Monday, 5 August 2013

The need to float coarser particles

Much research effort is expended on the flotation of ultrafine particles but, as highlighted by Prof. Graeme Jameson at Metplant ’13, there is a need to reduce energy consumption by effectively floating particles at as coarse a size as possible.

Conventional flotation machines are effective for fine particle size classes. However, limitations due to particle buoyancy and bubble-particle detachment restrict their effectiveness when floating coarse particles. As a result, flotation circuits are generally configured to maximize the recovery of particles finer than 150-200 micron. In fact, grinding circuits expend significant energy reducing a feed stock to a particle size range suitable for flotation.

Increasing the upper size limit of coarse particle flotation has been a long-standing challenge in the minerals processing industry, and losses of values to tailings can often be attributed not only to ultrafines, but to particles too coarse to float. Some time ago I commented on the loss of copper in the final tailings at Nchanga (posting of 21st August), and Nchanga mineralogist Fuzail Siddiqui responded, attributing these losses to chalcocite particles as large as 0.5mm which were too coarse to float. He had even recommended the introduction of a step to regrind the coarsest fraction of the feed to bring the sulphide particles in floatable size range, but this was not implemented. Instead unsuccessful attempts to float the leach reside in columns were made.

If the particle size that could be effectively recovered in a flotation cell could be increased, the product size from grinding could be significantly coarsened, resulting in a more eco-efficient flowsheet. A number of strategies that could potentially increase coarse particle flotation recovery will be discussed at Flotation ’13 by Erico Tabosa and Kym Runge, of Metso, Australia, who performed tests using a pilot scale 3m3 Metso RCS flotation cell operated using a copper ore.  Turbulence was manipulated by changing the impeller speed, impeller size, feed pulp density and cell aspect ratio.  The work shows that coarse particle recovery is extremely sensitive to froth phase effects with recovery optimal at shallow froth depth and when turbulence at the pulp-froth interface is minimised.

HydroFloat Separator
The HydroFloat Separator at Metplant '13
The way forward might be fluidised-bed flotation, discussed in Graeme Jameson’s lecture, and demonstrated at Metplant ’13 by the Eriez Flotation Division. The Eriez HydroFloat Separator carries out flotation in a dense, fluidized-bed medium allowing for the selective recovery of coarser particles (>0.250 mm). Over the last 15 years, this technology has been successfully applied to industrial minerals with several full-scale units installed to recover particles up to and exceeding 3 mm diameter within the industrial mineral sector. More recently, sulphide-based laboratory test work has shown that this novel device is also capable of recovering metalliferous values at a coarse grind size. Benefits of this approach, such as improved recovery, low energy consumption and reduced reagent addition will be reviewed at Flotation ’13, and a timely peer-reviewed paper has recently been published in Minerals Engineering. Authored by researchers at Australia’s Ian Wark Institute, in collaboration with Eriez, the HydroFloat separator was used to float 250–1180 μm sphalerite particles in batch flotation tests and compared to results achieved utilizing a laboratory-scale conventional Denver cell. The quiescent environment within the HydroFloat cell significantly reduced the turbulent energy dissipation within the collection zone, hence decreasing the detachment of particles from bubbles during flotation. A comparison of recovery with a conventional Denver flotation cell indicated that the HydroFloat separator vastly outperforms the conventional flotation machine for the very coarse particles (+425 μm), and this is mainly attributable to the absence of turbulence and the minimization of a froth zone, both of which are detrimental to coarse particle flotation.

37 comments:

  1. Floating coarser particles sounds fine, but surely liberation is the key factor? We can grind coarser but if the values are not liberated they will not float.
    Sean Sutcliffe, Adelaide, Australia

