Abstract
Coffinite (USiO4) and thorite (ThSiO4) are conspicuous radiogenic silicates in the geonomy. They form U1−xThxSiO4 (uranothorite) solid solutions in zircon-type phase. Investigating the phase-evolution of these minerals is of utmost significance in realizing their applicability in the front-as well as at the back-end of nuclear industries. We carried out a systematic study of zircon- to reidite-type (tetragonal I41/amd to I41/a) structural transitions of U1−xThxSiO4 solid solution, and investigated their mechanical behaviour. We found a unique behaviour of transition pressure with the change in U-Th concentration in the solid solution. The phase transition pressure (p t) is found to be minimum for x = 0.5. We develop the necessary formalism and present an efficient method to estimate the longitudinal and angular distortions of U/ThO8-triangular dodecahedra (snub-disphenoids). We have parameterized two new factors: δ (longitudinal distortions) and σ2 (angular distortions) to quantify the polyhedral distortions. A detailed analysis of U/ThO8 snub-disphenoidal distortions is presented to address such variation of p t with U and Th concentration. We argue that our approach is independent of polyhedral volume and can be used for any AB8 (A: cation, B: anion) type snub-disphenoidal system.
Highlights
Coffinite (USiO4), its Thorium containing counterpart Uranothorite (U1-xThxSiO4) and Thorite (ThSiO4) are conspicuous members of the nesosilicate subclass of actinide silicates
Coffinite, accompanied by Uranothorite solid solutions are major phases frequently encountered as microcrystals in uranium ores[1] which are economically suitable for radiogenic uranium extraction, with the former appearing to be the second most abundant U(IV) mineral on earth
We have used Density functional theory to predict the variation of physical properties of Uranothorite solid solution as implemented in open-source Quantum ESPRESSO suite[37,38,39]
Summary
Coffinite (USiO4), its Thorium containing counterpart Uranothorite (U1-xThxSiO4) and Thorite (ThSiO4) are conspicuous members of the nesosilicate subclass of actinide silicates. Coffinite, accompanied by Uranothorite solid solutions are major phases frequently encountered as microcrystals in uranium ores[1] which are economically suitable for radiogenic uranium extraction, with the former appearing to be the second most abundant U(IV) mineral on earth They exhibit significant differences in physical and chemical environment of formation. Thorite and its high pressure-temperature monazite structured polymorph Huttonite occur naturally, they are a bit scarce relative to Coffinite Both are found as accessory minerals in medium grained metamorphic rocks like schists[3] and sometimes in unusually coarse grained plutonic igneous rocks i.e. in pegmatite, crystallized from magma during the ultimate stage[4,5].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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 call
