Thursday, 28 July 2016

How grinding circuits have changed!

Tim Napier-Munn emailed me earlier in the week with this remarkable photograph of roughly one half of the line of 28 ball mills in closed circuit with rake classifiers at the Mufulira copper mine, Zambia, in the 1970s.
The concentrator treated 20,000 tpd, which makes about 30 t/h per mill but that’s without circulating load.
Tim asks if anyone remembers the total throughput of each mill including the circulating load.
The current largest mill in the world (AG) treats 1350 t/h of hard ore so basically Tim is trying to assess how many of these small mills this is equivalent to. Although he realises that it is probably not fair to compare ball vs AG and medium hard vs hard, he is trying to make a point about how much increase in scale there has been in our professional life time.

9 comments:

  1. Hi Barry, this image comes from a group of photographs given to my father by the Mining Dept at Muf when we left in 1981. I shared this with Tim earlier this year when I rediscovered the photos cleaning out an old cupboard. Also found a really interesting mine publication from the Selection Trust Group called "Horizon", published in Oct 1959 - makes for a great read!
    Cheers
    Elaine

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    1. Hi Elaine, how can I get hold of that edition of Horizon?

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    2. Hi Barry, happy to send a scan of the edition through to you.
      Cheers
      Elaine

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    3. Yes please do. Thanks

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  2. One of my first jobs in the Met Labs R&D section of the then RCM/NCCM in Kitwe was to carry out a comparison of the one grinding circuit installed with a hydro-cyclone against the others with rake classifiers shown in the photo. Much to the disappointment of the Concentrator Superintendent of the time, a certain David Littleford who's innovation of installing the hydro-cyclone it was, the rakes gave a much cleaner cut with less fines and coarse so the RL must have been a little lower. I did this work in 1978 with Steve Lee who transferred to Mufulira smelter and from there I know not where. As far as I remember the RLs were all over the place from about 200 - 500%. There was virtually no automation although I recall David was also testing out the then new Autometrics PSM on stream particle size analyser. I believe the mills all converted to hydro-cyclones in due course as the rakes required a lot of TLC. If the hydro-cyclone had not come along (and it continues to be a fertile ground for R&D papers and PhD thesis) the industry would probably have come up with something better. David is still in Zambia and I met him at his ranch just outside Kabwe last year. Regards, Tony Francis

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  3. Similar comments about increase in scale of float cells are also interesting. The small float cells along the copper belt in 1970 were like milk shake mixers compared to today's huge tank cells.

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  4. I was told by others the answer, which is 28. I was trying to contrast the size of equipment then and now and I compared that example (because of the great photo!) with the 40-foot 28 MW AG mills at the Citic iron plant in Western Australia, just commissioned. The figures are: 28 mills for a 20,000 tonne per day concentrator, vs 6 mills for 200,000 tpd, so a capacity multiplier of 47 times. It’s an unfair comparison of course because of the different ore types and objectives, but it does rather dramatically illustrate the progress of equipment scale. I had an even better example in flotation (with pictures): 1.8m3 per cell in 1959 compared with 630m3 to-day!
    Tim Napier-Munn, Australia

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    1. Hello Tim, perhaps this is obvious and I have come to the party late, but would a comparison against the Lumwana mine be a better indicator? While I do not recall the size nor throughput of the Lumwana plant I recall them being very large mills and surely the ore type would be somewhat comparable.

      Cheers,
      Michael Myllynen

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    2. Thanks, Michael. You are right, a better comparison would be between two comparable ores, but at the time I was looking to make the simple point in a presentation that equipment sizes have increased a lot over the years, and I had two great photos to demonstrate that. The comparison was not strictly fair as the ore types and duties were different, as I point out in my 12th Sept post above, but the general point was valid I think. Tim Napier-Munn

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