ABIOTIC REDUCTION OF NITRITE AND NITRATE BY CHEMOGENIC MAGNETITE NANOPARTICLES: IMPLICATIONS IN NITROGEN CYCLING AND GREENHOUSE GAS PRODUCTION

The biogeochemical cycling of nitrogen in terrestrial systems is a major source of N₂O, which is among key greenhouse gases (GHG). While biotic processes are commonly accepted as the major drivers of N₂O production, the role of abiotic processes is less understood, and its importance may be underestimated. This study investigates abiotic reactions in the formation and breakdown of N trace gases, including NO and N₂O by naturally occurring nanoscale magnetite in soil as denitrification intermediates. Nitrogen biogeochemical cycling has been studied extensively with reference to microbial processes, atmospheric pollution and greenhouse gases. Nitric oxide catalyzes ozone production in the troposphere. Nitrous oxide contributes to the destruction of ozone in the stratosphere.

Iron oxides, such as lepidocrocite and ferrihydrite have been reported to reduce nitrite and nitrate to NO and N₂O. In this study, the potential of magnetite nanoparticles to abiotically reduce nitrite and nitrate to other nitrogen species, such as NO, N₂O, N₂ and NH₃, is investigated. This study examines the reactivity of chemogenic magnetite nanoparticles with nitrite and nitrate in bench-scale batch reactors by characterizing reaction kinetics and quantifying various product fractions. The study focuses on mass-fractions of NO and N₂O that may be produced from nitrite and nitrate with above magnetite. The results thus far confirm that chemogenic magnetite is capable of rapidly degrading nitrite into N₂O. Results thus far showed that 1.16 g L^-1 magnetite in batch experiments under anaerobic conditions can degrade almost all of 0.025 mmoles of nitrite resulting in significant amounts of N­₂O in about 2 days. Further, experiments conducted with the same amount of magnetite but with 0.5 mmoles of nitrite shows degradation of 0.085 mmoles of nitrite that produced gaseous N₂O. The influence of aqueous [Fe²⁺], dissolved O₂, solution pH, surface area concentration, and size of the magnetite nanoparticles on the distribution of reaction products are under investigation.