Monday, 19 August 2013

Enhanced Gravity Separation- a modern innovation?

A few months ago Stephen Grano made some interesting observations on froth flotation, and why it is still so intensively researched (posting of 11th April). He implied that journals may be publishing work similar to that carried out in the past, but now lost in the mists of time. Are we to some extent going round in circles?

In the many comments on this posting Liza Forbes of CSIRO agreed that older pieces of research (especially those older than 30 years) are not known as they should be. She feels that many young researchers base the majority of their knowledge on more recent work, resulting in a progressively increasing lack of citations of older work. She suggested that senior researchers should invest more time with junior staff, to make sure that they are aware of the work that took place decades earlier and of its significance. She even suggested that Minerals Engineering might publish an annual special issue, where people nominate and discuss an old piece of work which they consider to be important, yet largely overlooked, thus reviving/highlighting some golden oldies.

Gravity separation is perhaps the oldest method of concentration, but enhanced ‘centrifugal’ gravity separators began to be commonly used in the 1980s and 90s.  My old friend and colleague Tony Clarke send me this description of one of these devices:

The device consists of a cone, working at a minimum 200 r.p.m. (and up to 400 or 600 r.p.m. to increase throughput) with the operating conditions being capable of adjustment to suit. The feed is introduced into the top of a rapidly rotating vertical cylinder, within which there is a set of vanes, rotating in the same direction but at a lower speed. The centrifugal action ‘beds’ the heavier particles against the inner cylindrical surface, while the relative action of the vanes creates a washing motion, to help carry away the lighter gangue. All heavies are trapped within the cone, by centrifugal force, while the waste passes out over the rim. It is said to take less than a minute to stop, clean and restart and will treat 2 tons per hour, at a claimed recovery of 98 to 99 %, with little power and water consumption.

A description of an early Knelson or Falcon concentrator?  No, this is an extract from the Mining Journal, of 28th June 1902, describing the Maurice centrifugal gold separator, which was in use at the time in France on gold-bearing sands! This technique was resurrected many years later, in a laboratory separator marketed by Magstream, while Richard Mozley introduced centrifugal separation to Cornwall on a plant scale, with his MGS separator in the 1980s. Outside of the county of Cornwall, other centrifugal separators such as the Knelson and Falcon concentrators for fine gold, and the Kelsey jig also made an appearance. When one compares the description and operating instructions for some of these devices, one is immediately struck by the similarity to the description of the Maurice separator of 1902.

What do you think? Does the 1902 device highlight valid comments made by Stephen and Liza? Should we be trying to educate young researchers in the need to extend literature searches to way back in the mists of time?


  1. Yes Barry we should. Far too often in far too many fields researchers (extend to policy makers) "forget" what went before - resulting in waste of time and effort - as well as ignoring ideas that may not have worked at the time because the enabling technologies (for example, materials, computing etc.) were not there at the time, but are now. Build on the past, don't ignore it. The old lags have a duty to ensure that the youngters use their corporate memory, including of why things didn't work well - so they can improve on them rather than reinventing the wheen.

  2. Agreed, a lot of very good ideas were restricted by the tehnology of the time. However, the basic principles still stand. The use of old methods in innovative new ways is just as valid as developing something revolutionary (pardon the pun).

    Tony's translation of the Moissenet papers on tin dressing in the 1850's certainly showed that the understanding and control was extremely well developed given the technology of the time.

    1. Agreed anon, but could I ask people who do not have a Google account to leave name and affiliation if commenting as anonymous? Thanks

  3. I completely agree with Barry, in fact in Section 594 (P425/426) of Richards Text Book of Ore Dressing (1909) (which is based on his earlier works), he describes the use of centrifugal separation for fine particles, while in section 575 (P 415) he describes a cyclonic separator for dressing asbestos in Quebec.

    A few years ago I was doing some academic research ( ), the question I kept getting asked by my professor was what is "new" in the field. If the citation was over a few years old I had to describe how it was still relavent.

    There are many areas in mineral processing, where promising devices or techniques became side tracked because of a "new" method that became the rage. And now "everybody knows" that it was not worht looking at.
    Mike Albrecht,USA

  4. It is a funny thing... the laws of Physics and the principles of chemistry have not changed. I use the Onemine database quite a bit, and often find the older papers much more relevant to operating and troubleshooting a plant. I often see younger flotation metallurgists obsessing over advanced flotation cell theory while completely missing the basics of liberation, selectivity, and getting a good froth.

