ORIGINAL PAPER Nitrite reduction by Fe(II) associated with kaolinite S. Rakshit 1 • C. J. Matocha 2 • M. S. Coyne 2 • D. Sarkar 3 Received: 29 July 2015 / Revised: 3 January 2016 / Accepted: 22 February 2016 / Published online: 7 March 2016 Ó Islamic Azad University (IAU) 2016 Abstract Interactions of iron (Fe) with the nitrogen (N) cycle have emerged and contain elements of abiotic and biological reactions. One such abiotic reaction which has received little study is the reactivity of NO 2 - and Fe(II) associated with a major clay mineral, kaolinite. The main objective of this study was to evaluate the reactivity of NO 2 - with Fe(II) added to kaolinite under anoxic conditions. Stir- red batch reactivity experiments were carried out with 10 g L -1 kaolinite spiked with 25 and 100 lM Fe(II) at pH 6.45 in an anaerobic chamber. Approximately 500 lM NO 2 - was added to initiate the reaction with Fe(II)-loaded kaolin- ite. The rate of nitrite removal from solution was 2.4-fold slower in the high Fe(II) treatment when compared with the low Fe(II) treatment. A large portion of the NO 2 - removed from solution was confirmed to be reduced to N 2 O (g) in the Fe(II)-kaolinite slurries. However, NO 2 - reduction was also noticed in the presence of kaolinite-alone and to somewhat lesser extent in the presence of dithionite-citrate-bicarbonate (DCB)-treated kaolinite. Chemical extractions coupled with infrared spectroscopy suggest that Fe(III) oxide mineral impurities and structural Fe(III) in kaolinite may participate in NO 2 - removal from solution. Furthermore, a magnetite mineral was identified based on X-ray diffraction analysis of untreated kaolinite and DCB-treated kaolinite. Our findings reveal a novel pathway of NO 2 - transformation in the environment in the presence of Fe(II) associated (sorbed and impurity) with kaolinite. Keywords Nitrite reduction Á Anaerobic Á Abiotic XRD Á SEM Introduction Nitrite (NO 2 - ) is a soil anion that occurs as an intermediate in biological denitrification and nitrification. Incomplete NO 3 - reduction can cause NO 2 - accumulation in soils, sediments, and groundwater (Vaclavkova et al. 2015; Matocha et al. 2012). The presence of NO 2 - can impact dissolved organic nitrogen production, uranium bioremedi- ation, pyrite oxidation, and Fe(III) reduction (Obuekwe et al. 1981; Senko et al. 2002; Davidson et al. 2003; Picardal 2012, Yan et al. 2015). Regarding the latter process, several Fe(III)- reducing bacteria can simultaneously reduce NO 3 - and Fe(III) (DiChristina 1992; Krause and Nealson 1997). The biologically produced Fe(II) and NO 2 - can react chemically, producing Fe(III) and N 2 O (Moraghan and Buresh 1977). This chemical process has been invoked to explain the apparent inhibition of Fe(III) reduction in the presence of NO 3 - in pure cultures (Obuekwe et al. 1981) and anoxic soil slurries (Komatsu et al. 1978; Matocha and Coyne 2007). Cleemput and Baert (1983) showed that this reaction was more rapid as pH decreased. This may be attributed to the greater proportion of protonated nitrite species (HNO 2 ). Protonation promotes N–O bond breaking; thus, HNO 2 is a stronger oxidant than NO 2 - (Shriver et al. 1994). The production of nitrous oxide (N 2 O) in the Don Juan Pond in Antarctica was attributed to abiotic processes & S. Rakshit srakshit@tnstate.edu 1 Department of Agricultural and Environmental Sciences, Tennessee State University, 3500 John A. Merritt Blvd, Nashville, TN 37209-1561, USA 2 Department of Plant and Soil Sciences, University of Kentucky, N-122G Ag. Sci. Building-North, Lexington, KY 40546-0091, USA 3 Earth and Environmental Studies Department, Montclair State University, Montclair, NJ, USA 123 Int. J. Environ. Sci. Technol. (2016) 13:1329–1334 DOI 10.1007/s13762-016-0971-x