A Study of Metal Form Effect on the Efficiency of Extracting Heavy Metals from Soil with Supercritical Fluid
| Autor: | Yi-chen Jiang, 江懿宸 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 Acid flushing is commonly used for removing heavy metals from soil, but it thus creates the anxiety of soil reuse, therefore this research is to use the extraction of supercritical fluid and chelating agents with the control of pH and redox potential to enhance the removal efficiency of heavy metals from soil. The optimal addition of hydrogen peroxide and chelating agent was determined during the solution flushing experiment, and thereafter the condition was used in supercritical fluid extraction process. A non-polluting soil spiked with heavy metals and a practical contaminated site soil was used in this research. The results showed that the increase of hydrogen peroxide concentration in pretreatment, the higher extraction efficiency of chromium from soil. Different kinds of chelating agent (0.05 M EDTA、1% CA、1%CA + 200 mg/L Chitosan) held high extraction efficiency and therefore reveal no difference. When five heavy metals were spiked to the soil, regarding the extraction efficiencies of cadmium, copper, nickel and zinc, EDTA solution was the best compared to other chelating agents; however 10% citric acid solution held the best extraction efficiency for chromium from soil. In practical contaminated site soil study, coordinating the pretreatment of adding 1.4% hydrogen peroxide solution, 1% citric acid with 200 mg/L chitosan solution was illustrated the best solution for chromium removal from soil. In addition, the ratio of soil and flushing solution was studied in this research, the result showed that in the condition of using 1.4% hydrogen peroxide for pretreatment and 1% citric acid with 200 mg/L chitosan used as flushing solution, the 1:30 ratio of soil and flushing solution achieved the required extraction efficiency under the economic evaluation. In supercritical fluid extraction experiment, the extraction efficiency of chromium was about 20~40% without any modifier was not added, but the addition of chelating agent was proved to enhance the extraction efficiencies, however the extraction efficiency increased to more than 93% when methanol was added as modifier during the extraction. The same soil was also spiked with five different heavy metals in the experiment, the chromium was extracted individually 30% during a batch extraction process. Based on these two experiments, the average chromium extracted was about 0.035 mg/gCO2, and the total five metals extracted was about 0.038 mg/gCO2. It was concluded that a certain amount of heavy metals could be extracted by using a specific amount of supercritical fluid no matter a single metal or five different metals was spiked for the extraction. In addition, several concentrations of heavy metals were spiked in the soil for extraction, the partition coefficient of heavy metals between soil and supercritical fluid was determined to be 0.003, therefore the result can be used to determine the requirement of supercritical fluid for extracting specific amount of heavy metals in soil. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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