Monday, 6 March 2017

Flotation Chemistry vs Flotation Physics

I have had an interesting email from a very eminent flotation researcher, which I am sure will generate some debate. He/she would prefer to remain anonymous as he/she feels that industry has a reputation for judging the whole department by any individual. I publish the email below with only minor edits:
Question – currently, why is so much attention (≡ to money) being spent on the comparatively narrow study of the physical aspects of flotation, at the expense of flotation chemistry studies? A good example is the current preoccupation with coarse particle recovery.   
As a starting point we should ask ourselves - ‘What is flotation all about, really’? The answer is straightforward - the ‘Holy Grail’ of flotation is selectivity not recovery. After all if we take an ore body and do nothing we have 100% recovery, but the product, as such, is useless. Recovery without selectivity is all in vain. However there seems to be a meagre acceptance of the importance of grade.

Little is said about selectivity but there is a constant cry for increased recovery. This might be what industry wants but it is certainly not what industry needs. However, physics based studies are merely concerned with increased recovery not increased selectivity; selectivity in flotation is only achieved by attention to the pulp chemistry. Yet, currently, there appears to be little (research) money being directed towards chemistry based flotation studies. Strong, and successful, chemistry based research groups like those at CSIRO and The Wark have all but disappeared because of a lack of (financial) support. 
As natural resources become more and more scarce, and more and more complex, their value will be determined more and more by the degree of selective separation which can be obtained in processing. This can already be seen for arsenic contamination. And selectivity against pyrite will increase in significance, exponentially. So, we might well ask if the current strong financial support for the physical aspects of flotation is misguided. 
For example. An actual case study - the treatment of a sulphide ore. For the rougher stage, recovery beyond 85% was difficult. The rougher concentrate, at 85% recovery, could be worked up to a smelter acceptable product of 25% grade; the tailing assay was 0.09%, with most of the loss in the coarse (-500+40 micron) size fraction. With some effort (in a laboratory) it was possible to do a size split (at 40 micron), retreat the coarse fraction, and recover another 10% of the values in a scavenger product (ie lift overall recovery to 95%). Assay of this scavenger product was about 1%. This gives a ratio of concentration of about 10, similar to what was (and is commonly) achieved in the rougher stage. However, no amount of retreatment could raise the assay of this product above 6%, and this grade is not acceptable at the smelter. Accordingly, in practice, these particles, after initial recovery, would have ended up back in the tail. Therefore, in this case, any money spent on installation and operation of special cells for recovery of these coarse particles would be misguided.  
Second (obvious) question. How many of the researchers seeking special ways of increasing the recovery of coarse particles (for example) have thought of what they are going to do with these particles when they are recovered; perhaps the final recovered value is less than the cost of recovery? 

Third more important question. How many of the people putting up the money for this research even understand the problem? And would some of the currently available research money be better spent on further understanding the problems of, and developing techniques for, upgrading low grade concentrates?
Flotation chemistry studies are certainly more difficult than physical flotation studies; what is not generally recognized is that they are also more important.
And all this prompts the last question – does anybody really care?

Strong opinions and I invite further strong opinions! Personally I found "...but there is a constant cry for increased recovery. This might be what industry wants but it is certainly not what industry needs" contentious. Increased recovery may or may not be what industry needs. But what about society? As we move towards a circular economy isn't maximum recovery of natural resources, at optimal grades, what we should be aiming for? And is there more to increased recovery at optimum grade than just flotation? Comminution-liberation must play a big part in this (but that's another story). Hopefully we will hear much more about this at Flotation '17 and Comminution '18.

16 comments:

  1. When times are hard, funds will go to physical flotation as it offers more immediate potential for payback. Flotation chemistry is seen as more arcane and can be ignored through trial and error giving the optimum reagent combination. Why or how it works is a luxury which is pursued when times are good and money can be spent on the full optimisation.
    As usual, industry will only support things which will lead to short term goals bejng met.
    The death of specialist groups will not concern industry one jot, they will simply carry on as usual, blundering around in the dark until a solution is found for the speciffic problem at hand.

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  2. Strong words indeed, but the first author misses a major point - most collector reagent schemes currently used in sulphide mineral beneficiation have been known for long times, and they work fairly well. Each has its limitation, for example xanthate likes chalcopyrite and all disulphides, but this can be alleviated by changing to a dithiophosphate regime. Then, if some miners do not understand this, its their problem. And, of course, you need to grind to a fineness so the bubble may lift the particles out of the pulp.

