Speciation of major and trace elements leached from coal fly ash and the kinetics involved

The combustion of coal in thermal power plants may result in high concentrations of elements in the coal fly ash remaining that may be toxic to living organisms or pose a risk to the environment. This study was aimed at determining the concentrations of potentially toxic elements in coal fly ash leachates, in an attempt to simulate natural processes that influence the environment. Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and elemental composition studies were employed to characterize the physicochemical properties of the parent coal fly ash. The effect of various leaching parameters, including the pH of leaching solutions, the volume ratio of leaching solutions to the mass of coal fly ash, leaching time and temperature, were investigated. Moreover, the kinetics of the leaching of toxic elements from coal fly ash was also investigated by considering that the leaching process is governed by dissolution. Zero order, pseudo-first order, pseudo-second order, power function, simple Elovich and parabolic diffusion kinetic models were used to evaluate the leaching process. The experimental results indicate that the pH and leaching time had the most significant effect on the leaching behavior of elements from coal fly ash.