| Through the physical and chemical reactions such as dissolution, precipitation, condensation, complexing adsorption after into the sediment, heavy metals can be different chemical form and show different activity. So, the total amount of heavy metals in the environment can not fully reflect the situation of a certain area of heavy metal pollution, the characteristics of biological activity of heavy metal elements in a particular ecological environment, toxic properties and rational chemical forms are more important. At the same time, the existence of a particular form is closely related to the transition and transformation process of organism in surrounding environment. Therefore, to carry out the morphological analysis of uranium and heavy metals in sediments as well as their migration, rational property, biological activity and chemical poisonousness is one of the important theoretical basis for the control of heavy metal pollution in uranium ore.Recarding the uranium mine tailings downstream stream sediment in north Guangdong as the research object, using four different methods for sequential extraction procedure. After that, a comprehensive analysis was carried ou between the extraction effect of four chemical extraction method, discovered that Tessier procedure and standard BCR method had poorer parallelism(relative standard deviation was high and unstable) and higher extraction yield(the of various forms is more than one-step digestion) of uranium extraction. While, modified Tessier and improved BCR had better parallelism and extraction yield. But as a result of miscellaneous steps of modified Tessier procedure, which can easyly introduce more operation error in the process, the improved BCR was selected as a advantageous research method of this paper. Finally, use the procedure to conduct the chemical morphology research of sediment and the surrounding soil and plants for uranium and other heavy metals (chromium, copper, lead, zinc) in uranium ore.It can be found that, the content of U, Cr, Cu, Pb, Zn of different depth and different size in the sediment of mining area are respectively 0.845?1.034 (0.546±0.258) mg/g?0.189?0.957(0.367±0.174) mg/g?0.022?0.134 (0.073±0.032) mg/g?0.098?0.451(0.270±0.129)mg/g?0.141?0.560(0.374±0.146)mg/g. The average content of heavy metals was ordered by U>Zn>Cr> Pb>Cu. After sequentialextraction, uranium primarily in weak acid extraction, chromium was mainly of residue state, copper was given priority to oxidation state and residual state, lead in the shallow sediments (0 to 10 cm,15 to 20 cm) was given priority to the reducible extraction, in the deep sediments (25 to 30 cm,35 to 40 cm,45 to 50 cm) was oxidation extraction, zinc was given priority to the residual state.Simultaneously carried out the assessment of biological activity and potential ecological risk for the sediment samples with the indicators of bioconcentration factors (BCF), mobile element absorption coefficient(MAC) and the potential ecological risk index. The BAC of five heavy metal elements:0.06?BCFu?0.29, 0.14?BCFCr?0.25,0.23?BCFCu?0.25,0.25?BCFPb?0.55,0.29?BCFZn?0.40. MAC respectively was:0.07?MACU?0.34,0.02?MACCr?0.04,0.07?MACCu?0.08, 0.04?MACPb?0.08,0.02?MACZn?0.03. Both showed no strong biological activity. The potential ecological risk index respectively were:130.4?Ei(U)?838.0,10.9?Ei (Cr)?32.6,9.7?Ei(Cu)?38.3,16.9?Ei(Pb)?38.4,3.9?Ei(Zn)?15.7, which uranium got the highest potential ecological risk index. The total potential ecological risk index of studied sediments was 189.4 to 901.9. As a result, the studied sediment samples had serious potential ecological harm to the ecological environment.Through the preliminary study, the heavy metal element concentration in the root of plant(Miscanthus floridulus) and the shallow sediments(0 to 10 cm,15 to 20 cm) has significant correlation at the 0.01 level. The heavy metal element content of plant stem and sediment sample(25 to 30 cm) has negative correlation, which illustrated that plant mainly through the roots to transfer heavy metals from surface soil. |
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