2. EXTRACTION
• It is defined as the removal of solid
constituents from the solid or liquid or semi
solid by means of suitable solvents
• Extract- compound contain all the constituents
which are soluble in solvent
• Menstrum- Solvent used for extraction process
• Marc- residue obtained after the extraction
process
3. PRINCIPLE
• The solvent used for extraction which diffuse
into the compound to dissolve the desired
compounds
• The solution in compound pass in the opposite
direction and mix with the surrounding liquid .
• An equilibrium is established between the
solute inside the compound and the solvent
surrounding
4.
5. • Rate of solution = driving force/resistance.
dw/dt = KlA(ys - y)
• dw/dt is the rate of solution
• Kl is the mass-transfer coefficient
• A is the interfacial area
• ys and y are the concentrations of the soluble
component in the bulk of the liquid and at the
interface. It is usually assumed that a saturated
solution is formed at the interface
• ys is the concentration of a saturated solution at
Rate of extraction
6. Rate of extraction
A mass balance on the solute gives the equation
dw = Vdy
V is the quantity of liquid in the liquid stream.
Vdy/dt = Kl A(ys - y)
which can then be integrated over time t during which time the
concentration goes from an initial value of y0 to a concentration
y, giving
loge [(ys - y0)/ (ys - y)] = tKlA/V.
7. Factors influence the extraction
process
• Nature of compound
• Type of Solvent used
• Temperature
• pH
• Size of particle
8. THEORIES
• Schoenemann’s Diffusion theory
The rate of extraction depends on the rate of
diffusion
• Soaking theory
Not only the rate of diffusion but also the rate
of dissolution of the substances in the solvent
critically affect the rate of extraction
• Karnowsky’s Capillary velocity Theory
It represents the rate of extraction as a
function of the rate of flow in the capillaries.
16. Advantage
reliability, operating flexibility, high
capacity,
It can handle difficult-to-disperse systems
such as those having high interfacial tension
and large phase density difference
Disadvantage
their size and the inventory of material held
up in the equipmen
Mixer-Settler
18. • Low axial mixing
• High extraction efficiency which are due to
uniform distribution of energy over a cross-
section of the column
• Uniform distribution of droplets in the column.
Pulse Extractors
32. Washing
• Washing is identical to extraction
• Water is used as solvent
• Water is cheap and readily available
• The washing is designed to remove unwanted
residue material
33. • The concentration remaining with the solid
after washing
x1 = x[xw /xw(1 + y)] = x[1/(1 + y)]
after two washings:
x2 = x1[1/(1 + y)] = x[1/(1 + y)]2
and so after n washings:
xn = x[1/(1 + y)]n
Washing
