Monday, 6 January 2014

The impact of milling costs on total mine operating costs

Leading up to Comminution ’14 in April, I highly recommend a paper recently published in Minerals Engineering, by workers at the University of Newcastle, Australia. “Mine operating costs and the potential impacts of energy and grinding” highlights that savings in milling costs will significantly affect total mine operating costs.

The paper shows that energy costs typically comprise one of the largest on-going costs of mining operations, of which 70% is devoted to the comminution of the ore. Furthermore, the most significant energy cost occurs in the grinding circuit, where up to 97% of the energy cost is incurred. Indeed, the area of comminution, and particularly grinding, are flagged as areas where significant savings can be made in mineral processing circuits.

In a summary of comminution needs for reduced energy use, the paper indicates that pre-concentration, greater emphasis on crushing, improved grinding technologies and mineral separations at coarser grind sizes are required to achieve significant savings in overall comminution costs.

Innovation in particle reduction technologies has been an area of active research for some time, with new grinding technologies such as the IsaMill and high pressure grinding rolls (HPGRs). HPGRs in particular show promise in improving the efficiency of grinding at the head of the circuit, where the greatest savings may be made. It has been shown, for example, that the replacement of a SAG mill with a HPGR in a conventional SAG-ball circuit may reduce grinding energy consumption by 15–20%. Taking into account additional savings, such as media and liner wear, it was found that a grinding cost saving of 25–35% was potentially achievable with the use of HPGRs in such conventional circuits. Other studies have found the applicability of HPGRs dependent on ore characteristics. HPGR technology remains a fertile area for achieving significantly reduced comminution costs.

All these aspects of comminution will be covered in the programme in April, with keynote speaker Tim Napier-Munn asking the provocative question “Is progress in energy efficient comminution doomed?”



  1. There is nothing new in this discussion. In the world many have replaced SAG and BALL mill with HPGR + VERTI MILL and prooved to reduce 30% energy and opex by 20%. Addtional advantages gained are---
    1.Colsed particle size distribution.
    2.Good control on Grade and recovery.
    3. Avoided slime generation which hinders flotation.
    4.A true metallurgist will prefer such combination who could understand the particle size distribution problem in controling grade and recovery. HPGR could replace a rod mill efficiency to produce closely sized particle which is the heart of process in flotation technolgy.

    1. I would suggest that you read the full paper Siva. There is much in it which is innovative and important.

  2. The significant impact of comminution cost on total operating costs is indeed a proven fact;I believe that improved comminution economics will result from hybrid systems i.e. SAG Mill- HPRG systems; as the HPRG throughput is volume limited the easy work therefore should be done in a SAG mill and the hard work i.e.pebble crushing by HPRG.
    Art Winckers, Arthur H. Winckers & Associates, Canada

  3. I am a strong believer in an AG-Mill-HPGR hybrid system, followed by Ball/Pebble mills or even Stirred mills. The AG can be set at relative low specific energy, the screening at the AG discharge would scalp fines (coming from ROM and produced in the AG - as portion of the ROM may contain soft material). The HPGR brings the greater benefits when used for hard and very hard material. Such circuits can significantly minimize ball media and energy consumptions.
    Persio Rosario, Aura Minerals Inc., Canada

  4. it is not all about the type and design of the comminution circuit. The problem is that there is still a group of engineers and metallurgist's thinking that you need finer particle sizes to achieve better extractions. However, if you go and do the calculations you will see that there is a fine line between more complicated circuit (more energy and cost) vs the benefit from possible additional metal recovery, thus the economic benefit of such a circuit. The amount of valuable metal you will liberate by adding energy and cost with a more complicated circuit will not always be financially beneficial. So the approach should be to save capital and operating costs by looking at both the comminution circuit design as well as the economic added benefit such a circuit would provide with additional metal recoveries. Keep it simple


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