Direct CIP Route

Process Description

The Direct Carbon-in-Pulp (CIP) route is the most widely recognized gold extraction flowsheet for free-milling ores. It involves leaching the entire mass of tailings with a leaching agent before passing the slurry through a series of adsorption tanks containing activated carbon.

For historical tailings, however, this approach becomes technically inefficient and capital-intensive. The entire tonnage, including inert silicates, clays, and gangue, must be leached, agitated, and detoxified, even though only a small fraction contains gold-bearing minerals.

A typical Direct CIP plant requires:

• Large leach tanks (6–10 units, 3,000–5,000 m³ each)
• A full adsorption train (6–8 CIP tanks)
• Cyanide dosing across the entire slurry volume
• Lime addition for pH control
• A detoxification circuit for the entire mass flow
• A fully lined tailings storage facility (TSF)

This results in a linear scaling of both capital and operating costs with throughput.

Preg-Robbing Risk

Preg-robbing occurs when naturally occurring carbonaceous material in the ore adsorbs dissolved gold from solution, preventing it from loading onto activated carbon. This is a well-documented issue in historical tailings, especially those derived from graphitic shales or carbon-rich reefs.

In a Direct CIP flowsheet, preg-robbing is particularly damaging because:

• Gold is dissolved early in the leach tanks.
• Natural carbon is present throughout the slurry.
• Adsorption onto natural carbon occurs before the slurry reaches the CIP tanks.
• Once adsorbed onto natural carbon, gold is effectively lost to the final tails.

This can cap recoveries at 40–55%, even with aggressive cyanide dosing.

Historically, many mines abandoned CIP on preg-robbing ores for this reason.

Economic Profile

Direct CIP appears simple on paper but becomes one of the most expensive routes for tailings retreatment due to:

• High capital cost for large tank farms
• High leaching agent consumption across the full mass
• High lime consumption
• Large detoxification circuits
• High power consumption for agitation

The economic challenge is structural: CIP treats 100% of the mass, even though only a small fraction contains gold. This makes the process inherently inefficient for refractory or preg-robbing tailings.

In contrast, flotation-based flowsheets treat only 5–15% of the mass in the high-cost circuit, dramatically improving unit economics.