Chemical Reduction of Nitrate by Ferrous Iron

Publisher Website
Google Scholar
Abstract
Knowledge concerning the chemical reduction of NO3− to gaseous products, a process of potential practical significance as an antipollution device, is sparse. The influence of pH on chemical reduction of NO3−‐N (approximate concentration 25 ppm) by Fe2+ in the presence and absence of Cu2+ was studied over a pH range from 6 to 10. After 24‐hours of controlled pH incubations under a helium atmosphere NO3−, NO2−, N2O, NO, N2, and NH4+ were determined. The initial Fe2+/NO3− mole ratio was 8. Reduction of NO3− was negligible in the absence of Cu2+, but was pronounced above pH 7 in the presence of approximately 5 ppm Cu2+. Formation of NH4+ increased with pH and was the dominant process at pH 9 and 10. Nitrous oxide and N2 accumulations were greatest in the pH range from 8 to 8.5 and negligible at pH 6 and 10. Nitrite formation was small except at pH 9 and 10. Trace quantities of NO accumulated during incubation if the pH was allowed to drop below 6.Levels of Cu2+ and Fe2+ influenced the extent and nature of NO3− reduction at pH 8. Maximum reduction of NO3− (93%) and maximum gas production (equivalent to 61% of the original NO3−) occurred when the Fe2+/NO3− mole ratio was 12 and the Cu2+ level was approximately 10 ppm. The N2O/N2 mole ratio in the evolved gases decreased as the Cu2+ level was increased from approximately 1 to 10 ppm and as the Fe2+/NO3− mole ratio was increased from 8 to 12. Nitrate was relatively stable at a Cu2+ content of 0.1 ppm irrespective of the Fe2+/NO3− ratio.