HR: 0800h
AN: NS51A-04    [Abstracts]
TI: Using Nuclear Magnetic Resonance to Monitor Iron Mineralization Processes
AU: * Keating, K
EM: kkeat@pangea.stanford.edu
AF: Geophysics Department, Stanford University, Mitchell Building, Stanford, CA 94305-2215, United States
AU: Knight, R
EM: rknight@pangea.stanford.edu
AF: Geophysics Department, Stanford University, Mitchell Building, Stanford, CA 94305-2215, United States
AU: Tufano, K
EM: ktufano@stanford.edu
AF: Geological and Environmental Sciences Department, Stanford University, 450 Serra Mall Braun Hall, Building 320, Stanford, CA 94305-2115, United States
AB: Proton nuclear magnetic resonance (NMR) relaxation time measurements can be used to probe the molecular- scale physical and chemical environment of water in the pore-space of geological materials. In this study, we extend upon previous work to explore the use of NMR relaxation time measurements as a method for monitoring iron mineralization processes. Laboratory NMR measurements were used to monitor changes in the mineralogical form of iron oxide as it reacted with ferrous iron. Specifically, columns packed with ferrihydrite- coated quartz sand were reacted with anaerobic media containing ferrous iron under advective flow conditions at a pH of 7.5 and a flow rate of 5 pore volumes per hour. The experiment was conducted with two concentrations of ferrous iron: 2 mM and 0.02 mM. The NMR relaxation measurements were shown to be very sensitive to increases in the proportion of magnetite, a mixed ferrous-ferric oxide produced during ferrihydrite transformation in the sand columns. In both the 2 mM and 0.02 mM columns an overall decrease in the relaxation time was observed. In the 2 mM columns, intermediate reactions were indicated by an increase in the relaxation time following the introduction of ferrous iron to the system. The mineralogy was determined using extended x-ray adsorption fine structure (EXAFS) spectroscopy, and x-ray diffraction. Ferric and ferrous iron concentrations were determined spectrophotometrically using the ferrozine method. These results demonstrate the potential of NMR field instruments as a method for monitoring geochemical reactions.
DE: 0416 Biogeophysics
DE: 1859 Rocks: physical properties
DE: 5109 Magnetic and electrical properties (0925)
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly