| This study takes the original soil from Guangzhou Higher Education Mega Center (HEMC) as the object of condition experiment, then simulates the high concentration of lead pollution of soil in the laboratory and measures the contents of various states and its physical and chemical properties. In order to reasonably optimize the washing fixes, this study takes three types of classical drench lotion as washing repair agent to determine the result including the best reaction time. pH, drench lotion concentration, ratio of compound. Lastly collects the pollution soil sampled from Shangba village, washing the samples with optimum leaching conditions. Then it observes the effect of different drench lotion on the actual contaminated soil. This study has certain reference value in comprehensive treatment and repair of heavy metal pollution of soil. In this thesis, the main results are as follows:1. The soil sampled from HEMC is red soil, whose initial content of Pb is:141.513 mg/kg; the pH is 4.56; the organic matter is about 36.585 g/kg, the CEC is about 18.303cmol/kg, the moisture content is of 3.50%. The soil sand content is 15.80%, the silt clay content is 43.48%, the clay content is 15.72% and the porosity is 54.14%. The data above indicates that the soil is acidic soil, which has a suitable fertility and moderate texture. The soil and water conservation preserving fertility and permeability of the sample are both good, so it is suitable for the experimental conditions of remediation. The amount of soil Pb after simulation is 1883 mg/kg. The weak acid extraction state of Pb is measured 845.612 mg/kg by the improved BCR continuous extraction method, and the state of restored is 613.627 mg/kg; the state of oxidation is 188.508 mg/kg; the residue state is 96.326 mg/kg.2. Experiment shows that best conditions are the reaction time of 12 h and reaction pH 4.5. The best reaction concentration of Na2EDTA and citric acid are both 0.03 mol/L, and that of tea saponin is 2%. Considering desorption kinetics by the data, the best regression model of Na2EDTA and citric acid are constant equation. Their R2 and SE are 0.90322, 0.00460 and 0.82568,0.00930 respectively, which explains that the desorptions are broadly in line with heterogeneous diffusion process.However, tea saponin correlation coefficient of the four kinds of the regression equation is negative, so the fitting result is poor.3.The Pb of simulating polluted soil mainly exist in weak acid extraction state and restored state, accounting for 44.91% and 32.59% of the total. After washing with Na2EDTA they drop to 14.05% and 10.67% respectively; after using citric acid they drop to 15.93% and 17.08% respectively; after using tea saponin they drop to 17.40% and 18.43% respectively. However, the change of oxidation state and the residue state are relatively small, accounting for 10.01% and 5.12% of the full amount before washing. After washing with Na2EDTA, citric acid, and tea saponin, the oxidation state and the residue state reduce to 5.48%,2.73% and 7.75%,3.13% and 8.71%,4.14%. Mixs three drench lotion according to different proportion, both Na2EDTA with citric acid and Na2EDTA with tea saponin have high repair efficiency. The repair efficiency reaches the maximum when compound ratio is 5:5, and the maximum are 87.96% and 81.49%, respectively. The repair efficiency of citric acid with tea saponin remains at 50% to 60%. And increasing by the content of citric acid, the repair efficiency increases gradually, which reaches the maximum value on ratio of 7:3, and the maximum is 56.53%. To sum up, under the same conditions, the chelating ability of Na2EDTA is the strongest in three drench lotions, and the repair efficiency of citric acid is second, and that of tea saponin is the weakest relatively. With the consideration of reducing the dosage of the Na2EDTA, the optimum ratio between Na2EDTA and citric acid is of 3:7, the optimum ratio between Na2EDTA and tea saponin is of 5:5. As the cost of citric acid is lower than that of tea saponin, so the best ratio of citric acid and tea saponin is of 9:1.4. In Shangba village, single factor pollution index of five heavy metals (Pb, Zn, Cu and Ni) excluding Cd are more than 3, and the comprehensive pollution index is 5.02. The data shows that the sampling area achieves high levels of heavy metal pollution. Contents of different forms of lead in contaminated soil are by order of:Residue state> Reduced state> Weak acid extraction state> Oxidation state. The desorption ability of the agents containing Na2EDTA are better. Repair efficiency of tea saponin and citric acid to the actual pollution is inferior to that of simulating soil pollution. Na2EDTA, compound of Na2EDTA and citric acid, compound of Na2EDTA and tea saponin are all ideal repair plan. |
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