The Core Difference: Leaching vs. Adsorption Sequence

The fundamental difference lies in the timing of leaching (dissolving the gold with cyanide) and adsorption (capturing the dissolved gold onto activated carbon).

• CIP (Carbon-in-Pulp): This is a two-step sequential process.

  1. Leaching: The ground ore slurry enters a series of agitated tanks where cyanide is added and the gold is dissolved. This is the “Leach Circuit.”

  2. Adsorption: The leached slurry then flows into a separate, subsequent series of tanks called the “Adsorption Circuit.” Here, activated carbon is added to capture the dissolved gold.

• CIL (Carbon-in-Leach): This is a combined process.

  • Leaching and adsorption occur simultaneously in the same tank series. Activated carbon is present from the beginning, adsorbing the gold as it is being dissolved by the cyanide.

Detailed Comparison Table: CIL vs. CIP

Key Factors for Choosing the Right Process

The choice isn’t about which is “better” in a vacuum, but which is more suitable for your specific ore body and project economics.

1. Ore Type: The Decisive Factor for “Preg-Robbing”

This is often the single most important consideration.

• Choose CIL if your ore is “preg-robbing.” Preg-robbing ore contains naturally occurring carbonaceous material (shale, graphite, etc.) that acts like activated carbon. It “robs” the pregnant solution of its gold by adsorbing it, making it unrecoverable.

  • CIL Solution: By adding activated carbon immediately, you provide a more efficient and attractive surface for the dissolved gold than the preg-robbing material. The commercial carbon “out-competes” the native carbon, protecting your gold recovery.

• Choose CIP for non-preg-robbing ores. If your ore is “clean” and free of carbonaceous material, CIP is often the preferred choice. It allows for optimal leaching conditions without the complicating presence of carbon.

2. Capital and Operating Costs (CAPEX & OPEX)

• Choose CIL for lower CAPEX. Fewer tanks, less piping, and a simpler layout mean a lower initial investment. This makes CIL attractive for smaller projects or in locations where capital is a major constraint.

• CIP may have advantages in specific OPEX areas. Because the carbon is only in the adsorption circuit, it can have a longer life and require less frequent regeneration than in a CIL circuit, where it is subjected to harsher conditions for longer.

3. Operational Simplicity and Control

• Choose CIL for operational simplicity. The single-train process is easier for operators to manage on a day-to-day basis, with fewer moving parts and transfer points.

• Choose CIP for advanced process control. If you have a complex ore that requires precise control over leach kinetics, pH, and cyanide levels, CIP allows you to fine-tune the leach circuit independently of the adsorption circuit. This can be critical for maximizing recovery from refractory or variable ores.

Summary: When to Use Which?

Conclusion

There is no universal winner. The history of gold processing has seen a shift towards CIL becoming more dominant, primarily because:

1. Many new gold discoveries are in deposits with some degree of preg-robbing character.

2. The lower capital cost of CIL is highly attractive for project economics.

However, CIP remains a robust, efficient, and often superior process for well-understood, non-preg-robbing ores where maximum recovery through precise control is the primary goal.

The final decision must be based on comprehensive metallurgical test work that characterizes the ore’s leaching kinetics, preg-robbing potential, and response to both CIL and CIP flowsheets.