| With the further understanding of greenhouse effect,countries endeavor to adjust the energy structure.Meanwhile,nuclear energy,as the most potential energy source,has developed rapidly.The uranium mines that have been proved are sufficient to solve the energy crisis facing humankind.However,the mining of uranium ore will generate a large amount of waste slag.At present,these slags are piled in open landfill sites.Under the influence of natural conditions such as rainfall and wind erosion,the diffusion and migration of uranium and thorium in the site may pose a threat to the surrounding ecological environment.In this study,a decommissioned uranium landfill site in Jiangxi Province was selected as the research object.The physical and chemical properties of the uranium slag were analyzed through various characterizations,and digestion experiments,sequential chemical extraction experiments,static acid leaching experiments,and dynamic simulated column leaching experiments were performed.Quantitative analysis of uranium and plutonium in uranium slag revealed the uranium and plutonium diffusion and migration rules and influencing factors in the uranium landfill,and obtained the following research results:(1)Through characterization,it can be seen that uranium slags of different depths and particle sizes are basically similar in morphology,composition,and elements.Some physical and chemical properties have regular differences due to different sampling point and depths,such as large uranium slag particles and uneven particle size distributions,as well as fine and evenly distributed particles of deep uranium slag.The surface uranium slag has a low water content(the uranium slag with a sampling depth of over 30 cm is less than 10%),and the deep uranium slag has a relatively high water content(the uranium slag with a sampling depth of 80 cm has a water content of 47.64%).(2)According to relevant national standards,the average pH of this uranium slag is 8.98,which is weakly alkaline.According to the results of the digestion experiment,it can be known that the uranium plutonium in the uranium slag landfill site is mainly concentrated in the surface uranium slag,and he uranium plutonium content at the sampling point of the uranium slag discharge outlet is significantly higher than other sampling points.What else,the content of uranium and thorium in more than 95% uranium slag is higher than the relevant standards in China.(3)Based on the Tessier extraction method,uranium of different occurrence forms is extracted step by step.Due to the influence of the production process and the storage environment,the content of uranium in each occurrence form of some uranium slag is significantly different.The content of inert uranium in uranium slag accounts for more than50% of the total uranium in the sample,and the content of active uranium accounts for about 25% to 30% and the potential active uranium accounts for 15% to 20% of the total uranium respectively.(4)In this study,the static leaching of uranium slag with acidic rainfall at different pH was stimulated.The pH of the initial leaching solution can affect the solution acid-base system and the diffusion and migration of uranium and thorium elements,and the particle size of uranium slag is the main factor affecting the uranium leaching amount.(5)Uranium slag was dynamically leached by simulating rainfall at different pH.Leachate with a slightly acidic pH promoted the release and migration of uranium.Comparing the changes in the pH of the leachate,it was found that the pH of the leachate with a relatively neutral pH has a small fluctuation range,and the uranium slag has a certain buffering capacity for external acid rain. |
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