Study On Release And Mechanism Of Uranium And Thorium From Ta-Nb Tailing Landfill In Jiangxi Province

Tantalum niobium ore belongs to associated radioactive ore,which is accompanied by a certain amount of radioactive uranium and thorium.After strong acid smelting process,the slag has strong acidity,and a large number of radionuclides will be enriched in the tailings.The untreated slag is directly piled up in the open air.After weathering,natural rainfall and surface water erosion,radioactive uranium,thorium and some heavy metal elements are exposed or leached into the soil,which poses a great threat to the ecological environment and human health.In this paper,tantalum and niobium slag is selected as the research object,through a variety of mineralogical characterization analysis methods,tantalum and niobium slag related physical and chemical analysis,simulating natural rainfall,using static immersion experiment and dynamic leaching experiment,respectively,to study the release and migration law of radioactive uranium and thorium,through the preliminary discussion of release kinetics,approximately know the radioactive elements in tantalum and niobium slag,the release behavior and mechanism of elements.The main results are as follows:(1)Through the relevant characterization results: the morphology and composition of tantalum niobium slag change before and after soaking.After soaking,the soluble substances adsorbed on the slag surface dissolve into the solution,and the soaked slag becomes smooth with different particle sizes.After soaking,some elements react and recombine in the solution to form new substances,and the mass fraction of some insoluble metal compounds also increases.The specific activity of tantalum niobium slag before and after soaking is measured,and it is found that the specific activity after soaking is several times higher than that before soaking.The average p H of Ta-Nb slag is 1.79,which is highly acidic.Ta-Nb slag contains a variety of rare metal elements,nonmetal elements,radioactive elements and some salt compounds,and the content of thorium is higher than that of uranium.(2)The results of static immersion experiment shows that: the release of uranium and thorium is opposite,the release of uranium increases rapidly with time,and the release of thorium reaches the peak at the initial stage,and then decreases and increases with time.In the initial stage of immersion,the effect of different p H on the release of uranium and thorium is not very significant.With the progress of the experiment,the lower the p H is,the greater the liquid-solid ratio is,which is more conducive to the release of uranium and thorium.There is an inverse relationship between the temperature and the release amount,the temperature is low,the release is relatively higher,in which the liquid-solid ratio and temperature are the main factors affecting the release of uranium and thorium.The release of uranium is higher than that of thorium,which is due to the relatively stable chemical properties of thorium.The p H of the leaching solution is less than that of the soaking solution,ranging from 2.45 to 2.84,and the change with time is not obvious.(3)The results of dynamic leaching experiment shows that: in the initial stage of leaching,the higher the p H of leaching solution,the greater the leaching amount of uranium and thorium.With the leaching experiment come into middle and later time,the lower the p H of leaching solution,the stronger the release effect of uranium and thorium.Under the leaching action of p H = 4.0 leachate,the cumulative leaching amount of uranium and thorium reached the highest,which were 4.7 mg and 1.42 mg,respectively,indicating that acidic conditions were conducive to the release of elements.The release process of uranium and thorium can be divided into rapid release stage and slow release stage.In the first leaching cycle,the release of uranium and thorium reached the maximum.With the increase of leaching capacity,the leaching concentration of uranium and thorium gradually decreased,and the change trend became more and more stable.The p H of leaching solution is less than that of leaching solution.The p H changes greatly in the first cycle,but not obviously in the latter two cycles.(4)The results of Fick diffusion theory and elovich empirical equation fitting show that the release and migration mode of radioactive elements uranium and thorium in Ta-Nb slag is mainly surface elution,and the source of uranium and thorium in leaching solution is the material adsorbed on the slag surface and easily soluble in water;the release behavior of radioactive uranium and thorium is a heterogeneous external diffusion process,and the release and migration rate of elements in acidic environment is higher than that in acidic environment Faster.