Abstract
Systematic study of the surface chemical properties of uranium minerals is necessary to improve the uranium ore extracting process. The presented work aims to argue geochemistry and acid hydrometallurgy accessibility of uraninite from the Mianhuakeng (MHK) granite-hosted uranium deposit, South China, which provides insight on this ore extracting domain. Mineralogy, geochemical composition, U–Th–Pb chemical age, and uranium deportment of the uraninite were systematically analyzed by using scanning electron microscope with energy dispersion spectrum (SEM-EDS), an electron probe microanalyzer (EPMA), and x-ray photoelectron spectroscopy (XPS). The results showed that uraninite was intergrowth with coffinite, probably due to uraninite being partly metasomatized into coffinite along the fissures. The major element content of uraninite such as for UO2, SiO2, and CaO were 79.46 ± 2.03 wt%, 6.19 ± 1.36 wt%, and 5.09 ± 0.80 wt%, respectively. Single-point U–Th–Pb chemical ages for uraninite grains were calculated with the EPMA data, and the results showed ages ranging from a few million to dozens of million years, indicating Pb loss after uraninite formed. Uranium deportment in uraninite generally existed in the forms of UO2, U3O8, and UO3, and mostly showed high valence states suggested by XPS. Uranium on the surface of the uraninite grain was partially oxidized by sulfuric acid leaching, which led to tetravalent uranium converting to hexavalent uranium, suggesting uraninite in the MHK uranium deposit is accessible to be leached by sulfuric acid.
Highlights
As one type of mostly potential and practical non-fossil energy sources, nuclear energy has irreplaceable advantage, because of low carbon dioxide emissions, and in terms of operating stability relative to traditional fossil energy and renewable energy [1]
The analytical data fell short of 100%. This could be interpreted by the presence of structural water, undetected rare earth elements (REEs) as well as the hexavalent uranium due to the U completely calculated as UO2 [16,41,48,49]
Calcium was most possibly incorporated during crystallization, even if a small part of it could be related to post-crystallization alteration [13]
Summary
As one type of mostly potential and practical non-fossil energy sources, nuclear energy has irreplaceable advantage, because of low carbon dioxide emissions, and in terms of operating stability relative to traditional fossil energy and renewable energy [1]. Mineral processing techniques, which are used to extract uranium from low grade refractory uranium ores, have become a hot spot and are receiving renewed attention [5,6,7,8,9,10]. Nowadays, systematic study of the surface chemical properties of uranium minerals is still rare, which seriously slow down the uranium ore extracting process techniques [11]. It is still not very clear as to how the uranium valence changes during the acid leaching of uranium minerals
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