Supports for Zero-Valent Metal Dehalogenation

CARBON SUPPORTS FOR ZERO-VALENT METAL DEHALOGENATION 

The treatment of halogenated hydrocarbons by zero-valent metals, mainly iron, tin. and zinc, offers several attractive features for the remediation of contaminated waters relatively high reaction rates, and the low-cost and noncontaminating nature of the metal. These reactions can be enhanced by the use of a carbon support to increase the area of metal available for reaction. 

The emphasis of most research in this area has been on the use of iron [87-93], or a modified iron, such as palladium-plated iron granules [90]. Alternatively, relatively fast reaction rates have been obtained when using very fine divided Zn or Sn particles in an inert atmosphere [94], 

While the dehalogenation of chlorinated species is often referred to as zero-valent metal catalysis, it is not strictly a catalytic but rather an electrochemical corrosion process. The metal is consumed by reaction, leading to the formation of metal salts and dechlorinated by-products. 

In a pilot scale study of TCE dechlorination using iron filings, several factors were found to control the process [93]. The alkalinity of the groundwater and the concentration of dissolved oxygen affect the life of the catalyst bed the presence of carbonate- or oxide-forming species in the water can lead to the formation of an inert layer on the iron surface. This layer greatly reduces the overall reaction rate and shortens bed life [87,91,93,94]. A tenfold increase in aqueous alkalinity was found to reduce the reaction rate by a factor of 3. 

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V. Carbon Supports for Zero-Valent Metal Dehalogenation... 

The first section is mainly concerned with some of the emerging technologies for the production of novel activated carbons that may help to fulfill the increasing demands on performance as regulations on environmental pollution become more stringent. The next two sections deal with applications of conventional and new activated carbons in gas and liquid phase applications. The penultimate section considers the uses of carbons supports for zero-valent metal dehalogenation. The... 

V. CARBON SUPPORTS FOR ZERO-VALENT METAL DEHALOGENATION... 

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