Effect of Additive Material on Controlling Chromium (Cr) Leaching from Coal Fly Ash

A Role of Mineral Oxides on Trace Elements Behavior during Pulverized Coal Combustion

The issues of trace element emissions during coal combustion has been a concern in recent years due to their environmental pollutant. To study the trace element transformation, the thermodynamic calculation (FactSage 7.2) was used. Five kinds of pure mineral oxides (Al2O3, CaO, Fe2O3, K2O, and MgO) and As, B, Cr, F, and Se in fly ash were considered for trace elements. The results confirm that all mineral oxides have a good correlation with arsenic to form Ca3(AsO4)2, FeAsO4, K3AsO4, and Mg3(AsO4)2. Boron has a good relationship with Al, Ca, and Mg to form (Al2O3)9(B2O3)2, Ca3B2O6, and Mg3B2O6. Chromium has a good correlation with K and Ca to form K2CrO4, CaCr2O4. Furthermore, FeF3(s) KF(s), and AlF3(s) are predicted from the interaction of fluorine with Fe2O3, K2O, and Al2O3. The effect of mineral oxides on selenium partitioning are not observed. The inhibition order of trace elements by mineral oxides is as follow: As (Al2O3 > MgO > CaO > Fe2O3 > K2O), B (Al2O3, CaO, Fe2O3, K2O, > MgO), Cr (CaO > K2O > Al2O3, MgO, Fe2O3), F (CaO > MgO > Al2O3 > Fe2O3 > K2O). The results will be useful to control the trace element emissions.