Over the last few decades, the average grade of mined Australian ore has halved, while the waste removed to access the minerals has more than doubled.
Due to falling ore body concentrations, investment in energy efficiency opportunities will be increasingly important in managing operational costs and maintaining productivity.
There is significant potential to reduce energy costs through an integrated approach to energy efficiency investment. Applying energy efficiency strategies to comminution, the largest area of energy usage, usually offers the best scope for the largest energy and cost savings.
Energy is also used in blasting, drilling, de-watering and transporting of mineral ores away from the site. Other significant opportunities for energy savings exist in the areas of froth flotation separation, materials movement and ventilation.
Energy savings per tonne of up to 50% below business-as-usual are feasible in the design of new mining and mineral processing developments.
Opportunities to save
- Embed energy efficiency into corporate and site management practices.
- Upgrade the ore concentration.
- Adopt an integrated energy efficient comminution strategy.
- Improve the efficiency of sorting and separation processes.
- Improve the efficiency of drying and dewatering in mineral processing.
- Invest in materials movement energy efficiency opportunities.
- Implement air ventilation and conditioning.
- Implement mining and minerals processing site energy demand management and waste heat recovery options.
- Implement technology specific opportunities.
- Consider energy/water nexus efficiency opportunities.
- Improve energy efficiency in product transport from mine to port.
For more information, see Mining opportunities to save.
The overarching trend of energy usage in the mining sector is increasing, largely due to the historic trend of declining ore bodies. Two new strategies are being explored currently to address this are deep sea mining and froth flotation.
Deep sea mining
Deep sea mining is a relatively new process that a number of nations and companies are exploring because, in certain parts of the deep ocean, minerals exist at higher ore grades than on land. For example, copper ore grades can be as much as 79', which is unheard of on land.
Advances in underwater drilling and ocean draft mean that a number of mining companies are stating that they will undertake deep sea mining within the next few years.
Life cycle analysis studies are needed to determine if overall deep sea mining uses less energy than land based mining. The high ore concentrations in the deep sea beds suggest it may use significantly less energy to produce the same amount of valuable minerals.
Potential innovation in froth flotation
Currently, mineral ores are crushed and ground down to a size small enough to undergo froth flotation to separate out the valuable minerals from the mineral ore. There is an upper limit on the size of the particles that can be treated at present, so all the material to be floated must be ground to below this size.
The top grinding size for flotation with current technology is typically 150 microns, not much bigger than a human hair. If the top size were raised to 600 microns, the grinding energy would be reduced by half.
Research undertaken at Newcastle University has developed a process for the flotation of coarse particles, known as the fluidised bed flotation cell. The research reasons that the cause of the low recoveries achieved with coarse particles was the high degree of turbulence in conventional flotation cells.
Instead of using a mechanical agitator, the research found that if the particles were Ievitated with an upflow of water in a fluidised bed, a gentle environment for contacting bubbles and particles could be provided.
Very high recoveries have been achieved with mineral particles up to at least 1.4mm in size. This offers the potential to save energy in crushing and grinding by an order of magnitude. As well as saving energy, the fluidised bed cell has the potential for significant reductions in water use, because it can take feed slumes that are twice as dense as used in current practice.
A large energy consumer in underground mining is ventilation, and new technologies are continually being developed with the aim of optimising ventilation systems. Ventilation-on-demand means air is provided to underground tunnels and openings only when and where it is needed, reducing energy consumption in an underground mine by up to 40%.
Replacing diesel power underground
Diesel engines are widely used in underground mining vehicles, meaning ventilation systems need to work extra hard to dilute the toxic diesel fumes in the underground air. Alternatives to diesel, such as hydrogen, liquefied natural gas, and lithium-ion batteries, are advancing in their development and cost-effectiveness.
Comminution research, benchmarking and optimisation
There are many opportunities to optimise and innovate traditional comminution processes, but operators are generally unaware of the potential benefits in a given situation. A major barrier remains a limited understanding of how operating various comminution circuits compare in terms of energy usage and cost. Benchmarking has been difficult, due to the multiple factors that impact comminution energy use from site to site, and the lack of data sharing across firms.
Mineral exploration in Australia Geoscience Australia
Renewable energy in the mining sector Australian Renewable Energy Agency
Sustainable Minerals Institute University of Queensland.