Study on arsenic/lead adsorption characteristics by mineral oxides in coal-fired flue gas
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摘要: 选取典型的矿物质氧化物为吸附剂,在两段式固定床反应器中研究了模拟烟气气氛下吸附剂吸附As2O3、PbO的特性,吸附反应的原子态密度、吸附位、吸附能等通过密度泛函理论(DFT)计算获得。结果表明,CaO的砷吸附容量最大,900 ℃吸附砷容量为5.25 mg/g;其次是Fe2O3、MgO、Al2O3,吸附的砷以As3+和As5+的砷酸盐形式存在,高岭土和飞灰具有较大的PbO吸附容量,最大吸附容量分别为6.69和2.75 mg/g;其次是SiO2和Al2O3,并且50%SiO2/50%Al2O3混合吸附剂的铅吸附容量高于单一氧化物,吸附剂表面O原子是As2O3的吸附活性位点,吸附剂暴露的不饱和Si和Al原子是PbO的吸附活性位点,此外温度、烟气气氛对吸附容量和吸附产物有显著影响。Abstract: The As2O3 or PbO adsorption characteristics using typical mineral oxides as the sorbents were studied in a two-stage fixed-bed reactor under a simulated flue gas, and the density of atomic states, adsorption sites, and adsorption energy for the adsorption reaction were calculated by density functional theory (DFT). The results demonstrate that CaO has a large As2O3 adsorption capacity, with an arsenic adsorption capacity of 5.25 mg/g at 900 ℃, followed by Fe2O3, MgO, and Al2O3; and the adsorbed arsenic exists in the form of As3+ and As5+ arsenates. Kaolin and fly ash have large PbO adsorption capacities, with the maximum lead adsorption capacities of 6.69 and 2.75 mg/g, respectively, followed by SiO2 and Al2O3, and the adsorption capacity for lead with the 50%SiO2/50%Al2O3 mixture is higher than that with their single oxide. The oxygen atoms on the surface of the sorbents are the active sites for As2O3 and the unsaturated Si and Al atoms exposed on the surface of the sorbents are the active sites for PbO. In addition, the adsorption temperature and flue gas atmosphere have significant effects on the adsorption capacity and adsorption products of the sorbents.
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Key words:
- heavy metal /
- coal combustion /
- adsorption mechanism /
- oxide sorbents
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表 1 氧化物吸附剂的结构特性
Table 1 Structure properties of the oxide sorbents investigated
Sample Structure properties surface area A/(m2·g-1) pore diameter d/nm pore volumev/(×10-2 cm3·g-1) CaO 5.27 23.34 3.08 MgO 4.71 19.78 0.21 Na2O 3.62 10.18 0.74 Fe2O3 11.79 18.01 3.06 Al2O3 1.65 7.91 0.12 SiO2 1.87 8.93 0.11 表 2 吸附剂吸附砷的吸附能
Table 2 Adsorption energy of sorbents for adsorbing arsenic
Surface Adsorption energy E/(kJ·mol-1) CaO(001) -216.63 MgO(100) -170.21 Na2O(110) -336.98 Fe2O3(001) -358.00 Al2O3(100) -203.23 SiO2(001) -156.40 表 3 不同温度下SiO2(001)吸附PbO的ΔG
Table 3 ΔG of SiO2(001) adsorbing PbO
Temperature T/K ΔG /(kJ·mol-1) 300 -173.36 800 -133.47 1300 11.02 1800 32.42 -
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