| Selenium(Se) is an essential micronutrient element for animals and humans. The concentration range between deficiency and toxicity is very narrow. In recent years, selenium poisoning occurred frequently in the world. Research and development of selenium-rich products is getting the extensive attention of departments at all levels. For this reason, to research the adsorption mechanism, migration and selenium biological effectiveness of selenium in the environment is necessary and significant.In this dissertation, firstly, using a modified seven operationally sequential chemical-extraction technique to determine the morphology and valence of the 10 samples in two different kinds soils, which is paddy soil and maize soil, from Ziyang, the selenium-rich core in shanxi province.The results show that the dominant species of selenium from different kinds of soil are sulfide/selenide Se(48.43%) and organic-bound Se(18.74%), in paddy soils the ligand exchangeable Se is relatively high; in paddy soil organic-bound is 30.02% in average higher than that of maize soil which is only 11.40%. Sulfide/selenide Se in maize soil(67.81%) is 3.64 times comparing to that part of paddy soil(18.65%). For the Se valence analysis: water-soluble Se of paddy soil is priority to Se(â…³), whereas in maize soil coexists with Se(â…³) and Se(â…µ); For the organic-bound state, Se coexists in the form of Se(â…³) and Organic-Se.Secondly, based on the analysis of Se morphology and valence state in the soil of ziyang, two typical selenium-rich soils(W1 for paddy soil and H1 for maize soil) were chosen for the further research. In order to analysis of selenium the mechanisms and the possible influencing factors of the adsorption of Se in soil, the ORCHESTRA program was used. By analysis the physical and chemical properties of the soils and reference the ducuments to obtaine the basic parameters of ligand and charge distribution(LCD) model. Then, calculate the activity of Ca and Al of the batch experiments corresponding p H by the ECOSAT. Final adjust the fraction of ORCHESTRA and calculate the concentration of P and Se in the solution.The results showed that Se form inner-sphere surface complexes on aluminum and iron oxide from the soil. Phosphate and Se compete for the adsorption sites on the surface of Fe and Al-oxide is the main reason of the competitive adsorption between them. For the normal p H5~8 for these soils, the model can describe desorption of P well; for adsorption of Se for paddy soil(W1), the p H dependency of adsorption Se can be successfully described with the LCD model, but cannot for maize soil. Whereas considering the influence of Al-oxides, by reduce the parameters K of Se adsorption on goethite for 5 times, the LCD model results can match experimental data much well. This is because the Al contribution proportion in H1 is much higher than that of W1. But for Se desorption of Se-riched soil, the model cannot describe the change. Apart from the factor of organic matter, ratio of Al-oxide, the influence of valance of Se, diffusion action and the simplified of model should be considered. |
