Reactions of nitrite with goethite and surface Fe(Ⅱ)-goethite complexes

摘要

Chemodenitrification-the abiotic (chemical) reduction of nitrite (NO~－_2 ) by iron (Ⅱ)-plays an important role in nitrogen cycling due in part to this process serving as a source of nitrous oxide (N_2O). Questions remain about the fate of NO~－_2 in the presence of mineral surfaces formed during chemodenitrifkation, such as iron(Ⅲ) (hydr) oxides, particularly relative to dissolved iron(Ⅱ). In this study, stirred-batch kinetic experiments were conducted under anoxic conditions (to mimic iron(Ⅲ)-reducing conditions) from pH 5.5-8 to investigate NO~－_2 reactivity with goethite (FeOOH_(s)) and Fe(Ⅱ)-treated goethite using wet chemical and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Nitrite removal from solution by goethite was more rapid at pH 5.5 than at pH 7 and 8. Spectral changes upon nitrite adsorption imply an inner-sphere surface interaction (monodentate and bidentate) at pH 5.5 based on ATR-FTIR spectra of the nitrite-goethite interface over time. In iron(Ⅱ)-amended experiments at pH 5.5 with high aqueous Fe(Ⅱ) in equilibrium with goethite, nitrous oxide was generated, indicating that nitrite removal involved a combination of sorption and reduction processes. The presence of a surface complex resembling protonated nitrite (HONO) with an IR peak near ～1258 cm~(－1) was observed in goethite-only and iron(Ⅱ)-goethite experiments, with a greater abundance of this species observed in the latter treatment. These results might help explain gaseous losses of nitrogen where nitrite and iron( Ⅱ)/goethite coexist, with implications for nutrient cycling and release of atmospheric air pollutants.