Study On The Valence Regulation Of U(?)by Microorganisms Mediated Semiconductor Minerals Under ? Ray Irradiation

There are two stable valence states of uranium in nature,U(?)and U(?).The reduction of soluble U(?)to insoluble U(?)is one of the effective mechanisms to prevent uranium migration.The method of reduction of U(?)by microbial is a supplement and exploration to the current nuclide solidification method,which has a great application prospect.The directional control of heavy metal ions and radionuclide valence by semiconductor mineral photocatalysis has the characteristics of simple operation and environmental protection.The earth's surface layer is a very complex and multiple open system,and inorganic and organic communities are inseparable.The single treatment method of uranium bearing wastewater can not meet the strict environmental protection requirements and the goal of in-situ green pollution control.Therefore,based on the co-existence of irradiation filed,microorganism and mineral in the real uranium mine environment,we carried out the research on the regulation of U(VI)valence by microorganism mediated semiconductor minerals undrer y ray irradiation.This study can provide a reference for the in-situ ecological remediation of radioactive uranium pollution in open-pit mining areas,and also has an important guiding significance for the scientific understanding and evaluation of the environmental and health effects of semiconductor mineral-microbe-uranium system.In this paper,the influence factors and mechanisms of y ray on the photoelectric activity of semiconductor minerals are studied.The biological effects of photoelectrons and irradiation electrons produced by semiconductor minerals on microorganisms were compared and analyzed.The catalytic reduction of U(?)by photoelectrons and irradiation electrons,and the interaction between two kinds of microorganisms and U(?)were researched.The mechanism of U(?)valence state regulation by microorganisms mediated semiconductor minerals under y ray irradiation was explored.The main achievements and conclusions are as follows:(1)The research on the change of photoelectric activity of semiconductor minerals by y ray irradiation was carried out.It was revealed that y ray irradiation can adjust the band gap and change the photoelectric activity of semiconductor minerals.In P25 and sphalerite samples group,energy gap of semiconductor minerals decreased,the ratio of hydroxyl oxygen increased,the transient light response enhanced and the photocatalytic activity improved after irradiation.In anatase sample group,energy gap of semiconductor minerals increased,the transient light response decreased and the photocatalytic activity decreased after irradiation.The main mechanism of the narrow band gap of P25 caused by ? ray is that the oxygen defect produced by y irradiation can form impurity energy level which can be hybridized with the conduction band under the TiO2 conduction band.The spectral response range of P25 becomes wider after irradiation,and oxygen defects promote the effective separation of photoelectrons and holes,which promote the photoelectric activity of P25.(2)It was found that semiconductor minerals play a dual role of protecting cells and providing energy for them under UV-Vis or ? ray irradiation.In the system with photoelectrons or irradiated electrons,the biological survival rate of A.faecalis and K.rosea were significantly higher than that of the control group.Photoelectrons or irradiated electrons could be directly or indirectly absorbed by photoelectric microorganisms.Photoelectrons or irradiated electrons participate in the tricarboxylic acid cycle of microorganisms and generate energy for their own growth and metabolism or survival.There is no difference between irradiated electrons and photoelectrons when they are transferred to the photoelectric microorganism for energy utilization.(3)A measurement system for on-line detection of irradiated electrons that generated by semiconductor minerals under ? ray irradiation was established.The mechanism of the valence regulation of U(?)by semiconductor minerals under ? ray irradiation/simulated sunlight were explored.U(?)can be reduced by irradiation electrons and photoelectrons.The valence regulation of U(?)by semiconductor minerals under ? ray irradiation/simulated sunlight includes two parts:one is that irradiated electrons or photoelectrons are transmitted to U(?)directly or indirectly,which completes the reduction of uranium from sexavalence to tetravalence.The other is that the oxidation of U(IV)by hydroxyl radicals produced by the radiolysis of water.In the aspect of energy utilization,the effective utilization rate of irradiation electrons(irradiation dose rate of 60 Gy/min,t=6.0h)in U(?)reduction is lower than that of photoelectrons(the optical power density of incident light is 100 mW/cm2,t=6.0h).(4)Batch static adsorption experiment were used to investigate the adsorption behavior and mechanism of U(?)by A.faecalis and K.rosea.Both A.faecalis and K.rosea can effectively remove uranium from water.The maximum biosorption capacity of U(?)on A.faecalis was 642.7 mg/g,and that of K.rosea was 367.0 mg/g under the natural light.Under the of ? ray irradiation,the adsorption capacity of U(?)on A.faecalis and K.rosea were higher than that of the natural light.The interaction mechanism of A.faecalis and K.rosea with U(?)consists of four parts:biosorption,biomineralization,bioreduction and intracellular accumulation.In the process of adsorption of U(?),A.faecalis and K.rosea can provide bioelectronics and transfer them to U(?),which could complete the reduction of uranium from hexavalence to tetravalence.(5)The photoelectricity microbe mediated electrodes were constructed.The mechanism of the valence state regulation of U(?)by microorganism mediated semiconductor minerals were investigated.The mechanism of the valence regulation of U(?)by semiconductor minerals mediated by photoenergy microorganism includes three aspects:energy regulation,medium regulation and valence regulation.Energy regulation refers to the fact that P25 photocatalysis plays a leading role in the directional regulation of U(?)?U(?)when the excitation source is a simulated sunlight source.The reduction of U(?)by photoelectric microorganisms plays a leading role in the directional regulation of U(?)?U(?)when the excitation source is y ray.There are three medias could control the valence state of U(?),microbial medium,semiconductor mineral medium and photoelectricity microorganism-semiconductor mineral combination medium.Valence regulation includes the reduction of U(?)to U(?)and oxidation of U(?)to U(?).U(?)can be reduced to U(?)by obtaining bioelectronics,photoelectrons or irradiated electrons from three medias.The oxidation of U(?)to U(?)is mainly due to the hydroxyl radicals produced by radiolysis and the holes produced by semiconductor minerals in the solution system.