Study On Catalytic Ozonation Degradation Of Pyridine Wastewater By Zine-Magnesia-Alumina Hydrotalcite

Pyridine is the raw material of chemical industry,medicine,pesticide and other industries.Due to the high toxicity and low biodegradability of pyridine,ordinary biological methods can not effectively remove pyridine.However,ozone oxidation technology can degrade pyridine into small molecular compounds such as water and carbon dioxide,which can be used as pretreatment process of biological methods.A calcined Zn-Mg-Al hydrotalcite catalyst(ZnMgAl-CLDH)with easy recovery and low pollution was prepared by urea hydrothermal co-precipitation method.The catalytic potential of ZnMgAl-CLDH in the process of catalytic ozonation of pyridine wastewater was studied in a bubble stirred reactor,and the reaction kinetics and catalytic mechanism were discussed.The main conclusions are as follows:(1)By optimizing the catalytic performance of ZnMgAl-CLDH,the optimal conditions were obtained as follows:n(Zn2+):n(Mg2+):n(Al3+)=2:1:1,n(NO3-):n(Urea)=2 and calcination temperature was 500℃.XRD,FT-IR,TGA and BET analysis results showed that the lamellar structure of ZnMgAl-LDH was destroyed after calcined at 500℃ for 2 h,and the active components of ZnMgAl-CLDH were mainly composite metal oxides with ZnO as the main component,and the specific surface area increased from 15.67 m2/g to 190.46 m2/g.(2)Compared with ozonation alone,ZnMgAl-CLDH catalyzed ozonation significantly improved the degradation effect of pyridine.For the pyridine wastewater with an initial pyridine concentration of 300 mg/L,under the conditions of reaction time of 40 min,catalyst dosage of 0.6 g/L and initial pH of 10,the pyridine degradation efficiency and effluent COD can reach 96.9%and 71.7 mg/L,respectively.The lower the initial pyridine concentration,the faster the degradation rate of pyridine.At the same time,ZnMgAl-CLDH showed good catalytic potential and long service life in the process of catalytic ozonation degradation of pyridine wastewater.Through orthogonal test optimization,the optimal process conditions of pyridine wastewater containing ammonia nitrogen with initial pyridine concentration of 300 mg/L were obtained as follows:reaction time of 60 min,catalyst dosage of 0.7 mg/L,initial pH of 9 and initial ammonia nitrogen concentration of 50 mg/L.(3)The degradation of pyridine by O3 alone,ZnMgAl-LDH/O3 and ZnMgAl-CLDH/O3 are all approximately in line with the pseudo-second-order reaction kinetic model.The apparent reaction rate constant(kapp)of pyridine degradation by ZnMgAl-CLDH/O3 was 11.59 times that by ozone alone and 2.79 times that by ZnMgAl-LDH/O3,respectively.The results showed that·OH and surface hydroxyl were the main active oxygen free radicals and active sites for catalytic ozonation degradation of pyridine,respectively.According to analysis and calculation,about 93.7%of pyridine is indirectly degraded by OH.After 40 minutes of oxidation reaction,the degradation products of pyridine may be N-methylacetamide or N,N-dimethylformamide organic compounds and small molecular inorganic compounds such as NH4-N,NO2-N,NO3-N,N2,CO2 and H2O.