Study On NH₃-SCR Characteristics Of Microwave Roasting Rare Earth Tailings By Acid And Treatment And Rare Earth Ore Concentrate Catalyst

In this paper,a rare earth tailings and rare earth concentrates are used as raw materials to modify them to prepare high-efficiency denitration catalysts.The feasibility of using rare earth tailings and rare earth concentrates as raw materials for denitration catalysts is proved.Through the detection and comparison of each experimental variable in the preparation process,the best working condition is obtained:the ratio of tailings and concentrate is 1:1,the roasting method is microwave roasting,and the calcination temperature is 350?,and the corresponding alkali content can be added.The denitration efficiency of 82%was obtained,and a series of characterizations were carried out to verify and explain the reasons for the improvement of the desorption activity.?1?The peaks of CeCO₃F and Ce₇O₁₂2 exist at 350?,indicating that the decomposition of CeCO₃F exists from the first stage to the third stage.Since CeOF,Ce₂O₃ and Ce₇O₁₂2 all contain Ce³⁺,the content of Ce³⁺will increase.The addition of Ca?OH?₂ in the process is to increase the decomposition rate of CeCO₃F,and the addition of Na₂CO₃ is to react with CeOF to form a CeOF-CeO-like mixed crystal series material,which increases the amount of CeOF and Ce oxide.Although the peak of Ce₇O₁₂2 appeared in the calcination at 500?,the peak of fluorocarbon ruthenium disappeared,indicating that the decomposition of fluorocarbon ruthenium has reached the final stage,and CeOF and Ce₂O₃ are all converted to Ce₇O₁₂,thus limiting the content of Ce³⁺.Fe₂O₃ and some iron salts will react with the decomposition products of CeCO₃F to form FeCe composite oxides.In this process,the electron transfer of Fe will have a greater impact,that is,the conversion of Fe³⁺to Fe²⁺.?2?When the mixed ore has no treatment,the specific surface area is only 2.5895 m²/g,and after microwave heating,it increases to 5.3946 m²/g.It can be explained that microwave roasting can cause cracks on the mineral surface to increase the specific surface area,and the specific surface area of the sample after alkali baking is further increased.Increase,reaching 7.8211m²/g,adding alkali has the function of pore-forming,the reason why it does not increase too much,because the amount of alkali added is small,playing more of the reaction with CeOF,and is not increasing large specific surface area plays a more important role.The microwave roasting is selected because the absorbing properties of the minerals are improved after heating,especially after microwave heating,the absorbing ability is increased because after the heat treatment,the crystal particles interact to form different types of magnetic waves.The medium and dielectric enhance the magnetic loss and dielectric loss in the microwave electromagnetic field,thereby improving the absorbing characteristics.Adding weak magnetic materials and rare earths to the tailings will facilitate the formation of ferromagnetic phases,improve the absorbing properties,and the more obvious the response to microwaves.?3?The distribution of F,O and rare earth elements is concentrated.The place where F,O and rare earth elements accumulate is Ce oxide,but the F element remains in the crystal lattice.It is also mentioned in the literature that the addition of alkali has the effect of solid F,so During the reaction,the F element did not go out of the crystal lattice.And the positions of the Fe and Ce elements are also relatively close,which proves that the FeCe composite oxide is formed.?4?The effects of microwave roasting and acid-base treatment are also reflected on the surface of the mineral.The surface cracks on the surface of the particles are wavy,and acid corrosion occurs,which makes the surface of the particles rough,and pickling can increase the acid sites on the surface of the catalyst.Better adsorption of NO and NH₃.?5?The XRD of different proportions showed a huge change in the peak at a ratio of 1:1.The peak of fluorocarbon oxime decreased,and the reaction was consumed.Compared with the other two ratios,the peak of Fe₂O₃ was also the lowest.Comparing the samples at the three ratios,only the peak of Ce oxide appeared at the ratio of tailings and concentrate at 1:1,indicating that there is only decomposition of bastnasite in the sample at 1:1 ratio,and the other two ratios The corresponding peaks were not observed in the samples,and it was difficult to improve the denitration efficiency without the formation of Ce oxide.?6?It can be seen from the XPS results that the content of Ce³⁺and Fe²⁺decreases with the increase of the treatment step in the ratio of 2:1,although the ion content of the three proportions is different according to the data.Not large,but the two ion contents of the 1:1 sample are on the rise,and the tailings and concentrates have a good combined denitrification at a ratio of 1:1,moreover,the content of bastnasite in the 1:1 ratio is also matched with the content of alkali,which can react well and generate more Ce oxide,and Ce oxide reacts with Fe oxide to form The composite oxide improves the denitration efficiency,and there is a mutual restriction relationship between the tailings and the concentrate of the 2:1 ratio and the 1:2 ratio of the catalyst,so that the content of Ce³⁺and Fe²⁺ions is lowered,thereby reducing the denitration efficiency.?7?The increased oxygen vacancies on the surface of the treated catalyst provide a higher possibility for the adsorption of NH₃,and at the same time,the NH₃ adsorption amount of the L acid sites can be increased to form more H⁺,so that the adsorption amount of NH₄⁺is increased.More oxygen vacancies can cause O₂ to adsorb up to form oxygen atoms in the adsorption state.NO combines with surface adsorbed oxygen to form surface nitrate species,which enhances the adsorption of NO_X on the catalyst surface,providing a higher possibility for the overall reaction.NH₃ can adsorb to the B acid site and react with gaseous NO_X.When the adsorbed NH₃reacts,different kinds of nitrates and nitrites can occupy their activity and adsorb on the catalyst surface.The bidentate nitrate and bridge nitrate can react with the NH₃ and NH₂ species in the L acid position to achieve the NH₃-SCR reaction.