Calorimetry and structural analysis of uranyl sulfates with rare topologies

Abstract

Abstract Uranyl sulfate minerals are the most rapidly expanding group of uranium minerals, with dozens of species described in the past decade from the localities of White Canyon, U.S.A. and Jáchymov, Czech Republic. Synthetic analogs of a suite of uranyl sulfate minerals were crystallized, characterized, and the standard-state enthalpies of formation (ΔHfo) were determined. Synthetic lussierite is monoclinic, space group Cc, a = 9.2896, b = 28.685, c = 9.6155 Å, β = 93.504°. Synthetic geschieberite is ortho-rhombic, space group Pna21, a = 13.7408, b = 7.2713, c = 11.5844 Å. The standard-state enthalpies of formation from the binary oxides for lussierite, péligotite, shumwayite, geschieberite, and bluelizardite are –3214 ± 78, –2026 ± 33, –587 ± 22, –966.1 ± 10.9, and –2084 ± 21 kJ/mol, respectively, while the standard-state enthalpies of formation of each phase from its elements are –9743 ± 78, –7220 ± 33, –5255 ± 22, –3916 ± 20, and –7117 ± 21 kJ/mol, respectively. The ΔHfo of péligotite was accurately estimated using the ΔHfo of lussierite, bluelizardite, and literature values of the oxide components of each phase. This implies that estimates can be made accurately of the ΔHfo of uranyl sulfates of minerals without synthetic analogs.