| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系所 === 104 === The toxicity and mobility of heavy metals depend not only on their total concentration, but also their chemical fractions. The concentration of heavy metals in soil is not the same concentration as in plants. Only those heavy metals that are dissolvable or soluable from the surface of the soil can be absorbed by plants. Chemical amendments using acid and alkaline have been shown to be a cost-effective method for soil remediation. This decreases the bioavailable concentration of heavy metals in contaminated soil. In this study, we used carbonate crystal from drinking water processes and CaHPO4 to reduce the bioavailability of cadmium(Cd) via precipitation and absorption mechanisms. Acidic sandy clay loam textured soils contaminated with Cd were treated with Crystal and CaHPO4 (application rates of 1%, 5% and 10%), Crystal-CaHPO4 mixing ratio of 10%-1%, and 1% Crystal.The treatments were milled and sieved using 20mesh processing. The soils were incubated at room temperature for 120 days and sampled at 15~30 day intervals for sequential extraction and pH measurements. After 120 day incubation period, the efficacy of the amendments were evaluated with Ipomoea plant uptake and sequential extraction.
The results indicated that soil pH significantly increased with the addition of amendments, particularly the treatment with 1% carbonate crystal milled. The exchangable fraction was the dominant phase (70%) with weak binding capacity and high mobility in control group. This showed that the harmful Cd in the environment can be easily displaced. The concentration of Cd in shoot of Ipomoea with the control treatment was 270.35mg/kg. After 120 days, the addition of amendments was able to effectivey reduce the exchangeable fractions. This effect was shown best in 1% Crystal grinding milled process. This treatments also effectively inhibited the absorption of Cd by Ipomoea after two pot experiments. However, the lowest concentration of Cd (57.05 mg/kg) in plant shoot was found in the treatment with 5% CaHPO4. In conclusion, our study showed that soil remediation of cadmium could be achieved using chemical amendments, decreasing harmful risk to the environment.
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