A low energy rock fragmentation technique for in-situ leaching

Because over 60% of the total energy consumed in conventional mining consists of excavating, hauling, and liberating processes, the energy consumption in conventional methods of mining has increased exponentially with the decline in global ore-grades. In-situ leaching (ISL) is an alternative mining technology, which eliminates these processes. However, ISL is currently limited to porous rock. Expansion of ISL to impervious mineral bearing rocks requires controlled, artificial fracture stimulation and the current practice of hydraulic fracturing is not compatible due to the associated environmental impacts and uncontrolled fracture propagation. Therefore, to extend the application of ISL to impervious rocks, an alternative fracturing method using Soundless Cracking Demolition Agents (SCDAs), which is capable of producing controlled fractures in a rock mass, is proposed in this study. With the aim of understanding the fracturing performance of SCDA under in-situ stress conditions prevalent in ISL environments, a 3D numerical model for SCDA charging was produced using Particle Flow Code (PFC3D 5.0) and validated with experimentally obtained data. The model was then extended to investigate the fracture mechanism of SCDA charging at various confining pressures of 5, 10, 15, and 20 MPa. Simulation results suggest that during SCDA charging, the number of radial fracture propagations and the total fracture damage in the rock mass increase with the confinement and the fracture pattern is dependent on the confining stress of the surrounding rock. In comparison to a hydraulically fractured specimen with identical dimensions, the fracture density of SCDA charged specimen showed a ten-fold increase at high confining pressures (20 MPa). Furthermore, as opposed to an uncontrolled, unidirectional diametrical fracture generated by hydraulic fracturing, SCDA charging produces multiple radial fractures around the injection well facilitating better spatial distribution of fluid flow for ISL. The results of this study imply that SCDA charging produces a denser and a controllable fracture network compared to hydraulic fracturing, which could potentially expand ISL applications to impervious rocks.