pH control plays a crucial role in the dissolution and adsorption of gold in Carbon-in-Leach (CIL) and Carbon-in-Pulp (CIP) circuits used in gold processing. These processes involve the extraction of gold from ore by dissolving it in a cyanide solution and subsequently adsorbing it onto activated carbon. The pH level affects the efficiency of these processes in several ways:
Gold Dissolution: The dissolution of gold in cyanide solutions is pH-dependent. The optimal pH range for gold dissolution is typically between 10 and 11. At lower pH values, the dissolution rate decreases significantly, while higher pH values can lead to the formation of soluble gold-cyanide complexes that are less favorable for gold recovery. Therefore, maintaining the pH within the optimal range ensures efficient gold dissolution.
Cyanide Stability: Cyanide is an essential component in gold leaching processes as it forms complexes with gold, enabling its dissolution. However, cyanide is also highly toxic and must be carefully managed. The stability of cyanide is pH-dependent, with lower pH values leading to increased cyanide breakdown and decreased efficiency. By controlling the pH, the stability of cyanide can be maintained, ensuring the availability of cyanide for gold dissolution.
Carbon Activity: Activated carbon is used to adsorb the dissolved gold from the cyanide solution in CIP/CIL circuits. The adsorption efficiency of gold onto carbon is influenced by pH. Generally, a slightly acidic to neutral pH range (pH 9-10) is preferred for optimal carbon activity and gold adsorption. At higher or lower pH values, the activity of carbon decreases, resulting in reduced gold adsorption capacity and lower overall process efficiency.
Carbon Degradation: Extreme pH conditions can lead to the degradation of activated carbon used in CIP/CIL circuits. High pH levels can cause the breakdown of carbon structures and the loss of surface area, reducing the carbon's ability to adsorb gold effectively. On the other hand, low pH values can result in acid attack on the carbon, leading to its disintegration. Maintaining an appropriate pH range helps preserve the integrity and activity of the activated carbon.
To optimize the overall process efficiency in CIL/CIP circuits, careful pH control is essential. This is typically achieved by adding alkaline substances, such as lime (calcium hydroxide), to increase pH or acidic substances to decrease pH, based on the specific requirements of the process. Monitoring and adjusting the pH level throughout the leaching and adsorption stages allow for efficient gold dissolution, effective adsorption onto carbon, and the overall success of the gold recovery process.