Removal Of Elemental Mercury From Simulated Flue Gas By Cu-Fe Modified Magnetosphere

Mercury,as a toxic heavy metal,can cause long-lasting and serious damage to the environment and ecology.With the natural and human activities,mercury continues to enter the ecological environment.The main source of anthropogenic mercury emission is flue gas from coal-fired power plants,and the main forms of mercury includes Hg⁰,Hg²⁺,and Hg?p?.The pollutant control device can assist in mercury removal.The current common industry method of mercury removal is activated carbon injection.It has some problems such as high cost and difficulty in recovery.Therefore,more efficient,cheaper and recyclable mercury removal sorbents need to be developed.Coal combustion fly ash are one of the by-products from coal combustion flue gas.The magnetospheres in fly ash have superparamagnetic properties and it is good magnetic carriers.In our work,the magnetospheres?MF?obtained from fly ash by magnetic separation.In view of the problems of low Hg⁰ removal efficiency and weak magnetic properties of the original magnetic beads.FeCl₃·6H₂O and Cu?NO₃?₂·3H₂O are used as precursors,using sol-gel method and dipping method to load it on MF.Cu-Fe modified MF and Cu/Fe individually modified MF sorbents were prepared.The Hg⁰ removal performance of the modified MF was studied in a fixed-bed reactor,and the effects of preparation and reaction conditions on the magnetic properties of the modified MF sorbents were investigated.The physical and chemical properties of the modified MF sorbents were analyzed by TG/DTG,XRF,XPS,XRD,PPMS-VSM and N₂ adsorption-desorption.At reaction temperature of 200 ?,BFG?N₂+5%O₂+12%CO₂?atmosphere,the original MF has low mercury removal efficiency.After modified by Cu-Fe compound,Hg⁰ removal efficiency and magnetic properties have been significantly improved.When the calcination temperature is 400 ?,Hg⁰ removal efficiency of the sorbent is the best,and the magnetism of the sorbent is also significantly enhanced.When the MF are loaded with 6 wt%Cu-Cu:Fe in the modified solution is 1:2,Hg⁰ removal efficiency of the sorbent is the best?97%?.In the reaction temperature range of 100–350°C,the required time?Hg⁰ removal efficiency reaches80%?decreases with the increase of temperature,and it is just 3 seconds at temperature of300°C.The effect of flue gas composition on Hg⁰ removal indicated that HCl significantly shortens the required time,while NO and SO₂ prolong the required time.The magnetic properties of Cu?6?Fe-MF are significantly weakened in HCl or SO₂ atmosphere,but enhanced in NO atmosphere.The sorbent with low Cu-Fe loading also has a good Hg⁰ removal performance in HCl atmosphere.Hg⁰ removal efficiency is promoted at low NO concentration?100⁴00 ppm?but inhibited at high NO concentration?800 ppm?.In SO₂ atmosphere,the initial Hg⁰ removal efficiency of the sorbent show a decreasing-increasing-decreasing trend,but the overall Hg⁰ removal efficiency decreased.The Cu?6?Fe-MF sorbent keep good Hg⁰removal efficiency and magnetic properties after reaction in SFG?simulated flue gas?for 10h.Combining experiment and adsorbent analysis results,it is found that Cl is the main Hg⁰removal active material;Cu removal activity is greater than Fe.Due to the interaction between Cu,Fe and Cl,the Cl on Cu-Fe co-supported sorbent has stronger oxidizability,which makes the sorbent have better mercury removal performance.HCl is very beneficial to Hg⁰ removal of Cu?6?Fe-MF.Further,the sorbent was pre-treated with HCl?10 ppm HCl atmosphere at 50? for 1 h?,and it was found that the sorbent had good mercury removal efficiency at 50,200and 350 ?.