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Aiming at recovery of uranium (U) from low-grade uranium ore with a high fluorine content, column bioleaching of uranium extraction with an indigenous mesophilic consortium was studied. The performance of the bacterial community and the effect of chemical parameters on column bioleaching of uranium were investigated. The results showed that U extraction reached a high value of 95.69%, including acid preleaching (65.53%) and bioleaching (30.16%), in a 124-day period of the leaching process. The composition and diversity of the bacterial community were found to be significantly changing in the acid preleaching and bioleaching stages; nevertheless, they existed in residue and pregnant leaching solution samples for the same stage and showed little difference. Additionally, dominant genera in the solid samples, including Stenotrophomonas, Pseudomonas, Brevundimonas Clostridium_sensu_stricto, Bacillus, Clostridium XI, and Acidithiobacillus, and the Acidithiobacillus genus were ubiquitous throughout the leaching column, which was in favour of U extraction. [ABSTRACT FROM AUTHOR]

Due to high content of carbonate and sulfide in ore, precipitation of calcium compounds is blocking the in-situ leaching system at Mengqiguer sandstone type deposit. Autoclave CO2 + O2 leaching tests were conducted in respecting the blockage and uranium migration. Result shows that: Most uranium was recovered within the first hour. Calcite and dolomite precipitated in the initial stage of leaching because of high pH value. As pH decreases rapidly after CO2 injection, calcite and dolomite did not precipitate. Gypsum is not saturated during the whole test. HCO3-, pH and Eh, controlled by CO2 + O2 injection are key factors influencing uranium leaching. [ABSTRACT FROM AUTHOR]

In order to optimize conditions for bioleaching of the high-fluorine and low-sulfur uranium ore by the test acidophilic consortiums, the central composite design method and response surface method were applied to study the relationships between pyrite addition, pulp density, temperature and uranium recovery rate, respectively. The results showed that the pulp density, pyrite addition and temperature had a significant impact on the uranium recovery rate. The predicted optimum uranium leaching conditions were 2.20% of pyrite addition, 7.69% of pulp density and 31.90 °C of temperature, respectively. The actual uranium leaching rate under the optimal conditions was 94.84%, which was consistent with the predicted values with the model (95.21%). The results were of great significance for a large-scaled bioleaching practice of the high-fluorine and low-sulfur uranium or low-grade uranium ore. [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]

Due to the small size of uranium minerals, the occupations of U4+ and U6+, Th and Pb in uraninite is little studied. The coarse giant uraninite (CGU) from Miyi with size up to 1 cm is one of the best samples for studying uraninite mineralogical property. CGU mainly composed of UO2, ThO2, PbO, CaO. There are three forms of occurrence of U, namely UO2, UO3, and UO2+x; and impurity such as ThO2, PbO, CaO may entering the mineral lattice, which can affect mineral properties and facilitate the chemical reactions during mineralization and leaching processes. [ABSTRACT FROM AUTHOR]