Mineral Processing and Beneficiation
The exam tests the chain from run-of-mine ore to a concentrate grade a smelter or leach circuit will accept: liberation by comminution, separation by a physical property difference, and the recovery–grade balance that governs plant economics.
Core rules
- Comminution: crushing then grinding. The target is liberation of the valuable mineral without overgrinding, which creates slimes that flotation and gravity circuits cannot recover.
- Bond work index: W = 10·Wi·(1/√P80 − 1/√F80) kWh/t, with sizes in micrometres. It sizes mills and estimates grinding energy.
- Gravity separation needs a real density difference and a narrow size range; jigs, spirals and shaking tables work best in defined size bands.
- Magnetic separation: low-intensity for strongly magnetic magnetite, high-intensity or induced-roll for weakly magnetic hematite and ilmenite.
- Flotation reagents: collectors (xanthates for sulphides), frothers (MIBC, pine oil), depressants (cyanide for pyrite, zinc sulphate for sphalerite), activators (copper sulphate for sphalerite), and pH modifiers such as lime.
- Two-product formula: C = F(f − t)/(c − t), where F, C are feed and concentrate mass and f, c, t the respective assays.
Worked example
Feed 100 t/h at 1.20% Cu, concentrate 25.0% Cu, tail 0.10% Cu. C = 100 × (1.20 − 0.10)/(25.0 − 0.10) = 110/24.9 = 4.42 t/h. Recovery = 4.42 × 25.0/120 = 92.0%. Mass pull is only 4.4%, an acceptable rougher result.
Traps that cost marks
Confusing recovery with grade. Using the wrong stream in the two-product formula. Forgetting that ultrafine particles float poorly regardless of reagent dose, so more collector is not a universal fix.