| Microbial leaching technology has been widely used and developed in the field of leaching of metal minerals such as copper and gold,and its leaching mechanism has also been deeply studied.However,the relevant mechanism,influencing factors,leaching kinetics and electrochemical behavior of uranium ore leaching process are insufficient in the field of uranium leaching.In order to study the mechanism of uranium microbial leaching and to improve the leaching efficiency of uranium ore,the bituminous uranium ore in a uranium mine area in southern China was taken as the research object,and the mixed flora of A.ferrooxidans and At.thiooxidans was used as the test strain.The leaching effect of uranium ore in different systems of iron and bacteria and the characteristics of uranium leaching interface were studied by means of shaking flask leaching test,morphology analysis and phase characterization,and the influencing factors and leaching kinetics of uranium ore microbial leaching were systematically studied.The electrochemical behavior of charge transfer and surface passivation during uranium leaching was revealed by electrochemical method.The results of uranium leaching in different systems,such as bacteria Fe3+and aseptic Fe3+,show that the leaching rate of uranium was as follows:bacteria/Fe3+(20%bacteria 1.0 g/L Fe3+)97.01%>aseptic Fe3+(1.0 g/L Fe3+)87.54%>bacteria/Fe2+(20%bacteria 1.0 g/L Fe2+)81.11%>Aseptic and iron-free?dilute sulfuric acid?63.59%.The presence of bacteria is conducive to uranium leaching,iron plays an important role in the biological leaching process,and the biological leaching of uranium is dominated by indirect action.SEM and EDS analysis of ore samples before and after leaching showed that the surface morphology of leaching slag with bacteria and Fe3+system was most seriously damaged by corrosion,and the development of cracks was beneficial to the dissolution of uranium;XRD analysis showed that there was yellow potassium ferric alum precipitation in iron leaching system,thus hindering the contact between uranium ore surface and leaching solution and material transfer.This is not conducive to uranium leaching.Experimental results of influencing factors on biological leaching of uranium ore show that the bacterial inoculation amount,pulp concentration and temperature are the main influencing factors in the bioleaching process,followed by the concentration of pH and Fe2+.Under the optimized conditions of pH 1.8,30?,20%bacterial inoculation amount,10%pulp concentration and 1.0 g/L Fe2+concentration,the uranium leaching rate reached 99.83%.The biological leaching kinetics of uranium ore accords with the JMA model,and the leaching process belongs to diffusion control.Kinetic equation is-ln?1-x?=?1.49700.9027?t0.09310.2884;the oxidation rate and efficiency of bacterial uranium oxide minerals can be improved by controlling the reaction conditions of bacterial ferric oxide and ferric sulfate uranium oxide.The electrochemical behavior of biological leaching of uranium ore shows that the peak current in Fe3+system is obviously higher than that in other systems,the presence of iron promotes charge transfer,which makes bacterial leaching more advantageous.Tafel curve analysis showed that the corrosion potential and corrosion current density of Fe3+were higher than those of the other three systems.However,the polarization resistance is lower than that of other systems,indicating that bacteria and Fe3+can significantly promote the dissolution of uranium deposits.The results of the AC impedance show that the solution impedance RS=21.55?and the transfer impedance of R1=9.03?,all of which are lower than the other three systems,and the oxidation and dissolution of the uranium are more likely to occur.The electrochemical reaction on electrode surface can be promoted by decreasing pH or increasing temperature,inoculating amount of bacteria and concentration of Fe2+which results in a reduction in the resistance to arc radius and the transfer impedance R1.However,excessive temperature will affect the bacterial activity,and excessive pH and concentration of iron may result in the formation of iron colloid substance or yellow potassium ferric alum precipitation,covering the ore surface,increasing the resistance of the ore surface,inhibiting the electron transfer,and hindering the oxidation and dissolution of uranium ore.The results obtained above can be used as a theoretical reference for the study of the electrochemical behavior of uranium ore mining and leaching. |
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