表面溶解及過氧化氫分解對α-FeOOH/H2O2程序去除2-氯酚效應之探討

Abstract

針鐵礦是土壤中礦物成分之一，在土壤化學處理中扮演重要的角色，本研究係以針鐵礦╱過氧化氫系統分解2-氯酚，內容分為三大部份包括針鐵礦表面溶解實驗、未添加2-氯酚時遇氧化氫分解動力實驗及2-氯酚氧化反應作用機制之探討。 在針鐵礦表面溶解影響因子探討中，其表面溶解反應機制係為表面控制反應，溶解速率與各因子間的關係，可以經驗式表示。而錯合劑及還原劑的加入，因為兩者間與針鐵礦表面作用機制的不同，使得溶液中溶出離子的形態，分別以錯合態之三價鐵離子及亞鐵離子型態存在。 針鐵礦表面催化分解過氧化氫可以擬一階反應動力式表示，且所求模式值在固定PH值下，能有效預測不同過氧化氫初始濃度及針鐵礦添加量之實驗值。而過氧化氫分解速率常數隨PH值升高而增加，另外添加磷酸鹽會因競爭吸附作用而減緩過氧化氫之分解速率。 本實驗藉由改變針鐵礦濃度所求之2-氯酚分解速率與亞鐵離子溶出速率之間成線性之關係及比值可知，還原溶解反應為本系統分解有機物之反應速率決定步驟。經與文獻上Fenton法處理氯酚類化合物中間產物結果比較，提出本系統在酸性環境分解有機物可能之反應作用機制，此機制除受污染物本身性質影響外，其中間產物的種類對去除速率亦具有決定性之影響。

Gogthite is among the components of the subsurface mineral and plays an important role in the chemical remediation of contaminated soil. The treatment of 2-chlorophenol (2-CP) in the a-FeOOH/H2O2 Process has been investigated. This research is divided into three parts, including the studies of goethite surface dissolution, H2O2 decomposition and oxidation mechanism of 2-CP. The dissolution of goethite is substantially controlled by the detachment of the surface Fe center. Empirical rate equations have been showed with the related factors. The dissolution rate is enhanced markedly by oxalate and ascorbate. Different mechanisms for ligand (e.g.oxalate) and reductant (e.g.ascorbate) with goethite make the surface Fe(III) dissolve into cation Fe3+ and Fe2+, respectively. Kinetics of H2O2 has been investigated in the presence of goethite, and proceed with a first order relationship with respect to the H2O2 concentration. This kinetic model allows for a fairly good correlation of the experimental data. The dependence of the rate constant on PH is determined experimentally and explained in terms of the different structure of the surface active sites. The process toward 2-CP degradation is effective at acidic PH, whereas negligible at neutral PH and above. The oxidation rate of 2-CP is correlated with reductive dissolution(Fe2+ dissolution) rate at various dosages of goethite. The near linear relationship and the stoichiometric ratio indicate that the oxidation rate of 2-CP is surface-controlled. A probable mechanism has been suggested for the decomposition process, and implies that not contamination itself but its intermediate species would effect the degradation rate.