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This article in JEQ

  1. Vol. 5 No. 3, p. 320-325
     
    Received: Oct 24, 1974
    Published: July, 1976


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doi:10.2134/jeq1976.00472425000500030021x

Chemical Reduction of Nitrate by Ferrous Iron1

  1. R. J. Buresh and
  2. J. T. Moraghan2

Abstract

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.

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