Mineral Processing Fundamentals
from blasted rock to saleable concentrate
1 Why we process ores at all
Raw ore is a chaotic mix of valuable minerals, barren gangue, and a lot of water-filled voids. The aim of mineral processing (a.k.a. beneficiation) is to liberate the valuables, separate them economically, and deliver a product whose grade and moisture meet smelter, chemical, or filler-industry contracts.
2 The classic five-step flowsheet
| Stage | Core unit operations | What you watch |
|---|---|---|
| Comminution (size reduction) | Jaw/ gyratory crusher → SAG/ball/rod mill → sometimes ultrafine stirred mill | kWh t⁻¹, P₈₀ liberation size, liner wear |
| Classification | Hydrocyclones, screens, spirals | d₅₀ cut-size, bypass %, circulating load |
| Concentration | Gravity (jigs, spirals, shaking tables) | |
| Magnetic & electrostatic | ||
| Flotation, leaching, or dense-media | Recovery %, concentrate grade, reagent cost | |
| Dewatering | Thickeners, filters, centrifuges, flash dryers | % solids underflow, cake moisture, filtrate clarity |
| Tailings handling | Dams, dry-stack, paste backfill, water recycle | Residual metal ppm, water balance, geotechnical stability |
A real plant may loop or repeat steps (e.g., regrind -> cleaner flotation) but every metal industry—from iron ore to lithium brine—uses the same logic chain.
3 Liberation: the first governor of success
Too coarse → valuables locked in gangue, low recovery.
Too fine → excess slimes, reagent over-consumption, filtration headaches.
Optimal grind is where 80 % of the target mineral particles are just detached—nothing more.
4 Separation methods in one glance
| Mineral property exploited | Typical process | Commodity examples |
|---|---|---|
| Density | Jig, spiral, shaking table, DMS | Gold nuggets, tin, coarse spodumene |
| Magnetic susceptibility | Low-intensity or high-gradient magnetic separators | Iron ore, ilmenite, rare-earth monazite |
| Surface chemistry | Froth flotation | Copper, antimony (stibnite), sulphidic gold |
| Solubility / chemistry | Acid or cyanide leach, solvent extraction | Gold oxide ores, lateritic nickel, lithium |
| Electrical conductivity | Electrostatic belt separator | Rutile vs quartz, zircon cleaning |
A plant often combines two or more to hit both grade (purity) and recovery targets.
5 Balancing grade vs. recovery
A metallurgist lives on the classic curve:
Pushing grade up usually knocks recovery down (and vice-versa).
The “sweet spot” is defined by the net smelter return:
Profit per tonne ore = (Payable metal × price) – (Reagent + Power + Tailings cost)
Economic modelling, not just lab tests, decides whether to pull the concentrator knob toward higher grade or higher tonnage.
6 Process water & reagents—hidden cost centres
Water recycle loop keeps fresh-water intake < 0.3 m³ t⁻¹ in modern plants.
Reagent spend can hit US $3–7 t⁻¹ ore (xanthates, frothers, lime, depressants).
High ionic strength or residual organics in recycle water can swing flotation selectivity, so plants constantly tweak pH and dosing.
7 Typical performance benchmarks
| Ore type | Grind P₈₀ | Overall recovery | Concentrate grade |
|---|---|---|---|
| Oxide gold (CIL) | 75 µm | 90–95 % Au | Bullion after carbon elution |
| Stibnite (Sb₂S₃) flotation | 120 µm → regrind 40 µm | 85–92 % Sb | 50–60 % Sb conc. |
| Magnetite iron ore | 45 µm | 95 % Fe | 66–68 % Fe pellets |
| Talc (not floated) | 44 µm (325 mesh) | n/a — milled product | 96 %+ Ry brightness |
8 Common bottlenecks & quick diagnostics
| Symptom | Likely cause | Check this first |
|---|---|---|
| Rising mill kWh t⁻¹ | Liner wear, harder ore, low % solids | Grinding-media shape, cyclone pressure |
| Froth overflowing launders | Collector overdose, low pH, high air rate | Dosage set-point, airflow cube-law |
| Tailings dam approaching design limit | Poor thickener floccs, vacuum-filter cloth blind | Polymer grade, rake torque, filter ∆P |
| High arsenic in Sb conc. | Arsenopyrite activation | pH > 8.5, NaHSO₃ depressant trial |
9 Key take-aways
Liberation → separation → dewatering is the universal workflow.
Every circuit is a compromise between grade, recovery, energy, and water.
Good process control starts with mass-balance accounting—know every stream flow and assay daily.
The same fundamentals scale from a 300 kg/h pilot to a 100 000 t/d porphyry copper plant.
Get these foundations right, and any specialised flowsheet—be it gold, antimony, lithium, or industrial minerals—builds on solid ground.