Measures of Efficiency

7/27/2019 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

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Measures of Efficiency