    ReplyDelete
  2. Sean, at Flotation ’13 Graeme Jameson and Thomas Payne will present a paper on the effect of machine hydrodynamics on the flotation rate constant. It is well known that the rate of flotation of particles in mechanical cells is a function of the particle size. The rate constant, and hence the recovery, is low for fine particles, but it increases with particle diameter, reaching a peak in the size range 100 to 150µm, declining thereafter with increasing particle size. The reason for the decline in recovery with coarser particles has in the past been attributed to the increasing frequency of composite particles as the grind size increases. It has been thought that composite particles will float more slowly than liberated particles, because only a fraction of the surfaces of such particles will comprise the hydrophobic mineral, the remainder being composed of the hydrophilic gangue. However, it has been known for many years that the peak in the rate constant is found even with fully liberated particles. Jameson and Payne will show that composite formation cannot be the sole reason for the decline in recovery observed with coarse particles, Jameson having recently concluded that the decline in flotation rate observed with coarse particles is a function of the hydrodynamics of the flotation cell itself, and occurs independently of the fractional surface liberation, so the reduced turbulence in a fluidised- bed flotation cell may provide the way forward for coarse flotation.

    ReplyDelete
  3. Nagaraj Kulkarni5 August 2013 at 11:58

    is there any work done or potential to upgrade banded iron formations where liberation can be achieved at coarser size through this route?

    ReplyDelete
  4. Brings me the memory back from a SME annual meeting of more than a decade ago where Prof. Roe-Hon Yoon was presenting a paper about coarse particle flotation and Prof. Janus Laskowski asked him a question. I would paraphrase the question, "why would you worry about floating a coarse particle using froth flotation process if it can be floated using a dense-medium process" or enhanced-gravity process? Even if we have the technical ability of floating a particle using many different means, the right path recommended for the industrial practice should be the most economical one with due regard to environment.

    If the desired mineral particles are not liberated at coarse particle size, then only we need to grind those finer. But as you know, grinding finer hurts the industry both ways; it not only requires more energy (and increased cost), but also makes the down stream concentration process more difficult (meaning more cost intensive).
    By Dr. Manoj K. Mohanty, Southern Illinois University, USA

    ReplyDelete
  5. I will second Dr. Mohanty's comments and add that the same statements were being made 50 and 60 years ago, tha we should first look at what the coarsest size that can be processed to get the desired recovery wether by flotation or gravity, and then only look at grinding fine enough to make flotation grade on the coarse concentrate.

    The one statement I keep hearing is that gravity separation is limited to a lower feed rate than flotation, but I will agruew that we just haven't looked at it enough. It wasn't that long ago that people were surprised with 100 cubic meter float cells, while now 300 cubic meteres are relatively common. So why not 1,000 to 2,000 t/hr jigs and dense media baths. We know we can make very large cyclones.
    Mike Albrecht, San Francisco, USA

    ReplyDelete
  6. My dear Barry,
    I am extremely happy that you are, in your own subtle manner, bringing the mineral engns to carry out R&D in these important directions; no sensible mineral Engn would think of flotation if there is significant differences in density of minerals in question.What you might be having mind, if I understand right, is to explore the feasibility of using flotation for coarse particles where the minerals are not amenable by other techniques but the ore has to be ground to relatively finer sizes.
    I stand corrected if I am on the wrong track.
    Keep at it,Barry .
    Rao
    By Tadimety Rao, Hyderabad, India

    ReplyDelete
    Replies
    1. You are definitely not on the wrong track TC. It seems pretty obvious that we should use gravity concentration where possible, it being cheaper, simpler and more environmentally friendly than flotation. But the SME question is surprisingly naive. Very few ores produce an exploitable density difference at coarse size, and not even at fine size, which is why flotation dominates. There are exceptions of course, and many lead-zinc ores can be preconcentrated at very coarse sizes by DMS, but there is no way that you could treat a disseminated copper ore in this way.

      Delete
  7. A few comments. First, it's not just particle size but also its density that play a role; hence, particle-size vs flotation rate or recovery curves shift to smaller sizes with increasing density. Second, one can take a simple look at what Jameson, Wills, etc. are doing. Let's say you have a particle of density p and size d. What is its weight? If that particle were to attach to just one bubble, what bubble size would be just needed to make the particle/bubble just float (i.e., weight and buoyancy would just balance). The conditions of course would be quiescent for this to happen but, at the same time, the particle would have to be quite hydrophobic to get and maintain attachment. Now, lets assume the same thing is done with 10 bubbles. Obviously, the bubbles are smaller but the bubble volume is the same; however, attachmant has to occur on various sites of the particle suggesting that all of the particle must be hydrophobic further suggesting that liberation is going to be a factor. In my opinion, to obtain this level of hydrophobicity, collector concentrations will need to be increased and the collector will need to have more specificty as a result. Getting and maintaining bubble attachment in a turbulent environment of a flotation cell will only add to the difficulty. No doubt, all of these things are being considered by the researchers but it is easier said then done.

