The Migration Characteristics And Impact On Reservior Water Environment Of Radionuclides (U,Th) In 721 Mine Tailings

Dumps of uranium tailings which are opened to the outside environment weathered, leached, runoff and other external effects, and the radionuclide(U, Th) by leaching, uranium tailings will become a potential source of radioactive pollution.This article is mainly about the Xiangshan uranium tailings 721 mine and the surrounding area as the research object, through field investigation, sampling, indoor leaching experiment, simulated rainfall experiment and use the PHREEQC- II software on water chemical composition analysis, content, form of nuclide uranium tailings of distribution, and their migration behavior in water environment of the reservoir area.So,the main achievements are as followings:(1)Tailings sand uranium contents with sampling depth increase gradually, and thorium contents in tailings surface.Static soaking experiments with the volume ratio of 4% sulfuric acid tailing sand in different depth sampling, using spectrophotometric determination of content of leaching solution of U, Th, experiment and leaching solution cannot measure U, Th termination.The experimental results show that: the total tailings leaching of uranium with sampling depth shows a trend of increase in 60 cm content, the largest total uranium leaching. Total extraction of thorium tailings with sampling depth and produced significantly fewer total trend, thorium leaching surface is in the other layers, the main reason is exposed in the air of the tailings of uranium is oxidized to six price, static leaching dissolution precipitation, infiltration, in the deep accumulation, and thorium not elements, and not easy to dissolve, so not easy migration behavior.The leaching process of uranium,thorium analysis,found that the leaching process can be divided into fast leaching stage,slow release phase or s Tab stage,the saturation stage of these three parts,the early experiments will these soluble uranium,thorium in the presence of sulfuric acid into the leaching solution,leading to the leaching solution ion concentration higher,and leaching experiments of uranium,thorium late basic by internal diffusion control,slow leaching,leaching quantity is small.(2)Natural rainfall had a major impact on the leaching of uranium tailings.Under simulated acid rain conditions( p H=4,6), the leaching process of uranium tailings sand was similar.The time of the leaching of uranium tailings by leachate was continuedly increased with increasing depth.The p H of tailings leachate was higher than 8 and uranium in leaching solution was decreased to zero when the p H of leachate used to the experiment was 4.The p H of tailings leachate was higher than 7.85 and uranium in leaching solution was decreased to zero when the p H of leachate used to the experiment was 6.The results showed that the p H of leachate had a major impact on the p H of tailings leachate,and its acidity size would also affect the leaching amount and the exist forms of U in tailings sand.(3)Through the usage of PHREEQC- software of shallow groundwater, surface infiltration water,surface water and tailings leaching solution in the researching area calculation. The results showed that p H and PE value has a decisive influence for form of uranium ions in water distribution.The main changes in p Hassociated with these five forms-UO2F+,UO2F2,UO2F3-,UO2(CO3)34-,UO2(CO3)22-.The contents of UO2F+、UO2F2、UO2F3- reduced gradually with the increase of the p H value.UO2(CO3)34- content increased gradually with the increase of the p H value.When 4<p H<8,UO2(CO3)22- content increased,reached a maximum at p H=8, then began to decrease.This is because with p H increasing, the groundwater environment gradually from weak acid to weak alkaline, uranyl fluoride will gradually increase in precipitation, carbonate ion in groundwater, and combined with the formation of uranyl carbonate, with uranium, dissolved in water.When pe<6, U in the shallow groundwater exists mainly in the form of tohexavalent uranium,but there are also smaller amounts in the form of tetravalent uraniumis..When pe>6, U in the shallow groundwater exists in the form of six valence state,When pe value increased,the doxidation of shallow groundwater enhance,water tetravalent uraniumis in the water oxidized tohexavalent uranium.(4)The main innovation:1) Study migration behavior and existence form of Radionuclide(U,Th) in Uranium Tailings. 2)Calculate different types of water(shallow groundwater,leachate tailings,tailings leachate water and surface water)and study the presence of uranium in the form factor.