This document discusses types of classifiers used in mineral processing. There are two main types - wet classification and dry classification. Wet classifiers separate minerals based on differences in settling velocities in water, and include spiral classifiers, hydraulic classifiers, and hydrocyclones. Dry classifiers separate minerals using air flow and centrifugal forces, and include gravitational, centrifugal, and gravitational inertial classifiers. The document provides details on how different classifier types operate and the size ranges they can be used to separate.

1. TYPES OF CLASSIFIERS

2. CONTENTS
 INTRODUCTION
 Mineral processing
 Ore dressing
 CLASSIFICATION
WET CLASSSIFICATION
DRY CLASSIFICATION
Types of classifiers
CONCLUSION
REFERENCE

3. INTRODUCTION
 Mineral processing is that crushes and separates ore
into valuable substance and waste or gaunge by a
variety of techniques i.e beneficiation, mineral
dressing, ore processing, mineral extraction etc……..
 This mineral processing plays a major role in
Extractive metallurgy.
 This Extractive metallurgy has been defined as the
science and art of extracting metals from their ores,
refining them and preparing them for use.
 In extractive metallurgy there are commonly occurs
as
 Mineral processing
 Pyro metallurgy
 electro metallurgy
 Hydro metallurgy.

4. ORE DRESSING
 Ore dressing is also called as beneficiation
 Ore dressing is a primary stage in the
extraction of a metal from an ore in which as
much gangue is removed and the ore is
prepared for smelting, refining etc.
 Ore dressing is also called as concentration
of ores ,washing of ores, reduction ores
etc……

5. CLASSIFICATION
 Classification is define as a method of
separating mixtures of mineral particles into
two or more products according to their settling
velocities in water or air.
 Classification is performed on the basis of
velocity with which the material particles fall
through a fluid medium i.e water or air
 The velocity of particles in a fluid medium is
dependent not only in the size but also in
specific gravity and shape of the particles

6. TYPES OF CLASSIFIERS
 Based on their separation principles classifiers are
classified into two types
 Wet classification
 Mechanical classifiers
 Spiral classifiers
 Hydraulic classifier
 Hydro cyclone classifiers
 Dry classification
 Gravitational classifiers
 Gravitational inertial classifiers
 Centrifugal classifiers

7. WET CLASSIFICATION
 Wet classifiers are based on the principle that separation of coarse
particles from fine particles by water or any other liquid.
 In wet classifiers coarse particles move faster than fine particles at equal
density.
 High density particles move faster than low density particles at equal size.
 Industrial classification may be carried out in different types of classifiers
and these classifiers are normally
 (i) hydraulic classifiers,
 (ii) mechanical classifiers, and
 (iii) cyclones.
 Basically they all work according to the principle that the particles are
suspended in water which has a slight upward movement relative to the
particles.
 Particles below a certain size and density are carried away with the water-
flow, whereas the coarser and heavier particles settle.

8. SPIRAL CLASSIFIER
 The spiral classifier is also called as helical
classifier
 Spiral classifier is also comes under
mechanical classifier
 Spiral can be of single pitch or double pitch.
 Single pitch spirals consist of one continuous
spiral ribbon.
 The double pitch spiral has twice the raking
capacity of a single pitch assembly and consists
of two duplicate spiral ribbons.

9. CONT.……………..
 It is made by combining a gravity settler of rectangular section with a
sloped transport spiral for the sediment. It consists of a semi
cylindrical trough (a trough which is semi-circular in cross- section)
inclined to the horizontal.
 The spiral rotates about the axis with in the tank.
 The sediments, at the lower end are collected by the spiral, and lifted
upwards.
 If the spiral rotates in the clockwise direction from the top end, then
the sediments will move upwards.
 There are three designs of semi cylindrical troughs are available.
 Straight side design is generally suitable for coarse separations.
 Modified flare design increases pool area for intermediate to fine
separations and for washing and dewatering.
 Full flare design provides maximum pool area for fine to very fine
separations and for washing and dewatering where large volumes of
water are to be handled.
 wet classification with spiral classifiers using separation by gravity
typically covers the size range of 100 micrometers to 1000

