| Summary: | 碩士 === 東吳大學 === 化學系 === 96 === Soil is one of the most important interfaces of natural circulation and conversion for living system in the earth. Unfortunately, the human behavior causes lots of change or pollution that alter soil properties and qualities. This inferior alternation of soil natural status could be defined as soil contaminated sites that need to be remediation.
The pollution of soil, may create many adverse effects toward human health, animal survive, and plants growth. Therefore, adequate remediation is urgently needed to correct or cure as well to prevent, this problem.
Currently, there are many different concepts and methods for adequate remediation. leaching and washing can be used as one of the efficient and effective methods to treat heavy metals polluted soil with larger area, gain favorable economic concern and estimation, shorter treatment time, and with right results, make the treatment to meet the legal requirements.
This research is a study the treatment methods by using leaching as the tool on heavy copper and arsenic contaminated soil. We are using inorganic, organic, and mixed acid as leaching agent, also in consideration very complex factors that may affect the effectiveness of treatment. Thus, we used methods of systemic design such as orthogonal experimental design, plus uniform experimental design to estimate the existing and impact of various variables on remediation. To determine the weight of possible factors qualitatively. As well with Tessier’s sequential extraction procedure, to understand how the target heavy metals’ distribution and movement during the washing and leaching process, not only in quality wise but also for quantitatively.
From the experiments of sequential extraction procedure, we understood cooper concentration distribution in the samples we are testing. Also after the leaching, we found the different types of complexities of metal concentration and the movement, finally, removal from the soil. Based on the results, we could adjust conditions from experimental results and find most suitable parameters to run the leaching procedure. We found also from our preset condition, the estimation parameters, values, and results of using these conditions, are quite close. This, again, offer soil remediation a reasonable methodology and reasoning for further applications.
From the site study, we understood the property testing samples of soil, is sandy. From five heavily contaminated samples, after once leaching with inorganic acid, the removing ratio for copper reached 75.9% level, the best results is using sulfuric acid as leaching agent.
When copper contains in the sample is lower than four times of legal limit, i.e., lower than 1600 mg/kg, the leaching results obtained is met the regulation by using sulfuric acid, inorganic and organic acid in sequence for two leaching. From three samples tested, the best one could reached to 95.7% removing ratio, the averaging removing rate also be as high as 85.9%. Best result could be gained by using sulfuric and citric acid mixture.
For the results from sequential leaching, if using inorganic acid to leaching twice, the second time was less efficient than the first. The second removing rate is only obtained as 48.0%. If the second leaching agent is using the mixed acid, the removing rate is better to reach to 70.3%.
The copper content in these soil samples, after running the sequential extraction procedure, found the amount set much higher percentages in organic matter phase and residual phase when compare with exchangeable, carbonate, Fe-Mn oxides phases. In average, the organic phase with contents more than 30%, and residual phase with roughly 51%. With our leaching conditions used, it is able to leach out the cooper out successfully and effectively. This indicated that the methods we used could be a good approach to remediate the soil contaminated with both copper and arsenic heavy metals.
In summary, the factors affect the contaminated soil are many, thus, good planning in the experimental design is critical for successful action, and with effective work out, one can run smaller number of experiments but find the most important impacts. Thus, in reality, make the remediation a workable one.
This research combined the different experimental design methods, and in addition monitoring the removal of the targeted heavy metal, such as cooper, to facilitate the experiments with workable conditions according to the impact factors. As well, from the experiments done in this study, we also could improve the results by regression analysis to set up most optimal leaching conditions. We conclude that leaching is an efficient way to treat the contaminated soil with practical value.
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