Computer Science
Scientific paper
Apr 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988gecoa..52..863p&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 52, Issue 4, pp.863-875
Computer Science
13
Scientific paper
The solubility of UO 2 has been measured at temperatures from 100° to 300°C under 50 MPa H 2 in water solutions of HCl, NaOH, or LiOH at calculated pH values from 1 to 10. Fluoride contamination invalidated results in the pH range 2 to 4 and is probably responsible for a solubility maximum observed near pH = 3. At pH < 2, solubilities at 200°C and below agree, within combined experimental error, with measurements by and (1978) and et al. (1986a), and fall well within the range selected for amorphous and crystalline UO 2 by (1983). pH dependence suggests predominance of UOH 3+ . Solubilities in alkaline media are much lower than measured or estimated by previous investigators at all temperatures, suggesting that the U(OH) - 5 complex is very weak or non-existent and does not contribute to solubility significantly at any pH < 10. There are no published measurements of the solubility of UO 2 in the neutral pH range at subcritical temperatures. Existing thermodynamic data for the expected hydroxo complexes, U(OH) 4-n n ( n = 2, 3, 4), are estimated ( , 1983; and , 1980; , 1978). When pH = 4 to 8, our measured solubilities are up to three orders of magnitude lower than calculated on the basis of the estimated thermodynamic data for temperatures exceeding 200°C, and up to two orders higher than predicted at lower temperatures. Temperature and pH dependence are statistically insignificant in the experimental results for all pH4, suggesting predominance of the single species U(OH) 4 (aq), and the dissolution reaction. UO 2 + 2 H 2 O = U ( OH ) 4 ( aq ) for which, at all temperatures from 100° to 300°C, log ( K s 4 ) = -9.47 ± 0.3.
Parks George A.
Pohl Demetrius C.
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