2. SEPARATION OF SOLIDS
Techniques used to separate one material from the other
is called separation. Separations are extremely common
in chemical manufacture. In fact, much processing
equipment is devoted to separate one phase or
one material from the other.
Diffusional separation
is a technique used for the separation of homogeneous
mixtures. This separation includes the transfer of material
between the phases including distillation, crystallization
and absorption.
Mechanical separation
is used for the separation of heterogeneous mixtures.
These are based on the physical differences between the
particles such as size, shape or density. It can be applied
for separating solids from solids, solids from liquids and
also solids from gases.
4. Sieving
Sieves, or sifters, are devices for separating
wanted elements from unwanted material
typically using a mesh. Sieving is a simple
technique for separating particles of different
sizes. Coarse particles are separated or broken
up by grinding against one-another and screen
openings. Depending upon the types of
particles to be separated, sieves with different
types of holes are used. Sieving plays an
important role in food industries where sieves
(often vibrating) are used to prevent the
contamination of the product by foreign bodies
5. Magnetic Separation
A process in which magnetically susceptible
material is extracted from a mixture using a
magnetic force. This separation technique
can be useful in mining iron as it is attracted
to a magnet. In the machine, the raw ore is
fed onto a conveyor belt which passes
underneath two pairs of electromagnets
under which further belts run at right angles to
the feed belt. The first pair of balls are weakly
magnetized and served to draw off any iron
ore present. The second pair are strongly
magnetized and attracted the wolframite,
which is weakly magnetic. These machines
are capable of treating 10 tons of ore a day.
6.
7. Mechanical Screening
The practice of taking granulated ore
material and separating it into multiple
grades by particle size. This practice
occurs in a variety of industries such as
mining and mineral processing,
agriculture, pharmaceutical, food,
plastics, and recycling. A screening
machine consist of a drive that induces
vibration, a screen media that causes
particle separation, and a deck which
holds the screen media and the drive and
is the mode of transport for the vibration.
8. Leaching
The process of extracting substances from a solid by dissolving them in a liquid,
either naturally or through an industrial process. In the chemical processing
industry, leaching has a variety of commercial applications, including separation
of metal from ore using acid, and sugar from sugar beets using hot water.
9. Froth Floatation
Is another method to remove solids from
liquids used in mineral processing and wastewater
treatment. The froth flotation process is all about exploiting
the natural hydrophobicity of liberated metals and playing with
making them individually hydrophobic in order to accurately
separate them from one another. The particles of metal
sulphide are hydrophobic. Due to this property, they are
primarily wetted by oil. The gangue particles, on the other
hand, are hydrophilic and are wetted by water. As a result of
stirring the solution in the tank, sulphide ore rises to the surface
while the gangue particles settle. We use chemical reagents for
this purpose.
10. Centrifuging
Centrifuging is a common separation
technique that exploits the density
differences of different substances.
When solids are suspended in a liquid
gradually the densest substance will
settle on the bottom known as
sedimentation. Centrifuging is an
accelerated sedimentation.
12. Crystalline Solids
The solids having sharp edges and
well-defined planes are called crystals or
crystalline solids. Crystalline solids are
also called true solids. Sodium chloride,
quartz, gold, copper, and iron are some
examples of crystalline solids.
13. Classification of Crystalline Solids
1. Ionic Solids
In an ionic solid, the cations and anions are the
constituent particles. These ions are systematically
arranged in three-dimensional space. The strong
electrostatic force of attraction between cations and
anions is the binding force in an ionic solid.
Example of ionic solids- Sodium chloride, potassium
chloride, and lead bromide.
Characteristics
i). Ionic solids are hard, brittle, and have high melting
points and very high enthalpy of fusion.
ii). Ionic solids are insulators in solid state. But in the
molten state and in aqueous solutions, they conduct
electricity.
14. Classification of Crystalline Solids
2. Metallic Solids
The metals like iron, copper, gold, silver,
sodium, potassium exist in the solid state at room
temperature. In a metallic crystal, the atoms are held
together by a strong force of attraction called
metallic bonding. In the metallic crystals, the metal
occupies the fixed positions, but their valence
electrons move.
Characteristics
i). They are hard but malleable and ductile.
ii). They are good conductors of heat as well as
electricity.
iii). They are lustrous.
iv). They have high melting and boiling points.
15. Classification of Crystalline Solids
3. Covalent Solids
The solid substances in which covalent bonds
bond the atoms throughout the crystal are known as
covalent solids.
Covalent solids are also known as atomic solids,
network solids, macromolecular crystals or giant
molecules. Asbestos, silicon carbide, mica, graphite,
and diamond are examples of macromolecular
crystals.
Characteristics
i). They are very hard, except graphite which is
soft.
ii). They have high melting points.
iii). They are poor conductors of heat as well as
electricity (except graphite which is an atomic solid
and is a good conductor of electricity).
iv). They have high heat of fusion.
16. Classification of
Crystalline Solids
3. Covalent Solids
These are solid substances in
which the molecules are the
constituent particles. Iodine, ice, dry
ice (solid carbon dioxide), and
naphthalene are examples of
molecular solids. These can be
classified into three subgroups:
Nonpolar, Polar, and Hydrogen-
bonded.
