| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 94 === 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).
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