Preparation Of NH₃-SCR Denitration Catalyst By Magnetic Separation-flotation-sulfuric Acid Modification Of Bayan Obo Rare Earth Tailings

NH₃-SCR has become the mainstream of denitrification catalytic reduction technology nowadays because of its advantages such as high efficiency and economy.At present,the more studied Fe-based,Ce-based and Mn-based catalysts are mostly prepared in analytical purity,which have the disadvantages of high cost,not easy to obtain and obvious singularity.In view of the fact that composite catalysts exhibit better denitrification performance than single metal catalysts,mineral catalysts are gradually and widely studied.The rare earth minerals and iron-oxide containing ores contained in Baiyun Ebo rare earth tailings can both be used as active components of catalysts after activation.However,the complex intermineral cascade relationship and fine embedded particle size in the tailings of Baiyun Ebo lead to their low utilization rate.In this paper,the combined treatment process of magnetic separation-flotation-sulfuric acid modification was used to analyze the effect of the combined treatment process and its parameters on the performance of catalysts prepared from rare earth tailings with the help of process mineralogical analysis,BET,SEM,LPSA,XRD,NH₃/NO-TPD,H₂-TPR,XPS and other testing methods.The fine grinding of the rare earth tailings from Baiyun Ebo was subjected to magnetic separation at 1990 Oe,2550 Oe,2950 Oe,3200 Oe and 3500 Oe magnetic field strengths,and the results showed that the magnetic separation concentrate grade obtained from 3200 Oe magnetic separation strength was 57.78%,and the denitrification efficiency of the obtained magnetic separation tailings reached 48%at 400°C.Hematite was enriched in the tailings,and the active mineral fraction was more dispersed,the specific surface area of the catalyst was larger,more active and acidic sites,and the redox ability was enhanced,meanwhile,the fluorite in the magnetic separation tailings was also enriched,which provided favorable conditions for fluorite flotation,and secondly,the results of optical microscope analysis showed that the monomer dissociation degree of fluorite in the finely ground rare earth tailings was increased to 38.17%.Sodium oleate was used as the trapping agent(dosages of 440 g/t,660 g/t and 880 g/t,respectively),starch and water glass as inhibitors(both dosages of 800 g/t)and sodium carbonate as p H adjuster for flotation,and the fluorite crude concentrate grade was 52%at the trapping agent dosage of 660 g/t.The active mineral components such as rare earth minerals,hematite and manganese minerals were enriched in the flotation tailings,which made the adsorption of NH₃ increased and the synergistic catalytic effect between the active mineral components easier.The best reaction temperature of denitrification of the flotation tailings was reduced to 350°C,and the efficiency reached 66.4%.To further improve the denitrification activity of the catalyst,the flotation tailings were activated with sulfuric acid(sulfuric acid concentration of 4 mol/L,8 mol/L and 12mol/L,respectively)by picking fluorocerium and monazite,etc.When the sulfuric acid concentration was 8 mol/L,the denitrification efficiency of the catalyst reached 93%at350°C,and the temperature window was widened to 350°C?450°C,with better N₂selectivity and sulfur resistance.The catalyst showed recrystallization phenomenon,and(Ce,La)[CO₃]F,Fe₂O₃ and Ca(Mg,Fe)(CO₃)₂ reacted with sulfuric acid to form soluble sulfate,as well as a large amount of SO₄^2-groups,providing more Br(?)nsted acid sites while the ratio of O_?/(O_?+O_?)and the ratio of Fe³⁺and Ce³⁺in the catalyst appeared to be increased,increasing the oxygen vacancies in the catalyst,which accelerated the conversion rate of lattice oxygen to chemisorbed oxygen and promoted the catalytic reaction.