Crushing energy costs in the mining sector
Comminution – the grinding and crushing of ore – is the most energy intensive step in mining and accounts for around 40 per cent of the total energy used in mineral processing operations. It also accounts for four per cent of the world’s total electrical energy consumption. Ore grades in Australia are also continuing to decline, requiring more energy to move and treat additional waste material, so comminution could be increasingly relevant.
In this article we look at the energy efficiencies available to miners through developing and implementing a comminution strategy.
There are a number of integrated strategies which can improve efficiencies and reduce energy use. New grinding technologies combined with selective blast design, ore sorting and waste removal and advances in modeling are just some of the approaches companies are adopting to improve ore grades and cut energy costs.
Investment in modeling data, energy mass balance assessments and updated equipment has already delivered major savings to operators such as Barrick Gold to the tune of around $5 million a year.
The following are just a few of the strategies leading edge companies are putting in place to successfully reduce their comminution costs and improve throughput.
Selective blast design combined with ore sorting and gangue rejection significantly improves the grade of ore being fed to the crusher and grinding mill. It offers potential savings of up to 30 per cent and a 2.5 fold increase in average mineral ore concentration feed.
New and more energy efficient grinding technologies can improve the input of energy going into the grinding process by as much as 40 per cent. Choosing high pressure grinding rolls (HPGR) circuits over semi autonomous grinding (SAG) equipment has also been shown to deliver energy efficiencies of 60–80 per cent.
Screens and filtering devices can dramatically reduce energy use and increase grinding efficiency by providing consistent particle sizes.
Selecting the coarsest possible grind size also reduces energy use. Alternatively if minerals can be sufficiently liberated and separated from the ore before further comminution, less grinding energy is needed and more efficient separation can be achieved in downstream processes. This strategy, however, requires a good understanding of the particle composition at different product sizes.
Use of more advanced and flexible comminution circuits, preferably using two or more parallel milling circuits, to allow high and low grade ores to be processed simultaneously, but on separate circuits. This enables each grade to be ground closer to its optimal recovery size and again cuts energy costs through increased grinding efficiency.
How to get a comminution strategy up and running
Getting an effective comminution strategy up and running requires strong corporate support and a dedicated energy management team who can identify ‘mine to mill’ cost efficiencies. Companies also need capacity to measure and collect data to understand what impact operations have on each other and overall energy use across the business. Advances in modeling and data collection are increasingly offering better and more informative insights to managers to improve their comminution processes. This can include:
Energy-mass balance models which uses baseline data to identify energy and mass flows and any external factors likely to impact on the efficiency of processes and equipment
Geometallurgy data on the nature of ore bodies and rock feed to inform technological options for downstream crushing and grinding processes. These target the highest ore grade concentration when blasting which can reduce energy use 10–50 per cent of metal per tonne.
Discrete Element Method (DEM) modeling to provide a detailed exploration of particle flows and breakage processes. This can be used for the design and rapid manufacture of new comminution equipment as well as improving existing equipment.