Experimental Study On The Pore Structure Evolution Characteristics And U(Ⅵ) Leaching And Radon Precipitation Law Of Solidified Uranium Tailings In Acid Environment

With the rapid development of nuclear power and national defense industry,the demand for uranium is increasing.Jiangxi,Hunan and Guangdong provinces in south China are the earliest uranium production bases,and a large number of uranium tailings and uranium waste water reactors are stored in uranium tailings ponds.Over time,under the influence of complex external conditions,uranium and other radioactive elements in the uranium tailings reservoir migrate and diffuse through the soil and atmosphere into the surrounding environment,which not only pollutes the surrounding farmland and groundwater,but also affects nearby residents.The physical health of the country has had a serious impact.As the uranium production base gradually moved to the northwest region,the uranium tailings pond in southern China gradually entered the decommissioning management stage.According to the requirements of decommissioning treatment of a uranium tailings pond in the south,Portland cement is used as the main cementing material,and it is solidified with blast furnace slag and metakaolin.The relationship between the compressive strength,U（Ⅵ）leaching rate,radon leaching rate and pore structure of the solidified sample under the soaking environment of acid environment,admixture,dosage and soaking time was studied.The main research contents and conclusions of the paper are as follows:（1）In this paper,the uranium backfilling,Portland cement,blast furnace slag and metakaolin materials such as analysis of physical and chemical properties,on the basis of the above admixtures of physical and chemical properties,the blast furnace slag and metakaolin,graining blast furnace slag+metakaolin（mass ratio of 1:1）in Portland cement by 10%,15%and 20%respectively of backfilling materials content of uranium in curing.（2）The addition of mineral materials can enhance the compressive strength of the solidified body.With the increase of soaking time,the compressive strength of the solidified body samples declines to different degrees.When the soaking time is 60d,the compressive strength of P.O samples is at least 8.073mpa,which all meet the requirement that the compressive strength of the solidified body should not be lower than7Mpa.（3）Along with the increase of immersion time,curing body sample U（Ⅵ）leaching rate gradually decreased,soak time before 30d,U（Ⅵ）reduce the rate of leaching rate faster,as the growth of the soaking time,U（Ⅵ）leaching rate gradually flatten out,when the immersion time is 60d,solidified body sample U（Ⅵ）leaching rate steady at around 1.3 x 10^-4cm/d.（4）In this paper,the closed chamber method was used to measure the accumulated radon concentration of different solidified samples under different soaking time,and then the radon exhalation rate,the radon diffusion length and the radon diffusion coefficient were calculated respectively.Results show that with the increase of dosage of admixture,cumulative radon and radon exhalation rate is reduced,along with the increase of immersion time,a solidified body specimen corrosion degradation,its cumulative radon and radon exhalation rate increases,soak time for 60d,Portland cement sample single radon exhalation rate up to 0.238Bq·m²·s^-1,metakaolin sample single radon exhalation rate lowest 0.114Bq·m²·s^-1,meet the radon exhalation rate after treatment is not greater than 0.74Bq·m²·s^-1.（5）With the increase of the content of admixture,the T₂ spectral distribution curve of the solidified sample shifted to the left,and the peak value,integral area and porosity all decreased.With the increase of soaking time,dissolution reaction occurred in the pore structure of the solidified sample,resulting in the deviation of the distribution curve of T₂spectrum to the right,and the increase of peak value,integral area and porosity.When the soaking time was 60d,the T₂ spectral integral area and porosity of the sample with a content of 20%kaolin were the smallest,which were 6450.48 and 4.170%respectively.The results of this study can provide corresponding reference for the solidification treatment of medium and low-level solid waste in actual projects.