| With the continuous development of Chinese nuclear industry,the demand for uranium products is also increasing.During the decades of development of uranium mining and metallurgy in China,a large amount of uranium tailings have been produced.Although the amount of uranium in uranium tailings is very small,the residual radionuclides and other toxic and harmful substances will still affect the surrounding environment with water,gas and?radiation,which will cause great harm to the environment and human health if not disposed of properly.Since the 1980s,the technology of filling mine goaf with uranium tailings has been explored in the field of uranium mining and metallurgy in China,but the direct filling of mine goaf with uranium tailings will face some bottleneck problems,such as radon exhalation rate seriously exceeding the standard,poor mechanical properties and so on.In order to solve the above problems,we optimize the combination of uranium tailings,water,cement and superplasticizer to form uranium tailings filling paste,which is pumped into the mine to fill the goaf.Backfilling of uranium tailings filling paste into mine goaf can not only alleviate the pollution of uranium tailings to the external environment,but also effectively solve the problems of surrounding rock caving and surface subsidence in goaf,and reduce the cost of construction and maintenance of tailing reservoir.By means of sample preparation,sampling test,theoretical analysis and mathematical modeling,this study was studied that the radon transport of uranium tailings filling paste in porous media under heat-moisture coupling.Based on the problem of radon exhalation pollution from uranium tailings filling paste,the results of this study are as follows:?1?Experimental research was conducted on the mechanical and flow characteristics of the uranium tailings filling paste to determine the optimal mixing ratio of the paste that meets the requirements of mechanics and fluidity,and to prepare test samples for the experimental study of the paste migration law.The experimental results show that the optimum ratio of uranium tailings paste filling material to meet the requirements of flow performance is 75%,the ratio of lime to sand is 1:5,and the content of superplasticizer is between 0.6%and 4.4%.The optimum proportion to meet the mechanical properties requirements of uranium tailings paste filling material is as follows:lime-sand ratio is 1:5,superplasticizer content is 1.5%,paste mass concentration is 79%.The above conclusions have certain practical significance and can provide data support for paste filling in mine goaf.?2?Based on the theory of radon migration and diffusion in porous media,a test device for measuring radon diffusion coefficient of paste was developed to study the radon diffusion coefficient of paste filled with uranium tailings.The results show that the radon diffusion coefficient of the prepared uranium tailings filling paste sample is about2.02?10-8m2/s.The radon diffusion coefficient of uranium tailings filling paste is10 times lower than that of uranium tailings,and the radon exhalation rate of uranium tailings filling paste is 51.3 times lower than that of uranium tailings.?3?The microscopic pore structure parameters of the paste filled with uranium tailings were obtained by mercury porosis.the average porosity of the paste samples prepared in this batch is 34.82%.The pore sizes of the prepared paste samples are mostly distributed around 1000nm,and the overall pore size and pore size distribution frequency are consistent with Poisson distribution.The gas permeability of the uranium tailings filling paste sample is measured by using the uranium tailings multi-field coupling percolation tester,and the experimental results show that the gas permeability of the uranium tailings filling paste sample is about 1×10-14m2.?4?There is an obvious coupling effect between the distribution and migration of temperature field,humidity field and radon flux in unsaturated porous media.The radon transport model considering heat-moisture coupling condition is quite different from the conventional model.The higher the relative humidity,the slower the radon flux decreases with the radon migration distance,the radon flux decreases nonlinearly with the temperature gradient,and the radon flux decreases nonlinearly with the increase of radon migration distance.The radon exhalation rate of porous media decreases nonlinearly with the increase of relative humidity,and the relationship between them is consistent withF=F0-F'exp?7?w w0?8?.The radon exhalation rate of porous media increases linearly with the increase of temperature gradient.The effect of temperature gradient on radon exhalation rate is not dominant,and the overall effect is small.The radon exhalation rate of porous media increases sharply with the increase of permeability. |
PDF Full Text Request