The effect of H2O on formation mechanism of arsenic oxide during arsenopyrite oxidation: Experimental and theoretical analysis

The effect of H2O on arsenic release behavior was investigated via experiment and first-principles density functional theory (DFT). The experimental results show that sulfide-bound arsenic is the main form present in coal, and that H2O has a positive influence on the release of arsenic during coal combustion. Furthermore, DFT calculations were performed to investigate the mechanism for H2O influence on arsenic oxidation. Thermodynamic and kinetic analyses were also conducted to study the influence of temperature on the reaction process. From thermodynamic analysis, arsenic oxide formation on the FeS2 (1 0 0) surface with and without H2O weakens with increasing temperature. In addition, the equilibrium constant for the reaction with H2O addition is slightly higher than that for the reaction without H2O, which suggests that the degree of the chemical reaction in the presence of H2O should increase. From kinetic analysis, the reaction rate constants increase with temperature, and the activation energy of the arsenic oxide formation reaction with and without H2O is 100.72 kJ/mol and 124.08 kJ/mol, respectively. This indicates that H2O adsorption on the surface can decrease the energy barrier and accelerate the reaction forming arsenic oxide. Based on the thermodynamic and kinetic analyses, it can be concluded that temperature has an inhibitory influence on reaction equilibrium and positive influence on the reaction rate. The experiment and calculation results explain the influence of H2O on the formation mechanism of arsenic oxide and provide a theoretical foundation for the emission and control of arsenic.