How does the carbon leaching (CIL) method extract gold in six steps?

2025-09-12

The Carbon-in-Leach (CIL) process is a widely used method for extracting gold from ore. It involves six key steps, which are designed to efficiently recover gold using activated carbon. Here’s a detailed explanation of the process:

1. Crushing and Milling

• The gold-bearing ore is first extracted from the mine and then crushed into fine particles.
• The crushed ore is further milled into a powdery consistency to increase the surface area, facilitating the extraction of gold during subsequent steps.

2. Leaching (Cyanidation)

• The finely milled ore is mixed with water to form a slurry.
• Sodium cyanide (or potassium cyanide) is added to the slurry, which dissolves gold from the ore in a chemical reaction, forming a gold-cyanide complex.
• Oxygen is often introduced into the leaching tanks to enhance the gold dissolution process.

3. Adsorption onto Activated Carbon

• The slurry containing dissolved gold is transferred to a series of agitated tanks that contain activated carbon.
• Activated carbon has a high affinity for gold, and the gold-cyanide complex is adsorbed onto the surface of the carbon particles.
• This step occurs simultaneously with leaching in the same tanks, hence the name "carbon-in-leach."

4. Screening and Carbon Separation

• After the adsorption process, the carbon is separated from the slurry using screens or sieves.
• The gold-loaded carbon is removed for further processing, while the remaining slurry (tailings) is sent to residue treatment or disposal.

5. Elution (Gold Desorption)

• The gold is stripped from the activated carbon in a process called elution. A hot caustic solution (usually a mixture of sodium hydroxide and cyanide) is used to desorb the gold, resulting in a concentrated gold solution.
• The now "barren" carbon is typically reactivated by heating and returned to the adsorption tanks for reuse.

6. Electrowinning or Precipitation

• The gold-rich solution from the elution process is treated using electrowinning, a method that uses an electric current to deposit gold onto electrodes.
• Alternatively, chemical precipitation may be used to recover gold.
• Finally, the deposited gold is smelted into doré bars, which are unrefined gold products ready for further refining.

Summary:

The CIL process combines leaching and adsorption in one step, making it an efficient and cost-effective method for gold recovery. The six primary steps are Crushing and Milling, Leaching, Adsorption, Carbon Separation, Elution, and Electrowinning/Precipitation, culminating in the production of gold doré bars. This process is widely used in gold mining operations due to its ability to handle low-grade ores and maximize gold recovery rates.

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