Electrogenerative formation of ferric ions in a sulfur dioxide–sulfuric acid solution; Graphite catalysed sulfur dioxide oxidation

The electrogenerative oxidation of ferrous ions in 3m sulfuric acid, containing sulfur dioxide and subsequent sulfur dioxide oxidation, were studied in connection with potential regenerable sulfur dioxide remediation processes. The presence of sulfur dioxide in the feed stream did not affect cell performance. Oxidation of sulfur dioxide in the electrogenerative reactor took place when high ferrous to ferric ion conversions were obtained. Low cost graphite and iron ions served as an effective mediating system for promoting electron transfer to sulfur dioxide in strong acid solutions. In contrast, the homogenous reaction between iron(iii) and sulfur dioxide is relatively slow. In a separate batch reactor, the heterogeneous iron(iii) and sulfur dioxide reaction was found to be graphite catalysed, accounting for sulfur dioxide conversion observed in the electrogenerative reactor. Ferrous ion presence should be minimized, because it inhibits the desired catalysed reaction.