Monday, 26 August 2013

The increasing use of mixtures of collectors in flotation

Increasing use is being made of mixtures of thiol collectors in the flotation of platinum group and sulphide minerals. The use of mixtures is sometimes proposed to produce a synergistic effect, i.e., the flotation performance of the mixture is greater than the weighted sum of the individual contributing collectors. Some workers have reported a marked increase in galena recovery using mixtures of xanthate with either dithiophosphate or dithiocarbamate.

However, when such observations are made, there is no clarity on the mechanism by which this synergy may occur. This is not surprising given the complex chemistry associated with even single collector-mineral surface interactions in a flotation environment.

An interesting paper has just been published in Minerals Engineering. McFadzean et al of the University of Cape Town, tested pure galena and pyrite minerals. The findings showed that a higher galena recovery (92.2%) was obtained when using a 10:90 mixture of ethyl xanthate with diethyl dithiophosphate compared to 89.0% with the best single collector. Galena and pyrite minerals showed marked differences in their respective frothing effects and in their preferences for collector type,  the best collectors for galena being the worst for pyrite This showed that most collector mixtures achieved greater recoveries than would be expected based on their additive performance alone. This synergistic behaviour was most notable for mixtures of strong and weak collectors. Antagonistic behaviour was noted for mixtures of two strong collectors.

The results indicate that the collectors are mineral-specific and should have ramifications in the separation of different mineral types by using a collector that is specific to the mineral of interest. In addition it follows that, in the processing of complex ores, the use of collector mixtures should have a beneficial effect in targeting all of the various valuable minerals that are present in the ore.

It was also found that the performance of a collector or collector mixture was most pronounced when looking at coarse particle recovery. Thus, good collectors showed good attachment efficiency with less detachment occurring in the high energy, turbulent batch flotation cell environment than for poor collectors, which showed poor recovery of coarse particles.

Expect to hear much more of mixed collector flotation in future. McFadzean and O’Connor will propose mechanisms for their findings at Flotation ’13, and workers from Clariant in Germany will also propose a mechanism for how these synergistic interactions occur with sulphide minerals. A paper from China will discuss the use of mixed collectors for the selective flotation of antimony from a low-grade antimony-gold ore. Researchers from France will also discuss the effect of mixing anionic collectors (sodium oleate, hydroxamic acid, D2EHPA) with nonionic reagent on the selective separation of Ca-minerals.


  1. Nothing particularly new in this area for sulphide collectors based on previous work.
    For example, Professor Zaffir Ekmekci's team found that there appears to be two sites on some sulphide mineral surfaces for collection. By adding the collectors separately and sequentially, recoveries were maximized for a copper-zinc operation in Turkey.
    Bradshaw and Lotte presented a summary of findings on this topic in Flotation 09.
    However the use of mixed anionic collectors is particularly interesting; it has been mentioned in literature before but a study that provided some theory and application guidelines would be very well received.

  2. Increasing use of fire (the wheel, and the telephone) has been noted.
    Operators of flotation circuits (the early adopters) have taken advantage of mixtures of collectors for a long time (probably close to 8 decades). How is it possible that (some) researchers and (some) academics are learning of this just now? Is it possible that their work is irrelevant? When are these researchers and academics (late adopters) going to advance the science? Isn’t it time that some brave research work be done? Or should we expect these researchers and academics to continue their single mineral studies with xanthate.
    Coming Soon: Staged addition of collectors and SAG milling.

  3. An early example of this would be:

    Glembockij, V.A., Combined action of collectors in flotation, International Mineral Dressing Conf., Stockholm, 1957, 493-507.

