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Uranium was immobilized with hydroxyapatite and the dissolution stability of the immobilization product was investigated. The immobilization efficiency and capacity of U were respectively almost 100% and 105 mg/g at the optimal conditions that were experimentally determined. Meta-autunite was found in the mineral phases of the immobilization product, and its dissolved concentration of U was below 0.1 mg/L pH of 5–7 and only 34 μg/L from the toxicity characteristic leaching procedure (TCLP) test. A thermodynamic model of dissolution was established to reveal the mechanism of high dissolution stability of the immobilization product. [ABSTRACT FROM AUTHOR]

Citric acid and oxalic acid, the main metabolites of fungi, have different leaching effects on uranium ore. Herein, uranium leaching from a volcano-litho-type uranium ore using citric acid and oxalic acid was studied by performing soaking experiments in incubator shakers using pure water and H2SO4 as controls. The citric acid is advantageous over oxalic acid in terms of the uranium leaching rate (97% and 67%) and speed for 20 days of leaching. These findings will help optimize the isolation and cultivation conditions of organic acid-producing fungi used for uranium leaching. [ABSTRACT FROM AUTHOR]

We evaluated uranium bioleaching from low-grade, granite-type uranium ore using mixed acidophilic microbes from uranium mine leachate. A 4854-ton plant-scale heap bioleaching process achieved sustained leaching with a uranium leaching efficiency of 88.3% using a pH of 1.0-2.0 and an Fe dosage of 3.0-5.5 g/L. Acid consumption amounted to 25.8 g HSO kg ore. Uranium bioleaching follows a diffusion-controlled kinetic model with a correlation coefficient of 0.9136. Almost all uranium was dissolved in aqueous solution, except those encapsulated in quartz particles. Therefore, heap bioleaching by mixed acidophilic microbes enables efficient, economical, large-scale recovery of uranium from low-grade ores. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The smaller uranium ore particle size led to the faster leaching rate of uranium. • The maximum uranium extraction was 64.85% with ore particle size of <15 mm. • Uranium bioleaching process followed a diffusion-controlled kinetics model. Abstract This study evaluated the effectiveness of ore particle size on column bioleaching from low-grade uranium ore using an indigenous Acidithiobacillus ferrooxidans , isolated from local uranium ore. The uranium content was 0.033% by weight and ore particle size was crushed to <50 mm, <30 mm, and <15 mm. The additive content of sulfuric acid 5 g/L, Fe3+ dosage of 5.0 g/L, spray strength of 2.57 L/(h·m2) and temperature of 25 °C were controlled. After 150 days of leaching, acid consumption amounted to 2.73 g H 2 SO 4 per kg ore, the obtained maximum uranium extraction was 64.85% with the ore particle size of <15 mm. The results showed that a smaller particle size ore had a higher uranium extraction and that an economic uranium extraction can be obtained by correctly controlling the ore granularity. [ABSTRACT FROM AUTHOR]