Reactions of Nitrite with Goethite and Surface Iron(II)-Goethite Complexes.

Nitrite (NO₂^‑) is often observed in water and soil-water systems as a toxic anion that occurs as an intermediate in nitrification and denitrification processes.  In the presence of NO₂^-, microbial production of Fe (II) is halted.  One potential pathway explaining this is the reoxidation of surface-bound Fe(II) by NO₂^-.  In the past, there have been a few studies which have used iron oxides and iron oxy(hydr) oxide minerals as sorbents for microbially-generated Fe(II) to study NO₂^- reactivity.  These studies have shown that Fe(II) bound on iron minerals is capable of reducing NO₂^-.   Yet, spectroscopic measurements and kinetic data on reactivity of NO₂^- with goethite and goethite-bound Fe(II) are not found in the literature.  In this study, the sorption behavior of NO₂^- onto 300m²L^-1 goethite-water slurry was investigated under anoxic conditions as a function of pH and ionic strength for time periods up to 72 hours.  Nitrite sorption ranged from 11 to 15% of the initial NO₂^- added (100 µM NO₂^-) at pH 5, and it decreases with increasing pH (at 7 and 8).  The sorption was not affected by ionic strength.  Further experiments will follow sorption of Fe(II) onto goethite as a function of pH and ionic strength.  Additional experiments will be carried out using XRD, SEM, and ATR-FTIR to investigate mineralogical changes in goethite, and coordination chemistry of Fe(II) at the Fe(II)-goethite water interface in the presence of NO₂^-. It is expected that NO₂^- sorption in Fe(II)-goethite ternary system would be greatly enhanced, perhaps due to reduction processes.  This research has important implications in biogeochemical cycling of nutrients, global warming, and contaminant transport.