Froth Flotation (Sulphide & Oxide)

Froth Flotation (Sulphide & Oxide) 2017-03-23T09:43:25+00:00
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Phosphate Flotation Cell Size (7 replies)

Marshal Meru
1 year ago
Marshal Meru 1 year ago

Why is no one using mechanical cells larger than 30m3 for igneous phosphate beneficiation?This is a question for the suppliers/designers of mechanical flotation cells why can one have a plant with 200m3 column flotation cells for igneous phosphate recovery but when the equivalent plant with mechanical cells is specified no one goes above 30m3 mechanical cells?

Victor Bergman
1 year ago
Victor Bergman 1 year ago

There is no reason why igneous phosphate flotation, in mechanically agitated machines, should be limited to 30m^3. Foskor in Phalaborwa (RSA) is utilizing 42M^3 cells. Maybe one should look at when those machines were installed.

I know that Foskor progressed very slowly from 2m^3 to 8m^3 to 30m^3 to 42m^2.over a 50 year period and achieved 75% recoveries with 37% P2O5 concentrate grade. So this is proof that 75% recovery with 300m^3 cells is also achievable. The mineral particle does not distinguish between machine type and/or machine size. The mineral particle will respond in the same manner when it experiences the same macro environment.

I will design an igneous phosphate plant with 300m^3 cells which will achieve 90%+ recovery with 37% concentrate grade and 6-10% feed grade. My CFD friend HASAN has challenged me to design such a machine and I have completed the design. If you know how to achieve the conditions that will produce the required kinetic constant, then you are there.

Sturmbann
1 year ago
Sturmbann 1 year ago

I think you should be asking the phosphate plant operators why. I don’t claim to know much about phosphate flotation but I’d suggest that the shift away from mechanical cells may be part of an industry trend rather than based on actual performance limitations. Let me explain using the Australian Coal Industry as an example.

Back in the day most of the fine coal float circuits were mechanical cells, the 1980s pneumatic flotation cells became popular in the coal industry to the point that there was no new mechanical cells installed for over twenty years. I’d argue that in some cases the pneumatic cells far outperformed their mechanical cousins and the change was warranted. However the problem is it became the ‘industry standard’ and everyone installed this technology because it seems they didn’t want to be different. This saw pneumatic cells being installed in some duties that they weren’t necessarily the best for. Over the past 5-6 year’s we’ve seen a refreshing change with operators questioning what they are putting in and trying to find the best technology (pneumatic or mechanical) for the job not just the flavor of the month. This has seen mixed pneumatic and mechanical circuits and more recently a large increase in mechanical only float circuits. We may all be engineers but we are all definitely human and don't necessarily want to question the norm so we follow the prevailing opinion and propagate the trend.

I’d argue if a mechanical cell was setup properly it could likely perform in the phosphate duty. I’d be happy to discuss what the design criteria and needs of the circuits you are looking at are and see if we can’t find you a suitable large cell. Taking this a step further if you want to send me his parameters for a successful phosphate machine I’m happy to see if I can setup a cell (or cells) this way > I always like a challenge and this will be interesting!

Victor Bergman
1 year ago
Victor Bergman 1 year ago

The fact that all the machines in the phosphate plant performed at the same level is proof that there is no relationship between performance and machine size. The phosphate plant at Foskor has installed pneumatic columns with no success. After studying the design of the sparger nozzles I discovered that the nozzle cannot operate at exit Mach number > 2.5 with plant air at 7 bar supply. If the sparger nozzle expansion ratio is such that the exit match number will exceed Mach.2.5, then you will experience boundary layer separation which will produce a plug in the exit cone and it will reduce the air flow area which will result in a reduction of air flow. I tested this principle on a copper column with nozzles producing an exit match number of Me= 1, 2, and 3 and the Me=2 outperformed the other two by a "large" margin. I have developed the dimensionless numbers on machines ranging from Wemco OK, Metso, Denver and BQR and Agitair and on minerals ranging from phosphate, fluorspar, carbonates, copper, nickel, antimony, zinc, PGM's and copper slag. P80 represents the liberation condition. I argued that if you reduce particle size then you will reach a point whereall valuable mineral will be liberated unless it is trapped in solution or some of these weird mineral combinations such as Ti in magnetite. Chemical conditioning is represented by conditioning time and conditioner tank turn around. By multiplying the two will produce a dimensionless number. Referring to GIRR2: I think I have only scratched the surface.

Obergruppenfuhrer
1 year ago

50m3 mechanically agitated cells are used in the treatment of phosphate ores

Marshal Meru
1 year ago
Marshal Meru 1 year ago

I think the main take away point is that phosphate flotation has been carried out in a "coarse" particle size range which in turn means you do not want the loaded froth to travel over a great distance and so cause the p2o5 particles to disengage prematurely.

I suppose the question is what would happen if you dropped the P80 size down to below 100 micron without generating excessive slimes would you then be able to use a larger flotation cell?

The other challenge of course if the removal of concentrate from the surface of the flotation cells the traditional trough cells are equipped with paddle systems it would be interesting to see what would happen on larger trough cells with froth paddles. That said I am aware that OCP have installed Metso RCS 30m3 tank cells apparently with a good success.

I think it would be an interesting study, vendor and operations cooperating to investigate the use of larger trough cells and tank cells for phosphate extraction.

Unterstarm
1 year ago
Unterstarm 1 year ago

Why would you want to go that large? Throughput? There are other more cost effective ways, especially at the coarse end. In phosphates, the Hydrofloat fluidized-bed cell (Eriez) has been employed for many years. Being a fluidized bed, you can process at >60% solids and, with little froth and quiescent conditions, very coarse material is floatable. Don't know how large Eriez build the Hydrofloat but, with no moving parts, I'd imagine they could go quite large. Then again, why bother when you can float at such high solids?

Victor Bergman
1 year ago
Victor Bergman 1 year ago

Here is some information on recovery and grade vs. particle size for the Phosphate plant in South Africa: (Particle size-micron; Rec-%; Grade-%P2O5) <38, 71, 33; <53, 90,36; <75, 90, 38; <106,88,38; <150, 87,40; <212, 75,40; <300, 55,40.5; <425, 30,35.

So you see that igneous phosphate floats well when sized between 38micron - 212 micron. Interesting to note the grade as the grind becomes coarser .This tells you something about the liberation characteristics of this ore. Almost an abrupt drop with grind coarser than 300 micron. I think that liberation and suspension dominates after 425 micron. The poor recovery and grade with the -38micron is due to collector starvation and entrainment.

I am convinced that if you separate the fines from the coarse and float them separately with the correct conditioning you will achieve better recovery and grade. A second float of the -40 micron concentrate produced a 95% recovery with 38% P2O5 grade. The company installed a plant with their standard 8m^3 and 4.5m^3 cells but could never re-produce the same results. I investigated the deficiencies in this plant and found that there were absolutely no similarities between the two processes. I would love to be involved in a test program to run larger float cells on igneous phosphate but I can guarantee you that if you create similarity that the larger cells will perform the same if not better.

Another point that I should mention is that operational considerations can also impact on the choice of machine. In this plant the designers provided for more parallel tanks to reduce the chances of short circuiting and to continue production while maintaining one stream.

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