Mass transfer promotion in in-situ recovery processing

Elahe Karami

The primary trend in mining is a decline in mineral grades that are mined on a global scale. To sustain (or enhance) production, an increase is required in the amount of material that needs to be mined and processed, which, in turn, increases the demand for energy and water, with a higher resultant cost and carbon footprint and an undesirable increased waste and tailing generation, storage cost, and risk. Consequently, current mining methods are not sustainable and a new mining technology is required to address these issues. In-situ recovery (ISR), which uses a lixiviant solution to extract mineral of interest without physical excavation, could be an effective alternative approach. However, ISR can be challenging for low permeability deposits such as gold and copper. To increase the rate of mass transfer in ISR of low permeability deposits, one could consider using electrokinetic (EK), solution pulsing (SP) or ultrasonic (US) mass-transfer promotion methods. The EK method induces ion migration by applying an electric potential difference across a medium immersed in liquid. The SP method induces fluid flow by pumping solution into a porous medium intermittently instead of continuously, which drives the solution from less-permeable to high-permeability zones. Finally, the application of US wave emission into a porous solid immersed in liquid can create an intense pressure and increase in temperature. These temperature and pressure perturbations lead to increased mass transfer between the solid and solution, which can also increase the penetration of leaching solution into the solid. I investigate the viability of these three methods for ISR in this thesis, which is divided into three main parts. The first part of this study was designed to develop a standardised setup and methodology for EK-ISR studies that could be applied to a variety of lixiviant solutions and ore samples and yield reproducible results when different parameters were changed. Two laboratory scale EK-ISR setups were investigated, and a series of standardised experiments were revised to assess the effect of various conditions, such as voltage, membrane type, and sample permeability, on ionic flow and metal recovery, which are important in ISR. The standard method for EK involving a mostly reproducible synthetic sample, solution and laboratory scale apparatus allowed effective study of ISR conditions but also a comparative evaluation of the SP and US methods. In the second part of this study, SP was used to enhance mass transfer in the ISR setup. Experiments were designed to evaluate the effect of different parameters, such as pump on and off time and flow rate, on the movement of lixiviant ions through synthetic core samples. In the last stage of the project, the US method was used to increase lixiviant ion migration through synthetic core samples. A series of experiments was conducted and propagation of lixiviant solution was monitored through synthetic rock samples. The parameters investigated included ultrasound power, operating time and synthetic core sample permeability. The optimum conditions for the maximum migration of lixiviant ions through a synthetic core sample was determined. Overall, the work described in this PhD research is an early step towards exploring the commercial feasibility of all three proposed methods for application of ISR in a low-porosity environments. Results were encouraging and further investigation into the three techniques is warranted, for fluid flow stimulation in ISR.

Mass transfer promotion in in-situ recovery processing

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