ABSTRACT
As more nations strive to become part of the developed world, the demand for commodities continues to increase rapidly. However, the high-grade and easy-to-mine deposits are mostly on the decline and future mineral deposits are likely to be deeper with higher stripping ratios, lower grade and in more remote locations with little infrastructure and skilled labour pools. The reduction in feed grades will increase the comminution energy demand per unit of metal produced. In addition to decreasing grades, the amount of waste and haul distances will increase as the deposits get deeper thus significantly increasing the haulage energy requirement. Deeper pits also increase the risks of slope stability and wall failure and if not managed in a timely manner slope failures not only pose risk to regular production but also significantly increase the energy signature of the operations by increasing unplanned haulage. Producing commodities from such deep and low-grade deposits is likely to substantially increase the energy (fuel, electricity and embodied) requirements per unit of mineral/metal produced as well as the carbon footprint of the operations. Embodied energy is the quantity of energy necessary for the fabrication of material or consumable used in the process. In addition to higher energy requirements and operating expenses (OPEX), mining deeper and lower grade deposits also require higher capital expenditure (CAPEX), which has become a significant impediment to investment.
The value chain in most mining operations involves a number of complex inter-dependent processes in which each process is sensitive to a range of rock mass attributes within the mine block that are transformed by the previous processes. The value created per ton of rock within that mine block is the difference between the price it commands when sold as the final product and the cost to produce it. Even though it is obvious total mine-to-mill processes are interdependent, traditionally, mining and milling are managed separately right from feasibility studies to day-to-day operations. Such an approach will not only increase the risk of the project but also may ultimately lead to suboptimal operations.
During the past 15 years, the Julius Kruttschnitt Centre at the University of Queensland has been involved in implementing a holistic methodology ‘mine-to-mill optimisation’ to improve the efficiency of mining operations. One of the key components of this approach is proper understanding of rock mass attributes and its variability in terms of its breakage and separation during different processes within the mine-to-mill value chain. In this chapter, the authors use the mine-to-mill approach to demonstrate the energy efficiency of mining projects by using case studies and established process models and simulations.
