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According to Woodgrove, the Staged Flotation Reactor (SFR) was developed by going back to the first principles of flotation and examining how best to optimize the different stages of flotation without preconceived limitations. The result is a machine which optimizes the three stages of flotation into three separate zones, so that each zone is mutually exclusive of the requirements of other zones. The back drop of the foam is minimal and tightly controlled. Recovery zone "tight" pulp allows much more control in a scanning SFR, resulting in better recovery and upgrade

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woodgrove flotation reactors a revolution in flotation

Woodgrove Technologies developed the flotation cell called Staged Flotation Reactor (SFR). David mentioned the main features of the SFR cells. There are other similar flotation cells, but they have some operating and technical problems (e.g. sanding, circulating load is not handled properly, the residence time, etc)

I believe that Woodgrove design is more friendly and robust. Also, there is a very important point to keep in mind, the designers have a lot of experience in flotation, specially in the design of column cells. Some time ago, they established Minnovex, probably the main manufacturer of flotations columns. 

I have been involved in two projects now that have adopted SFRs, one for gold recovery accompanying a low sulphide content and the other for pyrite recovery from a copper cleaner circuit.  The latter is operating and apparently working well after some hydraulic modifications and the former has yet to be installed.  Bang for buck they are more expensive than tank cells and are probably best suited to smaller plants (<1 Mt/a).  They do however draw less power and have a smaller footprint.  It should be noted though that they need a greater step height between cells than an equivalent tank cell train which is an important consideration for a float plant in a building but no real issue for an outdoors plant.  Overall I think they could be a winner but its hard to get operating data.  They don't have a patent which is why they are understandably close lipped about their products but there are some smart guys behind the technology.  Ore can be piloted at their facility in Canada but there isn't really any small bench scale equivalent (1 or 2 kg) test that can be employed, they need around 80 kg as a minimum.  As a cleaner stage they have a lot of appeal as they can achieve remarkable upgrade ratios which means reducing the number of flotation stages.  Worth a look for your projects, especially for fine particle scenarios

woodgrove flotation reactors a revolution in flotation

Yes, I believe it is a case of prior art which is why they guard their technology closely, fair enough.  They claim that most of the energy in a tank cell, especially large ones, is spent on suspending particles rather than inducing collision, the latter being the forte of the SFR.  This make sense when you look at the kW/m3 which falls away with larger cells so less energy must be going into particle attachment.  Most of their blue chips are investing in SFRs so they must be taking them seriously.  Spence mine in Chile tried them out but I never saw the results.  Its worth talking to them to learn more about what they are up to. 

The SRF Woodgrove reviews are naturally or involuntarily biased by the fact that only SFR successes are published or promoted. When SFR is tested for Ore-A and does not show improvements/gains, the test results are quietly buried

If your flotation circuit needed extra flotation capacity and you test Woodgrove to see it if improves your situation, you are much likely to come out and say Woodgrove is a winner.  Truth is you would have tested old fashion column, Jamesons, or mechanicals cells with a similar positive outcome

woodgrove flotation reactors a revolution in flotation

I was involved in the SFR install and commissioning Greg H spoke of. (MRM days Greg) Both as the copper cleaners and latter the Pyrite roughers and cleaners. Like you Paul I was extremely sceptical....not any more. I now have a small involvement in Spence and have seen the test work

This may be true in terms of plant applications, but not so in laboratory. I am certain there are many cases where nothing conclusive resulted from lab tests but we, the general public, will not hear about it at the CMP

Sometimes a lower recovery rate in the small SFR pilot unit is seen and attributed to "the wall effect" ie: the adherence of froth to the walls of the test unit leading to coarse particle detachment. This wall effect is significant with small diameter pilot units and ultimately defines the lower limit of froth surface area that can be used for testing -Woodgrove explains

woodgrove flotation reactors a revolution in flotation

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reactor de flotación por etapas (sfr) de woodgrove - woodgrove

