Study On Phosphorus And Calcium Removal From Rare Earth Concentrate And Its NH₃-SCR Denitrification Mechanism

With the rapid growth of our country's economy,the problem of environmental pollution has become increasingly serious due to the increased consumption of fossil fuels,such as coal-fired power plants,which provide convenience for people's lives.China's nitrogen oxides emission rate has been on a downward trend since 2011,but its emissions are still very high.Controlling nitrogen oxides emissions is imminent.Flue gas denitration technology is the most important technology in the control of nitrogen oxides in the past ten years.The selective catalytic reduction method is commonly used in the industry.In this method,the catalyst is particularly important.The vanadium-based catalyst commonly used in industry has a high cost and poor durability.And other disadvantages,so research on new SCR catalysts is the current research hotspot.In recent years,more and more researchers have studied the catalyst prepared by mixing elements such as Ce,Fe,Mn,and La,and found that the doping of rare earth elements such as Ce and La will greatly improve the denitration performance.The Baiyun Ebo rare earth deposit in Inner Mongolia Autonomous Region is by far the most rare earth deposit in the world,with a total of 71 elements including iron,cerium,lanthanum and other elements,which provides a basis for our preparation of mineral catalysts.In this paper,sodium carbonate and ammonium chloride are used to dephosphorize and decalcify Baiyun Ebo rare earth concentrate.The catalysts prepared at different temperatures and different amounts were studied.The mineral phase and element content of the catalyst were explored by XRF and XRD;the morphology of the catalyst was studied by SEM and BET;the physical and chemical properties and redox properties of the catalyst were characterized by NH₃/NO-TPD and H₂-TPR;in-situ infrared experiment studies the adsorption of gas on the surface of different treated samples and the reaction path.The main research results obtained according to the above characterization methods are as follows:?1?The NOx conversion rate of the catalyst is detected by an NH₃-SCR activity evaluation device.The mass ratio of rare earth concentrate on sodium carbonate is 5:1,the roasting temperature is 500°C,the mass ratio of rare earth concentrate to ammonium chloride is 1:2,the chlorination temperature is 340°C,and the oxidation temperature is 500°C.The reaction temperature was 300°C.The catalyst showed the highest denitration activity,and the highest NOx conversion rate could reach 78%.?2?The mineral phase and element content of the catalyst were analyzed by XRF and XRD.Through XRD analysis,it was found that the rare earth concentrate treated with sodium carbonate and sodium carbonate-ammonium chloride found that Ce₇O₁₂ was locally formed on the mineral phase,but no other new substances were formed.The peak strength of apatite and monazite are reduced,and the relative content is reduced.It is obtained from XRF that the sodium carbonate-treated rare earth concentrate P-containing substances are partially removed under the action of Na₂CO₃,and the P content is reduced from 13.91%to6.94%,Ce,La and other active components increased,the content was 61.51%.Sodium carbonate-ammonium chloride treatment of the rare earth concentrate fluorocarbon cerium ore completely disappeared,the diffraction peak of fluorocarbon cerium ore decreased,and the effect of Ca-containing substances in the sodium carbonate-ammonium chloride composite treatment was obtained from XRF After removing most of it,the content of Ca was reduced from 16.16%to 4.91%,and the content of active components such as Ce and La increased to 68%.Through the BET,SEM,TPD and TPR characterization methods,it was found that with the cracks and depressions on the surface after sodium carbonate-ammonium chloride treatment,the specific surface area increased,and the reaction gases NO and NH₃ were treated with sodium carbonate-ammonium chloride the adsorption and desorption of the surface of the rare earth concentrate,the redox property is enhanced.?3?Adsorption of the reaction gases NO and NH₃ on the surface of rare earth concentrate after sodium carbonate-ammonium chloride treatment by in-situ infrared experiments.When the temperature is higher than 300?,the surface of the rare earth concentrate treated with sodium carbonate-ammonium chloride is mainly adsorbed in the form of NH₃ on the Lewis acid site,and a small part is adsorbed on the NH₄⁺on the Br?nsted acid site;Sodium carbonate-ammonium chloride composite treatment rare earth concentrate surface active sites are mostly occupied by monodentate nitrate and bridge nitrate species.Sodium carbonate-ammonium chloride composite treatment of rare earth concentrate surface has two reaction mechanisms at the same time.A small amount of adsorbed oxygen promotes the deamination of NH₃ to form NH₂.It then reacts with gaseous NO and generates intermediate product NH₂NO,which is then decomposed into H₂O and N₂ reaction process is E-R mechanism.Substances containing-NO₂ react with NH₃ species and produce NH₄NO₂,which is subsequently decomposed into H₂O and N₂.This is the L-H reaction mechanism.The reaction intensity of various nitrates and various NH₃ is relatively large,so the main reaction mechanism is L-H at 350?.