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

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.