Gold Processing Flow Diagram for Refractory Ore
Refractory gold ores are characterized by their resistance to conventional cyanidation due to the encapsulation of gold particles within sulfide minerals or carbonaceous materials. Processing such ores requires specialized techniques to liberate and recover the gold effectively. Below is a detailed flow diagram outlining the key stages in treating refractory gold ore.
1. Ore Preparation and Comminution
The process begins with crushing and grinding the ore to a fine particle size, typically below 75 microns. This step is critical to expose the gold-bearing sulfides or carbonaceous matter for subsequent treatment. High-pressure grinding rolls (HPGR) or ball mills are commonly used to achieve the desired fineness.
2. Pre-Treatment Methods
Refractory ores often require pre-treatment to break down the host minerals before cyanidation can be effective. The most common methods include:
- Roasting: The ore is heated in an oxygen-rich environment to oxidize sulfides, releasing encapsulated gold. This method is effective but can produce harmful emissions like sulfur dioxide, necessitating gas scrubbing systems.
- Pressure Oxidation (POX): The ore is subjected to high temperature and pressure in an autoclave with oxygen, converting sulfides to sulfates and freeing the gold. POX is environmentally preferable but capital-intensive.
- Biological Oxidation (Biooxidation): Bacteria such as *Acidithiobacillus ferrooxidans* are used to oxidize sulfides naturally. This method is slower but cost-effective for certain ores.
3. Cyanidation and Gold Recovery
After pre-treatment, the ore undergoes cyanide leaching, where gold dissolves into a solution as a cyanide complex. The slurry is then processed through carbon-in-leach (CIL) or carbon-in-pulp (CIP) circuits, where activated carbon adsorbs the gold from the solution.
4. Elution and Electrowinning
Loaded carbon is stripped of gold in an elution column using hot caustic solution. The resulting pregnant solution is subjected to electrowinning, where gold plates onto cathodes. The cathodes are then smelted to produce doré bars for refining.
5. Tailings Management
Tailings from the process are treated to neutralize residual cyanide and heavy metals before disposal in engineered facilities. Thickening and filtration reduce water content, promoting responsible waste management.
This flow diagram highlights the complexity of refractory ore processing,