carlin gold processing flow sheet

Carlin Gold Processing Flow Sheet: A Comprehensive Overview

The Carlin gold processing flow sheet is a well-established method for extracting gold from ore deposits, particularly those found in Nevada’s Carlin Trend. This flow sheet is designed to handle refractory ores, where gold is often locked within sulfide minerals, making direct cyanidation ineffective. The process involves several key stages, including crushing, grinding, oxidation, leaching, and recovery. Below is a detailed breakdown of each step.

1. Crushing and Grinding
The first stage involves reducing the ore size to liberate gold particles for further processing. Run-of-mine ore is crushed using jaw or gyratory crushers, followed by secondary and tertiary crushing if necessary. The crushed ore is then ground in ball mills or semi-autogenous grinding (SAG) mills to produce a fine slurry, typically achieving a particle size of 80% passing 75 microns.

2. Oxidation (Roasting or Pressure Oxidation)
Since Carlin-type ores are often refractory, oxidation is required to break down sulfide minerals and expose the gold for leaching. Two primary methods are used:
- Roasting: The ore is heated in a controlled environment to oxidize sulfides into porous oxides, allowing cyanide solutions to penetrate and dissolve gold.
- Pressure Oxidation (POX): The slurry is treated in autoclaves under high pressure and temperature with oxygen, converting sulfides to sulfates while releasing encapsulated gold.

3. Leaching (Cyanidation)
After oxidation, the slurry undergoes leaching with sodium cyanide (NaCN) in agitated tanks. The cyanide dissolves the liberated gold into solution as a gold-cyanide complex (Au(CN)₂⁻). Lime is added to maintain an alkaline pH (~10-11) to prevent cyanide loss as hydrogen cyanide gas.

4. Gold Recovery (Carbon Adsorption or Merrill-Crowe)
The pregnant solution containing dissolved gold is then processed using one of two methods:
- Carbon-in-Pulp (CIP): Activated carbon granules adsorb the gold from the solution, which are later stripped using hot caustic solution and electrolysis to produce doré bars.
- Merrill-Crowe Process: Zinc dust precipitates gold from clarified solution, followed by filtration and smelting to recover metallic gold.

5. Tailings Management
The remaining slurry (tailings) undergoes detoxification to neutralize residual cyanide before being pumped to