Removal Of Elemental Mercury From Simulated Flue Gas Over Peanut Shells Carbon Loaded With Iodine Ions,Manganese Oxides,and Zirconium Dioxide

As the most abundant and widely distributed fossil fuel,coal has a long application history in the world.Since the industrial revolution,it has been largely exploited to meet the needs of social and economic development,leading to a series of environmental problems.Gaseous pollutants produced during coal combustion include carbon dioxide(CO2),sulfur oxides(SOx),nitrogen oxides(NOx)and volatile organic compounds(VOCs).In addition,the toxic hazardous trace elements such as mercury(Hg),arsenic(As),selenium(Se)and plumbum(Pb)are also released.Mercury,a global pollutant with high mobility and bioaccumulation,can seriously harm the health of human beings and wildlife.Thus,controlling the mercury pollution resulted from coal combustion is one of the main tasks in the field of environmental protection.In this work,the raw pyrolysis product(peanut shells carbon)was employed as the support and halide ions(I-(NH4I))and metal oxides(MnOx(Mn(CH3COO)2·4H2O)and ZrO2(ZrOC12· 8H2O))were used as the active components to synthesize the sample 6Mn-6Zr/PSC-I3 for Hg0 removal.The effects of active components,loading value,reaction temperature,and oxygen concentration on Hg0 removal performances were investigated.The effects of simulated flue gas(SFG)atmosphere(N2 + 6%O2 +12%CO2 + 300 ppm NO + 400 ppm SO2 + 8%H2O)were also researched.A mercury speciation conversion system was applied to distinguish the adsorption and oxidation efficiency.In addition,the various characterization techniques were used to determine physiochemical property such as proximate and ultimate analysis,BET,SEM,ICP-AES,XRF,XRD,FTIR,and XPS.Further,the involved mechanism of Hg0 removal over 6Mn-6Zr/PSC-I3 was proposed.In this way,the theoretical basis of using modified peanut shells carbon to remove Hg0 from coal-fired flue gas was constructed.Results show that the sample has an abundant pore structure and the active components disperse well on its surface.The excellent total Hg0 removal efficiency(ET(2 h)>90%)was obtained in a wide reaction temperature range(150-300 ?)under N2 + 6%O2 atmosphere.Moreover,the Hg0 adsorption capacity in 1440 min was 5587.0 ?g/g and the Hg0 oxidation efficiency after reaching adsorption equilibrium(Eoxi(equilibrium))was more than 30%,which suggests that the introduction of both halide ions(I')and metal oxides(MnOx,ZrO2)on the surface of peanut shells carbon results in a high adsorption and oxidation ability.The involved reaction mechanism at 150 ? includes both adsorption and oxidation.The main chemical adsorption sites of carbon-iodine covalent groups(C-I)dominate Hg0 removal at initial reaction stage.As reaction progressing,the chemical adsorption is weakened due to the gradual saturation of adsorption sites whereas the catalytic oxidation caused by lattice oxygen([O])and hydroxyl oxygen(OH)substitutes chemical adsorption and dominates Hg0 removal at final reaction stage.Meanwhile,they can be replenished by gaseous O2 to keep the oxidation process continuing.In a word,the 6Mn-6Zr/PSC-I3 combining the advantage of halide ions and metal oxides was demonstrated to be a good material for Hg0 removal and had a promising prospect in industrial applications.