Nitrite (NO2-) is an important soil anion that occurs as an intermediate in biological and abiological denitrification and nitrification processes. Accumulation of NO2- in water supplies can pose a danger to human infants through methemoglobinemia. Therefore, it is important to understand NO2- transformation processes. We discovered that siderite, an iron carbonate mineral, abiotically transformed nitrite. Stirred batch reactions were performed in an anerobic chamber over a range of pH values (5.55, 6, 6.45, and 7.9), initial FeCO3(s) concentrations (5, 10, and 15 g per L) and initial NO2- concentrations (1, 3, 5, and 10 mM NO2-) for kinetic and stoichiometric determinations. Suspensions were removed with increasing time intervals and filtered to measure dissolved nitrogen and iron species. Nitrite reduction by siderite was rapid over a time period of 24 h and the major product identified was N2O. The molar ratio of Fe(II) consumed to NO2- reduced was 2 to 1. The reaction rates increased with increasing siderite, NO2-, and proton concentrations. The method of initial rates and isolation were used to derive an empirical rate equation. The derived rate equation indicated nearly first order dependence on both siderite (1.08) and NO2- (1.08), and fractional order dependence (0.21) on H+ concentration. These findings indicate that siderite can effectively remove NO2- from water by reduction to N2O.
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