| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系 === 91 === The problems caused by Zn and Cr contaiminated soils have been highly and widely concerned in Taiwan. The solubility product, desorption characteristics and column leaching experiment were used to evaluate the retention mechanisms and mobility of the two heavy metals in the studied soils. The results indicated that, due to high Zn and Cr content and pH value of around 10, the formation of hydroxide precipitates was one of the retention mechanisms of the in situ soils. The desorption experiments showed that the extraction ability of the three extractants applied was in the descending order of NaOAc < H2O < MgCl2. The highest accumulative desorption rate of NaOAc might result from the low pH (3.5) of its extraction solution which cause the dissolution of hydroxides. This result also confirmed that precipitation was a major retention mechanism. In comparison with the desorption rates of the two heavy metals, we might predict that Zn had less non-specific forms and was easier to form precipitates. The column leaching experiment indicated that the adsorption of the two elements by the soils followed Langmuir adsorption model. Therefore, adsorption was another available retention mechanism. The higher contents of Zn and Cr at the stratified layers of each leaching column proved that the retardation of infiltration solution at the layer due to contact resistance might conduct retention reactions with ample time. Finally, the maximum amounts of adsorption and distribution coefficients(Kd) revealed that Zn had higher mobility than Cr.
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