    ReplyDelete
  8. The topic of floating coarser is a typical "desire" of operations versus a "can". The proposed size range of 100-200 um, is already too small, as there are many operations already operating as coarse as 300-350um. So if these are operating at coarse sizes why are others not.
    The key being in liberation and mineral association. If the desired mineral is naturally occuring as 5 um particles asking a float machine to recover at 250 um is pointless. the starting point needs to be mineralogy and naturally occuring mineral grain sizes. In my experience i have only come across three Copper porphyry projects where the grain size is such that sufficient liberation for floation occurs at primary grind sizes of 80% passing 250 um and coarser. My limiited experience suggesting that this represents only 5% of projects i have been involved in.
    So if some operations can actually recover at what here is considered coarse, is it really a problem of equipment?
    Stuart Saich, Promet 101 Consulting, Chile

    ReplyDelete
    Replies
    1. Stuart,you have put the whole issue in correct perspective and well pointed; as Barry has already put it in its correct perspective.
      Mineral Engns sometimes get the technical feasibility and economic viability mixed up-- my view is let good R &D do think more on the first one;then identify the factors which can make it more economical and do R&D again to make it viable.
      t.C.Rao
      Tadimety Rao, India

      Delete
  9. Flotation of coarse particles is not new, and was looked at for the flotation of Florida phosphate many years ago. It was claimed that using the Deister Flotaire machine which had no impeller, that apatite up to 4mm diameter could be floated.

    However, the point is that you don't need to grind the rougher feed to its liberation size - a 70% liberation will probably give enough particle surface area for you to float a particle so that you can perform roughing at high recovery. You then have a reduced tonnage of rougher concentrate on which to do your costly liberating regrind. This principle was used in the flotation circuit design for the Ernest Henry copper gold concentrator in north west Queensland.
    Mike Wort, Cosmos Minerals, Australia

    ReplyDelete
  10. The coarse flotation always is a mater for discussion, there is not reason to go up to liberation grade, could be a extremely expensive in power consumption in the grinding circuit, in my point of view is to arrange a really coarse flotation and regrind only the rougher concentrate, the difficulties are that the efficiency of coarser flotation decrees in big flotation machines, specially in big operation (more than 100,000 MT/D), the challenge is to design a new flotation system for a coarse flotation., in the small operation is more easy to get a coarse flotation using small flotation machines.
    Alejandro Chavez Valencia, Metso Minerals, Peru

    ReplyDelete
  11. Barry et al., A few comments from the now much older grad student that worked diligently to prove-out this concept: Liberation is indeed the key, but not in the typical sense of providing for grade. It is key with respect to providing just enough surface area for the bubble(s) to attach without leaving too many 'locked' particles behind. One thing that is certain, is that a large hydrophobic surface is not required for successful flotation. During the MetPlant conference, I showed pictures of the "floated" product that was successfully recovered in the HydroFloat, and these 'middling' particles contained very little surface area of available sulfide.

    This observation (that was confirmed through SEM analysis) is consistent with Dr. Jameson's findings regarding k-rate vs. particle size with respect to turbulence. The HydroFloat is an aerated teeter-bed separator. These devices are known to be both plug flow and very quiescent. In fact, when running properly, they are about as quiescent as you can be while still maintaining particles in suspension. Another positive is that the HydroFloat is run without maintaining a froth of any discernible depth. This is where other flotation approaches falter because a coarser particle will not transfer between the pulp and the froth due to its relatively gravity. Just do the simple math and you’ll find that these traditional approaches fall-off (insufficient buoyancy) at around 250 micron given a typical bubble size - this is quite non-coincidently where traditional flotation is known to suffer.

