Characterization of Uranium Solids Precipitated with Aluminosilicates Page: 3 of 20
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WM'04 CONFERENCE, FEBRUARY 29-MARCH 4, 2004, TUSCON, AZ.
A) Structural Incorporation / Co-
O Si, Al
G o G so c
C) Specific Adsorption/ Chemi-
sorption / Inner Sphere Sorption
p". .4 fr
o 3 O G
B) Outer Sphere/ Ion Exchange /
D) Surface Precipitation/
7 O O C) n
Large dashed circles denote coordination shells.
Figure 1 Simplified diagram of the types of associations a metal could have with a surface: A) Structural
incorporation/co-precipitation, B) Outer-sphere (electrostatic) sorption, C) Specific or inner-sphere sorption and D)
Surface precipitation. Dashed rings denote first, second and third shell environments that can be probed with X-ray
absorption fine-structure (XAFS) spectroscopic techniques.
exchange is Structural Incorporation, which is the substitution of a solution species for a structural atom as shown in
the example below for strontium (Sr) ion substitution for calcium (Ca) ion in calcium carbonate or CaCO3(s).
CaCO3(s) + Sr
- * SrCO3(s) + Ca2* (Eq. 1)
This type of metal uptake typically requires ready access to structural atoms. An example of this process would be
the exchange of Na+ for Ca2+ within the interlayer region of a layered metal oxide material. Structural incorporation
includes co-precipitation, where a new atom substitutes for host structural atoms during the formation of the host
solid. Ideally, structural incorporation of anions could also occur. Therefore, the local environment of the
exchanged atom(s) would resemble the environment that of the newly exchanged atom prior to its release into
solution (Fig. lA). Two exceptions to this would be when the host structure is a nanoparticle (i.e., of vary small
dimension) and when the structure is amorphous or structure-less. In these cases, exact determinations of whether
the participating metal species resides in a structural vacancy or within an interlayer site are not straightforward (a).
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DUFF, MC. Characterization of Uranium Solids Precipitated with Aluminosilicates, article, January 9, 2004; South Carolina. (digital.library.unt.edu/ark:/67531/metadc739181/m1/3/: accessed January 19, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.