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Browsing by Author "Pan, Yuanming"

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    Thorium speciation in titania slag: Implications for environmental remediation and valorisation
    (Cambridge University Press, 2024-11-12) Chadirji-Martinez, Kamil; Hudon, Guillaume; Chernikov, Roman; Heredia, Emilio; Feng, Renfei; Crawford, Andrew; Pan, Yuanming
    Titania slag, produced from smelting placer ilmenite concentrates and used as a feedstock for TiO2 pigment production, contains low levels of radioactivity due to thorium and uranium. This study investigated the distribution and speciation of thorium in Rio Tinto Chloride Slag (RTCS), which contains an average of 170 ppm Th and 16 ppm U, using a variety of analytical methods from powder X-ray diffraction (PXRD) analysis to bulk and laser ablation inductively coupled plasma mass spectrometry (ICP-MS and LA-ICP-MS), electron microprobe analysis (EMPA), quantitative evaluation of materials by scanning electron microscopy (QEMSCAN), Raman spectroscopy, microbeam synchrotron X-ray fluorescence (µsXRF) mapping, synchrotron Laue X-ray diffraction (LXRD) and synchrotron X-ray absorption spectroscopy (XAS). Our data demonstrate that ∼99.4% of Th in the RTCS is hosted by a chevkinite-like Th–REE–Ti aluminosilicate containing an average of 8.05±0.64 wt.% ThO2. The Th–REE–Ti aluminosilicate occurs as acicular (∼0.3×12 µm) or tabular (∼5×15 µm) crystals in association with a Th-bearing aluminosilicate glass (0.41±0.35 wt.% ThO2) as infillings either in interstitials or along the fractures of the main Ti–Fe oxides of the sassite–ferropseudobrookite solid-solution series. The Th–REE–Ti aluminosilicate and associated Th-bearing aluminosilicate glass formed probably during the quenching stage of the titania slag production. LA-ICP-MS analyses and µsXRF mapping show that the main Ti–Fe oxides in the RTCS contain an average of only 0.32±0.60 ppm Th. Future pyrometallurgy operations that utilise Th- and U-bearing heavy mineral sands must consider their environmental effects and mitigate radioactivity. In addition, preferential acid dissolution of the Th–REE–Ti aluminosilicate in RTCS and other titania slags may be used to recover Th and REE for dual environmental and economic benefits.
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    Uranium mineralization in the Thrace Basin, NW Türkiye: Evidence from radiation-induced defects in detrital quartz and synchrotron XRF/ XANES analysis
    (Journal of Geochemical Exploration, 2024-06-30) Tunc, Ayetullah; Yakup, Çelik; Feng, Renfei; Inanç, Olcay; Pan, Yuanming
    The Paleogene-Neogene Thrace Basin in northwestern Türkiye has long been known to host economic gas and oil resources and has recently been reported to potentially host sandstone-type uranium deposits in the Oligocene Sülog ̆lu Formation. The latter discovery raises questions about the source and deposition mechanism of uranium mineralization in the basin. This contribution reports on the results of a detailed electron paramagnetic reso- nance (EPR) spectroscopic study of detrital quartz from four sandstone and one mudstone samples in the Sülog ̆lu Formation and documents the distribution and speciation of uranium using combined microbeam synchrotron X- ray fluorescence maps (μsXRF) and microbeam X-ray near edge structure spectroscopy (μsXANES). The EPR spectra of quartz separates are characterized by the presence of diagnostic radiation-induced defects (i.e., silicon- vacancy hole centers H′3, H′4, and H′7 with gmax = 2.049, 2.034, and 2.018, respectively, and the oxygen-vacancy electron center E′1), formed by the bombardment of alpha particles emitted from uranium, thorium, and their unstable progenies. Moreover, notable decreases in the intensity of silicon-vacancy hole centers in the EPR spectra of quartz separates after partial dissolution with hydrofluoric acid, provide compelling evidence for the circulation of uranium-bearing fluids in the Thrace Basin. The μsXRF and μsXANES data reveal the occurrences of mixed U6+ and U4+ species in hematite partially replacing pyrite aggregates but dominantly U4+ in disseminated pyrite and illite in sandstones of the Sülog ̆lu Formation. These results provide new insights into uranium transport, reduction, and deposition mechanisms, with important implications for better understanding sandstone-type uranium deposits in general and further exploration in the Thrace Basin.