Under iron (Fe(III))-reducing conditions, nitrate-dependent iron(II) oxidation is an important process in mediating the fate of both iron and nitrogen. One possible secondary reaction that might be involved is the coupling of nitrite (NO2-) reduction with surface Fe(II) bound to unreduced Fe(III) oxide minerals. The present study was designed to assess the role of goethite (a-FeOOH) in the presence and absence of added Fe(II) on the removal of nitrite using wet chemical and spectroscopic measurements. Nitrite removal by goethite alone was enhanced as pH was lowered from 7.5 to 5.5 and there was no evidence of nitrogen reaction products such as nitrous oxide. However, addition of dissolved Fe(II) to goethite slurries accelerated the rate of nitrite removal from solution at pH 5.5, with pseudo-first order rate coefficients increasing from 0.14 h-1 in goethite-alone experiments to 0.5 h-1 in surface Fe(II) slurries. Nitrous oxide was formed in the headspace indicating that a portion of the nitrite removed from solution was reduced. Furthermore, there was appearance of an infrared peak at 1791 cm-1 after 15 min and 60 min and it decreased in intensity after 120 min based on attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra. This peak was assigned to a surface bound NO species. Another peak appeared at 2305 cm-1, assigned to adsorbed nitrous oxide, and this band increased in intensity with reaction time. These results indicate the importance of the goethite surface in binding products of nitrite reduction where Fe(II) is added and might represent an important sink for unrecoverable nitrogen in natural systems.

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

249th National Meeting (2015)

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