Uranium（V） Compounds Derived from High-Temperature/High-Pressure Hydrothermal Reactions
作者单位：(台湾)中央大学
会议名称：《第十三届固态化学与无机合成学术会议》
会议日期：2014年
学科分类：081704[工学-应用化学] 07[理学] 08[工学] 0817[工学-化学工程与技术] 0703[理学-化学] 070301[理学-无机化学]
关 键 词：uranium(V) silicate germanate oxyhydroxide hydrothermal
摘 要：Most uranium minerals can be classified as oxidized species in which U is fully oxidized to U6+, and reduced species, in which U occurs primarily as U4+. Uranyl silicates are an important group of U（VI） minerals in the altered zones of many uranium deposits.[1] One naturally occurring U（IV） silicate exists, namely coffinite（USiO 4）,[2] which is the most important ore mineral for uranium after uraninite（UO2+x）. Numerous synthetic U（VI） silicates and germanates containing organic amines or alkali metals as countercations have also been reported.[3] In contrast to the U（VI） compounds, the chemistry of materials containing U（V） is considerably less developed owing to the tendency of U5+ to either oxidize to U6+ or disproportionate to U4+ and U6+. We have synthesized a U（V） silicate and a germanate by a high-temperature, high-pressure hydrothermal method in gold ampoules contained in a high-pressure reaction vessel at ca. 600 oC and 170 MPa.[4a],[4b] Following the synthesis of the U（V） compounds, a number of mixed-valence uranium silicates and germanates have been synthesized, for example, a mixed-valence U（IV,V） silicate, Cs[2K（UO）2Si4O12,4c] U（IV,VI） germanate, Cs8U（UO2）3（Ge3O9）3·3H2O,[4d] U（V,VI） germanates, A3（U2O4）Ge2O7（A = Rb, Cs）,[4e] and a U（IV,V,VI） silicate, NaI7UIVO2（UVO）2（UV/VIO2）2Si4O16,[4f] in which three oxidation states of uranium co-exist in one compound. In addition, tetravalent-uranium compounds, Cs2USi6O15 and Cs4UGe8O20,[4g],[4h] were also synthesized. All members in the family of uranium silicates and germanates with the oxidation states of uranium from +4 to +6 have been observed. In addition to silicates and germanates, a mixed-valence U（V,VI） oxyhydroxide, Na5[U5O16（OH）2], was synthesized.[5] This mixed-valence compound is a possible intermediate phase of alteration products of uraninite.