| Mercury,as a global atmospheric pollutant,has been widely concerned by domestic and foreign researchers in recent years due to its hypertoxicity,volatility,bioaccumulation and persistence.Coal-fired power plants are one of the biggest emission sources of anthropogenic mercury.Sorbent injection is regarded as the most promising technology for elemental mercury removal?Hg0?in coal-fired flue gas.However,most of the currently existing mercury sorbents are prepared by artificially synthesized or chemical modification,which exist the shortcomings of high cost,complicated preparation process,and others.The low cost,rich reserves and various metallic elements of natural ore make it to be potential mercury sorbent for coal combustion flue gas.Therefore,it is of great significance and value to investigate the Hg0 removal capacity of natural ore with low cost.Natural magnetite,ilmenite,delafossite and manganese ore were developed as the mercury sorbent.The physical and chemical characteristics of four natural ores were investigated using X-ray diffraction?XRD?,Brunauer-Emmett-Teller?BET?,X-ray fluorescence?XRF?.The mercury removal performances of natural ores were studied in the fixed-bed reactor under simulated flue gas.The surface modles of natural ores were constructed to calculate the adsorption energy of Hg0 by density functional theory.The natural ore sorbents with excellent mercury removal performance were developed by combining the experimental and calculated results.The results suggested that the descending order of mercury removal efficiency for four natural ores was:manganese ore>delafossite>ilmenite>magnetite.The mercury removal efficiencies of manganese ore and delafossite were more than 90%.The adsorption energy of delafossite and manganese ore could be higher than that of magnetite and ilmenite,indicating better mercury capture performance,which was basically consistent with experimental results.To further study the Hg0 removal capacity of natural delafossite,the magnetism and valence state of elements were characterized by vibrating sample magnetometer and X-ray photoelectron spectroscopy.The mercury removal performance,impact of flue gas components,reaction mechanism and regeneration performance were systematically investigated.The results indicated that the mercury removal efficiency of natural delafossite was more than 90%at low temperature and attained 96.7%at the optimal temperature of100°C.O2 and HCl could significantly enhance mercury removal efficiency,while the presence of SO2 and H2O played an inhibited role in Hg0 removal.The promoting effect of NO on mercury capacity was weakened with the increase of NO concentration.Hg0 was chemically adsorbed on the surface of delafossite,forming HgCl2 and HgO on the surface.The mercury removal efficiency during 10 cycles of Hg0 adsorption and regeneration were all more than 80%.After 10 cycles,the physical characteristics of delafossite were not significantly changed.Manganese ore had higher mercury removal efficiency than delafossite.Therefore,it is also necessary to investigate the adsorption capacity of Hg0,effect of flue gas components on mercury removal and reaction mechanism using manganese ore sorbent.The results showed that the Hg0 removal efficiencies from 100 to 250°C under simulated flue gas were over 90%,attaining approximately 98.7%with the optimal reaction temperature of 150°C.The sorbent at higher temperature still had excellent mercury removal performance.O2,NO,and HCl could promote Hg0 removal to different degree under 100-300°C.With the increase of temperature from 100-150°C,the inhibitive effect of SO2 on mercury capture of the sorbent was weakened.Further increasing the reaction temperature from 150°C to300°C would decrease the adsorption capacity sharply.The addition of 5%H2O to the simulated flue gas reduced the mercury removal efficiency from 98.7%to about 75%.The formed mercury compounds on the sorbent after Hg0 adsorption in simulated flue gas were mainly ascribed to HgO,HgCl2,Hg?NO3?2 and HgSO4. |
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