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Solid solution formation in the metatorbernite–metazeunerite system (Cu(UO 2 ) 2 (PO 4 ) 2− x (AsO 4 ) x . n H 2 O) and their stability under conditions of variable temperature

DOI: 10.1098/rsta.2018.0242 DOI Help

Authors: Joanna Kulaszewska (Loughborough University) , Sandra Dann (Loughborough University) , Peter Warwick (Loughborough University) , Caroline Kirk (University of Edinburgh; The Natural History Museum)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Philosophical Transactions Of The Royal Society A: Mathematical, Physical And Engineering Sciences , VOL 377

State: Published (Approved)
Published: June 2019
Diamond Proposal Number(s): 15103

Open Access Open Access

Abstract: Mineral phases which can be thought of as members of a metatorbernite–metazeunerite solid solution (Cu(UO2)2(PO4)2−x(AsO4)x.8H2O have been identified in radioactive samples from spoil heaps at the uranium mine site in South Terras, Cornwall (grid reference SW935523). A complete solid solution (0 < x < 2) was synthesized by precipitation from solution using uranium (VI) nitrate and copper (II) chloride and phosphoric acid/arsenic acid in the appropriate molar proportions. Refined unit cell parameters determined by Pawley fitting of powder X-ray diffraction data showed a linear variation in the a unit cell parameter according to Vegard's Law, allowing the composition of the natural mineral phases found at South Terras to be determined from measurement of their unit cell parameters. High-resolution variable-temperature synchrotron powder X-ray diffraction studies were carried out at the Diamond Light Source on three members of this solid solution (x = 0, 1, 2) and showed different structural behaviour as a function of composition and temperature. Metatorbenite (x = 0) retains its tetragonal symmetry at low temperatures and dehydrates to an amorphous phase at 473 K, whereas metazeunrite (x = 2) transforms to an orthorhombic phase at low temperatures, regains its tetragonal symmetry on heating to 323 K and undergoes a further transition to an, as yet, unidentified phase at 473 K.

Keywords: metazeunerite; variable-temperature; solid solution; metatorbernite; synchrotron; diffraction

Subject Areas: Chemistry, Materials


Beamlines: I11-High Resolution Powder Diffraction

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