Review of Fracturing Techniques (Microwaves, High-Voltage Pulses, and Cryogenic Fluids) for Application as Access Creation Method in Low-Permeability Hard Rocks for Potential in situ Metal Recovery

ABSTRACT Rising mining costs and fewer high-grade ore deposits have necessitated a search for alternative methods for the recovery of metals from deposits that are no longer economically or environmentally exploitable by conventional mining. One such alternative method is in-situ recovery (ISR). Although ISR has typically been used for mining uranium ores that are not economic to mine with conventional methods, it has also been used less frequently for the treatment of other low permeability rocks, such as hard rocks containing copper, nickel, and gold. The reason for the limited uptake of the technology for hard rock mineralization is primarily due to the low natural rock porosity and permeability and hence limited ability of a lixiviant to permeate the rock and contact the minerals. This review focuses on three novel potential access creation methods: microwaves, high-voltage pulses, and cryogenic fracturing procedures. Most research studies of microwaves and high voltage pulses have focused on energy savings in comminution, but little research has been done on their application of in ISR. In situ cryogenic fracturing has been used in the petroleum industry and may be a potential novel option for use for the in situ recovery of minerals in the mining industry. The aim of this review is to summarize available information on these three methods for increasing the permeability of hard rocks and thereby improving the rate of lixiviant-mineral contact and mass transfer in in-situ recovery. The review will start with an overview of considerations for the use of ISR. The mechanisms of microwave, high-voltage pulse, and cryogenic fracturing methods will then be discussed.