Application of magnetic nano-particles for phosphorus removal/recovery in aqueous solution

To remove or recover phosphorus (P) efficiently from various aqueous solutions is important as P is an essential nutrient and a key element to cause eutrophication. This study examines the feasibility of P removal/recovery using Fe3O4 nano-particles, generated from ferrite process. A rapid increased of P adsorption (0.17 to 2.38 mg/g) was detected when the solution pH decreased from 11.09 to 2.77. A maxima adsorption capacity was estimated to be 3.65 mg/g P at 318 K and pH 2.77, much higher than other iron-based adsorbents. Additionally, P adsorption increases with the increase of ionic strength from 0.001 to 1.0 N, indicating that the inner-sphere mechanism was importantly involved in the P adsorption. This P adsorption is spontaneous and endothermic, supported by the negative changed standard free energy with temperatures (ΔGo = −4.33, −4.56, −4.80, −5.02 kJ/mol at 288, 298, 308, and 318 K, respectively) and the positive ΔHo values (0.28 kJ/mol). The positive ΔSo (2.79 J/mol K) further indicates that the randomness increased at solid-solution interface during P adsorption. These results reveal potential applications of Fe3O4 nano-particles for P removal/recovery in wastewaters or freshwaters.