Study On Adsorption And Migration Of Thorium And Uranium In Uranium Tailing Area

In order to analyze the adsorption and migration law of thorium and uranium in a uranium tailing area and its health risks to residents,the soil and water near a uranium tailing were selected as research objects in this study,the specific activities of ²³⁸U,²²⁶Ra,²³²Th and ⁴⁰K in soil and water were determined,as well as gross?and?radioactivity.The distribution of different nuclides was comparatively analyzed.Based on these results,the effective dose and carcinogenic risk of drinking water to the residents and the dose of soil to human was evaluated to assess the health risk of uranium tailing.The indoor static experiment and the dynamic soil column experiment were conducted to study the adsorption and migration of uranium and thorium in soil near the tailing.For further study on the mechanism of adsorption and migration of thorium or uranium on soil surface,the form of the soil was analyzed by Scanning Electron Microscopy?SEM?and Fourier Transform Infrared spectrometer?FTIR?.The main conclusions are as follows:?1?The dispersion degree of gross?content is similar to gross?in 15 water samples from 5 sampling point.The dispersion degree of ²²⁶Ra is bigger than ²³⁸U and is distributed to the right area.The gross?content in the percolation water of the tailing and the tailings sewage treatment plant discharge water is relatively high,in which the tailing sand itself contain a large amount of radionuclides lead to?decay;the ²³⁸U content in farmland water is higher than the first water intake limit specified in GB23727-2009;the gross?and?spctific activity of four drinking water samples satisfied the limit of national standard,and the lifetime cancer risk is at a very low level.?2?The ²³⁸U,²²⁶Ra and ²³²Th and ⁴⁰K and total?and total?specific activities of the 7 soil samples collected in 5 different regions gradually decreased with increasing distance from the tailing.The gross?of soil samples is related to ²³⁸U,²²⁶Ra and ²³²Th.The contents of ²³⁸U,²²⁶Ra and ²³²Th are the highest in the uranium tailing,and the discharge ports on the tailing dam,the tailing entrance and the tailing water treatment plant are gradually reduced,the content of the farmland soil is the lowest,and exposure level of farmland soil to human is lower than the national standard limit;the ⁴⁰K content is close to the background value.?3?The results of static experiments show that pH,contact time,initial concentration and experimental temperature have a great impact on soil adsorption of thorium and uranium.The Pseudo-second-order kinetic model,Langmuir model and Freundlich model have good fittings on experimental datas.For the adsorption of thorium and uranium on soil,R_L is less than 1,which indicate that the soil has good adsorption properties for both thorium and uranium.The calculations of thermodynamic parameters enthalpy change,entropy change and Gibbs free energy show that the adsorption processes of thorium and uranium in soil are spontaneous,endothermic and entropy increasing reactions.?4?In the dynamic experiment,the soil with different scales and different initial pollution levels and with the thorium and uranium,there are two equilibrium periods with constant effluent concentration.Under the condition that the height of the experimental column is constant,before the first equilibrium,the amount of solution consumed to achieve the unit penetration rate increases linearly with the increase of the radii of the experimental columns,and the final breakthrough volume also has a linear relationship with the radii of the experimental columns.These can provide reference for soil pollution control.?5?Both the Yoon-Nelson model and the Thomas model have good fits to the dynamic experiment data,which can make a good prediction for some experimental results.Scanning Electron Microscopy?SEM?analysis revealed that the large gap slice-like rough structure existing in the soil became a relatively large block-like structure after the experiment,combined with Energy Dispersive Spectrometer?EDS?scanning analysis show that was caused by the adsorption of thorium or uranium on the soil surface;Fourier Transform Infrared spectrometer?FTIR?analysis revealed that there are functional groups such as-OH on the soil surface,which could easily adsorb thorium or uranium on the soil surface.