    What I find lacking in sulphide flotation reagent research are:
    * Poor understanding of gangue depressant's action, and links to their structure;
    * Poor understanding of the interaction between collector and frother, especially froth stability in large tank cells;
    * Add your favourite ---

    Some of the points above have been addressed by manufacturers of reagents, for example Cytec has developed polymeric reagents for gangue depression, but I haven't seen much academic research in this area.

    However, I believe that the major chance to develope new reagent regimes is in oxide and silicate mineral flotation. I see a need for:
    * Collectors that may float Ca-mineral selectively (Apatite-Calcite);
    * Less toxic alternatives to replace amines in silicate flotation.

    So, there are research challenges if you dare to check for them.

    Bertil Pålsson
    Minerals and Metallurgical Engineering
    Luleå University of Technology

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    Replies
    1. Flotation is not a panacea for all ills.
      Look wider. Only in this case you will have success. There are many methods of separation (concentration) of minerals:
      Gravity separation (There are more than 12 types ).
      Magnetic separation (There are more than 14 types).
      Electrical separation (There are 6 types).
      Flotation separation (There are more than 17 types).
      Special methods of separation (There are more than 15 types).
      Chemical separation (leaching) (There are 7 types).
      Also, there are many combinations of methods of mineral separation:

      •Flotogravity separation
      •Magnetohydrodynamic separation
      •Pyroelectric separation

      •Tribo-aero-electrostatic separation
      •Pneumoelectric separation
      •Fluidising-electrostatic separation
      •Crown-magnetic separation
      •Opto-electrical separation
      •Segregation-diffusion concentration

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    2. Yes Natalia, all those methods have their place, but it is impossible to over-emphasise the importance of flotation. Around 20 million tonnes of copper, arguably the most important base metal, are mined annually and virtually all this tonnage, if not all, is concentrated by flotation. As I have said before, it is the most important technological development since the discovery of smelting

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  3. I dont have a problem with researching coarse particle flotation as some ores will benefit from it and some won't. Let's understand its applicability. Coarse particle flotation is not about concentrate grade, it is about tailings grade. If you can't recognise that then you have missed the point. The holy grail of any recovery-targeting separation is to generate a tail that is throw-away grade. If that hasn't been achieved then there is an unacceptable revenue loss and the technology is not applicable. When successful, coarse particle flotation will be a wonderful energy minimisation tool that will convert some deposits into orebodies.

    There are many other neglected research areas, such as froth washing, which are purely physical and offer amazing benefits. I have seen massive froth washing benefits ( like generating +30% Cu concentrates with washing when detailed flotaton chemical studies couldn't get past 23% Cu) so I can't understand anyone wanting to concentrate on one aspect of flotation at the expense of the other. Let's keep up pressure and justification for looking in detail at both chemical and physical aspects of one of the most remarkable mineral separation tools we have.

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    Replies
    1. What type of ore did you write about? How many types of ores do you know? Do you understand that this advice is suitable only in a particular case?

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  4. I think everyone including the original writer has made very good points. However, the business of flotation and any other unit operation considering a separation, needs to consider the economic viability of a process. A large proportion of cost is dedicated to trying to liberate minerals to the extent that flotation will be an appropriate separation process, if we can float at coarser sizes (even if it is less liberated), it benefits the overall economics of the flotation process tremendously. That being said, the separation still ultimately relies on applying the appropriate chemistry, and there is plenty of research to be done especially around depressants/dispersants (as mentioned in one of the other comments), as well as furthering our understanding of reagents and how they perform under different water chemistry conditions.

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  5. This question is difficult to answer and exactly why flotation is referred to as a physicochemical separation. The chemistry is a balancing act of solution and surface chemistry, predominantly for frothers and collectors. The physics is a balancing act of particle/bubble sizes and hydrodynamics. With over 50 parameters to be concerned with, flotation is indeed an art/science and we are only now getting it to be truly engineering.
    Courtney Young, Montana Tech, USA

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  6. I would like to look at the question in a simple manner.. For me, maximum recovery at a given grade is a must. This depends on liberation and the size distribution of feed to flotation.If one is lucky with his ore characteristics, one may get maximum recovery at a grade higher than wanted by metallurgist; then one can blend lower grade concentrate obtained at higher recovery with the earlier higher grade concentrate.
    But water also has a role to play. One should look at fines going into concentrate/tailings and their mineralogy and liberation Is desliming before and after flotation necessary?Is regrinding of one of the streams necessary?
    I feel there is enough said on physics and chemistry of flotation--let us look deeply into the behaviour and characteristics of particles moving around in rougher/scavenger and cleaner circuits.
    Rao,T.C.