Woodgrove ha completado proyectos de planta piloto para múltiples clientes a nivel mundial. Podemos llevarte la planta piloto o nos puedes enviar tu producto! Resultados probados para una escala exacta hasta tamaño completo

The Staged Flotation Reactor (SFR) was developed by going back to the first principles of flotation and examining how best to optimize the various phases of flotation without preconceived constraints. The result is a machine that optimizes the three stages of flotation within three separate zones, such that each zone is mutually exclusive from the requirements of the other zones. Froth drop back is minimal and tightly controlled. The constrained froth recovery zone allows for much better level control in a scavenger SFR, resulting in better recovery and upgrading

reactor de flotación por etapas (sfr) de woodgrove - woodgrove

El Reactor de Flotación por Etapas (SFR) se desarrolló regresando a los principios basicos de flotación y examinando la mejor forma de optimizar las diversas fases de flotación sin restricciones preconcebidas. El resultado es una máquina que optimiza las tres etapas de flotación dentro de tres zonas separadas, de manera que, cada zona se excluye mutuamente de las necesidades de las otras zonas. La "caída" de espuma está estrechamente controlada. La zona de recuperación de espuma restringida permite un control de nivel mucho mejor en un Scavenger SFR, dando como resultado una mejor recuperación y mejora

O Reator de Flotação por Estágios (Staged Flotation Reactor - SFR) foi desenvolvido através da análise dos princípios básicos da flotação e de como otimizar as diferentes etapas da flotação sem as restrições já conhecidas. O resultado é um equipamento que otimiza os três estágios da flotação em três zonas distintas, de forma que cada zona é independente das necessidades das outras. O "drop back" da espuma é mínimo e minunciosamente controlado. A zona restrita de recuperação da espuma, permite um melhor controle de nível em um SFR Scavenger, o que melhora a recuperação e a concentração

the future of flotation

As design criteria go, removing the froth layer from froth flotation makes a bold statement. The fact that such a device not only exists, but has 50 operating installations, attests to the pressure on industry to find new solutions in the face of modern challenges. Low grades, complex ores and rising energy costs have prompted the development of entirely new flotation vessels, improvements to existing technology, and new thinking about flotation flowsheets

The froth-free flotation vessel comes by way of Eriez Flotation Division, which patented it in 2002 and marketed it under the name HydroFloat. It is intended specifically for an innovative flowsheet that addresses one of the biggest problems mining operations face: With more tonnages to process, and more fine-grained ore, comminution is demanding ever more energy. If flotation circuits could handle coarser particles, then energy could be saved in the comminution circuit

“Most mining companies are dealing with declining ore grades and complex mineralogy,” said Barun Gorain, director of Barrick Gold’s Strategic Technology Solutions Group. “The real problem is that more than 99 per cent of what we actually mine in the gold industry is considered waste.” He said that coarse particle flotation could allow mines to reject some waste earlier in the value chain, which will help reduce capital and operating costs

Second, even if they are able to attach, they tend to detach again. In most conventional tank designs, an impeller at the bottom creates turbulence that helps bubbles and particles collide; the bubbles rise up through a quiescent zone and congregate in a froth layer at the top

the future of flotation

Graeme Jameson, laureate professor at the University of Newcastle in Australia, explained that if particles are hanging on to bubbles spinning around in liquid vortices at 100 revolutions a second, there is some critical size at which a particle will simply detach from the bubble

High-energy turbulence is great for small-particle recovery, and by design the existence of turbulence is what keeps particles of all sizes in suspension. But that turbulence also discourages coarse particles from floating

“The coarser the particles you’ve got, the faster you’ve got to stir the liquid to keep them off the bottom of the vessel,” he said. “So it’s a self-defeating piece of equipment from the point of view of trying to float coarse particles.”

