Treatment Of High Concentration Cyanide-containing Waste Water With CWAO

Cyanide-containing wastewater is very toxic to person and ecosystem, so all thecountries pay widely attention to it. Catalytic wet air oxidation （CWAO） is an effectivemethod to treat the high concentration and toxic wastewater which is hardly degraded withnormal method. High effectiveness, low energy consumption, and no secondary pollutantsmake it attractive in the treatment of cyanide-containing wastewater.In this paper, we simulate cyanide-containing wastewater by KCN solution to study thegeneral law of catalytic wet air oxidation of high concentration cyanide-containingwastewater with Cu catalysts. We focused on the investigation of their relationship betweenpreparation method of Cu catalyst and activity and stability. Determine the optimal processparameters about catalytic wet air oxidation of high concentration cyanide-containingwastewater.Firstly, CuO catalyst was prepared with citric acid Sol-Gel method. The CuO catalystshows more active for CN^-removal when the catalyst was prepared under conditions: salts:Cu（NO₃）₂: citric acid （molar ratio）=1:1, preparation temperature60℃, dried on130℃,calcined6h at600℃. When the concentration of CN^-in the sewage is2000mg/L, the amountof CuO proves to be0.5g/L, the pH in the sewage is8, the reaction temperature is130℃, theoxygen partial pressure of0.6MPa and stirring speed is600r/min. If the reaction time last60min, the removal rate of CN^-from the sewage can reach over80%.Secondly, CuO/γ-Al₂O₃catalyst was prepared by soakage. The optimum conditions weredetermined as follows: concentration of Cu²⁺was6%, soakage temperature was30℃,soakage time was6h, calcination temperature was400℃, calcination time was4h. In thesimilar conditions, the CN^-removal was slightly lower than CuO catalyst when CWAO ofhigh concentrations of cyanide-containing wastewater, however the amount of Cu²⁺leakinghas been significantly reduced. XRD was used to characterize CuO/γ-Al₂O₃catalyst betweenthe fresh and reused. The results showed that the decreasing of the catalytic activity should beascribed to the phase change of the support and the dramatic loss of active component in hightemperature. Finally, chosen Ce as the aids, the doping modification of CuO/γ-Al₂O₃catalyst wasproceeded then CuO-CeO₂/γ-Al₂O₃catalyst was prepared by soakage. The investigation ofXRD shows that the introducing of Ce effectively addressed the problem of the phase changeof support and the dramatic loss of active component in high temperature during the reaction.In the similar conditions, the CN^-removal is more than90%when CuO-CeO₂/γ-Al₂O₃catalyst was applied in CWAO of high concentrations of cyanide-containing wastewater.