Valuable minerals are extracted from rock via the process of comminution (crushing and grinding). In the mining and mineral processing sector, most energy use and greenhouse gas emissions derive from comminution, separation (froth flotation) and concentrate drying. Of these areas, comminution is the most energy intensive.
In some mining sub-sectors, such as gold, copper and nickel, comminution comprises over 70% of total energy use.
Additional energy is needed to mine and process ore grades of declining quality. As well as being less profitable or cost-effective, this situation increases the energy embodied in primary metal production and its associated greenhouse gas emissions.
According to the Coalition for Energy Efficient Comminution, comminution accounts for 3% of the entire world’s energy consumption. Comminution energy costs are forecast to increase significantly over the next decade due to the overall trend of declining ore grades. Some of these costs could be better managed through adopting more efficient comminution processes and technologies.
Opportunities to save
Opportunities to improve energy efficiency of mineral processing technologies include activities in the following areas:
Implement a holistic comminution energy efficiency strategy
The selection of appropriate comminution technologies and crushing and grinding mill configurations depends on the feed size distribution, the desired product size and other physical properties which define the material. To achieve the full potential of energy efficiency opportunities, a holistic and ongoing approach should be adopted. Such a strategy should consider factors like resource characterisation, pre-concentration of ore grades, more efficient and fit-for-purpose technologies, flexible comminution circuits, efficiency of motor systems and indirect energy use.
Improve the energy efficiency of motor systems
Electric motors are used to drive crushing and grinding mills. These consume a significant percentage of energy in comminution. As comminution mills work to process more throughput, using the most appropriate combination of motor systems will directly affect performance, flexibility of operation, and total energy efficiency of the mill. This requires detailed investigation and selection of motors, and circuit design.
Improve the efficiency of drying and dewatering in mineral processing
Drying and dewatering in mineral processing reduces the energy required for materials movement. However, at mine sites where concentrate is processed, drying is itself a significant energy using activity. Therefore, where feasible, mining sites should use:
- waste heat to reduce the energy required for drying
- solar drying of concentrate