| Summary: | 碩士 === 國立臺灣大學 === 農業化學研究所 === 97 === The previous study had found that the soil with high content of Fe-Mn nodules can oxidize Cr(III) into Cr(VI). The effects of content and size of Fe-Mn nodules on its ability of oxidizing Cr(III) were investigated in this research. Besides, we predicted the oxidizing ability of Fe-Mn nodules based on its content of easily reducible manganese (Mnr), and compared with that of pure manganese dioxide. Furthermore, the effects of Fe-Mn nodules on Cr(VI) reduction by organic amendment added to Cr(VI)-contaminated soil was also studied to observe whether Fe-Mn nodules could re-oxidize Cr(III) or not.
The results showed the total Cr(VI) content increased with the Fe-Mn nodules content during the oxidation of 500 mg-Cr(III) kg-1 by different contents of Fe-Mn nodules. Compared with pure MnO2, Fe-Mn nodules could only produce 30 % Cr(VI) of pure MnO2 could. And we also knew that Mnr could not evaluate the oxidizing ability of Fe-Mn nodules. Cr would be adsorbed by soil particles and the available Cr(VI) was only 15 % of total Cr(VI). The results also showed the total Cr(VI) content increased with the Fe-Mn nodules content during the oxidation of 500 mg-Cr(III) kg-1 by different sizes of Fe-Mn nodules, the soil with smaller Fe-Mn nodules (0.2 mm) could produce more Cr(VI) than the larger one (4 mm), because of the well mixed soil and Cr(III) solution and the larger specific surface area. The larger one could still produce 27.6 % Cr(VI) of oxidizing 500 mg-Cr(III) kg-1 during the reaction.
To study the effects of Fe-Mn nodules on the reduction of Cr(VI) by organic matter, we added the soybean meal, which has confirmed its high ability to reduce Cr(VI), into the studied soils to raise 3 % organic matter and to reduce Cr(VI)-contaminated soil which has high content of Fe-Mn nodules. We found the total Cr(VI) was decreased with time and higher Cr(VI) was detected in the soil with higher content of Fe-Mn nodules. It was probably because of the re-oxidation of Cr(III) from Cr(VI) reduced by organic matter by Fe-Mn nodules. We also observed that the soil organic matter has low ability to reduce Cr(VI)-contaminated soil which has high content of Fe-Mn nodules. If we used less amount of organic matter, we could not reduce Cr(VI) obviously.
|
|---|
