I. Gold Ore Upgrading: Comminution & Size Reduction
The economic viability of gold extraction at Metanix depends heavily on the Degree of Liberation. This is the process of physically separating gold particles from the host rock (typically quartz or sulfides). To prepare the ore for industrial-scale purification, it must undergo a rigorous mechanical reduction process to reach micron-level fineness.
1. Primary & Secondary Crushing Phase
Run-of-Mine (ROM) ore often arrives in large blocks exceeding 100cm in diameter. The first industrial step is to reduce these boulders into manageable gravel-sized pieces (approx. 12mm to 20mm).
- Equipment Used: Jaw Crushers (for primary heavy-duty breaking) and Cone Crushers (for secondary shaping and sizing).
- Technical Objective: To achieve a uniform feed size while minimizing the generation of "slimes" (ultra-fine dust) which can complicate later stages.
2. Fine Grinding & Pulverization
To expose the gold surfaces for chemical reagents, the crushed ore must be transformed into a fine "slurry." This stage consumes the most energy in the processing plant.
| Machinery | Industrial Function |
|---|---|
| Ball Mills | Uses steel balls as grinding media to reach a fineness of < 75 microns. |
| SAG Mills | Semi-Autogenous Grinding; uses large ore rocks to grind smaller ones, reducing media costs. |
| Hydrocyclones | Centrifugal classifiers that separate fine particles from coarse ones for re-grinding. |
Refractory gold ores (where gold is locked within Pyrite or Arsenopyrite) require Ultra-Fine Grinding (UFG). Without reaching a particle size of 10-20 microns, chemical recovery rates will drop significantly, leading to massive economic losses.
End of Part 1: Mechanical Preparation.
II. Concentration & Enrichment: Separating the Value from the Gangue
Once the ore is finely ground, the next industrial priority is Concentration. This stage aims to remove as much "Gangue" (worthless rock) as possible, significantly reducing the volume of material that needs chemical treatment. This is achieved through differences in physical properties like density and hydrophobicity.
1. Gravity Concentration (Density-Based)
Gold has a high specific gravity (approx. 19.3) compared to quartz (approx. 2.6). Industrial plants leverage this massive weight difference to "trap" free gold particles using centrifugal force and vibration.
- Equipment Used: Knelson Concentrators, Falcon Concentrators, and Shaking Tables.
- Technical Process: The slurry is spun at high speeds; the heavy gold particles are forced against the walls and trapped in "rifles," while lighter sand is washed away.
2. Froth Flotation (Surface-Based)
For gold locked within sulfides (like Pyrite), gravity alone isn't enough. Froth Flotation uses chemistry to make gold-bearing minerals "float" on bubbles.
| Component | Industrial Role |
|---|---|
| Collectors (e.g., Xanthates) | Chemicals that coat the gold particles to make them water-repellent (Hydrophobic). |
| Frothers | Stabilize the bubbles so they can carry the gold to the surface. |
| Flotation Cells | The large tanks where air is injected to create the mineral-rich foam. |
Integrating a Gravity Circuit before flotation is a "best practice" in modern mining. It captures "Coarse Gold" early, preventing it from settling in the bottom of flotation tanks and ensuring a much higher overall recovery rate for the final concentrate.
End of Part 2: Concentration Techniques.
III. Extraction & Refining: From Chemical Leaching to Final Gold Bars
This is the final frontier in the gold production cycle. After mechanical crushing and physical concentration, the gold is still microscopic or locked in a concentrate. To transform it into a tangible industrial product, we utilize Hydrometallurgy and Pyrometallurgy.
1. Cyanidation & Carbon-In-Leach (CIL)
In modern industrial plants, the CIL (Carbon-In-Leach) process is the gold standard. It involves dissolving the gold into a solution and then capturing it using activated carbon.
- Chemical Reagent: Sodium Cyanide (NaCN) solution is used to dissolve gold under alkaline conditions (pH 10-11).
- The Capture: Activated Carbon (made from coconut shells) acts like a sponge, attracting the dissolved gold ions onto its surface.
- Equipment: Large Leaching Tanks equipped with heavy-duty agitators to keep the slurry in motion.
2. Elution, Electrowinning & Smelting
Once the carbon is "loaded" with gold, it undergoes Elution (stripping) to move the gold into a highly concentrated liquid, which is then ready for the final physical transformation.
| Stage | Process & Machinery |
|---|---|
| Electrowinning | Using Electrolytic Cells to pass a current through the solution, plating the gold onto steel wool cathodes. |
| Calcination | Drying and heating the gold sludge in a Muffle Furnace to remove impurities like mercury or moisture. |
| Smelting | Melting the gold at 1,064°C in an Induction Furnace with fluxes (borax/silica) to pour Dore Bars. |
The final Dore Bar produced at the mine site typically contains 60-90% gold. To reach "Investment Grade" (99.9% purity), these bars are shipped to a secondary refinery for the Wohlwill Process or Miller Process, completing the bridge between raw mining and the high-end industrial/jewelry sector.
--- Full Article Concluded: From Earth to Industry ---