11. HYDRO CYCLONE CLASSIFIER
 Hydro-cyclones are used by in mining industry to separate minerals
based on size and density.
 Slurry is given a vigorous rotation in the cyclone which generates a
radial force field.
 Large/dense particles are driven to the outer regions and underflow,
 while small and light particles are attracted to the core and overflow.
 Wet classification with hydro-cyclones for using separation centrifugal
force covering the size range of 10 micrometers to 100 micrometers.
 Although the hydro cyclone by nature is a size controlling machine
the number of applications in mineral are many such as
 (i) classification in grinding circuits,
 (ii) dewatering and thickening,
 (iii) desliming and washing,
 (iv) enrichment of heavy minerals (dense media separation

13. HYDRAULIC CLASSIFIER
 Hydraulic classifier is a device used to
concentrate an ore based on difference
between the densities of ore and gangue
particles. This process is called levigation.
 The powered ore is feed into a conical
reservoir. A strong current of water agitates
the powered ore, lighter gangue particles rise
up while heavier ore particle sink down.

15. DRY CLASSIFICATION
 Dry classifiers are based on the air fluidization.
 Air classification is a process of separating categories of
materials by way differences in their respective aerodynamic
characteristics.
 Dry classification using separation by centrifugal force typically
covers the range of 5 micrometers to 150 micrometers.
 The process consists of interaction of a moving stream air ,
material particles, and the gravitational force within a confined
volume .
 The confined volume in which the separation takes place is called
an Air classifier.
 Air classifiers may be one of a number of designs. The three
principle group of designs are horizontal , inclined ,vertical .
 Gravitational, centrifugal, gravitational inertial classifiers comes
under Dry classifications.

16. GRAVITATIONAL CLASSIFIER
 Gravitational classifier are design for coarser separation
in the range of 12 mesh size 100 mesh size.
 The feed material is spread over the width of the
classifiers and drops as continuous feed curtain through
the top of the classifier.
 Low velocity air enters the classifier through the front
inlet and is drawn through the feed curtain which is
dropping in front of the angled vanes on the air outlet. The
air stream enters the feed curtain perpendicularly and
draws the finer particles from the curtain of material. The
air current then draws the particles up almost vertical
through the vane rack.
 Gravitational classifiers are suitable for closing grinding
circuits, de-dusting of coarser feeds, reducing a high feed
loading rate to a finer classifier and it can also be used as
a density separator.

18. GRAVITATIONAL INERTIAL CLASSIFIERS
 The feed material enters the top of the classifier in a
downward
 The primary air enters the top of the classifier in a
downward direction
 The air makes a 120° change in direction and exits
through the vanes carrying fine particles with it
 The coarse particles, too heavy to make the turn, fall
to the bottom to be discharged by a valve.
 Secondary air, injected below the vanes, passes
through the curtain of falling particles. Those particles
near cut point in size are diverted by the secondary air
stream into an eddy current within the heart-shaped
chamber. The fines, some captured as they enter the
unit and others drawn from the eddy, are carried by
the exiting air to a fabric filter or cyclone for final
recovery.

20. CENTRIFUGAL CLASSIFIERS
 The centrifugal classifier utilizes centrifugal forces in a
similar way to cyclones to in- duce fine particle
separation
 The classifier has widespread acceptance in industrial
minerals, cement and fly ash applications where its high
degree of separation accuracy and exceptionally low
maintenance requirements exceeds operator
expectations.
 The classifier is used in conjunction with a dust collector
and system fan.
 Systems can have an open or closed loop dependent
on application and numerous dust collector and silo

22. CONCLUSION
 Ore dressing is a primary stage in the extraction
of a metal from an ore in which as much gangue
is removed and the ore is prepared for smelting,
refining etc.
 Classification is the method of separating
minerals mixtures of minerals into two or more
products on the basis of velocity with which the
grains the fall through a fluid medium the fluid
medium is usually water and wet classification is
applied to mineral particles which are considered
too fine to be sorted.
 There are so many types of classifiers which is

23. REFERENCES
 Mineral Processing by Pryore.J
 Course of mining Geology by
R.N.P.Arogyaswamy
 Basics in Mineral Processing
 Ore dressing by Robert H. Richards, S.B

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