CHEMICAL DEGRADATION OF CYANIDES BY FENTONS REAGENT IN AQUEOUS AND SOIL-CONTAINING SYSTEMS

A study was conducted on the effects of pH of the medium, composition of Fenton's reagent, and the effect of soil's preequilibration with the chemical, on the degradation of C-14-labeled free and complex cyanide in aqueous and soil-containing systems. The application of Fenton's reagent (1% H2O2, 10 mM FeSO4) resulted in degradation of 80% and 67% of potassium cyanide in aqueous systems at pH 7.2 and 10.0, respectively. No appreciable amount of K-4[Fe(CN)(6)] was degraded at either pH tested. Under the alkaline condition, negligible amounts of cyanide were converted to HCN and were removed from liquid phase due to precipitation. In the soil systems containing uncontaminated topsoil or manufactured gas plant (MGP) soil, both freshly amended with free cyanide, 80% of the compound was degraded by the Fenton's reagent of the same composition. Similar to the aqueous systems, no complex cyanide was degraded in soil slurries. In both soils, previously equilibrated with free and complex cyanides, the extent of degradation caused by Fenton's reagent was not more than 6% at either pH. However, at alkaline pH, up to 21% of previously added complex cyanide was leached out into a liquid phase where it could be further degraded. The optimum composition of Fenton's reagent under alkaline pH was found to be 1% of H2O2 and 1 mM FeSO4. We suggest that the application of Fenton's reagent under alkaline conditions may be useful in a combined physicochemical treatment for the remediation of sites contaminated with cyanides.