UNDERSTANDING THE EFFECT OF MICROWAVE IRRADIATION ON PHYSICAL PROPERTIES OF ROCKS USING LABORATORY TESTING AND NUMERICAL MODELING

The scope of the research work presented in this study is to understand the changes in physical properties of different rock samples (granite, granodiorite and quartzite) when exposed to microwave irradiation for different exposure times. Rocks experience selective thermal loading when exposed to microwave irradiation. The extent of this loading strongly depends on the dielectric properties (dielectric loss and dielectric constant) of individual minerals. Consequently the grain boundaries of these minerals will experience thermal stress gradients, serving as sites for fracture generation and development. This phenomenon could be tapped to develop viable technologies for preconditioning rocks in a range of mining and mineral processing applications.

Results of laboratory experiments investigating the response of physical properties like p-wave velocity and uniaxial compressive strength to microwave irradiation of different rock types indicate a decrease in the integrity of the investigated samples. A finite element modelling (FEM) chain was developed in order to simulating the development of thermal stresses in a granodiorite sample. The constitutive minerals: quartz, biotite and feldspar were arranged in different patterns and exposed to different external temperatures. Preliminary modeling results are in good accordance to laboratory tests, indicating that minerals with high thermal properties (coefficient of thermal expansion, thermal conductivity, and heat capacity at constant pressure) such as quartz cause high stresses to be developed along grain boundaries.