Dielectric properties of hard rock minerals and implications for microwave-assisted rock fracturing

Abstract

Understanding microwave-assisted breakage and fracturing of hard rocks necessitates the characterisation of the dielectric properties of basic rock-forming minerals. In the literature, there is a significant discrepancy in the loss factors (i.e., the ability of minerals in absorbing microwave energy) of the gangue minerals due to the fact that different unsuitable and inconsistent measurement techniques are used. In this paper, the dielectric properties (i.e., the dielectric constant $\varepsilon^{\prime}$ and loss factor $\varepsilon^{\prime\prime}$) of 14 high-grade minerals, including 11 gangue minerals and 3 ore minerals that form most of the commonly found igneous and metamorphic hard rocks, were obtained using a customised resonant cavity and the effective medium theory at 2.45 GHz and room temperature. These minerals could be classified into three categories (i.e., low, medium and high loss) based on the magnitude of their loss factors. For the low-loss and medium-loss gangue minerals, their loss factors hardly correlate to either one or a combination of the metal elements or the crystal system. The dielectric properties of minerals were then used to explain the behaviour difference of granite and basalt when exposed to microwave radiation.