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.

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.

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.

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

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

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

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