the future of flotation

Instead of an impeller, Eriez’s HydroFloat uses a fluidized bed to lift up coarse ore particles. Fed from the top, the vessel has a water inlet about two-thirds of the way down. As coarse particles sink to the bottom, the constant flow of water gently pushes them back up, continuously disrupting a region that is about 65 per cent solids. The water has been treated with compressed gas and a frothing additive to generate bubbles the coarse particles can attach to. While mineralized particles float into the overflow launder, coarse gangue settles to a dewatering zone in the bottom third of the vessel. When that zone reaches a certain density, its contents are released into the underflow outlet

Ken Roberts, global sales director at Eriez, said that HydroFloat can extend flotation up to 400 or more microns. In some sulfide ores, it has recovered two-millimetre particles – translating to 2,000 microns. Moreover, he said, “We’ve proven with research with the University of Utah that we can float a particle with two per cent surface mineralization showing.”

HydroFloat is explicitly not intended to float fine particles. The idea is that it would be part of a split circuit, presorted into coarse and fine, with technologies tailored to each. The practice has been proven in non-metal ores like potash and diamonds; Eriez has just been broken into the metals market in the last couple of years

the future of flotation

Jameson has been doing lab work on his own fluidized-bed solution since 2006. His design adapts the eponymous Jameson Cell he patented in the late 1980s. In contrast to the HydroFloat, his cell treats fine and coarse together. The flotation feed cycles past an airjet first, where it encounters the high energy useful for attaching fine particles to bubbles. “That’s like the Jameson Cell, actually,” he said

Then it flows into a fluidized bed, where the lower-energy environment allows coarse particles to attach. The ore-laden bubbles float up to a froth layer and overflow into a launder. A recycle line takes liquid off the top and recycles it into the base to be used for fluidization. Any fine particles washed out in the recycle line get another go at attaching to a bubble near the base. Fine gangue tends toward an overflow outlet

A year ago, Jameson got his hands on a porphyry copper ore from South America, and his recently completed test work shows encouraging results. “We can get 100 per cent recovery up to about 300 microns,” he said

the future of flotation

Now Jameson is looking for a mine site willing to trial a full-scale installation of about 50 to 100 tonnes per hour. “The point of that size is that the single unit is reasonably easy to handle and to build,” he said. “You can take it to a site on a truck and install it there and do your testwork, and then you’ve got something you can reliably scale up from.”

Although proven technology supports floating coarse ore, that is nowhere near the norm. “The mining industry has a history of addressing dropping feed grades and higher costs by leveraging economies of scale,” said Walter Valery, global director of consulting and technology for mining and mineral processing at Hatch. The tendency is to “treat large tonnages, grind all the material finely and let the downstream separation processes sort it all out. However, this is generally very inefficient and is neither responsible nor viable during downtimes.”

Major equipment suppliers meet that demand by designing ever-bigger flotation cells. Thirty years ago, a cell 30 cubic metres in volume would have been unusually large. Now, 300-cubic-metre cells are commonplace. Outotec has a 500-cubic-metre cell in operation and several 630-cubic-metre cells in delivery, while FLSmidth has one 660-cubic-metre cell in operation

the future of flotation

Building one big tank does provide energy economies of scale. That shines especially bright for mining companies newly interested in the energy cost of flotation – previously a major theme only in comminution, but now entering focus as cost pressures generally intensify and flotation tonnages rise

“When we double the size [of a tank], we get down by at least 10 to 20 per cent energy in practice,” said Antti Rinne, vice-president of beneficiation sales at Outotec. “That’s a huge amount of money in most countries in the world at the moment.”

