Reactions between cement components and U(VI) oxide
- Univ. of Aberdeen (United Kingdom). Dept. of Chemistry
Reactions between CaO and SiO{sub 2}, representing the principal components of cement, and schoepite. UO{sub 3} {center_dot} 2H{sub 2}O, have been studied in aqueous suspensions at 85 C to evaluate the solubility of uranium at high pH, which is a principal control of the immobilization potential. Supplementary experiments with preformed C-S-H (calcium silicate hydrogel) are also reported. U loadings are in the range 10--80 mol%. Study of the reaction products of 46 compositions has led to the identification of phase compatibility regions. Several solubility-limiting but hitherto uncharacterized CaO-UO{sub 3}-SiO{sub 2}-H{sub 2}O phases are described; their X-ray powder diffraction data are given. The synthetic phases are compared with natural analogues and it is concluded that similarities exist: weeksite- and becquerelite-like structures are probably developed in the synthetics. With formation of crystalline phases, U solubilities decline to 10{sup {minus}8}--10{sup {minus}9} mol/l. Solubilities correlate well with the observed compatibility regions, with lowest solubilities obtained among the uranium-containing phases which are also compatible with C-S-H gel. Some slight U sorption into the gel may occur and is postulated to inhibit its crystallization at 55--85 C. The solubility values are, in general, less than in previous studies which, by omitting SiO{sub 2} from simulants and using relatively brief reaction times, fail to achieve the characteristic immobilization potential.
- OSTI ID:
- 131607
- Journal Information:
- Waste Management, Vol. 15, Issue 3; Other Information: PBD: 1995
- Country of Publication:
- United States
- Language:
- English
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