GEOC
048.
IN-SITU EXAFS STUDY ON AQUEOUS COBALT(II) AND STRONTIUM II) SORPTION AT CLAYWATER INTERFACES AS A FUNCTION OF VARIOUS SOLUTION CONDITIONS. C.C. Chen*, K.F.
Hayes*, and C. Papelis**, 'Department of Civil and Environmental Engineering, The University of Michigan,
Ann Arbor, Ml 48109-2125, "Desert Research Institute, University of Nevada System, Las Vegas, NV
89132-0040
Two types of surface complexes, inner-sphere complexes and outer-sphere complexes, can be formed
between sorbed metal ions and clay surfaces. The formation of different surface complexes is controlled by
sorbent, sorbate characteristics as well as solution conditions. The experimental conditions in this study were
varied by different ionic strengths, background electrolytes, and pH values. Different clay minerals, kaolinite,
illite, hectorite, and montmoriiionite, were used to represent solids with different structures, surface areas, and
cation exchange capacities. Different surface complexes may be investigated by EXAFS which provides
information about the local coordination environment between metal ions and solid surfaces. The results from
EXAFS studies will be presented that distinguish between inner and outer-sphere surface complexes with
clay minerals under different solution conditions.
049 NICKEL SORPTION KINETICS/MECHANISMS ON THE CLAY FRACTION OF A SOIL: AN XAFS
S T U D Y. D . R . R o b e r t s , A . M . S c h e i d e g g e r a n d D . L . S p a r k s . D e p a r t m e n t o f
Plant and Soil Sciences, University of Delaware, Newark, DE 19717-1303, Waste
Management R+D, Paul Scherrer Institute, Villigen, Switzerland.
Soil mineral surfaces are capable of sorbing and retaining heavy metal Ions and
are therefore important in assessing the fate of heavy metal contaminants in the soil
environment. Most x-ray absorption fine structure (XAFS) spectroscopic studies of
heavy metal sorption have focused on pure components, with less emphasis placed on
m i x e d s y s t e m s . H o w e v e r, s o i l c l a y f r a c t i o n s i n n a t u r a l e n v i r o n m e n t a r e r a r e l y, i f
ever, composed of only one pure mineral component. This study examines Ni(II)
sorption kinetics/mechanisms on the clay fraction (<0.002mm) of a Matapeake silt loam
at different reaction conditions using XAFS. The data suggests that it is possible to
propose sorption mechanisms responsible for Ni uptake in the soil clay fractions based
on the XAFS analysis, the mineral composition of the clay fractions and an under
standing of the sorption mechanisms in pure components.
0 5 0 . S I M U L AT I N G E X A F S S P E C T R A F O R M E TA L S AT WAT E R / M I N E R A L O X I D E I N T E R
FACES, Maureen I. McCarthy.* Gregory K. Schenter,* Gordon E. Brown, Jr.,' and John J. Rehr,'
^Pacific Northwest Laboratory, Richland, WA 99353, 'Stanford University, Stanford, CA 94305,
and 'University of Washington, Seattle, WA 98195.
Many of the molecular scale processes that control the fate and transport of contaminants in the subsurface can
be probed using X-ray absorption spectroscopy. These methods are especially effective at probing the uptake
and transformation of metals in the environment. Theoretical methods have been developed which allow us
to predict and interpret experimental XAFS spectra on complex systems such as, metals at mineral/water
interfaces. Our theoretical approach combines classical mechanics simulations with the ab initio high order
multiple scattering theory implemented in the computer code FEFF7 to determine the effects of thermal motion
on EXAFS spectra and to deconvolve the EXAFS signal into contributions from individual scattering paths.
This paper will present a description of the method for studying metals at aqueous/mineral interfaces and will
discuss applications of this approach to systems in the soft and hard x-ray regions. The results of studies on
transition metals (Co, Cr, Fe) at the a-A1203/water interface will be presented.
051.
T E C H N I Q U E S A N D A P P L I C AT I O N S O F S Y N C H R O T R O N X A S T O M E TA L B O N D I N G I N
CONTAMINATED SEDIMENTS AND SOILS. Peggy O'Day, Geology Departnnent, Arizona State
Univ., Tempe, AZ 85287-1404, S. Carroll, M. Nevwille, LLNL, Livermore, CA 94551, C. Fuller, U.S.
Geological Survey, Menio Park, CA 94025; J. Villinski, Univ. of Arizona, Tucson, AZ 85721-0011
Synchrotron X-ray absorption spectroscopy (XAS) is a useful spectroscopic probe for determining
the local bonding of toxic metals in soils and sediments. These materials contain mixtures of
crystalline, amorphous, and disordered solid phases, low concentrations of metals (10's-1000's