Presentation is loading. Please wait.

Presentation is loading. Please wait.

Froth Flotation.

Similar presentations


Presentation on theme: "Froth Flotation."— Presentation transcript:

1 Froth Flotation

2 What is Flotation ? Flotation is a mineral separation process, which takes place in water-mineral slurry.  In this process by attaching mineral particles to air bubbles to provide selective levitation of them.  1. The surfaces of selected minerals are made hydrophobic (water-repellent) by conditioning with selective reagents.  2. The hydrophobic particles become attached to air bubbles that are introduced into the pulp  3. These particles are carried to a froth layer above the slurry thereby being separated from the hydrophilic (wetted) particles. Hyrophobic particles Flotation concentration method utilizes the differences in physico chemical surface properties of particles.

3 The process can only be applied to relatively fine particles, as if they are too large the adhesion between the particle and the bubble will be less than particle weight and the bubble will therefore drop its load. (smaller particles than 0.5 mm) Flotation is the most important and versatile mineral processing technique used in mining industry. In flotation concentration, the mineral is usually transferred to the froth, or float fraction, leaving the gangue in the pulp or tailing. This is direct flotation as opposed to reverse flotation, in which the gangue is separated into the float fraction.

4

5

6 Contact Angle The grater the contact angle the greater is the work of adhesion between particle and bubble and the more resilient the system is disruptive forces.  The floatability of a mineral therefore increases with the contact angle; minerals with a high contact angle are said to be aerophobic.

7 Classification of Polar Minerals
Minerals with strong covalent or ionic surface bonding are known as polar types. The polar surfaces react strongly with water molecules, and these minerals are naturally hydrophilic. Classification of Polar Minerals 1. group 2. group Galena PbS Barite BaSO4 Chalcopyrite CuFeS2 Anhydrite CaSO4 Covellite CuS Gypsum CaSO4.2H2O Bornite Cu5FeS4 Anglesite PbSO4 Chalcocite Cu2S Pyrite FeS2 Pyrrhotite Fe7S8 Sphalerite ZnS Stibnite Sb2S3 Cinnaber HgS Natives Au, Ag, Pt, Cu 3a. group 3. group Malachite Cu2CO3(OH)2 Flourite CaF2 Azurite 2CuCO3.Cu(OH)2 Magnesite MgCO3 Cerrusite PbCO3 Dolomite CaMg(CO3)2 Scheelite CaWO4 Siderite FeCO4 Monazite (Ce,La,Di)PO4 4. group 5. group Hematite Fe2O3 Zircon ZrSiO4 Goethite FeO(OH) Beryl Be3Al2Si6O18 Chromite FeCr2O4 Garnet Ca3Al2(SiO4)3 Borax Na2B4O7 Rutile TiO2 Cassiterite SnO2 The degree of polarity increases from sulphide minerals through sulphates, to carbonates, halites, phosphates etc. then oxides-hydroxides and silicates and quartz.

8

9 Most minerals are not water repellent
Most minerals are not water repellent. When these minerals put into the water these get wet. The surfaces of selected minerals are made hydrophobic (water-repellent) by conditioning with selective reagents. Air bubble Hydrophobic Particle

10 micelle

11 Flotation reagents must be added into the pulp to render the particles hydrophobic (or hydrophilic) and to facilitate the bubble attachment. These reagents are; 1. The Collectors. 2. The frothers help maintain a reasonably stable froth. 3. The regulators are used to control the flotation process; these either activate or depress mineral attachment to air-bubbles, and are also used to control the pH of the system.

