Why Ore Milling Matters
Most valuable minerals are locked inside waste rock. Ore milling — crushing and grinding the ore to a fine size — is what liberates those minerals so a recovery process can separate them. The efficiency of the whole plant hangs on how well the milling stage is designed.
Liberation: The Core Goal
Liberation means breaking the ore down until individual mineral grains are free of the surrounding rock. The finer you grind, the more mineral you liberate — but grinding finer also costs more energy and can create slimes that are hard to recover. The target is the coarsest size that still liberates enough mineral, which is exactly what testwork finds.
Grind Size and the Bond Work Index
Grind size is often expressed as P80 — the size at which 80% of the material passes. The energy needed to reach a given grind size is measured by the Bond work index, a laboratory test that quantifies how hard the ore is to grind. That number sizes the mill, the motor and the circuit configuration.
Designing the Circuit
A milling circuit combines crushing, grinding and classification:
- Crushing — jaw and cone crushers for the coarse reduction.
- Grinding — rod and ball mills for the fine reduction, with ball mills up to 7 m in diameter.
- Classification — hydrocyclones that return oversize for regrinding and pass correctly sized material forward.
A circuit designed from test data — not from a catalogue — protects recovery and controls both capital and operating cost.