This document discusses types and principles of particle classification. It describes how particles in a classifier are subjected to drag, centrifugal, and gravitational forces, with different forces dominating depending on the particle size. Particle size distribution is represented using cumulative and independent distribution curves plotted with percentage passing versus size. Key equations for classifier operation cover feed rate, fines and tailings outputs, proportions of undersize and size fractions in each stream. Parameters like fines output percentage, tailings output percentage, precipitation efficiency, and recycle ratio are defined. Selectivity characterizes what percentage of a given size ends up in the tailings. The cut size is the particle diameter where half the particles report to the fines and half to the tailings.

1. By
Dr Y C Naidu

2. Types of classsification
 Basis of Volume ie geometric dimension- screening
 Basis of Mass ie materila properties
 Cyclone Separators
 Air Separators

3. Principles of Separation
 A particle is subjected to three sets of forces
 Fd-Force exerted by air
 Fc- Centrifugal force
 Fg- Force of gravity
 If Fd> Fc and Fg, particle air borne
 Fg prevails particle sink
 Fc prevails particle flung outward of separator

4. Particle Size Distribution
 Cumulative distribution curve
 On different sieves/micron sizes, the cumulative passing
% is plotted.
 Independent particle size distribution curve

5. Size Distribution Curve
0
20
40
60
80
100
120
0 50 100 150 200 250
%
passing
Size, um
Cumulative Size distribution

6. Particle Size Distribution
0
2
4
6
8
10
12
14
16
0 20 40 60 80 100 120 140 160 180
%
of
distribution
Partcle Size, um
Particle Size Distribution Curve
Series1

7. Classification
 A= F+G
 A- Classifier feed rate, tph
 F-Fines output, tph
 G- Tailing output
 a,f,g- proportion of undersize in A,F,and G in %
 ∆a, ∆f, ∆g – Proportion of particular size fraction of
A,F, G in %

8. Equations- Separators
 A.a = F.f+G.g
 A. ∆a = F. ∆f+G. ∆g
 Vf- % of output fines
 Vg- % of output tailings
 P- Precipitation efficiency
 µ- recycle ratio

9. Fines Output
 Vf =F/Ax100
 Vg=G/Ax100
 Vf+Vg =100

10. Calculated from particle size
Vf= a-g x 100
f-g
Vg = f-a x 100
f-g
Recycle ratio = A/F = (f-g)/(a-g)
Precipitation Efficiency = (Fxf)/(Axa)x100
= Vfxf/ax100

11. Selectivity
 It is characterized by what % of given particle size in
classifier feed is discharged in tailings
 T – (Gxdg)/(A.da) x100 = Vg x dg/da

13. Cut Size
 Particle size dt of which half the particles are
discharged in fines and half in tailings.
 If sharpness of separation poor, more than 50% of even
finest particles may end up in tailings, so no definite
cut size exists