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Flotation Kinetics & Flotation Circuit Design

Flotation Kinetics & Flotation Circuit Design. DMR Sekhar. Contents. Introduction Bubble Particle Attachment Order of Rate of Flotation Flotation Kinetic Data: Sargepalli Copper Lead Ore

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Flotation Kinetics & Flotation Circuit Design

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  1. Flotation Kinetics &Flotation Circuit Design DMR Sekhar

  2. Contents • Introduction • Bubble Particle Attachment • Order of Rate of Flotation • Flotation Kinetic Data: Sargepalli Copper Lead Ore • Flotation kinetic Data : Jhamarkotra Phosphate Ore • Flotation Circuits • Conceptual Flotation Circuit & Material Balance • Rougher/Scavenger: Flotation Times & Scale Up • Summary • References

  3. Introduction • Flotation kinetics is the study of mineral recovery as a function of time. • The results of kinetic studies are useful in optimising primary grind of ores, comparing the performance of flotation reagents and designing of flotation circuits.

  4. Bubble Particle Attachment • (1) Initially air bubbles are fully loaded with floatable particles as the total of area of bubble surfaces is less than the area required for floatable particles. This condition is described as inhibited/explosive/loaded flotation. (2) After some time air bubbles are sparsely loaded as the total of area of bubble surfaces is more than what is required by the floatable particles at a particular time. This condition is described as free flotation. (3)Transitional flotation is where all the conditions of (1) and (2) may exist. v v v v v v

  5. Order of Rate of Flotation • Where N is the number of bubbles per unit volume at any time t, n is the number of particles per unit volume of pulp floated in time t and n0 is the number of particles when t = 0, according to Tomlinson and Fleming, Condition 1) All the bubbles raising through the pulp are fully loaded such that dn/dt is dependent on the rate of aeration only and if this is constant, dn/dt = kN = k0 which represents zero order law. Thus under inhibited/loaded conditions flotation process obeys zero order. (continued)

  6. Order of Rate of Flotation(continued from previous slide) (2) The relationship between N and (n0 - n) where floatable particles are sparsely attached to the air bubbles and at no time there is deficiency of air bubbles for a single species of particle at constant bubble rate, dn/dt = k1 (n0 – n) which on integration takes the form, log 1/(1-r) = k1t where r the recovery = n/n0 , which is a form of 1st order rate law. • Under practical conditions the flotation process initially is loaded/explosive flotation followed by free flotation and depending on the persistence of loaded or free flotation the net effect may appear as zero, first or any other order by chance.

  7. Kinetic Data of Pb flotation, Sargepalli copper/lead Ore 100.00 80.00 60.00 Cumulative Pb recovery 40.00 20.00 0.00 2.000 3.000 1.000 0.000 4.000 Normal Xanthate Floatation Of Lead : Sargepalli Copper Lead Ore (1/t), t = Cumulative time r = R - R/(kt), where r is recovery of mineral at time t, R is ultimate overall recovery at infinite time and k is the rate constant. This is a version of Klimpel’s model as modified by Prof. TC Rao that shows flotation as “apparently first order rate process”.

  8. 4.5 7.8 2.47 14.9 90 35.6 80 70 41.7 % Pb in concentrates, incremental % Pb in feed 6.7 60 Cumulative recovery of Pb 50 40 66 30 20 Free floatation Loaded floatation 10 0 1 3 9 5 6 0 2 4 8 7 t (cumulative time) Sargepalli copper-lead ore: xanthate floatation of lead (galena)

  9. Kinetic Data of Dolomite Floatation: Jhamarkotra phosphate ore

  10. 9.2 MgO in the feed= 12.5% Incremental grade of MgO for each float 12.10 14.5 15.30 16.1

  11. Flotation Circuits • Any process run in stages is efficient and this applies to the flotation circuits as well. Thus flotation circuits have rougher, scavenger and cleaner stages. • Scavenger stage is necessary to recover slow floating fine sized minerals and interlocked mineral particles. • Rougher concentrate will invariably have gangue minerals “mechanically entrapped” between bubbles and water in the froth will also carry gangue minerals into the froth. And hence the need to clean the rougher concentrate. • The recirculating streams, scavenger concentrate and cleaner tail, should have higher grade of the mineral being recovered than the receiving stream say feed to rougher. That is the streams being mixed should have “quality resemblance”.

