Study On The Combined Denitration Of Semi Coke And Rare Earth Tailings

Nitrogen oxides are one of the important pollutants that destroy the atmosphere in our country,and will cause many environmental problems such as acid rain,photochemical smog,and destruction of the ozone layer.Among them,the combustion of coal will generate a lot of NOx.At present,the selective catalytic reduction technology?SCR?of mainstream flue gas denitration method using ammonia as a reducing agent is becoming more and more mature,but the problems of ammonia escape and ammonium salt clogging still exist.CO is also a good denitration reducing agent,and the use of CO to reduce NO has received extensive attention and research in recent years.Baotou Baiyun Ebo rare earth tailings are the remaining tailings of Baotou Steel's beneficiation.Although they have low taste,they still contain more rare earth elements and transition metal elements.It has the effect of catalyzing the reduction of NO by CO.However,the reduction of NO by CO is a non-selective catalytic reduction reaction,and the denitration rate drops suddenly after encountering oxygen.The study found that a certain concentration of oxygen will promote the reduction and denitrification of coal char.This feature gives coal char reduction and denitration technology the advantages under aerobic environment.However,a large amount of CO is generated during the reduction and denitrification of coal coke,causing secondary pollution to the environment.Therefore,based on the semi-coke reduction denitration technology and CO catalytic reduction of NO as the background,and rare earth tailings as the research object,a new idea of flue gas denitrification is proposed:semi coke-rare earth tailings combined denitration.The aim is to achieve high denitrification,high anti-oxidation,high anti-sulfur,low CO generation technical indicators and comprehensive utilization of tailings.In this work,the effect of temperature,O₂,CO₂,and SO₂ on semi-coke denitration was first studied.Secondly,the denitrification performance of semi-coke and tailings was investigated for the denitrification of semi-coke,and the denitration effect and CO generation of semi-coke and rare earth tailings and semi-coke and magnetic separation tailings that obtained from rare earth tailings after magnetic separation were investigated.Finally,the tailings were characterized by means of XRD,XPS,EDS,H₂-TPR,quantitative analysis of minerals,etc.,and the tailings were comprehensively analyzed from the crystal phase,element valence state,embedding relationship,redox ability,composition content,etc.The main conclusions are as follows:?1?Semi-coke-tailing combined denitration and denitrification efficiency and CO generation inhibition effect are significantly better than semi-coke denitration.The combined denitration of semi-coke-magnetic separation tailings can achieve more than90%NO conversion at 500?under aerobic conditions;the combined denitration of semi-coke-magnetic separation tailings under aerobic conditions,when SO₂ and CO₂ are introduced separately The denitration efficiency has been further improved.The denitration rate can be stabilized at more than 98%for a long time at 500?,and zero CO generation can be basically achieved.The semi-coke-tailing joint denitrification achieves the technical purpose of high anti-oxidation,high denitrification,and ultra-low CO generation.?2?XRD shows that the cerium ore?CeCO₃F?in the tailings will be thermally decomposed,and the Fe²⁺iron formed by pyrolysis of pyrite?FeS₂?will gradually become Fe₂O₃ as the reaction progresses,there will be more Fe²⁺in the reaction Change to Fe³⁺to promote reduction and denitration.XPS shows that the denitrification activity of the magnetic separation tailings and the effect of suppressing the formation of CO are better than those of rare earth tailings:the magnetic separation tailings Ce³⁺has a higher specific gravity,and the higher specific gravity Ce³⁺can promote the formation of oxygen vacancies and the decomposition of NO;the magnetic separation tailings Fe²⁺specific gravity The higher,the higher the Fe²⁺specific gravity,the stronger the catalyst reducing ability;the specific gravity of adsorbed oxygen on the surface of magnetic separation tailings is higher,and the adsorbed oxygen on the surface can promote the oxidation of CO and the chemical adsorption of NO.?3?There are many mineral phase components in the tailings,and the continuous relationship between the mineral phases is intricate.H₂-TPR shows that the main active mineral phases in the tailings are bastnaesite,monazite,hematite and pyrite;there is a synergistic catalytic effect between the mineral phases,and this synergistic effect is beneficial to catalytic denitrification.XPS characterization of tailings in different reaction stages revealed that the surface adsorbed oxygen will participate in the reaction,and the specific gravity of Fe²⁺and Ce³⁺in the reaction will increase,accelerating the migration rate of lattice oxygen and surface adsorbed oxygen,and promoting the catalytic reaction;the contents of Fe,Ce and O in the tailings form a closed cycle throughout the denitration reaction,indicating that the tailings denitrification follows the oxygen transfer theory.