    Ultimately, success of this approach will be dictated based on the economical/engineering question as to whether the grind size can be increased sufficiently without significant losses of the locked values.
    -Jaisen Kohmuench, EFD|USA

    ReplyDelete
  12. It is always preferable to use gravity concentration circuits wherever possible for the recovery of coarser particle size. Hydro float separator (Basically fluidised bed flotation) may be suitable for the recovery coarser fraction for some minerals, but needs more research to apply for specific minerals and coal.
    SUNIL TRIPATHY, Tata Steel, India

    ReplyDelete
  13. Its true that we have to save the energy and environment while processing. Ores and associated gangue minerals are site specific.Unless there is a good characterization studies we never select a process.
    Though gravity separation techniques are well established a rigorous validation is still required with the change in the feed characteristics.
    Dr. Rama Murthy Yanamandra, Tata Steel, India

    ReplyDelete
  14. My viewpoint.... The opening discussion was mainly to encourage brain-storming and thinking laterally.

    At JKMRC I would suggest alternatives that would focus on decreasing the rate of sinking of large particles in a flotation cell - yet the argument against this was always use A OR B; DO NOT think laterally and use both A AND B.

    Therefore I suggest - better to get some people with limited 'real' experience who are prepared to look at the problem from a fresh perspective.
    Stephen Gay, MathsMet, Australia

    ReplyDelete
    Replies
    1. Thanks Stephen, yes the purpose of all this is to encourage lateral thinking and discussion, and I thank you all for your comments. However I feel that some of the correspondents have misinterpreted the original remarks. This was never intended to be a discussion on flotation versus gravity concentration. As Prof. Rao correctly points out, gravity concentration would always be the preferred option if an economical density difference can be developed at coarse particle size. If not, then flotation may be the only option, and, as it has been shown that flotation is possible even if only a small fraction of the valuable mineral is exposed, then the limitation of coarse flotation may be cell hydrodynamics, as explained clearly by Jaisen Kohmuench.

      Delete
  15. While flotation is mainly a surface chemistry phenomenon, people tend to forget the physical factors such as bubble size, vessel size and shape, engagement/disengagement factors, etc.

    Many people (let us say most and myself included) discuss physical separation as gravity/density separation and fixate on the relative density differences as being the key. This needs to be considered as an over simplification, where other factors such as particle characteristics (size, shape, and surface chemistry) do play a part.

    The actual effect that matters is the relative motion of the particles to each other, whether in upwards flowing stream, downwards flowing stream, or quiescent stream. And what mineral engineers need to consider the is best (from an overall economics perspective) method to get this separation at a reasonable grade and recovery.

    We do seem to have locked ourselves into a vicious loop where the answer is to make it bigger, grind it finer, and float the h*$$ out of it. And even the miners are taking the attitude that they can mine it all and let the process people sort it out. But with energy and capital costs rising, perhaps a more holistic approach IS needed, where we start in the mine, and work forwards to determine the way to achieve best results. I believe this can done with the “modern” low grade deposits.
    Mike Albrecht, San Francisco, USA

    ReplyDelete
    Replies
    1. Mike, it is interesting that you bring up the relative motion of the particles to each other. In an open flotation vessel, especially for the coarsest particles, the collision rates may be high, but the relative velocity of the settling particle to the rising bubble is very fast. This is why some industries (think industrial minerals) purposely increase the fines content of the flotation pulp. This increases the pulp viscosity, reduces the settling rates and ultimately improves attachment.

      The aerated fluidized-bed approach also decreases this relative velocity. The rising air bubble is slowed by the particle concentration of the teeter-bed, and the settling particles are also slowed due to the hindered environment, but also the rising current of elutriation water. Together, the sliding time and attachment probability increases substantially when compared to traditional flotation.

      As an aside, I'm a big proponent of split-feed flotation. In my opinion, there is no one magical device that can float a wide size distribution efficiently. And as long as the industry tries to float from the very coarse to the very fine in one device, there will always be losses on either end of the size distribution.
      Jaisen Kohmuench, Eriez Flotation Div., USA

      Delete
    2. Jason, On the basis this is technical discussion, I would like to make a few comments - although I recognise some would regard these as pedantic.

      Fines changes both the slurry density and hindered settling.

      Hindered settling is an important variable for coarse particle flotation and it would be confusing to label this as viscosity.

