Study Set Content:
When F > 1 then
Vu>Vo
Sediment volume is greater than the original volume due to the () and so loose and fluffy sediment and extra vehicle is needed(added) to contain sediment
network of flocs formed in the suspension
The sedimentation volume gives qualitative account of
flocculation
It is the ratio of the sedimentation volume of the flocculated
suspension, F, to the sedimentation volume of the deflocculated
suspension, F∞
Degree of flocculation (β)
The minimum value of β is
1
when flocculated suspension
sedimentation volume is equal to the sedimentation volume of
deflocculated suspension
β=1
For particles having a diameter of about 2 to 5 μm (depending
on the density of the particles and the density and the viscosity
of the suspending medium), (blank) counteracts
sedimentation to a measurable extent at room temperature by
keeping the dispersed material in random motion
Brownian movements
Difference in potential between the surface of the tightly bound
layer (shear plane) and electro-neutral region of the solution.
Zeta Potential
the zeta potential is reduced below a certain value, the
attractive forces exceed the repulsive forces, and the
particles come together. This phenomenon is known as
flocculation
The flocculated suspension is one in which zeta potential of
particle is
-20 to +20 mV.
Thus, the phenomenon of flocculation and deflocculation
depends on
zeta potential carried by particles
Formation of flocs (loose aggregates) will cause increase in
sedimentation rate due to increase in size of sediments.
Flocculated Suspensions
Hence, flocculated suspensions sediment more
rapidly
Sedimentation depends not only on the size of the flocs but also
on the
porosity of flocs.
High porosity
low porosity
Rate of sedimentation is slow, which prevents entrapping of liquid medium, which makes it difficult to re-disperse by agitation. This phenomenon called
caking or claying
Larger particles settle fast and smaller remain in supernatant liquid so supernatant appears
cloudy
It proposed that an energy barrier resulting from the electrostatic
repulsive force prevents two particles approaching one another
and adhering together.
DLVO Theory
If the particles collide with sufficient energy to overcome the
barrier, the (blank) attractive force will attract them
strongly and cause them adhere together irreversibly.
Van der Waals
