Chemical Reduction of Nitrite and Nitrous Oxide by Ferrous Iron

Abstract Little is known about the reduction of NO 2 ‐ and N 2 O by Fe 2+ in the pH range from 6 to 8, a range of importance in many natural environments. Reduction of 25 mg NO 2 ‐ ‐N (approximate concentration=25 ppm) and 5 mg N 2 O‐N in a distilled‐water medium containing 800 mg Fe 2+ with a helium atmosphere in the presence and absence of Cu 2+ at pH 6 and 8 was studied at 26°C. Reduction of NO 2 ‐ to N 2 O (the principal product), N 2 and NH 4 + was rapid and quantitive at pH 8 and not greatly affected by Cu 2+ . However, addition of Cu 2+ decreased the mole ratio of N 2 O to N 2 in the evolved gas mixture from 4.2 to 3.1. Reduction of NO 2 ‐ at pH 6 was incomplete, but was favored by Cu 2+ addition. Nitrous oxide was the dominant reduction product at this pH value. Small quantities of NO accumulated at pH 6. Irrespective of Cu 2+ addition, N 2 O was stable in the Fe 2+ medium at pH 6. In the pH 8‐system in the presence of Cu 2+ 84% of the N 2 O was reduced to N 2 . Nitrous oxide was relatively stable at pH 8 in the absence of Cu 2+ . Small quantities of H 2 accumulated in the atmospheres of vessels containing the pH 8, plus Cu 2+ N 2 O − N treatment. No H 2 accumulated in the NO 2 ‐ series of treatments.