| Summary: | 碩士 === 朝陽科技大學 === 環境工程與管理系碩士班 === 98 === Phytoremediation used in heavy metal contaminated soil remediation preserves soil properties, causes no great damage to soil structure, and impacts litlle on soil environment. Phytoremediation proceeds mainly through the extraction and metabolism of heavy metal pollutants in soil by plant growth. Heavy metals in soils can be exchangeable, carbonate-bound, Fe-Mn oxide-bound, organic-bound and in residual forms. Heavy metal absorption capacity varies with plant species, which release materials in root zone to further complicate the metal forms in soil. In this study, the types and heavy metal forms in soil are cross- examined to determine the vegetation restoration efficiency.This research is divided into two parts, the first part is the acquisition of heavy metals contaminated soil, analyzing their absorption capability of heavy metal forms by Triticum aestivum L.and Amaranthus. Tricolor L., and exploring the effects of vegetation on the fractional distributions of heavy metals in soil.Experimens show that the maximum absorption capacity of plants to cadmium up to 251 mg kg-1, maximum uptake of copper up to 213 mg kg-1, the maximum absorption of chromium up to 128 mg kg-1, the maximum absorption of nickel up to 165 mg kg-1.As the number of cropping increase , soil has a slightly downward trend in metals concentration, except Amaranthus. Tricolor L. which is not growing well in winter.Cadmium, copper, nickel, show no trend in fraction distribution with vegetation .Chromium is showing increasing concentration in residual state.
Cation-exchange capacity of soil (CEC) is the important reference information for heavy metals contaminated soil remediation method selection and remediation efficiency prediction. The Sodium Acetate Method is the most common used standard method for determining soil CEC. According to ion exchange theory, the cation with high valence or smaller hydrated radius has stronger exchange potential, Na+ is not the high-exchange-potential ion, thus the suitability of using Sodium Acetate Method to determine CEC of soil contaminated by heavy metal is dubious. In this study, chlorides and acetates of metal ions such as Na+, K+, NH4+, Mg+2, Ca+2, Zn+2, Pb+2, Al+3 and Sn+4 at the same ion concentration were used to run exchange extraction reaction with cadmium in soil, and the reliability of Sodium Acetate Method in determining CEC of Cd,Cu,Cr,Ni-contaminated soil was studied. The results showed that when metal cation is the same, chloride usually has higher exchange extraction capacity with Cd in soil than acetate, e.g., sodium chloride has higher extraction capacity than sodium acetate . Among extract agents used in this study, sodium salt is not the best one for exchangeable Cd,Cu,Cr,Ni in soil ; instead, extraction capacity of the highest-valence stannic chloride is the strongest. extraction capacity of the highest-valence stannic chloride and potassium chloride are the strongest.
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