Monday, 20 May 2013

Could comminution be eliminated from the mining process?

This provocative question will be posed at next year’s Comminution ’14 in a keynote lecture, The Next Stage in Evolution in Comminution, by Alan Muir, Vice President Metallurgy at AngloGold Ashanti, South Africa.

Alan Muir
In the current mining environment, the need to reduce cost whilst maintaining throughput and recovery, places existing technology in a precarious position. Having evolved over time to adapt to the new environment, Alan feels that current comminution activities are rapidly becoming unsustainable. Whilst there is still value to be had in reducing the unit cost efficiency of existing processing methods by applying “known science” in different ways, this is ultimately an evolutionary dead end. Tumbling mills are inherently incapable of making the jump to a new evolutionary curve and will become extinct sometime in the not too distant future, as has been discussed at previous comminution conferences (posting of 14th March 2013).

Alan will show that it is important that the industry begins to focus on the next “species” of comminution devices and indeed on a new paradigm where the actual comminution step is eliminated from the mining process. Whilst this will require significant investment to conduct fundamental research work, the potential benefits are expected to be considerably greater. The solutions which survive will probably be those that address more than one step in the mining value chain.

How this will be achieved? We will have to wait for Alan’s keynote, which will outline some thinking on a roadmap aimed at facilitating this fundamental evolutionary change.


  1. I'll be first to cop a serve from respondants!

    Comminution is practised to ensure the valuable product we intend to recover is liberated from the guange (Minerals Processing 101). Comminution begins in the mine and is completed in the process plant. In my mind - No comminution no mine, no process. No mining and where are we - Freezing in the dark.
    Peter Steckis, Consulting Metallurgist, METS, Australia

  2. No one in the indusrty want to increase cost just like that. It not a facy item. Today almost all know cost plays a major role. How to further reduce is a subject of R&D. There are many ways to do.
    1.Preconcentration at 12 to 1mm size.
    2. Direct reduction of ore 12mm to 0 micron in fastmelt furnaces.
    3.Insitu leaching of ores.

  3. Not completely but yes we can minimize it if
    (a) Get liberation in coarser sizes by preferential breakage
    (b) Advance leaching technology
    Veerendra Singh, India

  4. This was one of the ways that oil shale was going to be processed. Use a sub-level caving mining method to create insitu reorts, ignite some of the bitumen, and then allow the bitumen to drain down and be pumped out. Some trails were under way when the bottom fel out of the oil shale back in the early 1980's. They are probably still burning.

    A simialr method was proposed (I believe) down in Arizona in the 1970'2 or 80's for copper. Sub-level cave and then drive a top entry for leachate injection, and collect the loaded solution at the bottom. I do not know if it amounted to anything.
    M. C. (Mike) Albrecht, USA

  5. Thats kind of difficult for achieve that contact in such low grade minerals is a difficult thing. Even after communition you might find some minerals which are not fully liberated at a magnitude of microns, and cant be accessed. It will be interesting to see how this may evolute, although nothing is impossible in this world full of innovative people.
    Thamsanqa Ncube, Freda Rebecca Gold Mine, South Africa

  6. Apparently any process without comminution cannot be imagined. Depending upon the process, more or less liberation of material is required.

    Based on energy consumption and wear of machines (crushers and mills), I think the more attention has to be paid on machine designing (including mechanical and electrical engineers) as well as on processes improvement in order avoiding some stages of comminution either crushing or grinding.

    Also the blasting is playing the crucial role in size reduction and can affect the selection the stages in comminution.
    Ninoslav Pavlovic, Canada

  7. What about ultrasonics ? Gall bladder stones are broken up by ultrasonic vibrations.
    R Sudhakar, India

  8. Comminution to liberate valuable minerals & metals began in the Stone Age and continues to progress. Today, SAG mills replaced secondary&tertiary crushing - now, SAG mills are being replaced by HPGR (High Pressure Grinding Rolls). The need to 'Comminute' rocks will always be necessary - it is the way in which it is accomplished that is changing - QUICKLY.
    Louis Bernard, Snowden Consultants, Canada

  9. I just find his arguments contradictory:

    Alan will show that it is important that the industry begins to focus on the next “species” of comminution devices and indeed on a new paradigm where the actual comminution step is eliminated from the mining process

    So he has hedged both ways:

    improve comminution
    get rid of it.

