Isolation And Identification Of Predominant Bacteria Of A Uranium Mill Tailing Piles And Its Influence On Leaching Of Uranium

Bioleaching is a new method by which the low-grade ores can be processed economically and eco-friendly. However, there are many factors in the application of uranium bioleaching, such as operational parameters regulation, microbial tolerance and so on. Therefore, it is valuable to screen and culture uranium-tolerant microorganism.This study was aim to isolated predominant uranium-tolerant bacteria from an opencast uranium tailing piles in Shaoguang, Guangdong. It was identified on its colony morphology as well as 16 S r DNA sequence analysis, determined its growth curve and examined for a series of assays including optimum growth conditions, then explored its ability of uranium-leaching and-resistant, and investigated the uranium-tolerant mechanism by SEM and FTIR.The predominant bacteria was identified as Bacillus thuringiensis(Bt). It wan believed that 0~5 h was dead time, 5~27 h log phase, 27~43 h stable phase, and then changed to decline phase. Single-factor growth experiments showed the appropriate temperature, p H and salinity range for the strain growth were 20~30, p H=4.0~10.0 and 0~60 g/L Na Cl, respectively. ℃The uranium-tolerant experimental results indicated that inoculating dosage, p H and the initial concentration of uranium affected the uranium-tolerant capacity. The uranium-tolerant capacity increased with an increase of inoculating dosage. The strain could tolerate to 150 mg/L U6+ at 25%(V/V) incubation amount, initial p H was 4.0 and 30℃ separately. In low uranium concentration wastwater treatment, the removal efficiency was highly to 79.49% for 24 h when bacteria incubation amount was 25% with 5 mg/L uranium.we compared the results of Bt bioleaching with sulfuric acid leaching to explore uranium-leaching capacity. The results showed that the bacteria was better for leaching of uranium at 77.93% leaching rate in 10 h, almost 40% higher than that of acid leaching. In bacteria leaching of uranium test, p H was closer to the optimal growth p H of bacteria, so the higher uranium leaching rate was obtained. Uranium leaching rate was 70.51% at initial p H 7.0. Pulp density had a great influence on bacteria leaching of uranium, when the pulp density was less than 7.5%, the leaching rate was 68.05%. While, the pulp density was more than 7.5%, the highest leaching rate was only 24.13%. Incubation amount also had some influence on uranium bacteria leaching. The optimum leaching rate was achieved when bacteria suspension vs nutrient medium was 1:3.The bacteria morphology of before and after reacting to uranium(Ⅵ) were identified using SEM(scanning electron microscopy), obvious changes had taken place in the surface of the traits, before the reaction the cell surface was smooth, however, it was rough after that. FTIR further confirmed that the amino, carboxyl and phosphate group play an important role in the process of reaction.