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This technology uses hydrogen peroxide and an iron catalyst to destroy contaminants either in situ or ex situ.
Applying destructive chemistry to site remediation reduces contamination levels by destroying the undesirable chemicals and producing innocuous ones. Oxidation is an example of such a destructive technology.
This article covers one specific advanced oxidation process, known as Fenton's reaction. It discusses the underlying chemical principles and possible means of applying Fenton's reaction to contaminated sites, as well as recent developments and their possible implications. An earlier CEP article (1) provided some general background on Fenton's chemistry and explained how it can be applied to industrial wastewater.
In this reaction, hydrogen peroxide reacts with ferrous sulfate (also known as Fenton's reagent) to produce hydroxyl radicals, which destroy organics, eventually producing water and carbon dioxide. The use of this chemistry in treating contaminated water was realized in the early 1970s. More-stringent environmental regulations and the increasing demand for destructive chemistry increased its importance in the last decade.
Fenton's chemistry
The Fenton reaction involves two components in addition to the contaminated medium, namely the catalyst and the oxidizer. The iron catalyst can be either Fe(II) or Fe(III) salts, although some researchers suggest that ferrous iron may be preferred. Both the sulfate and chloride salt of the iron can be used. However, with the latter, chlorine may be generated at high rates of application. It is possible to recycle the iron following the reaction by raising the pH, separating the iron floc, and re-acidifying the iron sludge. The oxidizing agent commonly used is hydrogen peroxide, which is inexpensive yet effective. The hydroxyl (OH*) and perhydroxyl (HOO*) radicals formed are very powerful oxidizers and are short-lived species. OH' is one of the most powerful oxidizers known, second only to fluorine in its reactivity (Table 1).
Several mechanisms for the reaction of the hydroxyl radical are possible. However, two mechanisms are most effective in the destruction of organics.
The oxidation of an aromatic ring compound such as phenol is a classic example of the use of Fenton's reagent to reduce the toxicity of an industrial effluent. In the process, carboxylic and dicarboxylic acids are produced, and, if the oxidation is carried to completion, CO^sub 2^ and water are formed. Substituted aromatic ring...