以鐵負載銅及貴金屬微粒還原水中鉻酸鹽之研究

Reduction of Chromate by Bimetallic Iron Particles

許雅雯(Ya-Wen Hsu)

指導教授 ： 駱尚廉

國立臺灣大學/工學院/環境工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.02283

摘要

鉻酸鹽通常被使用或產生於工業製程之中，舉凡電鍍、冶煉、冷卻水等，因此在工業區附近的地下水體之中，鉻成為常見的汙染物之一。
鉻酸鹽在環境中屬活潑、容易發生氧化還原反應之金屬，其普遍存在三價或六價的型態，這兩種氧化態彼此之間能夠互相轉換。然而六價鉻毒性約為三價鉻之1000倍，大量攝取六價鉻的化合物將引起嘔吐、腹痛、尿毒症、甚至有致癌性，因此理解地下水體中該潛在危險元素之命運(宿命)與其反應機制是必要的。
近年來，零價鐵還原技術已被廣泛地應用在整治地下水中可還原性污染物上，鉻即為其中一種。為降低六價鉻對人體及生態系統之危害，場址整治是必需的。因此本研究之主要研究目標為探討零價鐵以及雙金屬系統對六價鉻還原反應、去除效率和電化學腐蝕機制。並且，以批次實驗個別探討五種陰離子(氯離子、硫酸根、矽酸根、磷酸根、過氯酸根)，對六價鉻去除之影響。更進一步探討零價鐵、雙金屬微粒及所吸附鉻離子之成分與氧化價數。
研究結果顯示以雙金屬載體來進行實驗並且載體經氣相還原之前處理程序，將有助於反應持續進行，使反應效率提升。此外水體中存在不同的共存陰離子會對六價鉻還原反應造成干擾，其中氯離子、硫酸根離子、過氯酸根離子在本研究中均能幫助反應進行，矽酸根離子則對系統有極大之干擾，抑制反應的持續進行。
在分析塔佛電化學反應時，發現隨著負載第二金屬的比例增加，腐蝕電流上升，去除效率提高。可以知道鉻的去除效率與電化學的腐蝕電流相關。
接著進行貴重儀器的檢測，經由照SEM會發現，有前處理過後的商用鐵粉表面較為光滑，而負載第二金屬時也會比沒前處理過負載金屬的表面來的分布均勻，更可以驗證效果的提升。此外，經由XPSpeak曲線配湊之結果，分析目標元素的價數分布情形隨縱深深度而異，有以下趨勢：Fe2p3/2由表層0 nm至50 nm深，由Fe(Ⅲ)逐漸轉為Fe(Ⅱ)再轉為Fe(0)；Cu2p3/2由表層0 nm至50 nm深，由Cu(Ⅱ)逐漸轉為Cu(Ⅰ)、Cu(0)；縱深0 nm至50 nm，當Cr2p3/2訊號存在，其均是Cr(Ⅲ)型態存在。

關鍵字

六價鉻 ； XPS曲線配湊 ； 零價金屬鐵 ； 雙金屬

並列摘要

Chromates are often used or generated by a number of industrial process including electroplating, tanning, cooling with water, etc. so that chromium pollutants are often found to exist in groundwater in industrial region. Chromium is a redox active metal that persists as either Cr(Ⅲ) or Cr(Ⅵ) in the environment. These two oxidation states have opposing toxicities and mobilities. Cr(Ⅲ) is rather benign and immobile in soils while Cr(Ⅵ) is toxic, corrosive, readily transported, and a potential carcinogen. It is therefore essential to find out Cr reactions and mechanisms in groundwater to predict and understand the fate of such potentially hazardous element.
Remediation of groundwater contaminated with Cr species by using zero-valent iron (Fe0) has received considerable attention in recent years. Site remediation is necessarily required in order to reduce the risk to humans and ecosystems. Therefore, the main objectives of the study is to investigate the reduction, removal efficiency and electrochemical corrosion mechanisms of Cr (III, VI) aqueous solutions on the zero-valent iron and bi-metal (bi-metal)systems. Further more, to find out the composition and oxidize prices of the chromium absorbed, zero-valent iron and bi-metal particles.
The results show that bi-metal systems could effectively promote chromium removal and the step of pre-treated method leads to higher efficiency. And the presence of chloride, sulfate, and perchloride ions can increase the rate of chromium removal while silicate interfered the reactions in zero-valent iron and bi-metal systems.
It also shows that the corrosion current rise while bi-metal coating scale increase in Tafel electrochemical analysis. It is found that chromium removal efficiency is related to corrosion current. Carrying on the measuring of the valuable instrument, it is found that the surface of pre-treated iron powder is smoother, and the distribution of the coating metal on the surface of iron powder is comparatively even via SEM. This would verify the improvement of the chromium removal efficiency in the study. In addition, according to the XPSpeak fitting results, the oxidize prices of the goal elements vary with the depth profile. It reveals that Fe2p3 is trivalence, duad, zero-valent, and Cu2p3 is duad, monovalence, zero-valent from the Surface layer (0 nm) to bottom layer(50 nm).

並列關鍵字

chromium ； XPSpeak fitting ； zero-valent iron ； bi-metal system.

參考文獻

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