Uranium solubility in water saturated granitic melts has been experimentally determined under T = 750 - 1000 Centigrade degrees, P = 200 - 400 MPa, (Na+K)/ Al molar ratio in melt = 1.0 - 1.6 and oxygen partial pressure varied from -4 to -17 (in logarithmic units). Saturation level of melts in respect to uranium varies in range of 0.03 - 12.0 weight %. It increases with rise of temperature, oxygen fugacity and alkalinity of melt but decrease of total pressure. Solubility of uranium in haplogranitic melt of normative composition albite (40 wt. %) - orthoclase (26 wt. %) - quartz (34 wt. %) at p - 200 MPa and NNO oxygen buffer may be described by the following empirical equation: lg U (ppm) - 5.10 - 2700/T, where T is temperature in Kelvin scale. Comparative analysis of solubility of U, Th, Zr, and Ree in granitic melt is carried out. The possibility for magmatic uranium dioxide (uraninite) formation at the final stage of granitic melt crystallisation is shown. Role of uraninite bearing granites in genesis of hydrothermal uranium deposits is discussed.
Using redox titration analysis of uranium bearing quenched glasses and their study with optical spectroscopy method valent state of uranium in water-saturated granitic melts has been quantitatively determined. Runs were performed under 750 Centigrade degrees, 200 MPa water vapour pressure, oxygen fugacity was controlled by various solid phases buffers in range, in logarithmic units, from -4 to -17. It was determined that uranium exists in melts as ions of three valent states: U(IV), U(V) and U(VI). The amount of each valent form depends on oxygen fugacity value and composition of the melt, in the first turn its alkalinity. The most of natural granitic magmas were formed under restricted range of oxygen fugacity corresponding to values of QFM or NNO buffers. In these conditions U(IV) dominates among the other valent forms dissolved in melt. Role of the other valencies is significant under more oxidizing conditions and especially in alkaline granitic melts.
Data on uranium valent forms in alumino-silicate, alumino-phosphate and boro-silicate glasses considered as appropriate matrixes for High Level Wastes immobilization have been analysed. Peculiarities of uranium valent state in water-bearing and "dry" glasses are discussed.