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LOW-TEMPERATURE, LIQUID-PHASE PROCESSES 125 Equation 11 is an idealized equation, neglecting possible by-products and losses at the anode. The hydrogen ions form hydrogen gas at the cathode. The oxidation can take place in bulk solutions either in a separate chamber or in the cathode chamber. The three metals identified above have been of greatest interest. Silver is the most active but will form insoluble AgCl if mustard is treated and may precipitate out. The solubilities of the phosphates, fluoride, and sulfate salts formed appear to be sufficient so as to cause few if any problems. Cobalt and iron salts are believed to be sufficiently soluble and would be used to avoid salt precipitation when treating mustard. The oxidized solution leaving the cell contains the mediating metal, which, for silver and cobalt, would require separation and recycling. Iron is not believed to present a special disposal problem and is relatively inexpensive, so that recycling may not be required. Iron and cobalt, however, are relatively inactive for oxidation of the more refractory compounds such as organic compounds containing carbonyl groups. It appears that a substantial R&D and systems design program would be required to establish the performance of this technique with the three agents and their products of chemical detoxification. Oxidizing Agents Plus UV Light UV radiation is capable of decomposing ozone (O3) or H2O2 to hydroxyl radicals (OH°) that are capable of oxidizing most organic compounds. For a mixture of 2:1 O3:H2O2 the stoichiometry is shown below: In a high-pH solution in the presence of UV light, ozone will also react with OH- m form the reactive radical OH° (EPA, 1990). Oxidation potentials provide a measure of oxidizing power, as indicated by Table 6-1. The hydroxyl radical is seen to be exceeded only by fluorine. Several processes have been developed by Ultrox, Halliburton NUS, Perox-Pure, Illinois Institute of Technology Research Institute, and others (Picardi, 1991; EPA, 1991) to treat water contaminated with a variety of organic compounds, including phenol and chlorinated solvents. Water flow rates have ranged from 10,000 to 1.3 million gallons per day. The contaminants have generally been found in concentrations of a few parts per
