Chemical Reduction of Nitrate by Ferrous Iron

Abstract Knowledge concerning the chemical reduction of NO 3 − to gaseous products, a process of potential practical significance as an antipollution device, is sparse. The influence of pH on chemical reduction of NO 3 − ‐N (approximate concentration 25 ppm) by Fe 2+ in the presence and absence of Cu 2+ was studied over a pH range from 6 to 10. After 24‐hours of controlled pH incubations under a helium atmosphere NO 3 − , NO 2 − , N 2 O, NO, N 2 , and NH 4 + were determined. The initial Fe 2+ /NO 3 − mole ratio was 8. Reduction of NO 3 − was negligible in the absence of Cu 2+ , but was pronounced above pH 7 in the presence of approximately 5 ppm Cu 2+ . Formation of NH 4 + increased with pH and was the dominant process at pH 9 and 10. Nitrous oxide and N 2 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 Cu 2+ and Fe 2+ influenced the extent and nature of NO 3 − reduction at pH 8. Maximum reduction of NO 3 − (93%) and maximum gas production (equivalent to 61% of the original NO 3 − ) occurred when the Fe 2+ /NO 3 − mole ratio was 12 and the Cu 2+ level was approximately 10 ppm. The N 2 O/N 2 mole ratio in the evolved gases decreased as the Cu 2+ level was increased from approximately 1 to 10 ppm and as the Fe 2+ /NO 3 − mole ratio was increased from 8 to 12. Nitrate was relatively stable at a Cu 2+ content of 0.1 ppm irrespective of the Fe 2+ /NO 3 − ratio.