Facile fabrication of nanoscale zero-valent iron/activated carbon fibers (nZVI/ACFs) composite with excellent capability for phosphate removal from water: Effect of nitrate ion

Novel nanoscale zero-valent iron/activated carbon fibers composite was successfully fabricated. • nZVI/ACFs exhibited excellent capability toward phosphate under the nitrate mediation. • Phosphate can be effectively immobilized and captured across relatively wide pH range. • Nitrate ion can accelerate nZVI corrosion and then enhance the uptake of phosphate. • Remarkable performance was obtained of nZVI/ACFs in fixed-bed column studies. Serious surface passivation and subsequent reduction of reactivity significantly restricted the application of nanoscale zero-valent iron. In this study a novel nanoscale zero-valent iron/activated carbon fibers (nZVI/ACFs) composite was successfully constructed via loading method to overcome the intrinsic defects and enhance the reactivity of nZVI according to the special physicochemical properties of ACFs, achieving excellent phosphate removal behavior and performance. High uptake of phosphate by nZVI/ACFs was maintained across relatively wide pH range and in the presence of co-existing anions, monovalent K + ion and HA, whereas divalent Ca 2+ and Mg 2+ cations could further enhance the phosphate removal due to the chemical precipitation and cation bridging effect. Phosphate adsorption isotherms and kinetics could be well described by the Langmuir model and pseudo-second order model, indicating that phosphate experienced monolayer sorption and this removal process and mechanism was dominated by chemisorption. Notably, the presence of nitrate ion in nZVI/ACFs-phosphate remediation system significantly enhanced the uptake of phosphate on account of the nitrate mediation effect. Specifically, as a special oxidant and electron acceptor, nitrate ion can promote nZVI surface corrosion and generate abundant soluble irons, then transformed into corresponding iron (hydr)oxides, which were favorable to phosphate immobilization through multiple mechanisms containing adsorption, coagulation/co-precipitation. Furthermore, the remarkable performance in fixed-bed column studies under condition of natural water system indicated nZVI/ACFs was a promising candidate for the practical applicability in actual phosphorus wastewater treatment. Download: Download high-res image (131KB) Download: Download full-size image