| Summary: | 碩士 === 朝陽科技大學 === 環境工程與管理系碩士班 === 100 === Farmlands in Taiwan are seriously polluted by heavy metals, in which, chromium (Cr) is more harmful than the others to human body. Cr exists mainly in the forms of Cr (III) and Cr (VI) in nature, the toxicities of which are significantly different. Cr (III) and Cr (VI) are not differentiated strictly by Taiwan in the regulation of the heavy metal Cr in soil. This study intended to explore the difference of Cr forms in the Cr-polluted farmlands and the removal effects of Cr in different forms cleaned by different cleaning solutions. The results can serve as a reference for the cleaning and treatment technologies of soil pollutions.
This study was divided into four parts: 1) discussion on the distribution difference of the bonding states of Cr in different forms, i.e. anion Cr (VI) and cation Cr (III) in soil with different characteristics; 2) discussion on the transformation of Cr in the soils polluted by Cr (VI) and Cr (III); 3) analysis on the characteristics of the soil with different pollution sources and characteristics, as well as analysis on the bonding states of the heavy metal Cr; 4) removal effects of Cr in different forms cleaned by HCl, citric acid, mixed acid, and other acid pickling agents.
Based on the results, after pretreatment, such as stoving or air drying, part of the heavy metal anion Cr (VI) would transform and reduce into Cr (III) mainly under ferric-manganese oxidation state and organic state. In the currently polluted soil, Cr was mainly in the form of Cr (III), while some farmlands were likely to be polluted by Cr (VI) and Cr (III) discharged from factories. However, under long-term solarization and air drying, most of Cr (VI) and Cr (III) would transform into trivalent Cr. According to the cleaning results, removal effect of Cr in the soil at Zhongxing pollution site in Taichung City by 0.5M citric acid was the best, with a removal rate of 54.5%, followed by mixed acid with a removal rate of 49.1%, and HCl with the poorest removal effect with a rate of 44.47%. Removal efficiency of Cr from Cr-polluted soil by acid pickling was higher under exchangeable state, carbonate state and residual state.
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