燃煤飞灰中矿物质对烟气中As、Se、Pb形态分布影响的热力学研究

Thermodynamic study on effect of minerals in fly ash on morphological distribution of As, Se and Pb in flue gas

    摘要
  • 摘要: 基于热力学平衡的原理，研究了燃煤烟气中As、Se、Pb三种重金属与飞灰中主要矿物质CaO、Al2O3、Fe2O3、MgO的反应。结果表明，As在1600 K时与CaO反应开始生成Ca3(AsO4)2，且随着CaO含量的增大，Ca3(AsO4)2的温度区间变窄，说明CaO对煤中As的挥发有抑制作用；As与Al2O3在1700 K时开始反应，随着温度降低最后全部以AlAsO4的形式存在；As与Fe2O3反应生成FeAsO4；As与MgO在600-1500 K以Mg3(AsO4)2(s)形式存在，低于600 K时转化为As2O5(s)。Se与CaO和MgO在低于600 K时分别以CaSeO3(s)和MgSeO3(s)的形式存在，与Al2O3、Fe2O3不发生反应；CaO与Pb在900-1100 K时反应生成了(CaO)2(PbO2)(s)；Pb与Al2O3会发生反应，在900-1200 K时有固态(PbO)(Al2O3)6(s)生成。Fe2O3、MgO对Pb的形态分布基本没有影响。

     

    Abstract: Based on the principle of thermodynamic equilibrium, reactions between heavy metals As, Se and Pb in flue gas of coal burning and main minerals CaO, Al2O3, Fe2O3 and MgO in fly ash were studied. The results show that As reacts with CaO at 1600 K to form Ca3(AsO4)2, and its temperature range becomes narrower with increasing CaO concentration, indicating that CaO can inhibit volatilization of As in coal. As reacts with Al2O3 at 1700 K, reaction of As with Fe2O3 forms FeAsO4. As and MgO exist in the form of Mg3(AsO4)2(s) between 600 and 1500 K, and turns into As2O5(s) below 600 K. Se and CaO, MgO exist in the form of CaSeO3(s) and MgSeO3(s), respectively, below 600 K, but does not react with Al2O3 and Fe2O3. CaO and Pb react at 900-1100 K to form (CaO)2(PbO2)(s). Pb reacts with Al2O3, and solid (PbO)(Al2O3)6(s) is formed at 900-1200 K. Fe2O3 and MgO have no effect on species distribution of Pb.

     

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