HR: 08:55h
AN: B31F-04    [Abstracts]
TI: Nanoparticle-host interactions in natural systems
AU: * Becker, U
EM: ubecker@umich.edu
AF: Dept of Geological Sciences, University of Michigan, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Reich, M
AF: Departamento de Geologà­a, Facultad de Ciencias Fà­sicas y Matemà¡ticas, Universidad de Chile, Plaza Ercilla 803, Santiago, 00000, Chile
AU: Utsunomiya, S
AF: Dept of Geological Sciences, University of Michigan, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Wang, J
AF: Dept of Geological Sciences, University of Michigan, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Kesler, S
AF: Dept of Geological Sciences, University of Michigan, 2534 CC Little, Ann Arbor, MI 48109, United States
AU: Wang, L
AF: Dept. of Nuclear Energy and Radiological Sciences, Bonisteel Blvd, Ann Arbor, MI 48109, United States
AU: Ewing, R C
AF: Dept of Geological Sciences, University of Michigan, 2534 CC Little, Ann Arbor, MI 48109, United States
AB: Natural nanoparticles are attracting a great deal of attention due to their unique role as agents of elemental transport and their increased reactivity in geologic systems. Although significant progress has been made in understanding their behavior in the Earth's critical zone (i.e. near-surface environments), there is a severe lack of information on their stability for a wider range of geologically relevant temperatures. Here, we describe the first direct observations of the dynamic behavior of natural nanoparticles at near atomic scale, revealing that their thermal stability is not only dependent on particle size, but also on the surrounding host mineral. Native Au nanoparticles (mean diameter ~4 nm) incorporated in an As-rich pyrite from "invisible" Au ores were observed during in-situ heating up to 650°C. While isolated Au nanoparticles melt, with their melting point being a function of size, we show that when incorporated in a sulfide host, Au nanoparticles react to increased temperature by dissolving into the pyrite matrix and forming larger particles in an Ostwald-type ripening process. The dissolution temperatures are much lower than melting temperatures of isolated nanoparticles and are as well strongly size-dependent. These findings provide new insights into the fate of nanoparticulate Au and other metals during geological processes and throughout their metallurgical recovery from refractory ores. The size distribution of the particles may be an indicator of the geologic history of the ore because, as we show, the mean particle diameter sets un upper limit to the maximum temperature of the host rock. Furthermore, results suggest that nanoparticulate minerals, usually documented in low-temperature (T<100°C) aqueous environments, can also occur and survive at higher temperatures when incorporated into refractory host phases.
DE: 0461 Metals
SC: Biogeosciences [B]
MN: 2007 Fall Meeting