    Personally I just don't like this style of writing; but if others like it and find it inspiring then don't let me dampen your enthusiasm.
    Stephen Gay, Australia

  10. Since comminution is the process in which solid materials are reduced in size, by crushing, grinding and "other" processes. To "eliminate" comminution from mining implies no size reduction following the basic mining (even that has aspects of comminution). Any method used to reduce the size of the ore, even sledge hammers or ultrasonics is comminution.

    It might be possible to reduce comminution by transporting it in as large sizes as possible, and using simpler concentrating stages (gravity) to pre-concentrate before going for liberation. But eliminating comminution and still produce a simialr grade and have a similar recovery, my be difficult.

    The only concept I can think of would be som insitu leaching process.
    M. C. (Mike) Albrecht, USA

  11. The only process I can think of is straight to the smelter.

    Suddenly comminution looks efficient!

    My only analogy is avoid chewing food; let it go straight to the stomach.

    Incidentally straight to the smelter wouldn't be such a bad idea if the heat can be recycled.

    I don't know much about smelting, but is the heat recycled in anyway?
    Stephen Gay, Australia

    1. The Warner Process for direct smelting of complex sulphide ores was developed at Birmingham University in the 1980s, and although proven at pilot scale has never found any industrial application. The basis of the process is direct smelting of complex sulphide ores and recovery of the heat from the exothermic reactions. See ttp://

    2. Well that is interesting....

      Maybe it was ahead of its time?

      So is the author retired?

      Obviously I am not currently in a position to pursue this line of enquiry, but the various member Innovation Managers might be interested.
      Stephen Gay

    3. Noel Warner, now in his 80s, is Emeritus Professor of University of Birmingham, and I last saw him at the IMPC in Brisbane in 2010, where he gave a keynote on direct smelting. Philip Gray, also in his 80s now, has been attempting to promote the virtues of the Warner Process for many years. He was very recently awarded the IOM3 Futers Gold Medal for outstanding services to the international minerals industry ( I have lost touch with Philip. Does anyone know how he can be contacted?

  12. This is a topic which concerns me and I don't think the solution is or ever will be clear.

    My opinion is that one day mine sites (the ones that havn't been superseded by recycling plants) will be powered by alternative energy methods. Once energy costs become sufficiently high, renewable energies may become more viable. Processes that require 24hour operation will require energy storage (such as solar thermal) and will incur additional cost.

    Operations that can achieve metal recovery with the lowest energy input will become the most viable. LOM will be increased and possibly low recovery-low energy input-multiple pass operations will become the norm.

    If this is not feasible than indeed, hard-rock mining as we know it may one day cease. perhaps it will be more viable to extract minerals from brines and seawater.

    Production of non-essential commodities such as gold and gem-quality diamonds will be substantially reduced, and boutique alloying agents will be superseded by more abundant, easily extracted elements.

    I think the current approach to extraction and production is not sustainable.
    Aleksander Zawadski, Orway Mineral Consultants, Australia

  13. Barry:- I thinking out of box designed a process for mining on asteroids which avoided comminution. I guess you will like to read it.

    What I could come up with, may sound completely insane but I would be happy to read your opinion
    on this. *this will not be applicable to coal" In space, the solar energy can be used much more efficiently than on earth. So what I thought was using focused sunlight, we could melt the rock. The feasibility can be seen with this point that on earth the grade is less, but on asteroids it’s in very pure form so melting temperature would be less. The molten rocks can be vacuum pumped and then for complete concentration, the concept of magma tic differentiation can be used.

    The pros of this are:-

    1. It will be a universal tech, which means gravity, material composition and all other factors
    can not affect.
    2. The area ore will take, will be very compact.
    3. The main source of energy is sunlight only, so if we employ crushing units and other techs, a lot of energy will be wasted in form of resistance for electrical. There is no phase change of energy in this case. So efficiency will be better.
    4. Because there is nothing certain until we reach the surface regarding geographical conditions
    therefore this can overcome any changes.
    5. It will combine all the mining, processing and metallurgical processes into one.

    Rishi Kumar, Indian School of Mines

    1. I have to agree with you Rishi. It does sound completely insane. But then stranger things have happened- not many though.

    2. I know it sounds insane but think about when during magmatic diffrentiation, the distribution of ore can take place so if we can control it our way then we can 100% concentrate any mineral
      Rishi Kumar, India

    3. Rishi, although I am sceptical I am in no way mocking you. We need visionaries, so keep using your imagination. It may seem like science fiction, but the great SciFi writer Arthur C. Clarke was once the subject of great cynicism in his predictions of satellites, space stations etc. So don't be put off and you are obviously not afraid to air your views in public!

