Study Of Extraction Method For Different Mercury Fractionations In Soil

In this paper, the occurrence of mercury in the soil was systematically discussed. At the beginning of the project, based on the continuous extraction method of Tessier, the risk assessment of a mercury pollution field was carried out by using the Delayed Geochemical Hazard Model?DGH?.In the mercury contaminated field, the total mercury concentration in the soil ranged from 0.0250-44.3 mg kg^-1. The organic binding and residual fractionations of mercury are the main forms of mercury existing in soil,and the mobility fractionation of mercury is between 5.9-9.7%, revealing the potential risk of the site. The correlation analysis between soils and soil physical and chemical properties shows that soil organic matter is a major factor in the distribution of soil morphology, and is positively correlated with the concentration of iron and manganese oxides.Combined with partial correlation analysis, the DGH model was introduced to reveal the potential intrinsic transformation path between mercury forms, which provided more in-depth knowledge for the evolution of risk. The results show that about 10.5% of the sample is out of the DGH critical burst, the risk is relatively low, but which can not be ignored is that the contaminated field DGH critical burst value is very low,thus the risk can not be ignored.Then, for the fractionation analysis method of mercury, four kinds of continuous extraction methods ?Tessier, BCR, CIEMAT and Chinese standard? applied to mercury were selected for their recovery,fractionation distribution and bioavailability identification. On the comparison. The results show that the four methods show a satisfactory recovery rate from the viewpoint of recovery rate, but the seven-step extraction is the lowest due to its cumbersome steps. At the angle of fractionation distribution, both Tessier and BCR show an approximate fractionation distribution, while CIEMAT and Chinese standard methods take into account the humic acid-bound fractionation of mercury and extract them from the organic bound states of mercury. In addition,CIEMAT also takes into account that elemental mercury can not be covered by the other three methods. The results of the partial correlation analysis showed that the correlation between Tessier's fractionations and plant ?Ipomoea aquatic? was consistent with the previous study. The exchangeable fractionation of each method was compared with that of the four methods, are positively correlated with total mercury uptake by plants, and the carbonate-bound fractionation show a relatively weak positive partial correlation with the total mercury absorption of plants,which may be attributed to the mechanism by which plants absorb mercury and the proportion of complexation is higher than acidification.The reduction in the form of mercury in each method is most positively correlated with the total mercury absorbed by the plant, further supporting this conclusion. For the humic acid-bound fractionation of mercury alone, the organic binding states different from mercury are positively correlated with the total mercury that the plant absorbs,revealing more informative information about the bioavailability of mercury in the soil.Finally, based on the CIEMAT method, the optimal extraction of mercury was carried out. The extraction temperature was measured by using nitric acid as the extractant, considering the reaction temperature, the reaction time and the concentration of the extractant. The optimum reaction conditions were determined as follows: the optimum reaction conditions were 70 ?, 5h and the concentration of HNO3 was 3 mol L-1. On the basis of this, the extraction of mercury under this condition was carried out for validation. The amount of mercury extracted from the extract was mainly from the organic binding state. In the correlation analysis, the amount of mercury extracted under this condition was higher than that of the plant, and the amount of mercury extracted from the extract was more than 60% of the total mercury absorbed by the plant. Total mercury has been associated with the definition of the form are showing a high correlation, thus to a certain extent, the optimization method that identifying bioavailable mercury is feasible.