      Yet if I look up a definition for hindered settling (which I don't truly agree with):

      Settling of particles in a thick suspension in water through which their fall is hindered by rising water.

      Read more: http://www.answers.com/topic/hindered-settling#ixzz2bQP9ZP2C

      However my point here is that the most obvious way to hinder settling is to cause an upward flow of water.

      I am quite sure it would be an effective contributing mechanism.

      Of course I do not know the economic feasibility but suspect if designed well it would be cheap.
      Stephen Gay, MathsMet, Australia

      Delete
  16. Yes you have stirred the hornet's nest Barry
    And it has been well addressed by the many responses. A couple things need to be emphasised, since recovery of coarse particles is generally driven by economics and not technical requirements, assuming that the mineralogy is favourable. Afterall, the porphyry copper operations that Stuart describes are based on floating composites and regrinding the concentrate - allowing significant savings in equipment and operating costs.
    Coarse flotation of base metal sulphide has been around a long time - I can remember the 'unit' cells at WMC's Kambalda operation floating up to 70% of the pentlandite from the rod mill discharge. They were seriously 'beefed up' conventional cells and the 'froth' was like a 'carpet' noisely splashing into the launders. Very impressive.
    Of course, Outotec with Skim units have considerable success and apparently improvements are in-hand. Professor Jameson has been working on coarse flotation for some years and is developing a solution.
    Mineral SG has naturally a significant effect - in industrial minerals, as noted with phosphate flotation, they already float small 'rocks' e.g. coal!
    As Stuart implies, there is a natural cut-off size between the two technologies - gravity and flotation - and we need to understand what this value is and target the appropriate technology. And as Mike suggest, more research into improving the unit capacities of gravity separation units for finer feeds may be required although spirals are quite acceptable while hectares of tables may find a place where labour costs are low.
    Andrew Newell, PAH, Australia

    ReplyDelete
    Replies
    1. In response to Andrews comments on larger gravity units; fine coal jigs of 500 ton/hour capacity have been around for a long time, which would be almost 1000 tons/hour for mineral jig, so why not 1,500 or 2,000 ton/hour?

      As for the labor concerns for tables, why not use optical methods and software to make an automated table 20' x 40' (6 m x 12 m)?
      Mike Albrecht,USA

      Delete
    2. Excellent points Mike and a good pointer for industrial research for larger and automated tables. Jigs, depending upon the SG differential, are useful down to a few hundred microns and there are no problems with having parallel circuits...so the 'problem' may be solved!
      Andrew Newell

      Delete
  17. Aren't Skim Air and flash floats supposed to be for floating coarse material?
    Greg Cox, Process Plants International, Australia

    ReplyDelete
  18. It is certainly correct that Skim Air and flash floats are for floating coarse material.

    But I couldn't actually find anything to explain exactly how Froth flotation and Skim Air were specifically designed for coarse particles.
    i.e. explanations on 'how it works' tend to say: it is applied to coarse particles.

    Please elaborate if you know. I don't.
    Stephen Gay, Australia

    ReplyDelete
    Replies
    1. Flash floats basically "high grade" the grinding cut coming through so yes, a lot of coarser material gets returned to the grinding circuit. The Mass pull is usually 1-3% because it is only catching the highest grade material but as the Tail usually goes back to the grinding circuit it does come back through again for another cut.
      Greg Cox, Australia

      Delete
  19. We are having good time on this topic, thanks to Barry
    If a particle is floating in a flotation circuit after getting attached to air bubble(s), it is because the effective specific gravity of the total(particle and bubble ) is less than water; so it is how one can manipulate the total volume of air bubble(s) and particle effective mass is the answer.
    Particle mass, as we use in heavy media,is still there in flotation also
    T.C.Rao, India

    ReplyDelete
  20. TC Rao hit the nail on the head. In my opinion, fluidized flotation is really a hybrid approach that combines methods of gravity concentration with flotation fundamentals. By attaching an air bubble to the particle, the 'effective' specific gravity of the bubble/particle aggregate becomes much less than the hindered-bed (i.e., the dense medium). An efficient separation results. This approach has been developed over some time and there are many papers as early as 1999 for work done under a FIPR grant (Florida phosphate).

