土壤中重金屬在植生復育過程中之濃度變化及型態轉換

Variation of Concentrations and Distributions of Heavy Metals during Soil Remediation Process

陳盈伊(Ying-Yi Chen)

指導教授 ： 程淑芬

朝陽科技大學/理工學院/環境工程與管理系/碩士(2010年)

摘要

植生復育法在重金屬污染土壤整治的同時，仍可兼顧土壤特性的維持，不會對土壤結構產生極大的破壞，對土壤環境衝擊較小。植生復育技術主要藉由植物生長代謝過程萃取土壤中之重金屬污染物，重金屬在土壤中以可交換態、碳酸鹽態、鐵錳氧化態、有機態及殘留態等不同型態存在，植物對不同型態之重金屬有不同的吸收能力且植物根部所釋放出的物質可能改變重金屬之存在型態，本研究探討植物對各種型態重金屬的吸收效率以及型態轉換之影響，有利於植生復育技術整治成效之判斷。
　　本研究內容主要分兩個部份，第一部分採集重金屬污染土壤，藉由連續多次栽種小麥與莧菜，分析小麥及莧菜對重金屬吸收能力變化，並探討土壤中各種型態重金屬含量隨著栽種次數的變化情形。研究顯示試驗植物對鎘最大吸收量可達到251 mg kg-1，對銅最大吸收量可達到213 mg kg-1，對鉻最大吸收量可達到128 mg kg-1，對鎳最大吸收量可達到165 mg kg-1，隨著栽種次數增加，土壤濃度都有略為下降的趨勢，對於試驗作物莧菜於冬季不適生長。在土壤中重金屬型態轉換方面，鎘、銅、鎳三種重金屬還未見明顯之變化趨勢，鉻則呈現殘留態逐漸增加情形。
　　第二部分針對以醋酸鈉法測定受鎘、銅、鉻、鎳污染土壤陽離子交換容量（Cation-exchange capacity of soil,CEC）之適宜性進行研究，依據離子交換理論，Na+並非具有最高交換潛力之離子，本研究以Na+,K+,Mg+2,Ca+2,Zn+2,Pb+2,Al+3及Sn+4等金屬離子之氯鹽及醋酸鹽進行土壤中鎘、銅、鉻、鎳的交換萃取反應，探討以醋酸鈉法檢測污染土壤陽離子交換容量之可靠性。結果顯示，對同一陽離子氯鹽對於土壤中重金屬的萃取能力高於醋酸鹽，如氯化鈉比醋酸納萃取能力高，本研究所使用萃取劑中鈉鹽對鎘、銅、鉻及鎳並非最佳萃取劑，鎘以氯化鉀之能力最強，銅、鉻、鎳則是以氯化錫萃取能力最好。

關鍵字

植生復育 ； 小麥 ； 莧菜 ； 重金屬 ； 陽離子交換容量

並列摘要

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.

並列關鍵字

Phytoremediation ； Triticum aestivum L. ； Amaranthus. Tricolor L. ； heavy metals ； CEC

參考文獻

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