Between 1980 and 2010, the average grade of ore bodies being mined in Australia has reduced by 50%. This has led to a 70% rise in energy use.
In recent years, the decline in the concentration of ore bodies has caused energy use to increase at an average rate of approximately 3% per year. Leading mining companies, such as BHP Billiton, Anglo American Coal and Rio Tinto have made public commitments to reduce energy use per tonne by 10-20% (a 40% reduction compared to 2000 levels) by 2020. Achieving these targets requires a strategic ‘mine-to-mill approach’ that addresses all sources of energy use and an integrated approach to energy efficiency investment across all areas of mining activity.
Energy use is typically dominated by comminution, i.e. crushing and grinding.
Other operations that use energy include:
- transporting mineral ores away from the mine site
- air transport of staff employed on sites in remote locations.
In some mines and mineral processing plants, such as gold and copper production, comminution can account for as much as 90% of all energy used and greenhouse gas emissions produced.
The energy used for comminution is forecast to increase over time, as ore grades continue to decline over the coming decades.As ore grades fall, the embodied energy of primary metal production and the associated greenhouse gas emissions will increase, particularly at ore grades below 1%, as a result of the additional energy that must be consumed in the mining and mineral processing stages to move and treat the additional gangue material.
It's important to keep ore grades above (or close to) 1% for as long as possible to prevent energy costs rising exponentially. For example, for copper and nickel, the amount of energy required for grinding increases exponentially once the ore grade becomes less than 1%. Keeping the concentration of the ore body as high as possible requires a holistic approach which starts at the resource characterisation stage.
There are numerous areas of opportunity for mining companies to improve energy efficiency and reduce greenhouse gas emissions. Applying energy efficiency strategies to comminution usually offers the best scope for the largest energy and cost savings. Other significant areas of energy usage tend to be hauling related transportation and movement of overburden and ore as well as ventilation (for underground mines).