| Summary: | 碩士 === 國立中興大學 === 土壤環境科學系所 === 100 === Chromium in soils exist as Cr(III) cation or Cr(VI) oxyanion forms. Cr(III) is an essential trace element for living organisms, Cr(VI) is toxic, carcinogenic, mutagenic, and teratogenic. The biochar derived from rice straw possessed of high surface area and cation exchange capacity is hard to be decomposed by organisms and plays an important role in the retention of organic and inorganic pollutants. The purpose of this study was to investigate the effect of amendment of rice-straw biochar (RB) into soil on the immobilization of Cr(VI) by mixing 5% RB with Chentsuo (Ce) and Wanho (Wa) soils at pH 2.0-7.0. The isothermal results showed that Cr(VI) was significantly immobilized by RB of the mixtures of the biochar and soils without adjustment pH. However, the increasing pH values resulted in increasing the dissolved organic carbon and in undermining the ability in immobilization and reduction of Cr(VI) by the biochar and soil mixtures. The reduction reaction of Cr(VI) to Cr(III) still had occurred at pH 7.0, supposing that the increasing dissolved organic carbon reduced Cr(VI) to Cr(III). Nevertheless, the immobilization and reduction of Cr(VI) was inhibited by RB of the mixtures under pH 3.0 due to anion competition. The dissolved chloride was increased with the deceasing pH value in both Ce and Wa mixtures. Among the nearly varied concentrations of anions (i.e. sulfate, nitrate, and phosphate) with the pH change in the Ce and Wa mixtures, the concentration of phosphate increased with decreasing pH in the Wa mixtures. Phosphate would more strongly inhibit Cr(VI) from the reduction than other anions (i.e. chloride, sulfate, and nitrate). The results showed that the amendment of RB could enhance Cr(VI) reduction in soils. However, with increaseing pH, the immobilization and reduction capacity of Cr(VI) decreased. Therefore, when rice-straw biochar is used in the remediation of Cr(VI)-contaminated soils for immobilized and redox amount of Cr(VI) is influential.
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