Chemically bonded phosphate ceramics for radioactive and mixed waste solidification and stabilization Page: 4 of 22
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Introduction
Chemically bonded ceramics (CBCs) are materials, which can be
processed at low-temperature (1, 2). Some of the CBCs, such as phosphates of
Mg, Al and Zr are refractory. They are ideal for applications, such as
containment of radioactive waste, where fabrication can be achieved at room
temperature or at warm temperature, but service conditions require stability of
the material at elevated temperatures. Phosphates have high solid solution
capacity to incorporate heavy metal, actinide and rare earth contaminants (3).
Also their very low solubilities of heavy metal, actinide and rare earth
phosphates (4) indicates that phosphate bonded ceramics should be effective
media for stabilizing these contaminants. A natural analogue of monazites and
apatites (5) suggests that phosphates may be natural hosts to radioactive
species and rare earths. Earlier results of leach testing for grouted phosphate
wastes at Argonne, support this view. These favorable properties of phosphates
motivated the present systematic study of this material for applications in
radioactive waste management in our laboratory.
This paper reports the results of an initial investigation of a chemically
bonded Magnesium ammonium phosphate (MAP) ceramic. Its chemistry is
fairly well understood (6 -8). It sets into very hard cement (9). Concretes of this
cement have been developed and their chemical composition (10) and
mechanical properties (11) have been well studied for structural applications.
Connaway-Wagner et al. (12) have compared the properties of magnesia-
orthophosphate and tripolyphosphate cements, and they show that
tripolyphosphates have very high compressive strength of 90 MPa with a
porosity of 16% as compared to the orthophosphate with a compressive
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Wagh, A. S.; Cunnane, J. C.; Singh, D.; Reed, D. T.; Armstrong, S.; Subhan, W. et al. Chemically bonded phosphate ceramics for radioactive and mixed waste solidification and stabilization, article, January 1, 1993; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1313838/m1/4/?rotate=0: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.