Mineral Liberation

 

馃挕 1. What Is Mineral Liberation?

When ore is crushed and ground, the valuable minerals (like magnetite, chalcopyrite, bauxite minerals, etc.) are broken away from the useless rock (gangue).
馃憠 This “freeing” is called liberation.

Liberation = breaking grains until the valuables are no longer glued to gangue.

馃挜 2. Why Do We Care About Liberation?

Because separation processes (flotation, magnetic separation, gravity separation) work ONLY if valuable particles are free.

  • Well-liberated = easy to separate = good recovery

  • Poorly liberated = mixed particles = losses in tailings


Separation efficiency depends directly on mineral liberation.

馃攷 3. What Controls Liberation?

a) Mineral Grain Size in the Ore

Fine-grained ore → needs finer grinding → expensive
Coarse-grained ore → easy to liberate → cheap processing

b) Texture of the Ore

  • Simple texture: clean mineral boundaries → easy liberation

  • Complex texture: minerals intergrown → difficult liberation

c) Breakage mechanism

Different minerals break differently because of hardness contrasts.

馃П 4. Types of Particles After Breakage

After crushing/grinding you get 3 particle types:

1. Fully Liberated Particles

  • 100% valuable or 100% gangue

  • Best for separation

2. Partially Liberated Particles

  • Valuable mineral + gangue stuck together

  • Hard to recover

  • Causes middlings

3. Unliberated Particles

  • Valuable totally locked inside gangue

  • Will report to tailings unless ground more

⚙️ 5. The Liberation–Size Relationship

General rule:

Smaller particle size → Higher liberation.

But too much grinding = money waste + slimes problem.

馃搱 6. How Liberation Is Measured?

a) Microscope/SEM Image Analysis

Cut sample → polish → look at mineral grains → computer classifies particles.

b) Chemical assay by size fraction

Coarse → medium → fine fractions
Valuable % increases as size decreases (usually).

馃М 7. Liberation Modeling 

There are two famous model types:

1. The Random Breakage Model

Assumes rocks break randomly → liberation depends on:

  • Grain size distribution

  • Particle size after grinding

Idiot summary:

If you grind until particles are smaller than mineral grain size → liberation is high.

2. Binary Breakage / Stereological Model

Used when particles contain only 2 minerals.

Predicts:

  • Probability of liberation at each size

  • Fraction of locked particles

Think of it like:

“How many chances does a valuable grain have to break loose when the ore is fractured randomly?”

馃И 8. Liberation Curves

These are graphs showing how much liberation occurs at different grind sizes.

  • X-axis = particle size

  • Y-axis = % liberation (free + partially free)

Useful for deciding grinding target.

馃幆 9. Practical Rules

  1. If mineral grains are large → coarse grinding is enough.

  2. If mineral grains are small/interlocked → very fine grinding is needed.

  3. Over-grinding creates slimes → bad for flotation.

  4. Liberation governs recovery more than anything else.

  5. Choose separation method based on degree of liberation.

馃摑 10. Summary 

  • Liberation = freeing valuable minerals from gangue

  • Achieved by crushing & grinding

  • Controlled by grain size, texture, hardness contrast

  • Produces free, partially free, locked particles

  • Finer grind = more liberation

  • Over-grinding = inefficient + slimes

  • Liberation measured using microscopy/SEM or assays

  • Modeled using random breakage principles

  • Critical for all downstream separation processes

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