That gradual scale-up comes with downsides. If the volume of the tank increases, the turbulence will not necessarily reach a commensurate height, which makes at least some of the extra tank volume a waste of space, steel and money

the future of flotation

“The proportion of the cell that is highly turbulent has decreased significantly as the size of flotation cells has dramatically increased over the last 20 years,” said Erico Tabosa, minerals processing engineer at Hatch

FLSmidth has addressed this problem through its new nextSTEP impeller design, which was developed to eliminate “dead” spaces without turbulence. As a result, the new design also makes the machine more energy efficient. “We found that we are consistently lower in power when compared to other forced-air flotation machines,” said Asa Weber, flotation technology director at FLSmidth

FLSmidth’s other major innovation is its Hybrid Energy circuit configuration, which addresses a problem of inconsistency in float cells. Because some ore is being recovered in each cell of a circuit, the mineralogical characteristics are changing from cell to cell but the cell design itself is not

the future of flotation

Outotec also developed ways to scale up while maintaining energy efficiency. Its own novel impeller designs, introduced in 2007, include a rotor/stator with similar turbulence-distributing benefits, called FloatForce. Outotec also invented an auxiliary impeller, called FlowBooster, that further improves mixing in the tank with very low additional energy

Significant effort has gone into finding the best impeller speed for the specific ore and application. “We’ve been doing a lot of work in recent years looking at variable speed drives on flotation cells,” said Ben Murphy, technology director of flotation at Outotec. The first large cells running operations with a variable speed drive were installed about five years ago. Since then such installations have shown they can maximize energy use, recovery or sometimes even both

“The interesting thing is we’ve actually been able to drill down a lot of the speed optimization and the energy reduction work to small cells,” added Murphy. “Which is kind of neat; it doesn’t always work that way.” For a small operation relying on diesel generators in a remote location, that could save real money

the future of flotation

Barrick uses large conventional cells at its operations. But it is also working with different consortiums to develop “the next generation” of more efficient flotation machines, according to Gorain. “Economies of scale still works for some ores, but for low grade complex ore bodies, these conventional cells are approaching their technical limits or their benefits are only marginal at best,” he said

The consortium sponsored work on a new design by Woodgrove Technologies. Instead of separate zones in one vessel, the staged flotation reactor (SFR) divides the flotation process into three chambers: a turbulent particle collection unit, a quiescent bubble disengagement unit, and a similarly quiescent froth recovery unit. Every SFR is custom-built for each mine’s projected ore characteristics

“We look at the grade and tonnage over the life of the mine, and then we design the froth recovery unit to manage the weighted distribution of metal units over this time,” said Glenn Kosick, president of Woodgrove Technologies. “For instance, if you’re on the back end of a bank of standard flotation machines, you might be removing 0.3 to 0.5 tonnes per hour per square metre. Whereas with this machine, you might be running at 2.5 to three tonnes per hour per square metre.”

the future of flotation

Kosick said the SFR’s efficient design cuts its energy use almost in half compared to a conventional flotation cell, and its limited use of floorspace makes it cheaper to install. “We’ve been selling it on the reduction in capital and operating costs,” he said. But its design also promotes better selectivity due to the large reductions of air used in these machines when compared to tank cells

“The data we’re getting back at full scale is showing us that we can float coarser material by constraining surface area, which results in very stable froths and short transport distances,” said Kosick. The coarsest cell operating now is running at a feed p80 of about 230 microns; the finest one is at 20 microns

Twenty-two SFRs have entered operation since 2010; more than 130 are under design. After a few successful installations at small mines, the consortium funded a trial scale-up to 930 tonnes per hour at Vale’s Sossego copper mine in Brazil. One of the consortium companies recently awarded Woodgrove the detailed engineering for an installation at a 95,000 tonne-per-day copper project in Chile

the future of flotation

These new solutions are often presented, and can be installed, as discrete projects. But they are most effective when seen holistically. For example, Woodgrove recently merged with the process control supplier Portage Technologies, allowing it to deliver equipment and process monitoring as one package. Woodgrove can now offer a froth characterization system to measure froth velocity, stability and colour; and bubble size, count and density, and it can provide timely suggestions for changes to equipment settings. Additionally, its upfront grinding and cyclone control can stabilize surges and prevent rocks from reaching the flotation circuit

