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High-resolution dielectric characterization of minerals: a step towards understanding the basic interactions between microwaves and rocks

Microwave energy has been demonstrated to be beneficial for reducing the energetic cost of several steps of the mining process. Significant literature has been developed about this topic but few studies are focused on understanding the interaction between microwaves and minerals at a fundamental level in order to elucidate the underlying physical processes that control the observed phenomena. This is ascribed to the complexity of such phenomena, related to chemical and physical transformations, where electrical, thermal and mechanical forces play concurrent roles. In this work a new characterization method for the dielectric properties of mineral samples at microwave frequencies is presented. The method is based upon the scanning microwave microscopy technique that enables measurement of the dielectric constant, loss factor and conductivity with extremely high spatial resolution and accuracy. As opposed to conventional bulk dielectric techniques, the scanning microwave microscope can then access and measure the dielectric properties of micrometer-sized mineral inclusions within a complex structure of natural rock. In this work a 5 by 20 micrometers size hematite inclusion has been characterized at a microwave frequency of 3 GHz. Scanning electron microscopy/energy-dispersive x-ray spectroscopy and confocal micro Raman spectroscopy were used to determine the structural details and chemical and elemental composition of mineral sample on similar scale.