Phase Analysis of Australian Uranium Ore Concentrates Determined by Variable Temperature Synchrotron Powder X-ray Diffraction

Abstract

The chemical speciation of uranium oxides is sensitive to the provenance of the samples and their storage conditions. Here, we use diffraction methods to characterize the phases found in three aged (>10 years) uranium ore concentrates of different origins as well as in situ analysis of the thermally induced structural transitions of these materials. The structures of the crystalline phases found in the three samples have been refined, using high-resolution synchrotron X-ray diffraction data. Rietveld analysis of the samples from the Olympic Dam and Ranger uranium mines has revealed the presence of crystalline α-UO 2 (OH) 2 , together with metaschoepite (UO 2 ) 4 O(OH) 6 •5H 2 O, in the aged U 3 O 8 samples, and it is speculated that this forms as a consequence of the corrosion of U 3 O 8 in the presence of metaschoepite. The third sample, from the Beverley uranium mine, contains the peroxide [UO 2 (η 2 -O 2 )(H 2 O) 2 ] (metastudtite) together with α-UO 2 (OH) 2 and metaschoepite. A core−shell model is proposed to account for the broadening of the diffraction peaks of the U 3 O 8 evident in the samples.

Cation and Lone Pair Order–Disorder in the Polymorphic Mixed Metal Bismuth Scheelite Bi3FeMo2O12

“…This assumes that the highly charged Mo 6+ and Fe 3+ cations have very little mobility over the temperature range of interest. The formation of amorphous intermediates has been previously observed in phase transitions requiring significant atomic displacements . However, as evident from Figure , no amorphization takes place; rather, the tetragonal to monoclinic transformation takes place via a first-order phase transition, with the coexistence of both polymorphs evident over a temperature range of about 157° (366–523 °C), as shown by the refined weight fractions as a function of temperature (Figure a).…”

“…This assumes that the highly charged Mo 6+ and Fe 3+ cations have very little mobility over the temperature range of interest. The formation of amorphous intermediates has been previously observed in phase transitions requiring significant atomic displacements 48. However, as evident from Figure7, no amorphization takes place; rather, the tetragonal to monoclinic transformation takes…”