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Integration is the key to the future of comminution

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World Cement,

Comminution '14, which was held in Cape Town in April, ended with an excellent panel discussion on the future of comminution, chaired by MEI consultant Dr. Aubrey Mainza, of the University of Cape Town. The four panelists were Dr. Rob Morrison and Prof. Tim Napier-Munn of Australia's JKMRC, Prof. Marcelo Tavares of University of Rio de Janeiro and Prof. Wolfgang Peukert of University of Erlangen-Nuremberg, Germany.

Prof. Peukert began by saying that much could be gained if the science of comminution and industry could come closer together. It is apparent that modelling now gives us a greater understanding of what is going on in a milling circuit, and there is a lot to be gained from detailed modelling. The models, however, must be checked by reality to give us a reliable toolbox to assess what is happening, particularly with complex multi-phase particles, which can be characterised to assess liberation, the balance between strength of grain boundaries and strength of grains. On a larger level, classification and mill throughput are critical, as they affect energy efficiency and overgrinding and we need a better understanding of the transport properties and an ability to remove particles that are properly stressed. We do not yet know how the particles are stressed and we have to accept that we do not as yet have ideal models for process simulation. He says that the universities are prepared to undertake work on these problems, and if industry comes in as well we can solve a lot.

Prof. Tavares said that it was important to compare what we saw two years ago at Comminution '12, particularly in crushing and dry comminution, and the potential now for grinding finer using compression crushers, which is important given the need to conserve water in our industry. This year we have seen different levels of comminution modelling living together, from the very basic Bond equation, which has its place in the minerals field, to the population balance models of the 1960 – 1980s, to the advanced models of today. He also stressed that it would be good to see at Comminution '16 some strong case studies with industry results to demonstrate the effectiveness of these modern methods, so it is important now for the researchers to strengthen their relationships with industry. He stressed again that we must increase our understanding of machine and material contributions, particularly fracture response and its contribution to liberation.

In Prof. Napier-Munn's opinion, Comminution '14 was an exceptional conference. He said he had been "blown away" by the vigour and enthusiasm of the smart people who are doing great work in a very mature field, and that it is extraordinary to see new ideas still coming along. He added that in terms of the future of comminution, "we really have to get rid of tumbling mills". The energy crunch will soon come and it will be very bad for our industry and we must put the next few years to work with the people who attended. It is obvious that there are many new ideas out there. New crusher developments, HPGRs, fine grinding devices and circuits offer new approaches and some hope for the future.

As with the others, Prof. Napier-Munn expressed his disappointment that the heavyweights of the mining industry did not attend the conference, with the exception of Anglo American, who were present in force. He warned that unless the operators, who are the users, drive these new ideas in a constructive and intelligent way, then we will not make progress as fast as he thinks we need to. He enthused about the modelling, which he feels has now given us a mature set of tools. DEM, CFD, SPH and their combinations, are now ready to solve problems, which was not true 20 years ago. However they are only being used to solve problems in a few patchy areas, and the challenge to change the comminution scene is to make much better use of these models with some real integration between the modellers and the people with the problems; this must be driven by the companies.

Jeremy Mann, of Anglo American, South Africa, remarked that we had fantastic tools available now, but we should look more towards understanding selective liberation rather than just breakage, and to use the models in process control systems, which means that we need better understanding of process mineralogy and the variability of our ores. Rob Morrison agreed with Jeremy, and noted that the few people at the conference who had talked about liberation had all been interested in the liberation of the valuable components, but the real challenge is to liberate and discard the major proportion of the ore, the gangue, at a coarse size. He congratulated Chris Greet for presenting a flotation paper at a comminution conference, but then said that if people followed his strategy most mines would go broke very quickly! He was disappointed that no one had mentioned at the conference that in rougher-scavenger grinding we are actually trying to liberate the gangue, we cannot afford to liberate the valuable minerals, and the most difficult decision is how far to grind, and this is largely an economic one.

Dr. Greet responded to this by agreeing with Rob, in that we only try to attain 60 – 70% liberation, dependent on the mineralogy, but we aim for much greater liberation in the regrind circuit. He made the point that comminution is not just crushing and primary grinding but regrinding as well, so basically both he and Rob are right!

Adrian Hinde of Mintek also highlighted again the need for integration between the researchers and industry, and also argued the case for more integration between the mining engineers, dealing with blasting, which is essentially the first stage in comminution, and the mineral processors.

I think the key message here is that there is a need for greater integration between academia, research institutes, suppliers, all of whom were well represented at Comminution '14, and industry, which was not. Hopefully the operators will be out in more force at Comminution '16, which will be held in Cape Town from 11 – 14 April 2016. There is much to be gained by their presence, preferably to present case studies on operating plants, validating the work of the researchers, or just to network. As Clifford Mutevhe, of Anglo American, Zimbabwe observed, "(Comminution '14) not only enhanced my knowledge but also helped me identify solutions to the milling circuit I manage. Some of the discussions we had we have carried forward as part of the business process improvements. I also managed to identify with a huge pool of knowledgeable people from across the world. I could not imagine communicating daily and interacting with people from RSA, USA, France, Iran, China, Australia and various other countries."

Written by B.A. Wills, MEI, UK.

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