Thermodynamic Basis And Experimental Study Of Leaching Of Waste CeO_x-MnO_x Catalyst For Denitrification

With the increasingly stringent ultra-low emission standards in the iron and steel industry,the high-efficiency emission reduction of NO_x in the sintering process has become the focus of pollutant emission reduction in the iron and steel industry in recent years.Selective Catalytic Reduction（SCR）technology has been widely used due to its significant advantages of low cost and high efficiency.CeO_x-MnO_x-based SCR catalyst has good low temperature activity and is currently the mainstream technology for low temperature SCR denitration application research.However,due to the complexity and particularity of the steel sintering environment,CeO_x-MnO_x-based SCR catalysts are more likely to be inactivated and discarded due to physical abrasion and chemical reactions,and their service life is shortened,becoming solid waste/hazardous waste,and posing potential threats to the ecological environment.Considering that the waste CeO_x-MnO_x-based SCR denitrification catalyst contains more valuable metal elements such as Ce,Mn,Ti,and the difficulty of disposal,its harmless disposal and resource utilization have become common technical problems in the industry.Therefore,the development of waste the theoretical and experimental research on the leaching of valuable metal elements in the catalyst,to realize the efficient recovery of valuable elements such as cerium,manganese and titanium,is of great significance to the harmlessness and resource utilization of waste catalysts,and is helpful to promote the green development of iron and steel technology.The physical and chemical properties of the spent CeO_x-MnO_x-based SCR denitration catalyst show that the main phase in the spent catalyst is anatase Ti O₂,and both cerium and manganese exist in the form of metal oxides,causing the poisonous elements to be corresponding salts（Chloride,sulfate）exists.The thermodynamic analysis of the sulfuric acid leaching of the spent CeO_x-MnO_x-based SCR denitration catalyst shows that the sulfuric acid leaching can only leach cerium and manganese in the low-priced state and convert them into the corresponding sulfate.The optimal process parameter is:the sulfuric acid concentration is 6 mol·L^-1,liquid-solid ratio is6:1,leaching temperature is 80℃,leaching time is 5 h,stirring speed is 350 r·min^-1,Ceand Mnleaching rates are 59.72%and 72.55%,respectively,with trace amounts of titanium leached.The main components of the leaching residue are anatase Ti O₂ and high-valence cerium and manganese oxides.In order to solve the problem of low leaching rate of Ceand Mnfrom sulfuric acid leaching,this paper selects the sulfuric acid maturation-water leaching process to dissolve cerium and manganese in the form of sulfate,and studies its leaching theory and technology to achieve high-efficiency leaching of Ceand Mn.The thermodynamic analysis results show that sulfuric acid maturation is beneficial to the conversion of cerium and manganese oxides into corresponding sulfates within a suitable temperature range,and the efficient leaching of Ceand Mncan be achieved through the water leaching process.Sulfuric acid maturation-water immersion experiments show that when the maturation temperature is 450℃,the addition of sulfuric acid is 60%,the aging time is 60 min,and the amount of water is 30%,the leaching time of the water leaching process is 120 min,the leaching temperature is 80℃,and the liquid-solid ratio is 6:1,Ceand Mnleaching rates are as high as 96.05%and 98.81%respectively,which are significantly improved compared to the sulfuric acid leaching process,laying a good foundation for the harmless and resource utilization of such hazardous waste.XRD,SEM-EDS,XPS and other characterization methods were used to study the law of phase transition during sulfuric acid curing and roasting-water immersion.The results show that with the increase of temperature,the degree of sulfation of the spent catalyst gradually increases.When the temperature is lower than 450℃,the degree of sulfation is not complete,which is not enough to realize the conversion of cerium and manganese oxides to sulfate.If the temperature is too high,it will accelerate.It reduces the decomposition of concentrated sulfuric acid and reduces the degree of sulfation of cerium and manganese oxides,which is not conducive to the leaching of Ceand Mn.Similarly,when the amount of sulfuric acid is less than 60%,the degree of maturation is insufficient.Too much sulfuric acid will increase the burden on the system,which will easily lead to the adhesion of raw materials,and it is difficult to fully mature,which is not conducive to the leaching of Ceand Mn.In this paper,through in-depth analysis of the physical and chemical properties and thermodynamics of the spent CeO_x-MnO_x-based SCR denitrification catalyst,it reveals the law of phase transformation in the sulfuric acid maturation-water leaching process.The efficient leaching of Ceand Mnis achieved through the sulfuric acid maturation-water leaching experiment.The realization of the harmless and resourceful disposal of waste catalysts has laid a good foundation to accelerate the green transformation and upgrading of the iron and steel industry.he iron and steel industry.