Enhanced destruction of Cu(CN)32- by H2O2 under alkaline conditions in the presence of EDTA/pyrophosphate

Oxidation of Cu(CN)(3)(2-) in water by H2O2 is less documented. The present study investigated the effects of pH, H2O2 dose and CN-/Cu(I) on oxidation of cu(CN)(3)(2-). Furthermore, oxidation of Cu(CN)(3)(2-) by H2O2 was investigated in the presence of ethylenediaminetetraacetate (EDTA) or pyrophosphate. The results indicated that Cu(CN)(3)(2-) oxidation was more favored at pH 9.5 and 11.0 than at pH 12.0. With the increase of H2O2 dose, rate of cu(cN)(3)(2-) oxidation was accelerated. Oxidation of Cu(CN)(3)(2-) was accelerated with CN-/Cu(I) decreasing from 4.0 to 2.8. In the presence of EDTA or pyrophosphate, oxidation of Cu(CN)(3)(2-) was significantly enhanced. 4.0 mM cyanide was nearly oxidized by 4.8 mM H2O2 in the presence of 1.0 mM EDTA. According to UV-Visible spectra variation of Cu(CN)(3)(2-) solutions, it was found that H2O2 firstly oxidized Cu(CN)(3)(2-) to Cu(CN)(2)(-). The successive oxidation of cyanide from Cu(CN)(2)(-) led to liberation of Cu(I). Cu(I) was oxidized into Cu(II) with formation of hydroxyl radicals (HO) or Cu(III). H2O2 was decomposed of into O-2 in the process. The strong bonding of Cu(II) to EDTA suppressed decomposition of H2O2 into O-2 and enhanced the effective utilization of H2O2 for cyanide destruction. By contrast, complexation of Cu(II) with pyrophosphate enhanced the catalytic redox reaction (Cu(I)/Cu(II) or Cu(I)/Cu(III)), improving cyanide oxidation. The results provide a possible way to improve treatment of Cu(CN)(3)(2-) wastewater by H2O2. (C) 2014 Elsevier B.V. All rights reserved.