    Stephen, regarding hindered settling, I agree that it cannot simply be described as a result of fluidization. It is more aptly defined when the high concentration of the teeter-bed is taken into account. When this bed is allowed to develop, the particle-particle interaction and the compression of streamlines is paramount. The effect on interstitial velocities will impact the hindered-settling rates.

    Regarding Flash cells, my understanding (and I'm no expert) is that they are designed to process very coarse feed, but I'm not sure what the effective flotation size would be. I believe they'll recovery most of the fast-floating material, but I think much of the really coarse material sloughs through without being affected. Perhaps someone with a better understanding can provide some information?
    Jaisen Kohmuench, EFD, USA

    ReplyDelete
  21. To provide some clarification on how skim air (flash cells) work: They are indeed designed to take a very coarse feed material (cyclone underflow), which often contains small rocks. The inlet/outlet of these cells is specifically designed to allow the very coarse material to bypass directly to the tailings stream (usually a secondary mill feed), whilst allowing the finer material to be drawn into the impeller region. The impeller (rotor/stator) set up is not dissimilar to a conventional tank cell. In the work I have been doing on the operation of these cells I have found that the region above the impeller is effectively acting as a classifier, and whilst coarse particles up to (for example) 850 micron are (apparently) attached to bubbles in the region directly above the impeller area, as they approach the froth they drop off, and you see a very clear trend of decreasing particle size with cell height as you approach the froth zone.
    I have had many years experience operating these cells in various sulphide flotation plants and have always found that whilst the P80 of the concentrates they produce are coarser relative to the other concentrate streams on the plant, the P80 is still within what I would consider to be a normal range for conventional flotation devices (typically around 150 micron). I have found particles up to 1mm in some of my flash concentrates, but the proportion of material in this size region is small. In terms of the mineralogy of the particles they recover, they are all very well liberated (majority being 90% valuable material or more), even into the +150 size classes. So the mode of operation of the modern flash flotation device is indeed to recover the very well liberated material within the floatable size range, or fast floating material. I will add one more point in that I have found some success in extending the floating size range by manipulating the operating conditions within these cells, slurry per cent solids and frother type in particular; and if you would like more detailed information on flash flotation just pull up some of my Minerals Eng. papers on the topic!
    Bianca Newcombe, Australia

    ReplyDelete
    Replies
    1. Bianca will be presenting three papers on flash flotation at Flotation '13 which will answer the most common question she is asked about operating flash flotation cells - such as how important is slurry density and how do you get it right?

      Delete
    2. Thanks Bianca for the explanation. I'll definitely pick up your papers. In my experience with the aerated fluidized bed separator, I've found that we operate on other side of the grade/recovery curve. Where the flash float operates and essentially picks up the almost completely liberated material (and likely finer), the HydroFloat tends to operate on the very high end of the recovery curve picking up not only the liberated material, but also all of the middlings, up to the coarsest sizes (2-mm?). In some of our work, we were able to produce a throw-away tail which would greatly reduce the amount of material that would have to be ultimately reground downstream.
      -Jaisen Kohmuench, EFD|USA

      Delete
  22. Liberation will be an issue in coarse particle flotation. If particles are liberated then the technique of "Classification Flotation" can be applied where the material is sized prior to flotation. The float cell will have to be modified to accommodate a "hydraulic lift". I have floated bauxite particles as coarse as 1700 microns. Coarse particle flotation is non-conventional and requires the knowledge of reagent scheme, conditioning methodology etc. Slimes in the feed is a great hindrance in coarse flotation.
    --Khiratt Husain, SGS, Toronto, Canada

