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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]

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]

Bioleaching has lots of advantages compared with traditional heap leaching. In industry, bioleaching of uranium is still facing many problems such as site space, high cost of production, and limited industrial facilities. In this paper, a continued column bioleaching system has been established for leaching a certain uranium ore which contains high fluoride. The analysis of chemical composition of ore shows that the grade of uranium is 0.208%, which is lower than that of other deposits. However, the fluoride content (1.8% of weight) is greater than that of other deposits. This can be toxic for bacteria growth in bioleaching progress. In our continued multicolumns bioleaching experiment, the uranium recovery (89.5%) of 4th column is greater than those of other columns in 120 days, as well as the acid consumption (33.6 g/kg). These results indicate that continued multicolumns bioleaching technology is suitable for leaching this type of ore. The uranium concentration of PLS can be effectively improved, where uranium recovery can be enhanced by the iron exchange system. Furthermore, this continued multicolumns bioleaching system can effectively utilize the remaining acid of PLS, which can reduce the sulfuric acid consumption. The cost of production of uranium can be reduced and this benefits the environment too. [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]

Abstract: A mesophilic acidophilic consortium was enriched from acid mine drainage samples collected from several uranium mines in China. The performance of the consortium in column bioleaching of low-grade uranium embedded in granite porphyry was investigated. The influences of several chemical parameters on uranium extraction in column reactor were also investigated. A uranium recovery of 96.82% was achieved in 97days column leaching process including 33days acid pre-leaching stage and 64days bioleaching stage. It was reflected that indirect leaching mechanism took precedence over direct. Furthermore, the bacterial community structure was analyzed by using Amplified Ribosomal DNA Restriction Analysis. The results showed that microorganisms on the residual surface were more diverse than that in the solution. Acidithiobacillus ferrooxidans was the dominant species in the solution and Leptospirillum ferriphilum on the residual surface. [Copyright &y& Elsevier]