Phosphorous removal by nanoscale zero-valent iron (Nzvi) and chitosan-coated nzvi (cs-nzvi)

Abstract

In this study, nanoscale zero-valent iron (nZVI) and chitosan-coated nZVI (CS-nZVI) adsorbents were synthesized and used for phosphorus removal from an aqueous solution under oxic conditions. The characteristics of the nZVI particles were assessed using scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area and atomic force microscopy. Results showed smooth and spherical Fe0 particles with a size in the range of 74–186 nm for the nZVI compared to a range of 117–200 nm for the CS-nZVI. Adsorption and kinetic experiments were conducted to evaluate phosphorus removal under varying conditions of initial pH (pH 5 and 7) and presence of 3– interfering anions (a mixture of PO4, Cl– 2–, SO4, NO3–). Overall, phosphorus adsorption by both nZVI and CS-nZVI was well represented by both, Freundlich and Langmuir isotherms, with the Langmuir isotherm providing a better data fit (0.950 ≤ R2 ≤ 0.996). The phosphorus adsorption capacity of nZVI reached 437 mg/g at pH 5 and 169 mg/g at pH 7. CS-nZVI demonstrated drastically lower phosphorus removal capacities than nZVI (289 mg/g at pH 5 and 152 mg/g at pH 7). The adsorption kinetics of both adsorbents, nZVI and CS-nZVI, were well represented by the pseudo-second-or-der kinetic model (0.899 ≤ R2 ≤ 0.999), with the initial adsorption rate being higher at pH 5 than at pH 7. Interfering anions did not significantly alter the phosphorus removal rate or capacity of nZVI particles at pH 5 and pH 7.