Study On Modification Molding Of Rare Earth Tailings And NH₃-SCR Denitrification Performance

Nitrogen oxides are one of the main factors causing atmospheric pollution.The large amount of NO_x emission not only causes pollution to the environment,but also causes harm to human body.NH₃-SCR technology is the most widely used NO_xcontrol technology.The most core part of this technology is the catalyst.At present,the most commonly used commercially is vanadium catalyst,but the active component of vanadium catalyst V₂O₅ is toxic and expensive.Therefore,the research focus of denitration catalysts has gradually shifted to transition metal oxides with lower price.Based on the denitration performance of composite metal oxides catalysts is better than that of single metal oxides catalysts,mineral catalysts have been gradually studied.The laboratory has carried out a lot of research on Bayan Obo rare earth tailings,and found that Bayan Obo rare earth tailings contain Fe,Ce,Mn and other active elements needed for denitration.After certain physical and chemical treatment,Bayan Obo rare earth tailings have good denitration performance and sulfur resistance ability,which is a good choice for denitration catalyst.At present,the laboratory stage mainly focuses on powdered catalysts.In the practical application process,powder catalysts may have problems such as large bed resistance,fragile and easy to produce local high temperature,which is difficult to meet the needs of long-term operation.The integral catalyst has the advantages of easy industrial amplification and improving the utilization rate of catalyst,so the molding process of rare earth tailings catalyst was studied in this paper.In this paper,nanometer alumina and pseudobaumite were used as binder to prepare strip catalyst,and the influence of binder amount on the performance of strip catalyst was investigated.Then,the striped catalyst was prepared from sulfuric acid modified rare earth tailings,and the effect of sulfuric acid concentration on the performance of the striped catalyst was investigated.The performance of the forming catalyst was analyzed by means of SEM,XRD,TG-MS,BET,NH₃-TPD,H₂-TPR,XPS,FTIR and other characterization methods.With Bayan Obo rare earth tailings as raw material,the rare earth tailings strip catalyst modified with binder and sulfuric acid has better denitration activity and mechanical strength.In the range of 100～500℃,the denitration efficiency of rare earth tailings is only 8.1%,and the N₂selectivity is general.The strip catalyst prepared by adding 15%nano-alumina colloids has the highest denitration efficiency of 60.4%,N₂ selectivity of less than 60%,and longitudinal compressive strength of 1.13 MPa.The strip catalyst prepared by sulfuric acid modified rare earth tailings has better performance.In the range of 300～450℃,the strip catalyst prepared by 8 mol/L sulfuric acid modified rare earth tailings basically maintains the denitration efficiency of more than 70%,reaches the maximum of 86.2%at400℃,N₂selectivity is higher than 91%,and has good sulfur resistance and stability.The longitudinal compressive strength is 2.82 MPa.After the tailings are treated with sulfuric acid,hematite,fluorite,dolomite in the rare earth tailings react with sulfuric acid to form Fe₂（SO₄）₃,Ce₂（SO₄）₃,Ca SO₄,Mg SO₄ and Al₂（SO₄）₃,respectively.With the increase of acid concentration,the amount of minerals reacting with sulfuric acid increases,and Ca SO₄ increases the most.The generated sulfate covers the surface of the tailings,which is not conducive to the exposure and dispersion of the active components.After calcination at600℃,part of Fe₂（SO₄）₃ was transformed into Fe₂O₃,and Fe₂（SO₄）₃ and Fe₂O₃ were the main active components of the catalyst,which were beneficial to the improvement of catalytic activity.Ca SO₄ is the main component of gypsum.It has a gelling effect,which makes the catalyst slime have fluidity and viscosity,and still has a certain mechanical strength after roasting.Si O₂ does not react with sulfuric acid,and plays a skeleton role after roasting,so that the catalyst has a higher mechanical strength.After acid treatment,the specific surface area and pore volume of tailings increase,which increases the contact area between reaction gas and catalyst.The S=O bond in SO₄^2-has a strong electron acquisition ability,which induces a strong migration of Fe-O bond electron cloud in Fe₂O₃,which enhances the acidity of Fe₂O₃ and the acid sites on the catalyst surface,thus enhancing the adsorption capacity of NH₃ in the reaction process of the catalyst.The content of O_αand Fe³⁺on the surface of the catalyst was increased by acid treatment.The conversion process of Fe+2 and+3 provided necessary electrons for the REDOX reaction,which promoted the catalytic reaction.The improvement of acidity energy and REDOX performance was conducive to the improvement of the denitration activity of the catalyst.The IR results show that there are both Br（?）nsted Nsted acid sites and Lewis acid sites on the surface of the tailings.After adding nano alumina,the number of Br（?）nsted Nsted acid sites was significantly increased;After acid treatment,the number of Br（?）nsted Nsted acid sites and the strength of Lewis acid sites on the surface of the rare earth tailings were increased.Rare earth tailings surface weaker E-R mechanism and the mechanism of L-H after adding nanometer alumina,E-R reinforced mechanism of the reaction,but inhibits the accumulation of nitrate species reactivity,E-R mechanism after treatment of sulfuric acid is stronger,the effect of adsorption on the surface of the catalyst and nitrate species absorption peak is weak,is advantageous to the reaction.