HR: 0830h
AN: V51H-0380    [PDF]
TI: Reactivity and Speciation of Heavy Metals With Nanoparticulate Goethite
AU: * Kim, C S
EM: cskim@lbl.gov
AF: Department of Earth and Planetary Sciences, University of California-Berkeley, 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: * Kim, C S
EM: cskim@lbl.gov
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, Building 70R0108B, 1 Cyclotron Road, Berkeley, CA 94720-8168 United States
AU: Banfield, J F
EM: jill@eps.berkeley.edu
AF: Department of Earth and Planetary Sciences, University of California-Berkeley, 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Waychunas, G A
EM: gawaychunas@lbl.gov
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, Building 70R0108B, 1 Cyclotron Road, Berkeley, CA 94720-8168 United States
AB: Of the many nanoscale mineral phases present in the environment, iron (oxy)hydroxides are among the most common and most reactive in terms of metal contaminant uptake. However, the effects of particle size on metal sorption to phases such as goethite ($\alpha$-FeOOH), particularly in the nanoscale range, have not yet been well characterized. To study the effects of particle size on metal uptake, a series of goethite batches was synthesized using a microwave synthesis technique followed by aging in suspension at 90$\deg$C. This method resulted in batches of goethite with discrete particle sizes ranging from 10-80 nm in effective diameter. Each batch was characterized by BET surface area analysis, laser light scattering, transmission electron microscopy (TEM), X-ray diffraction (XRD), and small angle X-ray scattering (SAXS). Goethite nanoparticle growth by this procedure occurs in two distinct stages: 1) rapid growth from 10-60 nm over the first 4 days followed by 2) slower growth from 60-80 nm over the next 28 days. This may represent a progression from aggregation-based growth to ripening-based growth, as suggested by TEM analysis. Goethite batches of 10, 25, and 75 nm in effective diameter were selected for use in batch uptake experiments featuring As(V), Cu(II), Hg(II), and Zn(II), metal(loid) contaminants frequently associated with acid mine drainage systems. Sorption products were analyzed with X-ray absorption fine structure (XAFS) spectroscopy to investigate potential changes in the mode of metal uptake as a function of particle size. While the speciation of the contaminants on the 10- and 25-nm goethites were effectively identical, subtle differences in both second-neighbor distances and coordination numbers indicate changes in the mode of uptake on the 75-nm sized particles (as well as on "bulk" 200-nm sized particles generated using a more traditional synthesis method). Such differences may be due to changing proportions of binding sites (e.g. edges, corners) and particle morphology evolution from oblong (10-nm particles) to more tabular/acicular (75-nm particles) as particle size increases.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1045 Low-temperature geochemistry
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting