| The spatial distribution of heavy metal in soil micro environment is effected by the distribution of aggregate in the soil. What's more, the environmental risk of heavy metal is influenced by the species and the distribution of different proportion of different species except of the total amount. Sequential extraction method can characterize the species of heavy metals in chemical level. This process is a non in situ analysis, and related to the selection of extracting agent. The species in this method can only represent the operation species and not the real state the heavy metals in soil. And there is some limitation on the extraction, because many factors will influence the extraction procedure, and it is difficult to compare the result of extraction among different samples. And Synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS) is widely used in the detection of trace elements in environmental samples terms for its in-situ, non-destructive, trace and other characteristics.In this paper, the state of heavy metals in polluted soil was studied combined the sequential extraction and XAFS, and the results were summarized as follow:1. The typical pollution area in this research was selected by the pollution level, that LF is the light pollution, YJ is the moderate pollution, while SM region is the serious pollution area.2. The research of soil aggregate has shown that the distribution of different aggregate in different regions was the same, and it presented as an N type, the >4 mm particle size fraction was the highest, and the< 0.053 mm particle size fraction was the least, The distribution of heavy metal in different particle size fractions was basically the same. With the decrease of particle sizes, the content of heavy metals increased gradually. In the research of distribution factor, the distribution factor of F6 particle size fraction was higher than other fractions except for Cr, and this showed that the heavy metals are more easily to enrich in F6 fraction.3. The typical sample was selected to further study the lead species in different particle size fractions. The result of sequential extraction showed that the species of Pb was not changed with the change of particle fraction. The distribution of lead species in different particle size fractions was Fe/Mn oxides with state> carbonate combination state> organic combination state> residual fraction> water soluble?exchangeable. The result of correlation analysis showed that the residue was significantly negatively correlated with the total content of Pb, the Pb in Fe/Mn oxidation with S and the organic with total C were highly significant positive.4. Studies by XANES showed that the spectroscopy of lead in different particle size fractions was similar, which showed that the Pb in different particle size fractions presented as similar species. The Pb in the soil was was the mainly formed by Pb2+. Through principal component analysis, the possible components of Pb in soil were PbO, Pb3O4, PbO2, Pb(OH)2 and PbSO4. Analysis of linear combination fitting showed that the PbSO4 was the domination species with 41.3%-46.7%, and then were Pb(OH)2 and PbO, which accounted for 27.5%-39.2%and 15%-27%, respectively. Pb3O4 was only found in F5 fraction with about 8.2%, and the PbO2 did not exist in any particle size fracitons.5. Combined the sequential extraction with XAFS results, it is inferred that most of Pb in soil is in the form of sulfide, and will be absorbed on the iron manganese oxide or iron oxide, while the residue is mainly exist in the form of PbO.6. The Fe in soil was performed as +3 valence. The domination species of Fe in soil were Fe2O3 and ?-FeOOH. The total proportion of these two species in the soil were up to 75%-85%, which indicated that Fe in soil were mainly existed as oxides and hydroxides. The correlation between Fe and Pb performed as a positive correlation, which showed that Fe had some effect on the environment behavior of lead in soil. |
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