    4. Thanks a lot sir for the motivation.
      I always think out of box and that helped me a lot. Infact to tell you, I am recently working with sandvik to design a liner which will reduce energy of jaw crusher. Initially the idea seemed very simple and ridiculous but when put under scrutiny it was found to be good.

  14. I agree with Mike's earlier comments that in-situ leaching is likely to be the best solution - but I suspect the future may lie in greater use of micro-organisms as more than just catalysts for chemical reactions (as with current bioleaching technology). Already there are a number of bacteria identified which have naturally evolved to metabolise valuable metals directly, incorporating them within the cell wall and subsequently concentrating them within the environment. There is evidence to suggest some alluvial gold deposits were formed in this manner, and so in a way bacteria have already played a major role in mining.

    Artificial changes to DNA however allows behaviour which is not evolutionarily beneficial, and suitably modified bacteria could be added to a carrier fluid and pumped through rock that is fractured either naturally, or with the aid of explosives. Once a certain concentration of metal has been acquired the bacteria could be "programmed" to then move independent of the fluid flow, to seek out and congregate with other loaded cells. Similar quorum sensing behaviour already exists in nature, so it's simply a matter of using it to the advantage of humans, rather than the bacteria. It may even be possible for the bacteria to also seek out the surface by sensing temperature and/or pressure, though any reduction in the degree of dissemination would at least serve to reduce the degree of comminution required for liberation.

    There's also been some interesting developments in the creation of non carbon based artificial lifeforms (ie the Cronin Group's iCHELLs), which further broadens the possibilities. Perhaps it may one day even be possible to create something which sees a large silicate vein as nothing more than an all you can eat buffet, greatly reducing the energy and effort required for breakage. The biggest downside is that in-situ biological process may take decades to achieve the desired results, and companies seem to have enough trouble already just planning one or two years ahead.
    James Rowe, Australia

  15. In situ recovery is indeed an interesting technolgy and has been successfully employed commercially, but I wonder how universally it can be applied. This is not my field, but I have read about more valient attempts than successes over the decades. Among the challenges to overcome, perhaps the biggest is concern about environmental damage (groundwater) and close behind, the ability to control where the injected fluids go and how to capture the value that you have leached (the old path of least resistance phenomenon - faults, permiabilities, etc.). But as an old extractive metallurgical engineer who chose 20 years ago to morph into an energy efficiency consultant, keep up the quest regarding comminution. One challenge that I have run into in my work is that the crushing/grinding energy so dominates the mill energy consumption that many managers are not aware of or willing to pursue the many other attractive energy efficiency opportunites within their operations (poorly designed/operated compressed air systems, low efficiency pumping systems, etc.).
    Tony Teske, Energy Consultant, USA

  16. This interesting discussion continues on Minerals Engineers Group on LinkedIn

  17. -------------------------------
    Rao's comments---------------
    To all GREAT Scientists,
    There is an age old process till now we have not discussed.
    ROCK: In olden days in INDIA while making roads big roks were found on the way. They were very hard rocks like granits. There were no M/C s to drill, blast, etc. The rock was heated at high temperature, and suddenly put cold water on it. Due to sudden shrinkage rock used to crack, or develop cracks. Thus huge mass was reduced to pieces.
    MINERALS: Yes we need to understand how minerals react to such process. Each mineral to be studied. We say cleavages. May be these cleavages may react more to this heat and help us to reduce in size. How to use it in mining is R&D.
    Yes each mineral may crack at different temperatures. Thus we may try to separate gangue and minerals in underground without blasting.
    Underground leaching: Yes it is a good idea. In VRM what we do. Similarly we can make use of such VRM holes for processing, and undeground filling of such holes back.
    Back filling: Yes small pockts can be leached and waste filled back in the same pocket.
    REVOLUTIONARY MINING----This will not only solve all problems of mining but also save environment, cost, etc.
    IN SITU BIO-LEACHING OF COPPER--- This is a new discovery every one knows. It was aslo age old process, discovered and scientificall prooved. But it has limitations. Only oxidised copper is leached.
    IN SITU OTHER MINERALS: Now we need to study how to make a mineral---called AQUAIRED property for leaching. Here there are two steps,
    1.Make mineral aquair such property that it becomes ammenable for leaching,
    2.Then do leaching in situ.

  18. There are already some mining methods that do not require comminution and some methods require only a small part of the ore require comminution. Examples are: ISL, solution mining of potash, recovery of potash from the ocean, etc. Some methods that need partial comminution is the jet boring method applied in some uranium ores.


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