Download - Measures of Efficiency
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Measures of Efficiency
Comminution and Concentration
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Some definitions
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Some definitionsParticles can consist of a
single mineral; called
free particles
When a particle consists of 2or more minerals, this iscalled locked particles
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Contains both valuable and gangueminerals!
A large proportion of the difficultiesexperienced in mineral separation areassociated with the treatment ofthese particles
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In general
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Optimum Mesh-of-Grind In practice, the ores generally break
into randomly sized particles
No uniform size Results in size distributions
Grinding is performed to attainsufficient degree of liberation for
concentration
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Mesh-of-Grind The size up to which the ore is ground to
ensure sufficient liberation of wantedmineral
Normally taken as 80% passing product Balance between liberation and economics
Particle
size
time
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Particle Size Analysis Control of quality of grinding Measure of degree of liberation Determining the optimum feed size Establishing the grinding limit to reduce
losses
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Methods of Particle Size Analysis
Test Sieves 100000 10 Elutriation 40 5 Microscopy 50 0.25 Sedimentation (Gravity) 40 1 Sedimentation (Centrifuge) 5 0.05 Electron Microscopy 1 0.005
Method Useful Range(m)
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Sieve Analysis
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Test Sieves Designated by nominal aperture sizes
Sides of square or diameter of circle aperture Mesh no. # of square apertures/inch2
Standards German, DIN 4188, ASTM, E11, American Tyler,
French, ANFOR, British BSS 410
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Test Methods Machine Sieving using the Ro-tap Sieves are stacked in increasing mesh
no.
Sample is placed on topmost, coarsestsieve
Agitated vertically and horizontally Fraction retained per sieve is weighed
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Screen Movements
a. Throw-action sieving(vertical movement/stroke)
b. Horizontal sieving(frequency)
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Complications in Sieving
Irregularly shaped Particles
Near-size Particles Blinding
D1
D2
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Presentation of Results Weight per fraction / % Weight Cumulative passing / Cumulative
retained
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Presentation of Results
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Gates-Gaudin-Schuhmann Plot Cumulative Passing vs.
LOG(particle size)
Generates a straight line Interpolation for Cumulative
80% Passing is easy
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Concentration
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Measures of Concentration Efficiency Direct Statement:
Lacks in interpretative convenience!
0.0890.7Tailings (Tails)
27.59.3Concentrate
1.86100.0Feed
MetalContent,
%Cu
Weight, %Product
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Measures of Concentration Efficiency
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Black Box ReactionInput
Output
Concentration /
Separation
Processes
Assume:
Steady State
=
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Some pertinent definitions Feed the material entering for
treatment in a plant or individual
machine Concentrate anyproduct of
treatmentof a given feed thatcontains more of a given ingredient
than the feed
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Some pertinent definitions Tailings that product of treatment
of a given feed w/c is distinctly
impoverishedin content of a giveningredient as compared to the feed
f, c, t assays of the respectivematerials; expressed as %, g/MT, oz/
t, etc.
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Material Balance For the same process:
We use the Two-Product Formula
Feed
Concentrate Tails
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Illustrative Example
Feed
Concentrate
Tailings
Valuable Mineral
Gangue Mineral
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Material Balance
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Metal Balance
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Concentration Ratio
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Recovery
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Recovery
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Illustrative Example
1
2
Gangue
Valued
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Concentration Ratio & Recovery
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Additional Notes
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Additional Notes
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Other numbers used
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Flashback to: Bonds Work
Index