METMTB1
(Extraction Metallurgy)
Learning Unit 4: Screening and classification
(Tutorials 3)
Question 1
A mill in closed circuit with a classifier receives 300 dry tons of crude ore per day and the
percentages of solid are respectively 25,50, and 84% in the classifier overflow, feed to classifier
and sand, equivalent to L:S ratios of 3.0,1.0, and 0.190. Calculate the circulating load ratio.
Question 2
Particle size analysis is carried out on a primary crusher discharge. The analysis results revealed
57%+1 size particle. The primary crusher product (57%+1) is screened and the screen oversize is
further crushed to -1 size in a secondary crusher. With the aid of a neat diagram, calculate the rate
of material crushed in a secondary crusher if the screen efficiency is 80%. The primary crusher is
fed at a rate of 100 tons/hr.
Question 3
The feed to a gyratory crusher is 100tph of run of mine (ROM). The crusher discharge is screened,
and the size analysis of the screening product indicated 54% < 2’’ and 46% >2’’. The screening
efficiency is found to be 85% based on the screen oversize. Draw a neat diagram showing the
circulating load. If the screen efficiency is dependent on the screen undersize, calculate the
circulating load.
Question 4
A slurry of density 1.140 t/m3 is classified in an hydrocyclone which produces two products i.e.
underflow and overflow from the feed. The overflow of slurry density of 1.030 t/m3 is further
processed to concentrate valuable minerals while the underflow of pulp density of 1.290 t/m3is
recirculated. With the aid of a neat diagram showing the flow of materials, calculate the following:
4.1. The mass flow rate of feed to cyclone when 3 litres sample of underflow takes 4s. The density
of the dry solid is 3t /m3.
4.2. The mass flowrate of water in the hydrocyclone underflow
4.3. The volumetric flowrate of water in the hydrocyclone overflow.
4.4. The volumetric flowrate of solids in the hydrocyclone underflow
Hint
The screen efficiency is obtained using different equations, depending on whether your product is
the oversize or undersize fraction from the screen. The following is required to calculate the two
screen efficiencies.
▪ Qms(f) = Mass flow rate of solid feed
▪ Qms(o) = Mass flow rate of solid in the screen overflow
▪ Qms(u) = Mass flow rate of solid in the screen underflow
▪ Mu(f) = Mass fraction of undersize in the feed
▪ Mu(o) = Mass fraction of undersize in the overflow
▪ Mu(u) = Mass fraction of undersize in the underflow
The screen efficiency based on the oversize (𝐄𝟎 ) is then given by the equation
Qms(o) ∗ [1 − Mu(o)]
E0 =
Qms(f) ∗ [1 − Mu(f)]
and the screen efficiency based on the undersize (Eu) is then given by the equation
Qms(u) ∗ [1 − Mu(u)]
Eu =
Qms(f) ∗ [1 − Mu(f)]
The screening efficiency is also calculated using the formula below:
100(e − v)
E(%) = ∗ 100
e(100 − v)
e = percentage undersize in feed
v = percentage undersize in overproduct
And more https://www.911metallurgist.com/blog/vibrating-screen-working-
principle#screen_capacity
