Jan Drzymala
Mineral processing – lab exercise
Oil agglomeration
Oil agglomeration can be used for separation of particles suspended in water
differing in affinity towards oil drops. Any liquid, which is not soluble in water, can be
used as agglomerating medium. The affinity of particles suspended in water towards
oil drops is called aquaoleophilicity. The term aquaoleophilicity reflects the fact that
particles like oil drops in water. This property in similar to the hydrophobicity utilized
in flotation in which the oil drop is substituted with the gas bubble. Successful oil
agglomeration requires vigorous stirring to disperse oil drops and particles to facilitate
sufficient number of collisions between them (Fig. 1.)
particle
particle
woda
oil
+ oil
agglomerates
Fig.1. Oil agglomeration
The degree of aquaoleophilicity depends on the contact angle formed between
the oil drop and particle surface in water as well as on the solid – water interfacial
tension. It results from the thermodynamics of the system. A collision of an oil drop
and a particle (Fig.2) leads to a change in the free entalphy (Gagl) of the system:
water
particle
+
oil
=
agglomerate
Fig. 2. A collision of oil drop and particle leads to formation of oil-particle aggregate
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Gagl = so – sw – ow
(1)
where:
s
– solid
o
– oil
w
– water
so – solid - oil interfacial energy
sw – solid - water interfacial energy
ow – oil - water interfacial energy
water
 ow
0
 sw
oil
 so
particle
sw = so + ow cos o
Fig. 3. The Young equation
Equation 1, when combined with the Young equation (Fig. 3):
sw = so + ow cos o
(2)
(where o is the contact angle measure between the solid surface and water phase
through the oil phase (Fig. 3)) gives
Gagl = –ow (cos o + 1),
(3)
which is the main equation delineating oil agglomeration. It indicates that the main
parameters responsible for oil agglomeration are ow and o which together determine
the aquaoleophilicity. The contact angle in oil agglomeration systems can be between
0 and 180o (Table 1).
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Table 1. Contact angle o for the solid-oil (hekxadekane)–water
system measured through the oil phase
o
Soild
Teflon
Sulfur
Graphite
Graphite
Coal (Upper Freeport)
Coal (Illinois #6)
Plexiglas
Pyrite
Cellulose
Quartz
Nylon
19,5o
38°
45°
47°
68°
75°
75–90°
105°
120°
165°
170°
When the aquaoleophilicity is sufficiently high (below 90o) the agglomerates
are compact (Fig. 4) and form spheres (spherical agglomeration). Their diameter of the
spheres depends on the amount of oil (Fig. 5).
a
water
water
0
particle
particle
oil
o
oil
particle
particle
b
a
Fig. 4. When the contact angle is small (o < 90°) the agglomerates are strong and
spherical agglomeration is possible. Weak agglomerates are formed when o > 90°
The extent of agglomeration depends not only on the aquaoleophilicty of the
system but also on the amount of oil used for agglomeration. Too small amount of oil
leads to the formation of weak agglomerates, which are difficult to recover . Higher
concentrations of oil provide formation of two phases, that is the oily and aqueous
phases. An optimal amount of oil should be used for successful oil agglomeration.
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log 10 (diameter of agglomerates, mm)
1.60
0.80
lump, 3 cm
0.00
-0.80
-1.60
-2.40
0
2
4
6
8
amount of n-heptan, cm 3
Fig. 5. Relationship between the amount of oil (heptane) used in agglomeration of
graphite and average size of formed spheres during spherical agglomeration
The agglomerates can be separated from the non-agglomeration particles by
screening. Other techniques such as siphoning and decanting are also possible.
Exercise 1. Oils agglomeration of coal. Take a 1 dm3 container, pour in it 750 cm3 of
water and add 100g of finely ground coal. Stir the mixture for 3 min to wet the coal.
Then, insert to the container 2 cm3 of fuel oil. After 3 min of stirring stop the mixing
and separate the oil aggregates from non-agglomerating particles using a 0.2 mm
sieve. Repeat the experiments with greater amounts of oil, for instance with 10 cm3
and 50cm3 of fuel oil. Analyze the products of agglomeration for ash content and plot
two different upgrading curves. Determine, on the upgrading curve, the optimal point
of agglomeration and read the expected separation parameters including ash and
carbonaceous matter contents and recovery in concentrate and tailing as well as the
yield of the concentrate.
Exercise 2. Spherical agglomeration. Conduct oil agglomeration using graphite (5g)
suspended in 750 cm3 of water by adding 2 cm3 of fuel oil. Use optical microscope to
determine the diameter of formed spheres. Run one more experiment using 4 cm3 of
oil. Make a graph relating the size of spheres and the amount of fuel oil.
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