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

Area of Science:

• Environmental Chemistry
• Geochemistry
• Biogeochemistry

Background:

• Chemodenitrification, the abiotic reduction of nitrite (NO2-) by iron(II), is a key process in nitrogen cycling and a source of nitrous oxide (N2O).
• The fate of nitrite in the presence of iron(III) (hydr) oxides, common mineral surfaces in chemodenitrification, remains unclear, especially concerning its interaction with dissolved iron(II).

Purpose of the Study:

• To investigate the reactivity of nitrite with goethite (FeOOH(s)) and iron(II)-treated goethite under anoxic conditions.
• To elucidate the role of mineral surfaces and dissolved iron(II) in nitrite transformation and nitrous oxide production.

Main Methods:

• Stirred-batch kinetic experiments were conducted at pH 5.5-8 under anoxic conditions.
• Nitrite removal was monitored using wet chemistry.
• Surface interactions were analyzed using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy.

Main Results:

• Nitrite removal by goethite was faster at pH 5.5 than at pH 7 and 8.
• ATR-FTIR spectra indicated inner-sphere surface interactions (monodentate and bidentate) at pH 5.5.
• In the presence of iron(II) and goethite, nitrous oxide was generated, suggesting combined sorption and reduction of nitrite.
• A surface complex resembling protonated nitrite (HONO) was observed, with higher abundance in iron(II)-amended experiments.

Conclusions:

• Nitrite sorption onto goethite is pH-dependent, with faster removal at acidic conditions.
• The presence of iron(II) promotes nitrite reduction to nitrous oxide via surface complexation.
• These findings help explain nitrogen loss and nitrous oxide emissions where nitrite and iron(II)/goethite coexist, impacting nutrient cycling and atmospheric pollutants.