Characterization of Coal Fly Ash by Electrical Impedance Spectroscopy, Magnetic Susceptibility and Mössbauer Phase Composition

Fly ashes contain iron-bearing phases with diverse magnetic properties, and their rapid identification may support assessment of their potential for raw-material recovery. The aim of this study is to develop a non-destructive method for characterizing ashes produced from lignite and hard coal combustion. The novel approach integrates electrical impedance spectroscopy (EIS) with magnetic susceptibility measurements and Mössbauer spectroscopy. The investigations were carried out on ashes collected from storage silos and electrostatic precipitators located at power plants. Forster-type impedance characteristics enabled differentiation of the ashes both across a broad frequency range and at a single frequency of 131.8 kHz. The share of spinels among the magnetically ordered phases was very strongly correlated with the real component of impedance and magnetic susceptibility (rs = 0.964). The results indicate that impedance spectroscopy can be used for a rapid, non-destructive assessment of the proportion of ferrimagnetic phases and the ash suitability for beneficiation.