    Much the same can be said for use of blended collectors as in the discussion re enhanced gravity separation (posting of 19th August)

    Robert Seitz, USA

    1. Thanks Robert (and the nameless ones above) for highlighting some important points. Are we indeed going round in circles, as suggested earlier by Stephen Grano in the posting of 19th August? There is no mention of the Stockholm paper in the McFadzean et al paper but they do refer to a paper also co-authored by Glembockii:
      Plaskin, I.N., Glembockii, V.A., Okolovich, A.M. Investigations of the possible intensification of the flotation process using combinations of collectors. Original report in Reports of the Mining Institute of the Academy of Sciences of the USSR, 1954, Report No. 1, 213–224. Translation No. 1313, February 1989, Mintek.
      In the 19th August posting one of the contributors to the discussion suggests that among the reasons for old research being ignored is 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)”. Note that the cited USSR report by Plaskin et al (1954) was probably brought to modern attention only by the 1989 translation by Mintek.

  4. Your posting about mixed collectors has reference. I think that it is pertinent to recognise that however important the subject may be, it is not a new one. Its level of understanding and best practice is, however, steadily advancing. Glembottski and his co-workers in Moscow were amoung the early workers to document inter-collector synergy in 1958. This was published in Tsvetnye Metally. Thankfully at the time that Prof Dee Bradshaw and I were writing our review in 2009, I was mentor to a Ukranian engineer-in-training who kindly translated the article for me. So the first point is probably that there is significant reference literature on the subject outside of the English medium journals.
    That said, the integration of published reference information in a review (2010) has consolidated our thinking to some extent, and has provided a focus for further work. We have only discovered the tip of the iceberg at this stage. Much more needs to be done.
    It is thus encouraging to see the growth of the mixed collector author group, who re expanding the field of application into a wider range of ore types and associated challenges. One of these is certainly understanding the interactive mechanisms. Another is to develop a predictive approach to the selection of a mixed collector suite before starting the flotation testwork.
    The other remarks on the blog to the effect that many people have used mixed collectors over 8 decades may be true, but have they used these mixtures optimally - or like the discovery of fire centuries ago to which the same commentator refers, was their “mixed collector” suite a chance combination that “worked – but no-one knew why or how”? We want the optimum, not a go-between that ‘half-works”.
    Norman Lotter, Xstrata Process Support, Canada

  5. Yes indeed, are we going around in circles! The practical use of mixtures of collectors has been known for a long time. But as pointed out by Robert Seitz some of the early academic work was done in the former Soviet Union and not easy to get access to, although Tsvetny Metally was translated regularly by Primary Sources in New York with a delay of about one year. The name was then Soviet Journal of Non-Ferrous Metallurgy, maybe later changed to Russian Journal ---.

    So to the practical use. When I was plant metallurgist at the Boliden Kristineberg concentrator we had one tricky lead-zinc ore with high silver content. It needed a collector mixture of amyl xanthate and AeroFloat 242, approx. 1:1 or 2:1 on a g/ton basis, to get a low Pb level in the middlings from the copper-lead flotation. We did several practical experiments but could not run without AF242. The ratio 2:1 was the best to use from an economical point of view, since the xanthate was much cheaper. We also did speculate on why it worked int his way, but never came to any explanation.

    With this I want to say - we are revisiting certain research topics because we nowadays have better instruments, it is not just forgetting to read old literature or running in circles. And still we do not know why flotation works ---
    Bertil Pålsson, Lulea University of Technology, Sweden

    1. Bertil, I would largely agree that, "we are revisiting certain research topics because we nowadays have better instruments, it is not just forgetting to read old literature or running in circles." However, we have also lost descriptive and reflective aspects with the instrumentation. It's still informative / thought provoking to reflect on the the descriptive parts of textbooks by Gaudin, Sutherland and Wark, Plaksin, Glembotskii, etc...

      As for not knowing how flotation works, the state of our knowledge as veneer vs. comprehensive is often revealed for most (perhaps all) processes through industrial practice as opposed to the constrained research environment.

      Tsvetny Met. was interesting to read and provided an opportunity to see development of flotation understanding through differing points of view. In the same time frame I had the opportunity to read proceedings of several conferences which had been translated from English to Russian, and then through some mysterious government sponsored program the Russian version was translated back into English. Often it made for quite a different paper - sometime the doubly translated version was much more interesting. This provided considerable insight into the power of the translator in controlling information flow.
      Robert Seitz, USA


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