    ReplyDelete
  23. Dr. Fuzail Siddiqui P. Geo.20 October 2013 at 11:48

    I return to this forum almost a year later and see that the issue of coarse particle size, triggered partly by my report of coarse particle losses at Nchanga, is still hotly debated. In this debate the main issues discussed are 1) liberation 2) hydrofloat 3) flash flotation and 4) gravity separation. When I joined Nchanga in 1973, as a process mineralogist, my first task was to look at final tailings that had high 'acid insoluble Cu (AICu)' (mainly sulphides) losses. The coarse ore mineral particles, I saw under the microscope in my very first sample, were almost entirely liberated. I remember conducting fractional analysis on the sample that demonstrated that AICu content increased with particle size; pretty convincing evidence that coarse and well liberated sulphide particles were leaving with the concentrator final tailings. A daily average 27000 tonnes of current tailings were piped to the Tailings Leach Plant (TLP) where they were joined by about 23000 tonne of stockpiled tailings from past operations and the combined material was fed to leach Pachucas. The leached pulp was allowed to reach the CCD thickener system via numerous launders. Any time one walked along a dry launder one could see coarse and well liberated copper sulphide particles settled in every crevice/depression in the launder bottom. further proof of validity of the reports from process mineralogy. So liberation was not a real issue at Nchanga. As to options for a solution, this debate seems to have taken the coarse sulphides losses as inevitable. I am not so sure. Should one not first of all look at possible preventive steps? I would nave liked to do some tests at the cyclone feed, overflow and underflow. It is obvious that sulphide particle size which should have reported to underflow was finding its way into the overflow and reaching the flotation circuit. May be all one needed was to fine tune cyclone operations. If that doesn't work then of course one can look at post-concentrator recovery, but with test work under careful process mineralogy/chemistry controls. Buying magic cures is likely to meet the same fate as that of the defunct 'leach residue flotation' columns.

    ReplyDelete
    Replies
    1. Jaisen Kohmuench28 October 2013 at 14:01

      In response to Dr. Fuzail Siddiqui...I agree that if you see coarse liberated particles in the launders, then these particles are recoverable. I know that I am partial to the HydroFloat, but that is because I have worked with this technology since its infancy in the late 1990's - well before others. If you can segregate the coarse from the fines (preferred method), then you can easily achieve a fluidized-bed through which you can disperse some air. Once the air-bubble attaches to the particle, you've essentially created a bubble-particle aggregate that is more buoyant than it was in a conventional-type cell. The conventional cells are simply too turbulent and detachment is too great to maintain any consistent recovery. For the application you describe, the additional recovery could be relatively straight-forward to achieve. I for one, do not believe that coarse losses are inevitable. I have seen too much data using this novel approach that says otherwise. From a fundamental perspective, fluidized-bed flotation improves the flotation rate beyond that achievable by any other methods: collision properties are increased; detachment is reduced, turbulence is minimized, sliding times are increased, retention times are increased, and improved buoyancy is achieved. All these are good ingredients for coarse particle recovery.

      Delete
  24. The concept of regrinding minerals was started with coarse particle separation. But due to inefficient design of cells this could not be continued. Cells got jammed heavily. Tailing losses were high--could not be analysed due to jamming problems. For all heavy minerals and high sp.gr particles this problem is encountered. But for coal Dr.jameson has done a good job. I dont know if this technology is useful for heavy minerals. Till now there is no report. Flash flotation was one of the best equipment, but due to improper installation of monitoring instruments it failed. We can once again try with good instruments and a separate cell for collection.

    ReplyDelete
    Replies
    1. Jaisen Kohmuench28 October 2013 at 14:10

      If the cell is designed properly, than it should not get 'jammed.' In fact, when we started working with the HydroFloat, we specifically designed it to handle coarse particles that you would normally see in the industrial minerals sector. These particles can range from 150 microns to well over 3-mm with a wide range in densities. The teeter-bed conditions in this type unit are designed to handle these larger sizes. Unfortunately, conventional type machines induce too much turbulence which is required to keep the larger particles in suspension and create a nice bubble dispersion. This turbulence causes detachment of the coarse particles. I don't have much specific data that I can share regarding heavy minerals, but will say that we have successfully treated this type material in numerous lab tests. While it is denser, the tighter and finer size distribution lends itself well to fluidization. Some of our earliest papers have some results from heavy mineral applications which I can share if you are interested.

      Delete
  25. For me, the first step id to find the size at which the targeted mineral (could be valuable or gangue) gets liberated. Then decide which process i.e. physical/magnetic/flotation is most cost/energy/environmentally acceptable. That is the process I will select.Flotation reagents are also costly.
    Rao,T.C.

    ReplyDelete

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