Study On Heterogeneous Fenton Process Catalytic Oxidation Treatment Of Electroless Nickel Plating Wastewater

The electroless nickel plating process is suitable for non-conductive materials surface like plastics,and it's widely used for simple production process.However,the nickel-complex and the copper-complex used in the production of plating parts,is difficult to purified by conventional chemical precipitation method,caused by their stable chemical properties.The heavy metal nickel with toxic carcinogen,has serious adverse effects on the human body and the ecological environment.The electroplating industry has a strict limit on the concentration of nickel after wastewater treatment.Therefore,how to effectively treat electroless nickel plating wastewater and ensure a lower treatment cost,is a major problem for related industries.In this paper,a new type of highly efficient composite metal oxide catalyst was developed for the nickel-complex in electroless nickel plating wastewater.The catalyst was used in heterogeneous Fenton-like reaction to break the nickel complex,and then remove the nickel ions in the wastewater by chemical precipitation method.As a result,the electroless nickel plating wastewater could achieve the effective purification and decrease the content of COD_Cr.In this paper,a novel heterogeneous Fenton-like composite catalyst with high catalytic efficiency,easy recovery and long service life was developed,and its catalytic performance was investigated by catalysing H₂O₂ to remove nickel-complex from electroless nickel plating wastewater.The researchs are mainly divided into two parts.The first part is the preparation of CuO-CeO₂-Co₃O₄ composite catalyst and the optimization of the reaction parameters of heterogeneous Fenton-like reaction.The catalyst was prepared by co-precipitation method and characterized by BET,XRD,SEM,TEM and XPS characterization methods.Take aim at the removal ratio of nickel citrate and its COD_Cr,investigated the factors?including the active element ratio,calcination temperature of catalysts,H₂O₂ concentration,catalyst dosage,initial pH and reaction temperature?which effect the removal rate of pollutants.In addition,the service life of the composite catalyst was studied,and the degradation mechanism of the catalyst was analyzed.In the second part,in order to recover and reuse the composite catalyst better,the CuO-CeO₂-Co₃O₄/Al₂O₃ composite ceramic membranes were prepared by various methods and characterized by BET,XRD,FESEM and EDX characterization methods.The Ni²⁺-complex in the actual electroless nickel plating wastewater as the research object,composite membrane and H₂O₂ as heterogeneous Fenton-like system.The influencing factors on the removal efficiency of Ni²⁺-complex were investigated,including preparation methods and calcination temperature of composite membrane,H₂O₂ concentration and initial pH.The findings are as follows:?1?In the heterogeneous Fenton-like system with 1 mmol/L nickel citrate solution,the CuO-CeO₂-Co₃O₄ composite catalyst atctive elements ratio?Cu:Co:Ce?was1:1:1,the calcination temperature was 450^oC,the addition of catalyst was 0.3 g/L,the H₂O₂ concentration was 75 mmol/L,the initial pH value was 3,and the reaction temperature was 50^oC.After 60min reaction,the removal rate of nickel citrate and COD_Cr was 98.3%and 58.5%,respectively.Treat with chemical precipitation method,the removal rate of Ni²⁺and the residual Ni²⁺content in wastewater were 99.9%and 0.034 mg/L,respectively.In addition,the composite catalyst still exhibited good catalytic activity after repeated use for 5 times.?2?Take the Ni²⁺-complex in the actual electroless nickel plating wastewater?from Wujin NO.2 Electroplating Factory?as the target pollution.In the heterogeneous Fenton-like system composed of CCM-S and H₂O₂,the CCM-S prepared by spraying method and calcinated at500^oC,the usage of CCM-S was more than 2,and the H₂O₂ concentration was 12.5²0 mL/L.When the initial pH value was 3,the removal rate of Ni²⁺and its COD_Cr respectively were more than 99.35%and 50%,after treat with chemical precipitation.The results indicating the treatment process has a positive removal effect for metal-complexe with different concentrations and components in electroless nickel plating wastewater,and accord with the pseudo-first-order kinetics reaction.In addition,the removal rate of Ni²⁺in wastewater was still up to 84.1%when the CCM-S was reused for 6 times,which indicated that the CCM-S had a good recycling value.?3?The type of radicals in heterogeneous Fenton-like reaction were determined by EPR characterization methods,results show that the hydroxyl radical?·OH?was the main oxidation radical.The fluorescence spectroscopy analysis found that the production of·OH was the highest for 40 min of Fenton-like reaction.Meanwhile,the mechanism of catalysting H₂O₂ to generate·OH indicated that there was a strong synergistic effect among the redox couple of Cu²⁺/Cu⁺,Co³⁺/Co²⁺and Ce⁴⁺/Ce³⁺in Fenton-like reaction.