Sulfur dioxide oxidation rate enhancement

Sulfur dioxide is slowly oxidized to sulfur trioxide, but the reaction rate can be greatly enhanced by a platinum or vanadium oxide catalyst (see Section 13.6) ... 

This process represents another alternative to the double alkali process. Sulfur dioxide is absorbed in dilute sulfuric acid, oxidized to sulfate by air blowing, then precipitated as gypsum by the addition of limestone. The oxidation rate is increased by the use of iron as a catalyst in the circulating acid and is also enhanced by the low pH of the solution. The process, which was developed by Chiyoda Chemical Engineering and Construction Company, Ltd., of Yokohama, has been used quite extensively in Japan. Fourteen plants were reportedly in operation at the end of 1977 ( do, 1977). 

The remediation of chromium-contaminated sites requires knowledge of the processes that control migration and transformation of chromium. Chromium(VI) can be reduced to chromium(III) in the presence of ferrous iron, reduced sulfur compounds, or organic matter in soil. However, chromiu-m(III) also can be oxidized by manganese dioxide, a common mineral found in many soils (Bartlett 1991 Palmer and Wittbrodt 1991 Pandey etal. 2003). Usually, Part of any chromium(VI) added to a soil or sediment will be reduced very rapidly, especially under acid conditions. On the other hand, excess chromium(VI) may persist for years in soils or lagoons without reduction (Bolan et al. 2003). The addition of organic amendments such as manure enhanced the rate of reduction of chromium(VI) to chromium(III) in soils low in organic matter (Bolan et al. 2003). 

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