Study On Adsorption And Migration Of Uranium In Soil At Uranium Mine Tailings Reservoir

In this paper,the soil surrounding a certain tailing in the south is selecting as the research object.The pH,water content,organic matter,CEC and other chemical and physical properties of soil were measured by experiment.Besides,the effects of initial pH value,initial uranium concentration,adsorption time and organic matter on the adsorption of uranium were measured by static adsorption experiment;characteristics of migration,transformation and distribution in soil under different leaching amounts and pH values were investigated by dynamic migration experiments;and the mechanism of uranium adsorption of soil was discussed by fitting the observation data.The main conclusions are as follows:(1)The soil sample pH from the study area was 4.63,and shows acidic;the water content is 1.39%,which was high;Organic matter content of 46.98g/kg;cation exchange capacity(CEC)was 46.98cmol/kg;total uranium content of 3.21mg/g,which means the soil is uranium contaminated soil.(2)The results of static adsorption experiments show that the initial p H,initial uranium concentration,adsorption time,organic matter,phosphate and soil particle size had a significant effect on the adsorption of uranium.The heavy metal ions of Cu,Cd,Pb and Zn inhibited the adsorption of uranium,and K had no effect on the adsorption of uranium.At normal temperature,the temperature does not have significant effect on the ability of the soil in adsorbing uranium.Under the conditions of adsorption temperature of 25?,0.5g of soil samples of 100 meshes,the initial pH of 5.0,the adsorption time of 8h or more and the initial uranium concentration is 10mg/L,the adsorption rate reaches a maximum at about 96.36%,and adsorption capacity of about 0.1927mg/g.(3)The results of dynamic migration experiments show that the different amount of leaching and different pH leaching filtrate made the different migration distance of uranium in soil.The distribution of uranium speciation in soil was residuals > amorphous Fe Mn oxides/hydroxides > carbonates > organic bounds > exchangeable(including water soluble)> crystal Fe Mn oxides/hydroxides.And the speciation of residuals and the amorphous Fe Mn oxides/hydroxides in the soil was slightly higher than those in the original soil.The content of crystal Fe Mn oxides/hydroxides was the smallest,and the remaining three distribution of speciation of uranium is uneven.(4)The analysis of adsorption mechanism show that the structure of the soil samples remained relatively intact before and after adsorption,and the surface topography of soil was changed.There were a lot of functional groups with negative charge on the soil surface,such as C-N?C-O?C-H and so on,which enhanced the electrostatic adsorption capacity of soil to uranyl ions.The adsorption process of uranium on the soil was dominated by single molecular layer adsorption,and multi-molecular layer adsorption,physical adsorption and chemical adsorption existed side by side.It was suitable to use the Langmuir isothermal adsorption model(R2=0.9954)and the quasi-second adsorption kinetic model(R2=0.9977)to describe the adsorption process.And the adsorption process was spontaneous exothermic process.