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Richard J. Reeder
Geosciences Department
255 ESS Building
Stony Brook University
Stony Brook, NY 11794-2100
Phone: 631-632-8208
B.S., University of Illinois, 1975
Ph.D., University of California, Berkeley, 1980
Faculty member at Stony Brook since 1980
Visiting Scientist, Cambridge University, 1986-1987
Email: rjreeder@stonybrook.edu
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Role of surface structure in metal uptake by calcite
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Uptake of dissolved metals at mineral surfaces is one of the most important processes governing
the fate of contaminants and trace elements in nature. Among the dominant uptake mechanisms
in mineral-water systems are adsorption (binding at the mineral-water interface) and co-precipitation
(incorporation into a growing crystal). Co-precipitation may be particularly effective for long-term
sequestration of contaminant species because re-release to solution requires dissolution of the mineral.
Although co-precipitation behavior has been extensively studied for common minerals such as
calcite, our group was the first to demonstrate how mineral surface structure influences metal
incorporation. This delicate interplay between the mineral surface structure and the aqueous solution
has been documented best by the site-specific incorporation of divalent metal species at the {1014}
surface of calcite. |
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Crystals surfaces develop in response to anisotropy in attachment kinetics, which is largely
inherited from the underlying bulk structure. Surfaces that appear morphologically flat, such
as the common {1014} face of calcite, reflect the intersection of multiple directions of strongly
preferred attachment, referred to as periodic bond chains (PBCs). Growth on these surfaces
commonly occurs by a spiral mechanism in which steps, typically just a few Angstroms in height,
advance outward from a dislocation source. Owing to anisotropy on the surface, steps may have
several preferred orientations, and arrays of straight steps having similar orientation may be segregated
as vicinal surfaces composing the flanks of shallow growth hillocks (Panel 1).
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The spatial segregation of steps with different orientation may influence the distribution of structurally non-equivalent
attachment sites, depending on surface symmetry. On calcite {1014} faces, the c-glide acts as a mirror
symmetry element, relating two pairs of structurally non-equivalent steps that are typically present during growth.
Views along the length of the non-equivalent steps reveal that differences exist in the atomic structure at
the step edge. (Second Panel) |
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Divalent metal species present in the growth solution are found to exhibit distinct preferences for
incorporation between the different step types, resulting in distinctive heterogeneous incorporation patterns.
Synchrotron-based micro-X-ray fluoresecence allows mapping the metal distribution, which is shown
here by different colors. Research in our group has studied the surface step/site preferences for
different metals co-precipitating with calcite, and has allowed us to identify the surface structural factors
that influence incorporation. (Third panel)
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Outside of Science:
Weißkugel is the second highest mountain in the Ötztal Alps
and the third highest mountain in Austria. It lies on the border between Austria and Italy.
It features many glaciers. |