17. Type of solid
Constituent
particles
Attracting force
Examples (in
solid state)
Physical nature
Melting
point
Electrical conductivity
1. Ionic solids
Cations and
anions
Electrostatic
(Coulombic)
NaCl,MgO,ZnS,
CaF2NaCl,MgO,
ZnS,CaF2
Hard but brittle High
Insulator as solid but
conductor in molten
state and in aqueous
solution
2. Metallic
solids
Positive ions in
a sea of
electrons
Metallic bonding
Copper, silver,
gold, iron
Hard, but
malleable and
ductile
Fairly high
Conductor in solid and
molten states
3. Covalent or
Network
solids
Atoms
Strong covalent
bonding
Graphite
diamond, quartz,
silicon carbide
Soft Hard Very high Conductor Insulators
4. Molecular
(i) Nonpolar
molecules (ii)
Polar
molecules (iii)
Hydrogen
bonded
Molecules
Molecules
Molecules
Molecules
Dispersion force
Dipoledipole
interaction
Hydrogen
bonding
I2,I2, dry
ice, H2,H2, Ar,
CCl4NH3,SO2A
r,CCl4NH3,SO2
Ice, alcohol,
phenol, proteins
Soft
Soft
Hard
Very low
Low
Low
Insulator Insulator
Insulator
Types of Crystalline Solids Based on the Type of Attracting
Force
18. Amorphous Solids
The solids which lack in well-
defined structure and shape are known as
amorphous solids. Amorphous solids are
also called supercooled liquids or pseudo
solids. Glass, rubber, and plastics are
some examples of amorphous solids.
Uses of Amorphous Solids
i. Amorphous solids are useful as
inorganic glasses, fabrication of glass
apparatus for laboratory, and making
kitchen wares.
ii. Amorphous silica is used as a
photovoltaic to convert sunlight into
electricity.
19. Property Crystalline solids Amorphous solids
Structure
Crystals have a long-
range order.
Amorphous substances have
short-range order.
Melting
point
Crystalline solids have a
sharp and characteristic
melting point.
Amorphous solids either
decompose or change
gradually into liquid over a
range of temperatures on
being heated.
Cleavage
Crystals when cut with a
sharp edged tool, split
into two pieces and the
newly generated
surfaces are plain and
smooth.
Cleavage of amorphous solids
gives irregular fractures.
Difference between Crystalline Solids and
Amorphous Solids
20. Classification of Solids Based on Their Electrical Conductivity
i. Conductors
A metallic atom has more valence orbitals than the number of valence electrons.
Therefore, the electrons find more space to move and conduct electricity easily. This can easily be
understood by band theory which is also called the molecular orbital theory.
ii. Semiconductors
In semiconductors, the energy gap between the valence band and conduction band is not
very large. Therefore, The valence electrons have a tendency to jump into the conduction band.
Thus when an electric field is applied, some electrons move to the conduction band and conduct
electricity.
iii. Insulators
When the energy gap between the valence band and conduction band is very large, the
valence electrons cannot jump into the conduction band. Therefore, they do not conduct
electricity, and such substances are called insulators.
The conductivity of metals is large, whereas the conductivity of an insulator is very less. Between
these two are semiconductors.
21. Classification of Solids With Respect to Magnetic Properties
i. Diamagnetic – Diamagnetism is a property caused by an induced magnetic field of the orbital
electron. It is present more or less in all substances, but it is more pronounced in materials
like H2,KCl,NaClH2,KCl,NaCl and TiO2TiO2 in which all the electrons have paired spins. The
magnetic field weakly repels the substances that have diamagnetic properties.
ii. Paramagnetic - Paramagnetism is caused by the spin and orbital angular momentum of
electrons. Paramagnetism is shown by all the solids in which atoms, ions, or molecules have
unpaired electrons. Paramagnetic materials are weakly attracted to a magnetic field, and it is
shown only in the presence of the magnetic
field. O2,Cr3+,Cu2+,Fe3+O2,Cr3+,Cu2+,Fe3+ show paramagnetism .
iii. Ferromagnetic - This property is caused by particles arranged on the lattice and the electrons
with parallel spins. Iron (Fe),(Fe), cobalt (Co),(Co), and nickel (Ni)(Ni) are ferromagnetic
elements. They are attracted very strongly by a magnetic field. It is a permanent property of the
material at a given temperature.
22. iv. Antiferromagnetic - This property is caused by particles arranged on two lattices with
spins on one lattice antiparallel to those on the other lattice. This results in the
cancellation of magnetic moments on the lattice. The materials
like MnO,MnSe,KMnFe3MnO,MnSe,KMnFe3 are antiferromagnetic.
v. Ferrimagnetic - The particles on interpenetrating lattices cause this magnetic property
with the unequal number of electrons and with antiparallel spins. This represents a
situation with a net magnetic moment. FeO.Fe2O3≡Fe3O4 is an example of ferrimagnetic
material.
Classification of Solids With Respect to Magnetic Properties
23. 1. _____________ uses sifters for separating wanted elements
from unwanted material typically using a mesh.
Notes de l'éditeur
chalcopyrite, the most common copper mineral, a copper and iron sulfide, and a very important copper ore.