  5. I am feeling so happy that practicing mineral engns are taking such a keen interest on real issues facing mineral preparation--the focus shifting from "glamour research" to "work that helps the Practicing Person" Congrtulations, again to you, Barry.
    In this contest the recent comments made by Dr.Lynch in a personal mail to you are very timely/relevant and you may publish part of it.
    For me, the "classical equation" is m(dv/dt)=mg-m'g-R. May it be gravity or centrifugal or flotation, all the processes revolve around this equation and how a mineral engn would be able to manipulate each of the terms is the challenge in developing new equipments and application.

    1. Yes TC, Alban Lynch's remarks in the email to you and me are very relevant in this context and I submit an abstract from that email:
      "Comminution must be the key mineral processing technology during the next 50 years and in my opinion our efforts in comminution contrast poorly with those of our colleagues of 50 and 100 years ago. The reason is clear, there is little interest in defining a problem clearly and then in carrying out the hard, prolonged, physical and mental work required to solve it. Any problem that does not require this approach is trivial. I deplore the approach of sitting at a computer and believing the output without carrying out detailed experimental work. I have not attended many technical meetings in recent years but I have not heard a decent technical argument during those meetings I have attended, although presenters have often spoken nonsense. It would be useful to reprint some of the discussions in the AusIMM bulletin or the AIME proceedings during 1900-30 to understand the depth of knowledge and the intensity of feeling which led great progress."

    2. Interesting. My time at the JKMRC overlapped Alban's by only a couple of years, and I have to say I concur with his opinions (as applied in the general)

      But I would be hesitant to say that this is because of a lack of desire or vision on the part of the mineral processors - funding of this work plays a big role, and experiments are expensive. The students by and large would love to do the empirical validation - and then find they have to take outrageous short cuts and assumptions simply because there is no prospect of that equipment/laboratory setup being available.

      Looking back on my career, I have been quite astonished at how easy it is to make progress by taking old "forgotten"ideas and giving them a technology makeover - old ideas/equipment go out of favor for many reasons and it is then assumed they can never make a commercial comeback - new manufacturing/control techniques mean this is not so!

      Yes the old research is ignored for many reasons:
      a) it is not as accessible to the student.
      b) The history of mineral processing is usually not taught as part of the core subject
      c) the tyranny of distance and language in the past (for example the plethora of excellent old Russian papers very rarely get seen in English speaking countries)

      I would also suggest the change in modern education at universities from master/apprentice to service provider/client has a lot to do with young students not having the anecdotal history of the profession passed down any more.

      Finally, just on fine particle enhanced gravity separators, my view is the last word has yet to be said on low "G" separators - when you think about it, you only need to move a 5 micron particle 10 microns or so in order to separate it from its neighbor and this takes not much residence time at all - perhaps precision will help where brute force sometimes struggles..

    3. I totally agree with you Andrew. Point b) was particularly noticeable recently when I led a tour of Physical Separation ’13 delegates to the historic Camborne-Redruth mining district. I was surprised that many of them had not even heard of the early 20th century gravity concentrators- buddles, round frames, rag frames etc.

  6. Another side of people eliminating references to papers over a few years old is references to newer papers even where the initial work was decades in the past.

    Questions from the audience at many technical meetings are more associated with well established, but apparently not well known, process fundamentals.
    Robert Seitz, USA

  7. I agree that past work is not being researched for "new" discoveries. The majority of professional societies have past work on files. The USBM files are available. I recently found an SME article from 1950 on elution of gold from carbon. The process used was approximately the AARL process. The paper was on an operation in Arizona written by Professor Chapman. Note this paper was issued before the USBM issued the paper on Zadra elution.
    The past work may not be exactly what we are doing but the line of thought usually was comparable to what we are looking at today.
    Steve Dixon, Goldcorp, USA

    1. Unfortunately references don't go back 4500 years! Take a look at this blog posting of 13 December 2010. Geopolymerisation is regarded as a fairly new technology.

  8. It seems a lot of "modern innovations" are recycled or reinvented, leaving one to wonder if some Patent attorneys are sleeping when it comes to allowing patents on technology which has been around a while. However it is true I think that certain "old" technologies have been reborn so to speak, as instrumentation and process control technologies have advanced. An example of this would be column flotation cells, which languished at best for many years before experiencing this kind of rediscovery, if you like. The Knelson concentrator was also "reborn" after having mediocre success in its early years. No doubt the addition of continuous discharge machines helped.
    Steve Hearn

  9. In my opinion, we should certainly get information about the base of a specific technology which we use in our research. After that, we can study the previous works and correct the mistakes in them and also add something new to them. It causes that we move in a common way and reach to a better results in a relatively short time. Since gravity separation is one of the oldest methods in mineral processing, most of the researchers are interested in some new technologies. But we should know that this method is more effective than modern methods in some cases and can also be improved in different ways as a more healthier method.


If you have difficulty posting a comment, please email the comment to and I will submit on your behalf