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  7. It is time to move beyond the reductionist breakdown of flotation system that has served so well in the past and to progress with a more balanced approach such as suggested by some researchers, i.e., jointly considering particle characteristics, chemical mechanisms, and physical mechanisms. As a comment above mentions this is a physicochemical process working on a highly variable feedstock of natural origin.
    The differential development of hydrophobicity is definitely a critical sub-process in flotation. However, it is difficult to argue in the realm of sub-processes that it is the single one deserving of focus to the exclusion of others. Consider the journey of particles from orebody into the froth concentrate:
    • Breakage dependent on orebody geology and mineralogy and comminution process leading to liberation profiles and surface characteristics which set the stage for interacting with collectors, depressants, activators, frothers, etc. and development of a hydrophobic-hydrophilic character
    • Surface reactions leading to hydrophobic surfaces or not
    • In the pulp - bubble-particle interaction, collision, attachment, detachment, bubble-particle aggregate migration to the pulp-froth interface, particle elutriation to the pulp-froth interface
    • Bubble-particle transition or not across the pulp-froth interface, bubble-particle migration from the interface to the launder, particle elutriation across the interface and transport into the concentrate
    Should surface chemistry be the essential focus for process understanding and improvement with this knowledge? As further considerations:
    The importance of orebody characteristics, chemical mechanisms, and physical mechanisms.
    • Variability of ore as seen in geometallurgical analysis of orebody and lack of transparency in relationships between geological and comminution, flotation, and solid-liquid separation characteristics.
    • Is the low froth recovery observed in flotation systems, particularly for coarse particles, of physical or chemical origin?
    • Is the size-recovery behavior of chemical or physical origin?
    Ta,
    Bob Seitz

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  8. You need to look at both of them together, flotation physics and fotation chemistry. Flotation is a physical separation process but the attachment to the bubble is enhanced or affected by the chemical reactions in the slurry. Ultrafines are lost to tailings mainly due to flotation cells limitation. I would like to point out that selectivity and recovery are both important in flotation because you may reach recoveries in the range of 97% with very high selectivity so please do not dissociate and pick either selectivity or recovery ; similarly do not go looking just for hydrodynamics of flotation but also look at the chemistry at the same time. Please don't forget to include the noise introduced by operators and by control systems. Groups working to look at the flotation chemistry should not disappear but should be enhanced by asking them to include physical and chemical variables . One more thing, don't forget to include mineralogical studies in your research.
    Juan J. Anes, EM2PO, Canada

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  9. We have to look at it in a simple way==if the liberation is at coarse particle size, one should not even think of flotation which is expensive and environmentally nor accepted; go for gravity separation.
    There is only adsorption of the chemical on the particle and there is no chemical reaction. Bubble gets attached and makes up the total volume(i.e.particle and bubble) which in turn makes the total density less than water and floats.
    We have to realise that each particle of feed to flotation has its own size and specific gravity depending on the minerals content in that particle. It then follows that we have to give a bubble(s) of enough volume to get attached if we want that particle to float.
    Rao,T.C.

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  10. Both. When developing the flow sheet for a new deposit / project "known" reagents / chemical conditions are used in the test work (to enable ready comparison), yet conversely when the plant is built and operating the focus switches to developing 'bespoke' reagent blends and optimising reagent addition points / dosages (I include aeration as a reagent).
    Chris Smith, Rio Tinto, Australia

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  11. I suggest you read my book "Fundamentals of the theory of flotation"
    You will understand very much.
    Sincerely.

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  12. An interesting question Barry . . .

    There are two fundamental principals that guide the success or failure of all industrial flotation. They are: are the minerals adequately liberation; and do the minerals of interest have the right surface chemistry (i.e. hydrophobicity). Without liberation the grade of the concentrate produced will be below par. However, if liberation is adequate and the surface chemistry is not right then it is unlikely that the desired grades and recoveries can be achieved.

    So, in the first instance, in a real system along with liberation the chemistry of the system is the dominant parameter that controls the success of failure of a separation by flotation.

    No amount of tinkering with the physics of the system will significantly incease the probability of a particle of interest actually contact a bubble and remain attached if it does not have sufficient hydrophobicity. Understanding the chemistry helps with they physics.
    Chris Greet, Magotteaux, Australia

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  13. Well said,Chris.
    By using "highphy"terminology, we made flotation look as "rocket science"; break the process into mineral characteristics and liberation followed by how to make wanted particles to float by attaching them to air bubbles after making their surface hydrophobic.
    Rao,T.C.

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