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With the gradual depletion of high-grade uranium resources in southern China, it is necessary to recover uranium from low-grade complex and refractory uranium resources However, the traditional acid mining process has certain drawbacks such as high acid consumption, low uranium recovery, and potential environmental pollution. There is an urgent need to develop new technologies for the extraction of refractory uranium ores. A tonne-scale column bioleaching for low-grade refractory vocanogenic uranium ore containing brannerite and pitchblende was performed. The uranium leaching efficiency reached 85.86% with an acid consumption of only 10.15% after leaching for 130 d. In the bioleaching stage, the Fe3+ concentration had a good correlation with the Eh value; the higher the Fe3+ concentration, the better was the leaching of uranium. The solution pH was kept below 2.5 during the leaching process, which avoided the precipitation of iron and ensured a higher Fe3+ concentration in the solution. Efficient leaching of uranium from UTi2O6 and UO2 was achieved through oxidation of Fe3+ and the action of microorganisms. The results may provide technical support for industrial leaching of low-grade volcanogenic uranium deposits. [ABSTRACT FROM AUTHOR]

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]

The high level of fluorine and low sulfur in the ore could significantly undermine the bioleaching effectiveness. Here, a strategy to improve the bioleaching efficiency by introducing fluoride-resistant mesophilic eosinophils coupled with pyrite supplement was investigated in a bioleaching system with such ore. The results of column and heap bioleaching showed that 89.25% and 90.40% of uranium were recovered with the consortium and pyrite addition, which increased the uranium leaching rates by 13.22% and 8.96% as compared with the sulfuric acid leaching. Hence, it provides a method to improve uranium bioleaching efficiency of the high-fluorine and low-sulfur uranium ore by the consortium adding pyrite. [ABSTRACT FROM AUTHOR]

We evaluated the effectiveness of bioleaching uranium from a low-grade carbonaceous-siliceous-argillaceous type uranium ore using an indigenous iron-oxidizing bacteria, Acidithiobacillus ferrooxidans, isolated from local uranium ore. The effects of initial acidity, pulp density and ferrous ion concentration of the feed solution were investigated. The uranium (U3O8) content was 0.036% by weight. Using uranium ore acidified leachate as medium with initial ferrous ion concentrations of 3 g/L, pH 1.7 and pulp density of 20% as optimal conditions, the maximum rate of dissolved uranium recovery was 85.14%. This approach is thus, suitable for recovering uranium from low-grade CSA ore using bacterial 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]