Pollution Characteristics And Environmental Availability Of Uranium In The Soils Around Uranium Mining And Metallurgy

Large amounts of waste uranium rocks and uranium tailings have been produced during uranium mining and hydrometallurgy in China. A large number of chemical residues in tailings, including a large number of radioactive elements uranium. while the corresponding protective measures are used, but many problem of environmental pollution has been reported, waste uranium rocks are generally believed that their radionuclide contents are low, so these rocks are mostly open-air stacked along the valleys, and the percolation-proofing for the pile yards in which they are stored are not commonly done. Therefore, their potential environmental effects have yet not received extensive attention. In this study, the uranium tailings from Hunan Province and waste uranium rock from Guangdong Province,and their surrounding soil as the research object, we analyzed four uranium tailings and five soil profiles(two and the other three are used as background and potential uranium pollution, respectively) around a tailings from Hunan Province, China. We analyzed four waste uranium rock and six soil profiles(two and the other four are used as background and potential uranium pollution, respectively) around a waste uranium rock pile of certain granite-type uranium mine from Guangdong Province, China. We analyze and investigate the release ability of uranium tailings and waste rock. Through the comparison between uranium distributions in these profiles, we quantitively estimated the fluxes of exogenous uranium in uranium-polluted soils. The degree of soil pollution was evaluated on the basis of enrichment factor. In addition, chemical speciations( Ⅰ, exchangeable(including water soluble), Ⅱ, carbonate bound, Ⅲ, organic matter bound, Ⅳ, amorphous Fe Mn oxides / hydroxides bound, Ⅴ, crystal Fe Mn oxides / hydroxides bound,Ⅵ, residue.) and environmental availability(active state(Ⅰ+Ⅱ), potentially active state(Ⅲ+Ⅳ),inert state(Ⅴ+Ⅵ))of uranium in soil profiles have been analyzed by using the sequential chemical extraction techniques. And to explore the correlation between U and p H, organic matter, constant element. This paper provides reference for security evaluation of uranium mining and metallurgy regional, at the same time, the research provide a theoretical basis for the monitoring and management of radioactive elements U in soil.Our results can demonstrate the following points:1) U content in uranium tailings and uranium waste rock is generally higher than the base rock. The activity and potential activity uranium of proportion is more than 60% in uranium tailings and uranium waste rock(uranium tailings is 65.92%~96.02%, waste rock is 65.99%~84.36%), the uranium migration occurs easily under certain conditions, they threat the ecological environment.2) According to the enrichment factor, the uranium tailings and waste uranium rock piles produce a significant radioactive contamination to their surrounding soils(e.g., Uranium tailings: the average concentration of uranium in soil profile Wp2 near pollution source is 65.96 μg.g-1, and 17.36 times as much as its background value, waste uranium rock piles: the average concentration of uranium in soil profile Fp1 near pollution source is 4848 μg.g-1, and 635 times as much as its background value).3) According to the uranium mass transfer coefficient, we can show that the main contribution of pollution in soil by exogenous uranium that comes from the pollution source.4) Overall,surrounding contaminated soil(uranium) in uranium tailings and uranium waste rock has a decreasing trend with the increase of the depth in the soil profile. And the soil central is easy to appear peak. The content’s proportion in soil of active state uranium increases, but, potentially active state uranium proportion decrease when the distance between the soil and the pollution source becomes larger. With the increase of depth, the active uranium were decreased in different soil profiles, but the potential activity of uranium has increased.5)Compared with the background soil, the contaminated soil surrounding uranium tailings and uranium tailings have higher average proportion to the activity uranium. But they have lower average proportion to the potentially active state uranium.6) Overall, the flux of exogeous uranium of the soil is larger when it close to uranium tailings or waste uranium rock. Moreover, large amounts of exogenous uranium is preferentially gathered in the surface layer of soils near pollution source, but dominantly precipitated in the depth of soil profiles that are gradually distant from the pollution source.7) In seven uranium-polluted soil profiles studied, uranium tailings surrounding soil: the proportion of U is more than 40% for the active, plus the potentially active to nearly and more than 90 percent. Waste uranium rock piles surrounding soil: the proportion of U is nearly and more than half for the active, plus the potentially active to nearly and more than 90 percent. The contaminated soil has become the new and more active source of uranium pollution. Therefore, the impact of waste uranium rock piles on the ecological environment should be given full attention.8) In contaminated soil, U has good correlation with p H, organic matter, major elements(Si O2, TFe2O3, P2O5, etc).