contamination in agricultural runoff is a major environmental concern due to its contribution to eutrophication and deterioration of water quality. Ortho-phosphate extraction from aqueous model systems and agricultural runoff samples was investigated using cetyltrimethylammonium bromide-magnetic nanoparticles (CTAB-MNPs), sodium dodecylsulfate-magnetic nanoparticles (SDS-MNPs), and Mill scale. It was monitored using UV–visible spectroscopy based on the molybdenum blue method, while the adsorption mechanism of P on MNPs was evaluated through time-dependent studies, FTIR, zeta potential (ζ), X-ray photoelectron spectroscopy (XPS), and FESEM-EDS. CTAB-MNPs promoted P adsorption through favorable electrostatic interactions between positively charged quaternary ammonium groups and negatively charged phosphate ions, while SDS-MNPs enhanced P uptake by improving nanoparticle dispersion, colloidal stability, and accessibility of iron oxide active sites. Time-dependent studies revealed that the adsorption kinetics followed the order SDS-MNPs > Mill Scale > CTAB-MNPs. IR, XPS, FESEM-EDS and ζ analyses confirmed the presence of adsorbed P on the surface of MNPs. The results demonstrated that P removal was also governed by inner-sphere complexation with iron oxide active sites rather than electrostatic interactions alone, highlighting the potential of surfactant-modified MNPs and Mill scale as effective materials for P extraction from agricultural runoff.