processing gold ore in a mill

Processing gold ore in a mill involves several steps to extract gold from the ore efficiently. Here’s a general overview of the process:

1. Crushing
– Primary Crushing: Large chunks of gold ore are reduced to smaller pieces (typically <6 inches) using a jaw crusher or gyratory crusher.
– Secondary Crushing: Further reduction (to ~1 inch or smaller) using cone crushers or impact crushers.

2. Grinding
– The crushed ore is fed into a ball mill, rod mill, or SAG mill (Semi-Autogenous Grinding) with water to create a slurry.
– Grinding reduces the ore to fine particles (~75 microns or less), freeing gold particles for extraction.

3. Classification
– A cyclone or screening system separates fine and coarse particles.
– Oversized material is sent back for regrinding, while properly sized slurry proceeds to the next stage.

4. Gold Extraction Methods
Depending on the type of gold ore, different extraction methods are used:

# A. Gravity Separation (For Free-Milling Gold)
– Uses centrifugal concentrators (e.g., Knelson, Falcon), jigs, or shaking tables.
– Effective for coarse gold particles that can be separated by density.

# B. Flotation (For Sulfide Ores)
– Chemicals (collectors, frothers) are added to make gold-bearing minerals hydrophobic.
– Air bubbles carry the gold concentrate to the surface for collection.

# C. Cyanidation (Most Common for Refractory & Free Gold)
– The ground slurry is mixed with a dilute cyanide solution (NaCN or KCN).
– Gold dissolves into the solution as a cyanide complex (Au(CN)₂⁻).
– Activated carbon (CIP/CIL – Carbon-in-Pulp/Leach) absorbs dissolved gold.
– The loaded carbon is later stred, and gold is recovered via electrowinning or smelting.

# D. Heap Leaching (For Low-Grade Ores)
– Crushed ore is piled on a lined pad and irrigated with cyanide solution.
– Gold dissolves and is collected in ponds before recovery.

5. Gold Recovery
– Electrowinning: Gold is plated onto cathodes from solution.
– Smelting: The gold concentrate is melted in a furnace with fluxes to remove impurities, producing doré bars (~90% pure gold