Rare-earth element fractionation in uranium ore and its U(VI) alteration minerals. (December 2017)

• Record Type: Journal Article
• Authors: Balboni, Enrica; Simonetti, Antonio; Spano, Tyler; Cook, Nathaniel D.; Burns, Peter C.
• Is Part Of: Applied geochemistry. Volume 87(2017)
• Page Start: 84
• Page End: 92
• Publication Date: 2017-12
• Subjects: Uranium ore -- Uranium ore alteration -- Extraction chromatography -- ICP-MS -- Rare-earth elements fractionation; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2017.10.007
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: A cation exchange chromatography method employing sulfonated polysterene cation resin (DOWEX AG50-X8) was developed in order to separate rare-earth elements (REEs) from uranium-rich materials. The chemical separation scheme is designed to reduce matrix effects and consequently yield enhanced ionization efficiencies for concentration determinations of REEs without significant fractionation using solution mode-inductively coupled plasma mass spectrometry (ICP-MS) analysis. The method was applied to determine REE abundances in four uraninite (ideally UO2 ) samples and their associated U(VI) alteration minerals. In three of the samples analyzed, the concentration of REEs for primary uraninite are higher than those for their corresponding secondary uranium alteration phases. The results for U(VI) alteration minerals of two samples indicate enrichment of the light REEs (LREEs) over the heavy REEs (HREEs). This differential mobilization is attributed to differences in the mineralogical composition of the U(VI) alteration. There is a lack of fractionation of the LREEs in the uraninite alteration rind that is composed of U(VI) minerals containing Ca 2+ as the interlayer cation (uranophane and bequerelite); contrarily, U(VI) alteration minerals containing K + and Pb 2+ as interlayer cations (fourmarierite, dumontite) indicate fractionation (enrichment) of the LREEs. Our results have implications for nuclear forensic analyses since a comparison is reported between the REE abundances for the CUP-2 (processed uranium ore) certified reference material and previously determined values for uranium ore concentrate (UOC) produced from the same U deposit (Blind River/Elliott Lake, Canada). UOCs represent the most common form of interdicted nuclear material and consequently is material frequently targeted for forensic analysis. The comparison reveals similar chondrite normalized REE signatures but variable absolute abundances. Based on the results reported here, the latter may be attributed to the differing REE abundances between primary ore and associated alteration phases, and/or is related to varying fabrication processes adopted during production of UOC. Highlights: Extraction chromatography method developed to separate REE from U rich matrix. Determination of REE concentration in four uranium ore samples and their associated U(VI) alterations. REE fractionation may occur between uranium ore and its associated alteration. Differential mobilization of LREE over the HREE attributed to differences in mineralogical composition of U(VI) alteration.