Gold Ore Plant

How Does A Gold Ore Plant Work?

A gold ore plant is a specialized facility designed to extract gold from raw ore through a series of physical, chemical, and mechanical processes. The workflow varies slightly based on the type of gold ore (oxide ore, sulfide ore, or refractory ore), but the core process follows a standard sequence: ore preparation → gold separation → gold recovery → tailings disposal. Below is a detailed, step-by-step explanation of how it works, including key processes and equipment.

1. Ore Preparation (Crushing & Grinding)

The first stage is to reduce raw ore to a fine particle size, which exposes gold particles and enables effective separation. This stage has two sub-steps:

Step 1: Crushing & Screening

• Raw ore is transported from the mine to the plant via trucks or conveyors.
• Vibrating feeders evenly feed the ore into a jaw crusher (primary crusher) to break large rocks into smaller pieces (50-150mm).
• The crushed ore then goes to a cone crusher or impact crusher (secondary/tertiary crusher) to reduce the size to 10-20mm.
• A vibrating screen separates the ore into uniform particles; oversized particles are recrushed, and qualified particles move to the grinding stage.

Step 2: Grinding & Classifying

• The crushed ore is fed into a ball mill (the core grinding equipment), which grinds the ore into a fine slurry (typically 70-80% passing 200 mesh). This ensures gold particles are fully liberated from gangue (waste rock).
• A spiral classifier or hydrocyclone classifies the slurry: coarse particles return to the ball mill for regrinding, and fine, qualified slurry proceeds to the gold separation stage.

2. Gold Separation (Based on Ore Type)

This is the core stage, where gold is separated from the slurry. The method depends on the ore’s characteristics:

Option A: For Oxide Gold Ore (Most Common)

The most widely used processes are CIP (Carbon-in-Pulp) or CIL (Carbon-in-Leach), both based on cyanide leaching:

1. Leaching: The qualified slurry is mixed with sodium cyanide (leaching agent) and lime (pH control) in leaching tanks. Gold reacts with cyanide to form soluble gold cyanide complexes ([Au(CN)₂]⁻).
2. Adsorption: Activated carbon is added to adsorb the gold cyanide complexes from the slurry.
   • CIP: Leaching and adsorption are performed in separate tanks (leaching first, then adsorption).
   • CIL: Leaching and adsorption happen simultaneously in the same tanks, reducing gold loss.
3. Loaded Carbon Separation: Screens (vibrating/curved screens) separate the loaded carbon (gold-loaded activated carbon) from the barren slurry (tailings slurry).

Option B: For Sulfide Gold Ore

Sulfide ores are refractory (gold is trapped in sulfide minerals like pyrite), so flotation is used first:

1. Flotasi: The ground slurry is mixed with flotation reagents (collectors, frothers) in a flotation machine. Gold-bearing sulfide minerals attach to air bubbles and float to the surface, forming a gold concentrate.
2. Oxidation: The gold concentrate is treated via roasting, bio-oxidation, or pressure oxidation to break down sulfide minerals and expose gold particles.
3. Cyanide Leaching: The oxidized concentrate is then processed with cyanide leaching (CIP/CIL) to dissolve gold.

Option C: For Low-Grade Oxide Ore

Heap leaching is a low-cost, large-scale method:

1. Low-grade ore is stacked into large heaps on an impermeable pad.
2. Dilute cyanide solution is sprayed over the heap, and the solution percolates through the ore, leaching gold into a pregnant leach solution (PLS).
3. The PLS is collected and treated with activated carbon to adsorb gold, then recycled back to the heap.

3. Gold Recovery (From Loaded Carbon)

Loaded carbon contains gold cyanide complexes, which are processed to extract pure gold via three key steps:

Step 1: Elution (Desorption)

• Loaded carbon is placed in an elution column (stripping column) and washed with a hot eluent (sodium cyanide + sodium hydroxide solution).
• Gold cyanide complexes desorb from the carbon into the eluent, producing a high-concentration gold solution (pregnant eluate).

Step 2: Electrowinning

• The pregnant eluate is pumped into an electrowinning cell, where an electric current is applied. Gold ions are reduced to metallic gold, depositing on the cathode as gold mud (gold concentrate with 90%+ gold content).
• Barren eluate is recycled back to the elution column.

Step 3: Smelting & Refining

• Gold mud is filtered, dried, and melted in a smelting furnace (e.g., induction furnace) with fluxes (borax, silica).
• The molten gold is cast into crude gold bars, which are further purified via electrolytic refining to produce 99.99% pure gold bullion.

4. Tailings Disposal & Water Recycling

• The barren slurry (tailings) after gold separation is thickened in a thickener and pumped to a tailings dam for storage.
• Process water (from thickeners, filters, and tailings dams) is recycled back to the plant to reduce water consumption and environmental impact.

5. Auxiliary Systems

A gold ore plant also relies on critical support systems:

• Reagent Dosing System: Precise addition of cyanide, flotation reagents, lime, and other chemicals.
• Material Handling Systems: Conveyors, pumps, hoists for transporting ore, slurry, and activated carbon.
• Automation & Control System: PLC systems monitor slurry density, pH, temperature, and flow rates to ensure process stability.
• Environmental Protection Systems: Dust collectors, wastewater treatment units, and gas scrubbers to comply with environmental regulations.

The whole gold ore process workflow is: Raw Ore → Crushing → Grinding → Leaching/Flotation → Adsorption → Elution → Electrowinning → Smelting → Pure Gold

This efficient, multi-stage process ensures maximum gold recovery while minimizing costs and environmental impact, tailored to the specific properties of the gold ore being processed.