Aging Study On The Occurrence Form And Migration Law Of Uranium In Tn The Vertical Layers Of Soil In The Uranium Tailings Reservoir

Under the conditions of the coexistence of the energy growth demand of economic development and the pressure of emission reduction and carbon reduction,we have to seek new energy sources,and nuclear energy is one of the ideal energy sources we have found.The increase in the use of nuclear energy has led to an increase in uranium mining and processing activities.With the development and utilization of uranium ore,a large number of uranium tailings ponds have been left.Factors such as climate and natural disasters pose a huge threat to the safety management of uranium tailings ponds.Once leaked,the consequences would be unimaginable.Therefore,the safety protection of existing uranium tailings ponds and post-leaking pollution assessment have become the top priority.In this study,uncontaminated soil samples such as leaching,sedimentation,and parent material layer in the brown red soil profile of a uranium tailings reservoir area in the south were used,and the column was loaded with a single-layer soil sample or a mixed-layer soil sample.The soil column was leached with different uranium source aqueous solutions to simulate the behavioral changes of uranium in each layer of soil after the soil in the uranium tailings reservoir area was polluted,and to explore the effects of different pollution conditions on the occurrence and migration process of uranium in the soil.In order to study the effect of aging on the behavior of uranium in the soil,the chemical distribution of uranium in the soil was studied by the BCR extraction method after 30days and 360 days.The underlying causes of the changes were explored by means of X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscope（SEM）,X-ray fluorescence（XRF）and so on.The main results are as follows:The leaching experiment of uranium-containing simulated liquid shows that the transverse dispersion a _Tof eluvial,illuvial,and parent-material horizons and mixed column are 0.0702,0.0698,0.0252and 0.0424 m,respectively.The longitudinal dispersion a _Lis 0.351 m,0.349 m,0.126 m and 0.212 m,respectively.The transverse and longitudinal dispersion of the eluvial layer is higher than that of the other two layers,U（VI）,and the migration and diffusion ability of the leaching layer is the strongest.The distribution coefficients（Kd）of eluvial,illuvial,and parent-material horizons column and mixed column are164.64,187.76,234,202.58 respectively.It can be seen that the adsorption capacity of U（VI）by eluvial layer is obviously higher than that of the lower two layers.Because the content of organic matter in the eluvial layer is significantly higher than that in the lower two layers,the adsorption capacity of U（VI）is also the strongest.BCR analysis shows that with the increase of soil column depth,the content of reducible,oxidizable and residual uranium increases obviously,while the content of exchangeable uranium decreases.The leaching experiment of leachate in the reservoir area shows that the content of exchangeable uranium increases gradually with the increase of soil column depth,and the accumulation trend of the other three existing forms of uranium is similar to that of simulated water leaching in the reservoir area.The difference is that the content of reducible and oxidizable uranium in each sampling site is significantly higher than that in the simulated reservoir area,while the residual uranium content is significantly lower than that in the simulated reservoir area.The leachate in the reservoir area contains a large number of cations such as Ca²⁺and Mg²⁺.The inorganic colloids formed by these ions in the solution have a significant effect on the migration of uranium in the soil.Many uranyl ions originally located in the upper layer of the soil are absorbed by inorganic colloids and transported to the middle and lower layers of the soil,resulting in a significant increase in the content of reducible uranium and a significant decrease in the content of residual uranium.The aging experiment shows that after one year of aging,the content of soluble uranium in each soil layer increases and the content of uranium in residual state decreases.Air,mica,iron and manganese oxides,organic matter and other substances will have an important impact on the existing form and proportion of uranium in soil,thus changing the adsorption and migration behavior of uranium in soil.