Monday, 6 February 2017

Superior comminution circuit performance: integrating classification during design is the key

The synergistic relationship between comminution and classification in comminution circuits is well known and has been extensively proven both in research and plant operation practice – but why do we often get it wrong? This will be the subject of a keynote lecture at next year's Comminution '18, by Prof. Aubrey Mainza of the University of Cape Town.
Aubrey is Head of Comminution and Classification Research in the Centre for Minerals Research, his research areas including comminution and classification, where he uses Discrete Element Method, Computational Fluid Dynamics, and Positron Emission Particle Tracking as tools in his modelling methods. Aubrey is a familiar figure at international conferences, particularly MEI's comminution series, where he has acted as a consultant for a number of years.
Aubrey (centre) with Magnus Evertsson and Hakan Benzer at Comminution '16
The comminution circuit is usually made up of comminution devices operated in closed circuit with different types of classifier. The closed circuit arrangement can have separate comminution and classification devices linked through pump-sump arrangements or integrated comminution-classifier systems. It is well documented that the choice and operation of the classifier have a major influence on the performance of the comminution circuit as a whole. An inefficient classifier can increase the energy consumption of the comminution circuit and in most cases also compromise the quality of the product reporting to downstream processes, leading to losses in recovery of the valuable mineral. Despite the known pitfalls of inadequately designed classification components of the comminution circuit the status quo has continued in most design teams. Substantially more effort and resources are expended on testwork for selecting and sizing comminution equipment compared to the accompanying classifying equipment, which is subjected to minimal or sometimes no confirmatory testwork.
In his keynote Prof. Mainza will ask why clear evidence of inefficient circuit performance that is directly attributable to a mismatch of the comminution and classification devices often appear to be totally ignored, and how can this perennial problem be eliminated in our standard comminution circuit design approach? He will ask what solutions have mining research and innovation programs provided in resolving the subtle incompatibility problems between comminution and classification devices and he will address the problems encountered when common approaches are used in selecting key comminution circuit equipment, proposing amendments that should be considered to avoid the known deficiencies.  


  1. Proper intermediate classification is really key to Comminution circuits!
    Holger Lieberwirth, Director of Institute of Mineral Processing Machines at Technical University Bergakademie Freiberg, Germany

  2. Great article Mr. Wills. We've been asking ourselves similar questions as to why so many good engineers seem to ignore the importance of classification.
    Jobe Wheeler, Derrick Corp., USA

    1. Hopefully Derrick Corp. will be at the conference to hear and contribute to the keynote

    2. If only there was a means for significantly increasing the specific loading on screens without losing efficiency.
      Robert Seitz , Arizona, USA

  3. Reading the responses to date, no one seems to disagree that classification is important in comminution. Many of the comments discuss classification efficiency, which I must agree is important. But then you go to operating plants and find that the classification circuit is being operated very inefficiently. I have wondered about taking a look back at an old technology and replacing the cyclones with very large screw classifiers, which can run efficiently at a lot higher feed density than cyclones.
    Mike Albrecht, Roberts Companies, USA

  4. we made some test on different minerals and to close the mill circuit with derrick screens is the best modern way to work on the concentrator plants: high efficiency, better recovery, and less reagents on the flotation and better grade.

  5. Bary, I am happy you brought out such loaded information and I am sure Prof.Mainza selected a very timely topic. I personally feel that talking about a grinding unit alone does not help any one. It is the classification unit (cyclones in many cases) who play the deciding role because the retention times of particles in the mill and cyclone are much different. Circulating load characteristics are very different from new feed--more so in volume.
    Many times you have more than two cyclones in parallel classifying the mill product. The performance of the distributor box is another factor.
    I am sure mineral engns take a holistic view of comminution (even crushing and flotation circuits) so that plant people understand the influence a particular unit has in the composite operation.
    All the best.

  6. Cyclones work best and most efficiently when operated as consistently as possible. Consistently achieving consistent cyclone size split optimizes downstream beneficiation metallurgical results. That is first principles. For various reasons mills often struggle with fluctuating levels in secondary mill, cyclone feed sumps due to level measurement accuracy and response time issues with the standard ultrasonic devices. Fluctuating sump levels affect feeding cyclones and negatively impacts overall plant results. More and more of our customers are installing LTM-2 conductive level measuring probes in their sumps and getting much better level control since the probes are very accurate and provide essentially instantaneous readings without much signal integration. For reference, description is provided:


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