Study On Catalytic Denitrification Characteristics Of Modified Rare Earth Tailings Added In CO Atmosphere

The main energy consumed in China is coal,and coa l and other fuels will release a large amount of hazardous gases and solid pollutants during the combustion process.NOx is the most important one of the harmful gases.At present,the more mature denitration methods at home and abroad are selective catalytic reduction denitrification?SCR?.The use of CO as a denitration reducing agent can simultaneously remove CO and NOx generated by combustion,and has broad application prospects.The Bayan Obo rare earth tailings contain rare earth oxides,transition me tal oxides,alkali metal oxides and other substances with denitrifying activity.So tailings can be used as a natural denitrification catalyst.Because of the"poor,thin,and miscellaneous"technical reasons of tailings,rare earth tailings have not been fully utilized.Lead to the accumulation of nearly 200 million tailings.This paper modifies the rare earth tailings,and adds modified rare earth tailings to the simulated flue gas in the furnace to reduce the NO_X emission.In this paper,the acid-base modification of rare earth tailings is carried out.The purpose of acid treatment is to remove Ca-containing substances in tailings.The purpose of alkali treatment is to decompose bastnaesite in tailings.In this paper,The effect of the modification method of rare earth tailings,modified calcination temperature,liquid-solid ratio and different reaction temperatures on the catalytic reduction and denitrification performance of CO was studied.Then using XRF,XRD,SEM,BET,H₂-TPR,XPS and other detection methods were used to characterize the material,morphology,pore size,reduction capacity and valence state of rare earth tailings.The main conclusions are as follows:?1?The rare earth tailings themselves can effectively catalyze the reduction of NO by CO,and the modified rare earth tailings can catalytically reduce CO by a greater degree.The tailings acid-base co-treatment?microwave roasting for 15 min?and tailings acid-base co-treatment?muffle furnace roasting for 1 h?achieved good denitrificatio n activity at different reaction temperatures.This indicates that the denitration effect of the muffle furnace roasting for 1 h can be achieved by microwave roasting for 15 min.When the tailings treatment method is acid-base co-treatment,the roasting method is microwave roasting,the roasting temperature is 500°C,the liquid-solid ratio is 10:1,and the reaction temperature is 850°C,the denitration efficiency is best up to 96.2%.?2?XRD indicates that the main ore of rare earth tailings is fluorite?CaF₂?,hematite?Fe₂O₃?,magnetite?Fe₃O₄?and bastnasite?CeCO₃F?.After the rare earth tailings have been modified,the diffraction peak intensity and crystal form of CaF₂ and BaSO₄ did not change much,indicating that the stability of CaF₂ and BaSO₄ is strong.The crystal phase diffraction peak of the bastnasite ore of alkali treated tailings and acid-base co-processed tailings disappears..It indicates that the bastnasite ore?CeCO₃F?has been decomposed.XRF indicates that the Ca content of the tailings is reduced after acid treatment.Alkali-treated tailings and acid-base treated tailings such as CeO₂ and other rare earth metal oxides and Fe₂O₃ content have increased..Therefore,the denitrification activity of the modified tailings is higher than that of the original rare earth tailings.?3?SEM shows that the rare earth tailings are irregular blocks and the surface is smooth.However,the surface of the tailings treated by acid and alkali is uneven,and in addition to cracks,many debris and holes appear,which increases the pore structure of the tailings.H₂-TPR indicates that the acid-base co-treatment tailings reduction temperature moves to the low temperature direction,and the reduction peak increases,indicating that more substances exhibit redox capacity,and thus have better denitration performance.?4?It is proved that a part of Ce³⁺is converted into Ce⁴⁺and Fe²⁺is converted into Fe³⁺during the modification process.It is indicated that there is a certain amount of CeO ₂formed after the decomposition of the mineral phase containing Ce³⁺,and a certain amount of Fe₂O₃ is formed after the decomposition of the Fe²⁺containing mineral phase.And the lattice oxygen content of the rare earth tailings treated by acid-base co-treatment is obviously increased,which is beneficial to the catalytic reaction.The increase of CeO ₂ and Fe₂O₃ contributes to catalytic denitrification,so the denitration performance of acid-base co-processing tailings is better than that of rare earth tailings.