Issue 43, 2020, Issue in Progress

A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany

Abstract

Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany. The former Krunkelbach U mine with 1–2 km surrounding area represents a unique natural analogue site with the rich accumulation of secondary U minerals suitable for radionuclide migration studies from a spent nuclear fuel (SNF) repository. Based on a micro-technique analysis using several synchrotron-based techniques such as X-ray fluorescence analysis, X-ray absorption spectroscopy, powder X-ray diffraction and laboratory-based scanning electron microscopy and Raman spectroscopy, the complex mineral assemblage was identified. While on the surface of granite, heavily altered metazeunerite–metatorbernite (Cu(UO2)2(AsO4)2−x(PO4)x·8H2O) microcrystals were found together with diluted coatings similar to cuprosklodowskite (Cu(UO2)2(SiO3OH)2·6H2O), in the cavities of the rock predominantly well-preserved microcrystals close to metatorbernite (Cu(UO2)2(PO4)2·8H2O) were identified. The Cu(UO2)2(AsO4)2−x(PO4)x·8H2O species exhibit uneven morphology and varies in its elemental composition, depending on the microcrystal part ranging from well-preserved to heavily altered on a scale of ∼200 μm. The microcrystal phase alteration could be presumably attributed to the microcrystal morphology, variations in chemical composition, and geochemical conditions at the site. The occurrence of uranyl-arsenate-phosphate and uranyl-silicate mineralisation on the surface of the same rock indicates the signatures of different geochemical conditions that took place after the oxidative weathering of the primary U- and arsenic (As)-bearing ores. The relevance of uranyl minerals to SNF storage and the potential role of uranyl-arsenate mineral species in the mobilization of U and As into the environment is discussed.

Graphical abstract: A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany

Supplementary files

Article information

Article type
Paper
Submitted
15 Apr 2020
Accepted
11 Jun 2020
First published
06 Jul 2020
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2020,10, 25529-25539

A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany

I. Pidchenko, S. Bauters, I. Sinenko, S. Hempel, L. Amidani, D. Detollenaere, L. Vinze, D. Banerjee, R. van Silfhout, S. N. Kalmykov, J. Göttlicher, R. J. Baker and K. O. Kvashnina, RSC Adv., 2020, 10, 25529 DOI: 10.1039/D0RA03375H

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