12

13

14 2. Frothers The frother acts entirely in the liquid phase and does not influence the state of the mineral surface A good frother should have negligible collecting power, and also produce a froth which is stable enough to facilitate transfer of floated mineral from the cell surface to the collecting launder. The acids, amines and alcohols are the most soluble frothers. Pine oil MIBC Polyglycol ethers (PPG)

15 3. The regulators Regulators or modifiers are used extensively in flotation to modify the action of the collectors, either by intensifying or reducing its water repellent effect on the mineral surface. Activators Depressants pH modifiers ZnS+Cu+2 = CuS+ Zn+2

16 g, reagent per ton of feed, g/t
The Dosage The amount of reagents used in flotation defined by the term «dosage» Special feeders or dosage pump are used to add the collector into the conditioner or cells g, reagent per ton of feed, g/t Reagents are generally liquid, therefore volumetric feed rates must be defined for reagent addition Homework Flotation feed: 100 t/h, the density of the reagent: 0.9 g/cm3 The reagent solution is containing 10% w/w reagent (diluted with water) The reagent dosage is 100 g/t A dosage pump will be used. Calculate the reagent feed rate as cm3/min (flowrate)

17 The Dosage

18 Reagent addition Conditioners Grinding circuit pH control acid or base
Feed Modifier addition pH control Collector addition Frother addition Grinding circuit pH control acid or base Reagent addition at different stages Conditioners

19

20

21 Performance Calculations_1
Ratio of Concentration: the weight of the feed relative to the weight of the concentrate, The Ratio of Concentration is F/C, where F is the total weight of the feed and C is the total weight of the concentrate. One limitation with this calculation is that it uses the weights of the feed and concentrate. While this data is available in laboratory experiments, in the plant it is likely that the ore is not weighed and only assays will be available.

22 Performance Calculations_2
Starting with the mass balance equations, and the definition of the ratio of concentration: F = C + T, Ff = Cc + Tt, Ratio of Concentration = F/C where F, C, and T are the % weights of the feed, concentrate, and tailings, respectively; and f, c, and t are the assays of the feed, concentrate, and tailings. We now need to eliminate T from these equations so that we can solve for F/C: Ff = Cc + Tt, and multiplying (F = C + T) by t gives us: Ft = Ct + Tt, so subtracting this equation from the previous eliminates T and gives: F(f - t) = C(c - t), and rearranging produces the equation for the ratio of concentration: F/C = (c – t)/(f – t)

23 Performance Calculations_3
% Metal Recovery, or percentage of the metal in the original feed that is recovered in the concentrate. This can be calculated using weights and assays, as (Cc)/(Ff)·100. Or, since C/F = (f – t)/(c – t), the % Metal Recovery can be calculated from assays alone using 100(c/f)(f – t)/(c –t).

24 Performance Calculations_4
% Metal Loss is the opposite of the % Metal Recovery, and represents the material lost to the tailings. It can be calculated simply by subtracting the % Metal Recovery from 100%. % Weight Recovery is essentially the inverse of the ratio of concentration 100·C/F = 100·(f – t)/(c – t). Enrichment Ratio is calculated directly from assays as c/f, weights are not involved in the calculation.

25 Problem: A copper ore initially contains 2. 09% Cu
Problem: A copper ore initially contains 2.09% Cu. After carrying out a froth flotation separation, the products are as shown in Table 1. Using this data, calculate: (a) Ratio of concentration (b) % Metal Recovery (c) % Metal Loss (d) % Weight Recovery, or % Yield (e) Enrichment Ratio

26

27 From Table 1, the Ratio of Concentration can be calculated as
If only assays are available, the ratio of concentration equals (20 – 0.1)/(2.09 – 0.1) = 10 So, for each 10 tons of feed, the plant would produce 1 ton of concentrate.

28 % Cu Recovery = [(10·20)/(2.09·100)]·100 = 95.7% Feed f = 2.09% Cu
(b) Using the example data from Table 1, the % Cu recovery calculated from weights and assays is: % Cu Recovery = [(10·20)/(2.09·100)]·100 = 95.7% Feed f = 2.09% Cu F = 100% Wt Concentrate c = 20% Cu C = 10% Wt Tailings t = 0.1% Cu T = 900% Wt The calculation using assays alone is % Cu Recovery = 100(20/2.09)(2.09 – 0.1)/(20 – 0.1) = 95.7% This means that 95.7% of the copper present in the ore was recovered in the concentrate, while the rest was lost in the tailings. % Cu Loss = 100 – 95.7 = 4.3% This means that 4.3% of the copper present in the ore was lost in the tailings.

