Abstract
Naturally occurring uranyl silicates are common constituents of the oxidized parts (i.e., supergene zone) of various types of uranium deposits. Their abundance reflects the widespread distribution of Si4+ in the Earth’s crust and, therefore, in groundwaters. Up to date, 16 uranyl silicate minerals are known. Noteworthy is that the natural uranyl silicates are not extremely diverse regarding their crystal structures; it is a result of possible concentrations (activity) of Si4+ in aqueous solutions derived from dissolution of primary Si minerals or the composition of late hydrothermal fluids. Therefore, in natural systems, we distinguish in fact among two groups of uranyl silicate minerals: uranophane and weeksite-group. They differ in U:Si ratio (uranophane, 1:1; weeksite, 2:5) and they form under different conditions, reflected in distinctive mineral associations. An overview of crystal-chemistry is provided in this paper, along with the new structure data for few members of the uranophane group. Calculations of the structural complexity parameters for natural uranyl silicates are commented about as well as other groups of uranyl minerals; these calculations are also presented from the point of view of the mineral paragenesis and associations.
Highlights
Uranyl silicates minerals are typical representatives of the oxidized parts of uranium deposits worldwide [1,2,3,4,5], forming during oxidizing weathering of uraninite, ideally UO2, or coffinite, ideallyU(SiO4 )
Besides the important role that uranyl silicate minerals play in the evolution of U deposits and controlling the mobility of U in their oxide-zones [6], they were identified as alteration products of spent nuclear fuel, which may have a significant impact upon the mobility of U and other radionuclides under geological repository conditions [7,8,9,10]
With increased attention many synthetic uranyl silicate compounds have been synthesized, usually with crystal chemistry divergent from the natural ones [23,24,25,26,27,28,29], and both experimental [30,31,32] and theoretical studies [33,34] have been undertaken in order to determine the thermodynamic properties of uranyl silicate minerals
Summary
Uranyl silicates minerals are typical representatives of the oxidized parts of uranium deposits worldwide [1,2,3,4,5], forming during oxidizing weathering of uraninite, ideally UO2 , or coffinite, ideally. The crystal-chemistry of uranyl silicates attracted much attention for a long time [11,12,13,14,15,16,17,18,19,20] namely in connection with the increased attention due to spent nuclear fuel waste management. Infrared and Raman spectroscopy data for natural uranyl silicates have been reported by [21] and recently by a thorough review of Raman spectroscopy of uranyl minerals and phases [22]. This paper aims to provide an overview of the known naturally occurring uranyl silicates, their mineralogy and crystal chemistry (including new crystal-structure data) and their complexity Minerals 2018, 8, 551 measures) with some implications for their occurrence It provides new diffraction data for sklodowskite, cuprosklodowskite, oursinite, and soddyite, including refinements of the H atoms, which remained undetermined for some of them until now. It aims to overcome a few inconsistencies regarding the structures and mineralogy of natural uranyl silicates that still appear in the literature
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
