Study On Adsorption And Migration Characteristics Of U(?) In The Soil Horizons Near Uranium Tailing Impoundment Area

The uranium containing in tailings is easy to enter the soil profile,groundwater and even the ecosystem under the influence of climate such as rainfall,for the tailings in uranium tailing impoundment are often open piled up.It causes great biological toxicity to humans and other living things,so,pollution assessment and decommissioning has become an urgent task to solve those environmental problem of the uranium tailing impoundment which is formed for a long time with backward technology and serious pollution.In order to understand the spatial distribution of U in uranium tailing impoundment soil profile,uranium-free soil samples such as eluvial,illuvial and parent material horizon in Brown red soil profile near a uranium tailing impoundment in south China are used,the adsorption and transport characteristics of U?VI?in different layers of soil profile were studied from static adsorption and dynamic leaching,and the spatial distribution model of U?VI?in soil profile was established.The static adsorption of U?VI?under the influence of adsorption time,initial concentration of U?VI?solution,pH value,temperature and particle size was be discussed,the isothermal adsorption model and the kinetic model were used for the fitting analysis,the physical and chemical properties of the soil horizons were characterized by means of surface area measurement,X-ray fluorescence,scanning electron microscope,fourier transform infrared spectroscopy,and x-ray diffraction;in the dynamic leaching experiment,a self-made one-dimensional dynamic leaching apparatus was used to carry out dynamic leaching experiments the migration ability of U?VI?in different soil layers was compared by means of hydrodynamic dispersion coefficient,dispersion degree,distribution coefficient and hysteresis factor.Meanwhile,the form of uranium in each soil layer was analyzed by BCR method.The main results obtained are as follows:The results of static adsorption experiments showed that the U adsorption capacity of soils is decreased with increased of the depth,which is closely linked to factors such as natural organic matter,constituent elements,carbonate content and pH value in each soil layer.The pH of eluvial and illuvial horizons is 6.2,and the parent material horizon is 4.1 at 25?.The maximum adsorption capacity of three soils to U?VI?are 23.60,22.82 and 13.05 mg·g^-1,respectively.The consequences of thermodynamics and kinetics showed that the adsorption isotherms are more consistent with the Langmuir equation?R²>0.999?and the second quasi order kinetic model?R²>0.98?,and the adsorption process is mainly chemical adsorption.The dynamic leaching experiment showed that the vertical and horizontal dispersion a_L and a_T of the eluvial horizon were larger than those of the illuvial and parent material layer,it indicates that U?VI?has stronger migration and diffusion ability in the eluvial layer.The K_d of eluvial,illuvial,parent material and mixed column were 164.64,187.76,234 and 202.58,respectively.The results are consistent with those of static adsorption,the adsorptive ability of eluvial horizon to uranium is obviously stronger than that of illuvial and parent material layer.The results of BCR analysis showed that with the increase of soil depth,the ratio of organic matter,Fe/Mn and residue bound increased significantly,but the exchangeable state decreased.Furthermore,the organic binding state of uranium and Fe/Mn in the upper eluviation layer can move vertically to the parent material layer under the soil profile.Meanwhile,the high pH value and carbonate content of the parent material horizon block the further migration of U?VI?.The results of this study can be used to a reference for the prevention and control of external uranium or other heavy metal pollution in the soil profile.