Treatment Of Pymetrozine Waste Salt By Heterogeneous Fenton Catalysis And Combined Process

A large number of inorganic salts are produced in various production processes of fine chemical industry.These salts are separated from wastewater or solvent and often contain a large number of refractory organic compounds.Chemical waste salt solidification landfill or sea disposal not only lead to a waste of salt resources,but also cause a risk of environmental pollution.As a new type of insecticide,Pymetrozine produce a lot of waste salts in the production process.In this paper,the mild physical and chemical methods are used to purify the waste salt as a byproduction of Pymetrozine.According to the production process of Pymetrozine and the characterization results of waste salt,the waste salt contains methanol,acetic acid,acetylhydrazine,oxadiazole,acetic anhydride,methyl acetate and dichloroethane,and the content of sodium chloride is 77.04%.The results showed that the removal rates of COD by reverse salt washing and sequential salt washing were 74.4%and 79.3%respectively,but the water consumption of reverse salt washing was only one third of that of the sequential salt washing method.After high temperature oxidation,only a small amount of acetylhydrazine,acetic anhydride and methyl acetate were left.The content of sodium chloride was increased to 85.09%and 87.81%respectively at 400℃and600℃,which indicated that the higher the temperature was,the more thorough the removal of organic matter in the waste salt was.The carrierγ-Al₂O₃was prepared by sol-gel method,and the loading material MIL-101（Fe）was prepared by solvothermal method.MIL-101（Fe）@Al₂O₃was synthesized by solvothermal method and low-temperature calcination method.Explored the removal effect of five heterogeneous Fenton catalysts on COD in the solution of Pymetrozine salt.The crystal structure,surface morphology,valence states of surface elements and specific surface area of five materials analysis show that05MIL-101（Fe）@Al₂O₃successfully supported MIL-101（Fe）on mesoporous alumina through the bridging and linking mode ofγ-Al₂O₃nanorods,and have strong catalytic reaction activity and adsorption of organic compounds.The degradation experiment of organic matter in waste salt solution shows that the COD removal rate can reach49.74%at 20℃when the dosage of 05MIL-101（Fe）@Al₂O₃is 2.0 g/L,the dosage of hydrogen peroxide is 120 mmol/L,the initial p H is 2.93 and the reaction time is 5 h.This is mainly due to the adsorption and enrichment of organics on the catalyst,and the·OH generated on the surface of catalyst directly contacts with organics and oxidizes,which reduces the capture and quenching of Cl^-in the diffusion process of·OH;the synergistic effect of iron and copper accelerates the interface electron transfer,promotes the circulation of·OH,and reduces the formation of Fe²⁺/Fe³⁺complexes with chloride ions.The results of repeat ability experiments show that the catalytic degradation efficiency of 05MIL-101（FE）@Al₂O₃is still above 40.40%after five times of reuse,and it has good stability.The high salt solution system slows down the heterogeneous Fenton reaction rate,prolongs the reaction time and increases the use of hydrogen peroxide,but it still has a good removal effect for the waste salt solution with less organic matter.Single treatment method has limited effect on organic matter removal of chemical waste salt.According to the applicable conditions of different methods,the effective combination of treatment of Pymetrozine waste salt can not only achieve the ideal purification effect,but also significantly reduce the energy consumption of single-step treatment.The waste salt solution treated by heterogeneous Fenton process is oxidized by sodium hypochlorite and adsorbed by adsorption materials,which can not only further remove the organic matter in the waste salt,but also remove the residual metal ions in Fenton reaction.The content of sodium chloride was 91.69%after the combined process was used to purify Pymetrozine waste salt.The main residual organic compounds were methyl acetate,acetamide,oxadiazole,acetic acid and a small amount of acetic anhydride.However,the overall removal effect of organic matter by the combined process is obviously better than that by the 600℃high temperature oxidation process,which has important theoretical significance for the purification of industrial waste salt.