On a larger scale, innovative flowsheet designs and reagent schemes are equally as important as the need for efficient flotation equipment. For example, Barrick is using its own patented flowsheet for a very complex refractory gold ore body. The process (“Mill-Chemistry-Float-Mill-Chemistry-Float”) involves floating the coarser particles in the feed first, regrinding, and then floating the fines but enabled with appropriate chemistry to suit the coarse and fines separately

A reinvented flowsheet might start with more targeted blasting; it might intersperse flotation with grinding. Kristy Duffy, a minerals processing engineer at Hatch, suggested that the new coarse flotation technologies might be useful in a pre-concentration stage to remove coarse gangue. The stages might run: coarse grind, pre-concentration flotation, grind, rougher flotation, regrind and cleaning flotation

the future of flotation

Gorain agrees that it could potentially be of use. “Non-flotation-based pre-concentration is actually much more attractive, because you’re trying to deal with the waste right in the mining before any major energy intensive comminution is pursued,” he said. Yet if the ore mineralogy is too widely and finely disseminated for other methods, then he thinks flotation could potentially be an effective first concentration step

More widespread interest is directed toward ore sorting, which can help toss out gangue early on and features heavily in mine-to-mill discussions. Roberts of Eriez said that several majors were investigating it hand-in-hand with a potential HydroFloat installation

The last several years of prolonged financial difficulties for the industry have forced some forward movement on innovation, as many projects simply would not be viable without new approaches. “I met with two majors that are on a joint venture in South America probably about a month ago and showed them not only the HydroFloat, but some other technology we have,” said Roberts. “And that was the whole point of the meeting: ‘Tell us what you have that’s new.’ Five, ten years ago, nobody would ever say that.”

the future of flotation

Woodgrove Technologies is also keeping busy during the downturn – without having to market itself, according to Kosick. “We’re hiring on almost a weekly basis here to try to keep up with the demand,” he said

But the downturn has also stifled research that could produce new innovations. “Most R&D divisions of companies have been severely affected by the mining downturn,” said Sergio Vianna, a minerals processing engineer at Hatch. “Therefore, there are a scant number of new solutions developed in mineral processing in the last few years.”

To help size and select conventional cells, Hatch would like to have a detailed study on the rate at which froth can stably transport recovered minerals over the lip of the float cell. But Vianna has doubts that such a study can happen in the current research climate

the future of flotation

Kym Runge, principal research fellow at the Julius Kruttschnitt Mineral Research Centre (JKMRC) at the University of Queensland in Australia, is concerned that Australia’s formerly healthy ecosystem of research centres, mine sites and consultancies is in danger, if trends continue, of being cut too far to spring back. Many global leaders in mineral processing have passed through JKMRC or use tools developed there

But research is continuing where it can. “We have a lot of other technologies which we’re working on,” said Barrick’s Gorain. “Obviously they are highly confidential, so we won’t be able to talk about it. But in general, the whole idea is to develop solutions for various complex ore bodies.”

Runge is working on a number of research projects. Progress made by equipment manufacturers notwithstanding, she thinks there is much more to understand about how turbulence affects flotation in the bigger cells. “A lot of people have just changed one variable and seen correlations and made conclusions from that,” she said

the future of flotation

She also sees a need to simulate the type of integrated, novel flowsheet envisioned at JKMRC. “Because they are low-risk beasts, the mining industry,” she said, “so being able to evaluate ‘What is going to be the economic benefit of putting a coarse particle flotation unit in the middle of my grind?’ will enable that to be adopted.”

Asked what flotation circuits would look like in ten years’ time, Runge was conservatively optimistic. “I’m hoping that we’ll start to see some of these new technologies start to be adopted,” she said. “I know we’ll be treating higher throughputs. And so they will need to get bigger, but hopefully we’ll also start to do things a little smarter.”

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