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Heavy Element Photophysics and Photochemistry
Sorption
from Solution to Final Waste Form in a Single Material
We have begun investigation of a functionalized silica gel (Diphosil)
as a potential means of generating nanophase, metal-bearing regions within
fused silica. Such materials offer potential advantages as laser gain
media and in other nonlinear optical devices as well as the potential
for serving as a superior nuclear waste form. The Diphosil that we have
studied was supplied by EIChroM Industries,
Inc. (Darien, IL) and was functionalized via attachment of diphosphonic
acid groups. The Diphosil concept was created by E. P. Horwitz and coworkers
in work funded by the U. S. Department of Energy, Office of Energy Research,
Division
of Chemical Sciences.
A s expected from past radiotracer work by Chiarizia and coworkers, our
metal ion luminescence work showed that this material strongly sorbs f-element
ions from nitric acid solutions. In addition, we obtained the first evidence
that heating metal ion-loaded Diphosil beads collapses their gel structure
and encapsulates the metal ions in fused silica. The reflected light color
photomicrographs below compare as-received Diphosil (the image on the
left) to Diphosil that has sorbed heavy metal ions from nitric acid solution
and then been heated to achieve densification (click on the image for
additional information).
 Ecapsulation
via thermal densification was achieved at a significantly lower process
temperature (1273 K) than that needed for making borosilicate nuclear
waste glass (~1600 K) or bulk fused silica (~2000 K). Unexpectedly,
we found that Diphosil sorbs trivalent metal ions from concentrated phosphoric
acid. Our work has shown that thermally densified Diphosil is a strong
candidate for treating spent solutions from the nitric-phosphoric acid
oxidation process being developed at Westinghouse Savannah River Company
for volume reduction of 1 million pounds of Pu-238 contaminated nuclear
waste.
Return to Heavy Element Photophysics and Photochemistry
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