29 The % Weight Recovery is equal to the % Weight of the concentrate in Table 1.
It can also be calculated from the assay values given in the table, as follows: % Weight Recovery = 100·( )(20 – 0.1) = 10% The Enrichment Ratio is calculated by dividing the concentrate assay in Table 1 by the feed assay: Enrichment Ratio = 20.0/2.09 = 9.57 This tells us that the concentrate has 9.57 times the copper concentration of the feed.

30 FLOTATION KINETICS

31 0-t1, R1 t1-t2, R1+R2 t2-t3, R1+R2+R3 t3-t4, R1+R2+R3+R4 t4-t5, R1+R2+R3+R4+R5 R1 R2 R3 R4 R5 R1 R3 R4 R1 R2

32 Recovery % Flotation time (h)

33 Example min. g %Pb Pb mass Cum Pb Mass Pb Rec. Cum. Pb Rec. Con 1 0-2
83.28 83.46 69.51 64.99 Con 2 2-4 44.33 43.41 19.24 88.75 17.99 82.99 Con 3 4-8 60.99 15.78 9.62 98.37 9.00 91.99 Con 4 8-16 106.20 4.02 4.27 102.64 3.99 95.98 Tail 934.80 0.46 4.30 106.94 100.00 Total

34 R: Recovery t: time K: Flotation rate constant

35 Similarity R1 R2 R3 R4 R5 V (m3) = Q (m3/h) x  (h) R1 R2 R3 R4 R5

36

37 Laboratory Scale factor: 2.8 for lab. t=2.8 x 12 = 33.6 min. = 0.56 h

38 Flotation Cell Selection 1
Sizing of the cells depends on the retantion time in flotation. Q = V / t Q: volumetric flowrate (m3/h) V: volume (m3) t: hours Q=m3/h V=m3 t=?

39 Flotation Cell Selection 2
Vf: total volume required (m3) Q: volumetric flowrate (m3/h) Tr: retention time S: Scale up factor Tr specified by customer S=1 Tr taken from continious pilot plant test S=1 Tr taken from typical industrial data S=1 Tr taken from laboratory scale test work S= Ca= Aeration factor to account for air in pulp. = 0.85

40 Feed W= 100 t/h =2.5 g/cm3 %solids = 40 Wpulp= 100/0.4 =250 t/h VWater =150 t/h=150 m3/h Vsolids=100/2.5=40 m3/h Qpulp= VWater + Vsolids = 190 m3/h Vtotal cell=190 x 0.56 = m3 / 0.86 =123.7

41 Retention time, min (normal)
Mineral % solids in feed Retention time, min (normal) No. of cells/bank Copper 32-42 13-16 8-12 V cell= /10 = m3/cell For cleaning applications use 60% of the rougher percent solids. Required retention time for cleaning is approx. 65% of rougher retention time.

42 Flotation Bank Design Mineral % solids in feed Retention time (min.) No. of cell/bank Barite 30-40 8-10 6-8 Copper 32-42 13-16 8-12 Flourspar 25-32 Feldspar 25-35 Lead Molybdenum 35-45 14-20 10-14 Nickel 28-32 8-14 Phosphate 30-35 4-6 4-5 Potash Tungsten 7-10 Zinc Silica (iron ore) 40-50 Silica (phosphate) Sand 7-9 Coal 4-12 Effluents As received 6-12 For cleaning applications 60% of the rougher percent solids. Required retention time for cleaning is approx. 65% of rougher retention time.

43 Rotational Speed R1 R2 R1 x d1 = R2 x d2 R1 x 60 cm = 1500 rpm x 10 cm
R1= R2 x d2 / d R1= 250 rpm R: Rotational Speed, rpm D: Diameter of the cell


Download ppt "Froth Flotation."

Similar presentations


Ads by Google