Biomineralization Of U(?) By Kocuria Rosea Mediated Photo-Generated Electrons From Semiconductor Minerals Under ?-Irradiation

The rapid development of the nuclear industry led the generation of massive uranium-contaminated wastewater in the environment.In this paper,U???that was easy to migrate was studied,and Kocuria rosea was used as the research object to study its survivability and tolerance on uranium under?-irradiation and natural environmental conditions.Compare with the reduction of U???by semiconductor minerals and the removal of U???by Kocuria rosea in?-irradiation and natural environment,the mechanisms of reduction of U???by photoelectron from semiconductor mineral electrode and the biomineralization of U???by Kocuria rosea were elucidated.The summation of U???removal rate by Kocuria rosea and reduction rate of U???by TiO₂ semiconductor mineral electrode in the irradiated and non-irradiated environments was compared with the U???removalrate of?-irradiation-catalyzedTiO₂semiconductormineral photo-electron-mediated Kocuria rosea,the coupling effect of photoelectron and Kocuria rosea on removal and biomineralization of U???in?-irradiation and natural environment was studied.The main conclusions are as follows:?1?The survivability and tolerance on uranium of Kocuria rosea under?-irradiation was studied.And the results showed that Kocuria rosea still had a high activity after irradiation with an irradiation dose of 6000 Gy and grew normally in the range of U???concentration of 0-100 mg/L,indicating that it had strong radiation resistance and tolerance on uranium.Even under the dual effects of?-irradiation and U???toxicity,Kocuria rosea still had a good activity,so it could be used as a microorganism for later experiments.?2?In the study of photocatalytic reduction of U???by semiconductor minerals in single-chamber,the effect of photocatalytic reduction of U???by TiO₂ and ZnS semiconductor mineral electrodes was compared,and the TiO₂ electrode with better reduction efficiency was selected as the semiconductor mineral electrode for subsequent experiments.The i-t curve and EIS results showed that after the photocatalytic reaction by illumination or?-irradiation,the resistance of the TiO₂ semiconductor mineral electrode transfer electrons increased,and the capacity of electron transmission decreased.Uranium minerals were formed on the surface of electrode,which occupied the active sites of photocatalytic reaction and reduced its photocatalytic activity.According to the analysis of the characteristics of semiconductor minerals after?-irradiation,the reason of reduction ability of U???by semiconductor mineral electrode under irradiation weaker than under xenon lamp photocatalysis was speculated that irradiation promoted the ionization of water molecules to produce hydroxyl radicals that oxidize U???,and at the same time irradiation changed the band gap of semiconductor minerals which made the amount of photogenerated electrons decrease,resulting in a decrease in reduction rate of U???.?3?The results of biomineralization of U???by Kocuria rosea showed that the removal of U???by Kocuria rosea under natural environmental conditions was best at pH=5.0.Increasing the biomass was beneficial to the removal of uranium by Kocuria rosea.and the maximum adsorption capacity was 184.0 mg/g.According to the results of the study,it was presumed that the removal and biomineralization mechanism of U???by Kocuria rosea as follows:firstly,U???was rapidly attracted to the surface of Kocuria rosea through electrostatic action,then adsorbed by phosphate groups,amino groups,hydroxyl groups and carboxyl groups on the bacteria in coordination form,and at the same time interacting with phosphate-containing substances released by the bacteria to form phosphorus-containing precipitation of uranium and then immobilized on the surface of the bacteria.At the same time,part of U???entered the inside of cell and combined with intracellular phosphate to form minerals.During this process,a large amount of the hexavalent uranium was reduced to tetravalent uranium by intracellular substances released by the Kocuria rosea and then settled.The precipitate were UO₂ uranium-phosphate compound.This result indicates that the phosphoric acid or phosphate group were the major biological group that causes the biomineralization of U???by the Kocuria rosea.In the case of?-irradiation,due to the large number of wrinkles generating on the surface of the Kocuria rosea,the surface area of the bacteria increased,which made the adsorption sites increase,so the removal rate of U???by the Kocuria rosea under irradiation was increased.However,since the phosphate group was reduced by irradiation,the biomineralization of U???by the Kocuria rosea was inhibited.?4?The results of biomineralization of U???of?-irradiation-catalyzed TiO₂semiconductor mineral photo-electron-mediated Kocuria rosea showed that the photogenerated electrons from semiconductor mineral and Kocuria rosea had synergistic effects on the removal of U???.However,in the non-irradiated environment,photoelectrons generated by TiO₂ semiconductor minerals promoted the biomineralization of U???by Kocuria rosea,while the the biomineralization of U???was still difficult to carry out in the irradiation environment due to the lack of phosphate group.