Kinetic Modeling and Simulation of Zero-Valent Iron Wastewater Treatment Process: Simultaneous Reduction of Nitrate, Hydrogen Peroxide, and Phosphate in Semiconductor Acidic Wastewater

A kinetic model for the simultaneous removal of nitrate, hydrogen peroxide, and phosphate in semiconductor acidic wastewater by zero-valent iron (ZVI) has been developed on the basis of the Eley-Rideal mechanism. The simultaneous removal process consists of the reactions linked up with the transformation of ZVI from Fe-0 to Fe2+ and then to Fe3+ under the acidic condition. The reduction of nitrate, degradation of hydrogen peroxide, and precipitation of ferric or ferrous phosphate took place as consequence of ZVI transformation. In modeling, nitrate reduction to ammonium and nitrogen gas, hydrogen peroxide degradation by Fenton reaction, phosphate removal by the complexation with ferric and ferrous ions, and reduction of adsorbed proton were considered as well as ZVI corrosion and adsorption of proton, nitrate, phosphate and ferric ion at the active site on the iron surface. The rate equations for iron ions and OH radical, which are key species in the transformation of ZVI, were also taken into account. The simulation results by the proposed kinetic model could satisfactorily describe the experimental results for the simultaneous removal of nitrate, hydrogen peroxide, and phosphate driven by the transformation of ZVI. The complicated dynamic behaviors of iron ions playing an important role in the synergy among the reactions could be simulated reasonably well. The kinetic model based on the Eley-Rideal mechanism may be useful to predict dynamic behaviors of ZVI wastewater treatment processes.