1、Bioleaching of low grade uranium ore containing pyrite using A. ferrooxidans and A. thiooxidansAbstract: A process of uranium extraction from ore containing 3.1 % pyrite by bacterial leaching was investigated in shaken flasks during 90 days. The highest uranium recovery amounting to 85.1% was obtain
2、ed using binary mixture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans that was exceeding results obtained by traditional acid leaching technique up to 27 %. High uranium recovery was founded to be due to the high degree of pyrite dissolution that can be readily achieved by bact
3、erial leaching (up to 98.0 %).Keywords：Uranium leaching；Bacterial leaching； Acidithiobacillus ferrooxidans； Acidithiobacillus thiooxidansIntroduction Acid leaching is known to be predominant process for uranium recovery from ores, usually with sulfuric acid because its relatively low cost. Uranium t
4、hat mostly presented in ores in tetravalent state must be oxidized to hexavalent state U(VI) before it can be dissolved. In acid leaching, the uranium oxidation reaction requires the presence of ferric ion, regardless of the reagent used as an oxidant, since that appears that the ferric ion actually
5、 oxidizes the uranium while the oxidant reagent oxidizes ferrous ion to ferric ion 1. So the dissolution of tetravalent uranium in sulfuric acid leaching system follows equation 2:UO2 +Fe2(SO4)3=UO2SO4 +2FeSO4 (1) Various oxidants such as MnO2, NaClO3, H2O2 are widely employed as a ferrous ion oxida
6、nt in uranium leaching processing 3. But these oxidants are very costly or cause very serious environmental pollution than sulfuric acid because of release of heavy metals to the environment. One more alternative to these oxidants is the use bacterial leaching of uranium. The bioleaching of uranium
7、ores arose from the need to develop economically viable processes in treatment of low grade ores. Of the total costs of the process of yellow cake production, 75 % is due to the first steps required to obtain the pregnant solution 3. The importance of having a cheap leaching process can therefore be
8、 understood. The capacity of the micro-organisms which take part in these transformations, principally bacteria of the genus Acidithiobacillus, to grow in highly acidic environment with high heavy metal content makes this technique a very interesting alternative to conventional processes. The only m
9、ain drawback from a commercial point of view is the long contact time needed for the uranium solubilization; if environmental conditions are suitable, the process is autosufficient. In addition, savings of up to 50 % of the operation costs of a conventional plant can be achieved 4. The principle of
10、the method lies in leaching the uranium ore with ferric sulfate produced from the pyrite of the ore by bacterial action and which, in turn, can be regenerated by the bacteria. In other words, during the process in the micro-organisms do not attack the uranium ore directly but create the chemical con
11、ditions necessary for its dissolution. Zajic 5, however, suggests that the bacteria might attack the uranium oxides directly since oxidation is more rapid in the presence of Acidithiobacilli than of ferric iron alone. Recent calorimetric and respirometric research 6 supports this hypothesis, althoug
12、h the rate of such reaction is 30 times less than that of the microbial oxidation of the iron. The literature 79 agrees that it is basically the indirect process which acts in this type of system since, during heap or dump leaching, the direct microbial leaching of the uranium ores is not significan
13、t, as a consequence of the large quantities of ferric iron generated from pyrite. That is to say, the bacterial leaching of uranium ores is two steps process: the bacterial leaching of pyrite and the leaching of uranium ore with the resulting metabolic products of the pyrite biological attack. So it
14、 is clear that this leaching technique can be readily accomplished in heap leaching of uranium ores that contains large amounts of pyrite. Ores of Russian deposit have large amounts of pyrite (up to 10 % wt). That is why in this work an attempt was made to investigate process of uranium bacterial le
15、aching from typical samples of ores.ExperimentalMaterials Sulfuric acid and microbial tests were performed on samples of uranium-bearing candy clay from typical deposits (Russia).The chemical composition of the sand (wt%): 0.052 U, 80.1 SiO2, 10.2 Al2O3, 3.1 FeS2, 0.00 FeO, 0.05 Fe2O3, 1.11 K2O, 0.2
16、1 CaO, 0.07 MgO, 0.17 Na2O, 0.003 MnO, and 0.025 P2O5. The all uranium content in ore was caused by occurrence of coffinite that was founded by means of X-ray diffraction spectroscopy and by making of scanning electron microscopy (SEM) images. In all tests samples of sand were used that had not been grinded. In each bioleaching experiment 1,000 ml of 9K medium according to Mackintosh 10, without
