Monday, 1 April 2013

Latest design improvements increase spiral concentrator efficiency


Spiral concentrators have, over numerous years, found many varied applications in mineral processing. Until relatively recently, all spirals were very similar, based upon the original Humphreys design, which is now obsolete. However, in recent years there have been considerable developments in spiral technology, and a wide range of devices is now available. The main areas of development have been in the introduction of spirals with only one concentrate take-off, at the bottom of the spiral, and the use of spirals without added wash water.

Spirals are now made with slopes of varying steepness, the angle affecting the specific gravity of separation, but having little effect on concentrate grade and recovery. Although a simple device, the separation mechanisms are complex, stratification being due to the combined effect of the differential settling rates of the particles, the effect of interstitial trickling through the flowing bed and the mild centrifugal force, often being likened to the stratification of particles in a river as it flows around a bend.

Southern and Northern
Hemisphere Spirals
A small team of workers at the Bodmin Institute in Cornwall has shown that this centrifugal force can be enhanced by that produced by the spin of the earth. Under the leadership of research director Dr. Corrie Hayles, they have shown that the orientation of the spiral pitch has an effect on performance, an anti-clockwise flow performing better in the UK than a spiral with a clockwise flow. Dr Hayles calls these spirals northern hemisphere and southern hemisphere devices respectively. He is now keen to develop collaboration with workers in the southern hemisphere to assess performance of the two devices, and he would be interested to hear from anyone who has any thoughts on this.

19 comments:

  1. It's seems logical as the water which evacuate from a sink. The vortex of water has a different sens in north or south hemisphere.
    I am curious to watch the results, and how much it's efficient.
    Olivier Notton, France

    ReplyDelete
    Replies
    1. Thanks Olivier. This effect has also been observed on centrifugal gravity separators, and has been reported by the southern hemisphere-based Gekko Systems. See http://tinyurl.com/bs678yq

      Delete
  2. I had seen at Yunnan China some spirals that also rotated on its own axis, so this also would affect the northern and southern hemisphere,jorge
    jorge lema patino (Bolivia)

    ReplyDelete
  3. I note the date ---
    Bertil Pålsson, Sweden

    ReplyDelete
  4. Can this be used prior to collectorless flotation?

    ReplyDelete
    Replies
    1. I assume you are referring, Chris, to the previous reported work from the Bodmin Institute ? They are a very innovative team, aren’t they?

      Delete
    2. Incredibly. It must be something in the water. :)

      Delete
  5. also remember the Gekko article, and there was a simlar one done by Falcon - funnily enough the announcements were made on exactly the same day of the year.

    This then led me to review the work of the prodigious Bodmin Institute, especially thier work on collectorless flotation. I do have one conundrum though - if water has a "memory", and we humans are at least 70% water - why can't I remember what I did an hour ago, never mind last week? I put it down to the inhibiting effect of decent beer.
    Nigel MacDonald, SGS Minerals Services, UK

    ReplyDelete
    Replies
    1. Yes, and coincidentally the collectorless flotation research was announced on exactly the same day a year ago. You probably missed the essential 'succussion' stage, where forceful striking is necessary for the water to retain its memory. May I therefore suggest a tap on the head?

      Delete
  6. So are equitorial spirals and concentrators bi-directional?
    Susan(Sue)Ritz (SGS/KD Engineering, USA)

    ReplyDelete
    Replies
    1. I put your question, Sue, to Dr. Hayles, and he suggested that spirals at the equator might perform better if laid on their sides.

      Delete
  7. 1. Kindly let us know the particle size limitations-- for 10 micron & upper limit mm.
    2. At what difference in solid specific gravity it works---between product and tailing.
    3. With which equipment we can compare its efficiency or any specific mineral is good for spiral.
    4. Yes Humpry spirals started with sand washing. But today many more minerals are beign beneficiated. New designs like double start, more angle of trough, more dia of trough, width of trough also increased.
    5. Spirals come under green technology. Zero power required. The only drw back ----you need hundreds of spirals to compensate huge capacity, and its control, cleaning, maintenence, supervison-- etc.
    Kshirasagara sivarao (India)

    ReplyDelete
  8. Further information on the Bodmin Institute can be found at http://tinyurl.com/d3r23zl

    ReplyDelete
  9. The liquors alledgedly also flow upwards counter current fashion, when installed downunder. (Relative to the direction of gravity in the northern hemisphere no doubt.)
    Patrick Jay, FLSmidth, Australia

    ReplyDelete
    Replies
    1. Yes that can be a problem. Have you tried operating the spiral upside down?

      Delete
  10. 1. A compas magnet needle responds to earth magnetism, then why particles will not respond. Particles are supposed to respond similar to needle direction at any place in the world. We need to confirm if this behaviour is for particles having strong magnetic properties. Will non-magnetic particles also behave in similar way, need to be confirmed.
    2. It is a good invention but , are results commercially viable, similar to flotation cells. For iron ores can spiral give 1-2% SiO2, similar to column flotation. If it is true then we can trust the above stements are correct.
    Kshirasagara sivarao (India)

    ReplyDelete
  11. I mentioned that I had seen spirals that rotates on their on axis. Also we had al the lab. here in Bolivia a spirals that moves up and down creating an additional jigging effect. This has shown for gold a better performance increasing 1% grade and 1% recovery. and has nothing to do with the rotation of the earth or the beer. Any way according to our experience the australian spirals are the best for fine tailings, for tn, and iron as we tested
    jorge lema patino, Bolivia

    ReplyDelete
  12. There appears to be a bit of subtle humor in todays MEI.

    First, Barry's reference to the BODMIN Institute ( http://tinyurl.com/d3r23zl - a mental hospital),
    then the statement in the brochure by GEKKO on SPIRALS - " In a parallel stream of research, the application of massive electrical currents during the initial stages of polymerisation is being investigated. However, access to this laboratory was temporarily suspended after the lead scientist, Professor Steven McKing, had a nervous breakdown and was isolated in the medical wing muttering over and over again “it creeps, and leaps, and glides and slides.”
    I am still laughing - what a great sense of humor!!!
    Louis Bernard, Snowden Consultants, Canada

    ReplyDelete
    Replies
    1. Glad you liked it Louis. Just a little light relief amongst all the serious discussions. You may also like last year's April 1st posting, which also fooled a few

      Delete

If you have difficulty posting a comment, please email the comment, and any photos that you might like to add, to bwills@min-eng.com and I will submit on your behalf