Zero-valent iron-facilitated reduction of nitrate: Chemical kinetics and reaction pathways

The kinetics and mechanisms of the reduction of NO3− in solution to NH3 by 1.5 μm diameter zero-valent iron (ZVI1.5) particles has been examined. The effects of initial pH, ZVI1.5 particle concentration and initial NO3− concentration were also investigated. Results indicate that denitrification by ZVI1.5 is primarily a pH-dependent, surface-mediated process. At an initial ZVI1.5 concentrations of 0.832 g/L, and an optimal initial pH of 1.62, the NO3− concentration was reduced by 95% from 12.50 mg/L-N to 0.65 mg/L-N, in 120 min. Several kinetic models were used to describe the denitrification process based on the ZVI1.5:NO3− ratio. Based on mineralogical and surface analysis of the reacted ZVI1.5, and detailed solution chemical analysis, the denitrification reaction pathway involves oxidation and partial dissolution of the ZVI1.5 with the generation of Fe2 + and NO2− intermediates prior to formation of Fe3 + oxyhydroxide (goethite) and NH3.