OXIDATIVE DESTRUCTION OF IRON-COMPLEXED CYANIDE AT ATMOSPHERIC PRESSURE AND TEMPERATURES BELOW 100°C

摘要

Due to leaching from purifier bed wastes, iron-cyanide complexes are routinely found in the groundwater of manufactured gas plant sites. Iron-cyanide complexes will persist in groundwater sources, and are difficult to destroy. As with other strong acid dissociable (SAD) cyanide complexes, iron-complexed cyanides tend to be chemically inert unless exposed to ultraviolet (UV) radiation. When exposed to sunlight, iron-cyanide complexes in surface waters may release the toxic free cyanide ion, which is potentially toxic to aquatic life. Although free cyanide and weak acid dissociable (WAD) cyanide complexes may be easily destroyed through oxidation at room temperature, SAD cyanide complexes are resistant to such measures. The research presented in this paper has been undertaken to adapt traditional oxidative techniques to iron-cyanide complexes in a cost effective manner Potassium ferricyanide and potassium ferrocyanide have been successfully destroyed (oxidized) at atmospheric pressure and temperatures below 100°C within a reasonable time frame (hours). Successful oxidizers include sodium hypochlorite (chlorine bleach), ozone, and potassium permanganate. Successful destruction was not achieved through the use of hydrogen peroxide. Based on a literature search into the chemistry of iron-cyanide complexes, it appears that the hexacyano-complex decays into the pentacyano-complex, that subsequently breaks down into free cyanide and the ferric or ferrous ion. When the oxidizer concentration is sufficiently high, these two dissociations become the rate limiting steps. The activation energies for the hexacyano- and pentacyano-complex dissociations were found to be 1.562 x 10~3 J/mol and 918.9 J/mol, respectively. The first and second frequency factors equal 3.245 x 10~(14) min~(-1) and 7.856 x 10~7 min~(-1), respectively.