Study On Peroxydisulfate Enhancing/Oxidation Destruction Of Cyanide Wastewater

Recently,heavy metal pollution is becoming serious with the with the development of economy.Electroplating wastewater effluent is one sources of heavy pollution and cyanides.A lot of heavy metal ions exist in the wastewater,such as Cu,Ni and Cr,so does CN^-,pyrophosphate(P₂O₇^4-),EDTA etc.In particular,the rinse water from cyanide copper plating process often contains free cyanide?CN^-?and copper cyanide complex[Cu?CN?₃^2-].Such complexes cannot be removed by conventional methods such as coagulation,precipitation,etc.Thus,advanced oxidation methods were developed.Persulfates,including peroxymonosulfate?PMS?and peroxydisulfate?PDS?,and hydrogen peroxide receive increasing interest in recent years in both research and application for the remediation of organic pollutants in groundwater and wastewaters.When activated by alkaline,UV,heat and transition metals,strong sulfate radicals can be generated,which can help treat the toxic wastewaters containing high concentrations of organic contaminants.Compared with hydrogen peroxide,potassium persulfate is easier to be preserved and transported.Therefore,potassium persulfate is used as the advanced oxidant in this paper.Oxidation destruction of Cu?CN?₃^2-by persulfate is discussed in detail,and so is the enhanced electrochemical oxidation of Cu?CN?₃^2-by persulfate.Cyanide-containing wastewater has the characteristics of high toxicity,wide range of contamination,long pollution time and difficult to deal with.In view of the above characteristics,this paper aims to explore efficient,environmentally friendly,energy-saving methods to deal with cyanide-containing wastewater.The contents and results of this paper are as follows:1.Oxidation destruction of Cu?CN?₃^2-by Persulfate was investigated firstly.Cyanide contaminants widely present in electroplating wastewater and metallurgical effluents and have attracted more and more attention due to their high toxicity,extensive pollution,long duration and difficult to degradation.Therefore,it is urgent to develop the highly efficient,environmental friendly and energy saving methods for the removal of cyanide contaminants.Potassium persulfate,as a green clean oxidant,is widely used in organic pollutants treatment.In this paper,the destruction of Cu?CN?₃^2-was investigated by homogeneous K₂S₂O₈ under alkaline conditions,and the reaction mechanism was analyzed.The effects of the amount of K₂S₂O₈ and the ratio of Cu to CN^-on the degradation of CN^-have been discussed.The removal efficiency of CN^-reaches up to 89.6%under the conditions of 2mmol/L K₂S₂O₈ and 60 min reaction time.Cu⁺was oxidized to Cu²⁺and finally existed in copper oxide powder.The reactive free radicals were identified by electron spin resonance and radical quenching experiments.The results indicated that the reaction between K₂S₂O₈and Cu?CN?₃^2-contains both radicals oxidation and non-radical oxidation.2.Peroxydisulfate?PDS/K₂S₂O₈?enhancement of the electrochemical oxidation of Cu?CN?₃^2-with RuO₂/Ti mesh anode and stainless steel cathode under alkaline conditions was investigated.With the addition of K₂S₂O₈,the removal efficiency of CN^-was increased to 82.1%from 19.4%with 2 mM K₂S₂O₈ addition for 6 min.The concentration of cyanide was lowered from 0.84 to 0.02 mM within 30 minutes.The Cu mass distribution onto the anode,in the solution,and onto the cathode was investigated.With the increase of K₂S₂O₈amount,the deposition amount of Cu oxides onto the anode increases.Combined with the SEM-EDX,XPS,XRD and In situ Raman analysis of the anode surface,it was concluded that the generation of copper oxides occurred at the anode surface,which exhibited catalytic activities for cyanide removal.Meantime,ESR results confirmed the generation of sulfate and hydroxyl radicals.Both the activated radicals and the generated CuO were responsible for the enhanced removal of CN^-.Cyanate was identified as the main product.3.Different processes of cyanide removal are compared.Many techniques,such as,ESR,XRD and XPS are used to identify the differences between K₂S₂O₈ oxidation and electrochemical oxidation,showing the difference between different processes.