Decomposition of Aqueous Cyanide Ions by Photocatalytic, Ozone and/or Hydrogen Peroxide Oxidation Routes

Abstract

Decomposition reactions of aqueous CN^- ions by TiO₂ photocatalyst, ozone and/or hydrogen peroxide were investigated. The principal findings obtained are as follows:
1) The presence of dissolved oxygen was necessary to decompose aqueous CN^- ions photocatalytically. CN^- was oxidized to CNO^- with TiO₂ catalyst, and then to CO₃^2- and NO₃^-. Oxidation reaction of CNO^- to CO₃^2- and NO₃^- was far slower compared to that of CN^- to CNO^-. Photocatalytic oxidation reaction of CNO^- at pHs 7 and 10 proceeded distinctly faster compared to that at pH 12.
2) Although ozone oxidation of CN^- took the same paths as photocatalytic reactions, but it was faster than that of photocatalytic routes. Combined use of photocatalyst and ozone for the decomposition of CN^- was more efficient.
3) Decomposition product of CN^- with hydrogen peroxide was found as CNO^- and N₂. Joint use of hydrogen peroxide and photocatalyst promoted reaction of CN^- to N₂.