Nitrite stability influenced by iron compounds

The decomposition of nitrite was studied in the presence of (1) different amounts of ferrous iron and (2) an amorphous and a crystalline (haematite) iron product at different pH and Eh conditions. It was found that ferrous iron positively influenced the nitrite decomposition. Even at pH 6, where self-decomposition is excluded, some nitrite was decomposed. It was shown that at all studied pH values the second order decomposition rate increased as the amount of ferrous iron increased. From the calculation of the activation energy it was found that the dependence of the rate constant on temperature increased when the medium was more acid, or when the amount of Fe²⁺ increased at the same pH. The nitrite half-life was longest at pH 6, 25°C and 200 mg Fe²⁺ l^?1; it was shortest at pH 4, 30°C and 800 mg Fe²⁺ l^?1. The experiments with Fe²⁺ derived from solid iron compounds showed that all conditions favouring a high amount of ferrous iron in solution, such as low redox potential, low pH, amorphous or less crystalline material, enhanced nitrite decomposition.