Recovery of Phosphate from Mixed Solutions Using Surface Modified Maghemite Nano-Adsorbents

Waste water is a potentially rich source of valuable materials including nutrients, such as phosphates. Recovering these compounds is difficult because of their relatively dilute concentrations and complex chemistry of the wastewater itself. The purpose of this study was to synthesize super-paramagnetic nanoparticles (maghemite, γ-Fe2O3) for recovering phosphate from simple and complex electrolyte solutions. The γ-Fe2O3 nanoparticles were coated with dimercaptosuccinic acid (DMSA) onto which a tetraethylenepentamine (TEPA) coating was attached using two different methods. The unmodified and modified nanoparticles were characterized with regards to their size/size distribution, surface charge (zeta potential), surface functionality, and specific surface area, using dynamic light scattering, transmission electron microscopy, laser Doppler velocimetry, Fourier transform infrared spectroscopy, X-ray fluorescence, and BET surface area analysis. The TEPA-functionalized nanoparticles, irrespective of the synthesis method used, achieved phosphate adsorption capacities between 11 to 16 mg PO4/g adsorbent. Adsorption increased with increasing solution ionic strength up to 100mM NaCl, and decreased with increasing solution pH. Both relationships were attributed to ionic interactions between the phosphate anion and the negatively charged adsorbent surface. The presence of competing anions, nitrate and sulfate, did not significantly affect phosphate adsorption by the TEPA functionalized γ-Fe2O3 nanoparticles.