  12. Conceptual Flotation Circuit & Material Balance Scavenger Bank Cleaner Bank Final tail Rougher Bank Feed F, f T, t Rougher concentrate Cleaner tail C + T = F F x f = C x c + T x t % Recovery = [(f-t) x c / (c-t) x f ] x 100 Cleaner Concentrate Weight % Recovery = C/F x 100 = [(f-t)/(c-t) ] x 100 C, c F = weight of feed, C = Weight of concentrate, F = mineral content in the feed, c = mineral content in the concentrate, t = mineral content in the tails.

  13. Special Cases • The conceptual flow sheet is what is generally followed. There may be special cases that warrant deviation. • Take for example galena flotation from a feed analysing 6.7% Pb. As per the “quality resemblance rule” scavenger concentrate analysing anything below 6.7% Pb is to be discarded. What if the scavenger concentrate has 4.5% Pb due to liberated fine sized galena particles? Should we lose them? This situation warrants a second scavenger bank and the concentrate of the second scavenger may be recirculated to rougher tails that is feed to first scavenger. • Some Lead/Zinc ores have graphite which is highly floatable. The current practice is to depress graphite while floating galena. However substantial quantity of graphite reports to lead concentrate spoiling the grade and some of it comes back to rougher feed! That is unwanted recirculation of graphite. The possible remedy is to remove graphite at the first instance before galena flotation (“pre floatation” of graphite) so that the highly floatable graphite is removed once and for all, giving a very short floatation time or provide a “cleaner scavenger” to collect galena from cleaner tails to send it back to cleaner and discard cleaner scavenger tails.

  14. Rougher/ Scavenger Flotation Times & Scale Up N = Vm t/ Vk k N= number of cells Vm = feed flow rate, m3 / minute Vk = volume of one cell K = cell constant (for effective volume which is 0.7 to 0.75), that takes care of air holdup and dead zones in the cell which depends on a particular type of cell design. t = floatation time which needs to be multiplied by a scale up factor from 1.6 to 2.6 , if t is taken from open cycle bench scale studies. Choosing a scale up factor depends on the recirculating loads from scavenger concentrate and 1st cleaner tail and number of cleaning stages. If t is taken from pilot plant studies or from similar industrial plant, scale up factor is 1.

  15. Notes (1) Rougher floatation time in the plant should cover till the loaded floatation exhausts. Rougher flotation may be in stages the first stage targeting good grade of concentrate and medium recovery and the second stage to maximise recovery. (2) Total volume of scavenger cells should be equal or may exceed the total volume of rougher cells in special cases. (3) Total cleaner cells retention time is 75% of the total retention time of the rougher cells. (4) On important factor that is often ignored is that the capacity of a cell or a bank of cells is dependant not only on the volume of the cell but also the air flow rate into the cell.

  16. Summary • Initially air bubbles in the flotation pulp are fully loaded (Loaded Flotation, LF) and reach the froth bed in the cell followed by sparsely loaded (Free Flotation, FF) air bubbles reaching the froth bed. • Depending on the persistence of LF or FF as time lapses, Flotation may appear following Zero, First or any other order by chance. • For rougher flotation bank, sufficient residence time is to be provided to collect all the fully loaded bubbles. • For scavenger flotation bank, residence time be provided to accommodate free flotation, till scavenger concentrate grade falls to “not less than the grade of feed to rougher flotation” to ensure “quality resemblance”. • It should be loaded flotation in the cleaner cells.

  17. References • Tomlinson,HS and Fleming, MG, “Flotation Rate Studies”, Mineral Processing Proceedings of the sixth International Congress, Cannes, May 26th to 2nd June, 1963. • Rao TC et al, “Effect of Mesh of Grind on Flotation of Rakha Ore”, IE(I) Journal,- MM,Vol.64, July 1983. • Glembotskii, V.A., Klassen, V.I., Plaksin,I.N., Flotation, Primary Sources, New York, 1972. • SekharDMR and Rama Shankar, Flotation Kinetics: an overview, Process and Plant Engineering, VOL. XIX. NO 5, Annual, 2001. https://www.researchgate.net/publication/235943994_Flotation_Kinetics • Sekhar, DMR, Scale up and design of flotation circuits, Plant and Process Engineering , Vol XIX, NO 3, 2001. http://www.researchgate.net/publication/235944468 • Basics in Minerals Processing, metso.

  18. Thanks • Thanks to Prof.ChVR Murthy, Principal, AU College of Engineering for making this Work Shop happen. • Thanks to Prof. V. Sujata, Prof. SV Naidu and Prof. P. King and to the Department of Chemical Engineering for whole hearted support. • Thanks to Prof. TC Rao and Er. DV Subba Rao Garu who are central to this work shop.

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