Gold ores, often containing copper, undergo a processing combination involving gravity separation, flotation, and cyanidation. Gravity separation separates gold from gangue minerals based on density differences. Flotation makes gold particles hydrophobic, enabling their separation in a froth flotation cell. The final step involves cyanidation to recover gold from the concentrate by treating it with a dilute sodium cyanide solution.
Concentration Process for Gold from Mixed Ore Types
The concentration of gold from a mixed ore type involves a series of steps, excluding references to copper. The process includes:
- Crushing and Grinding: The mixed ore is crushed into small particles and ground into a powder, increasing the surface area for better chemical contact.
- Flotation: The powdered ore is mixed with water, collectors, and frothers, then introduced into a flotation cell. Air is bubbled through the mixture, and gold minerals attach to the bubbles, forming a froth. The froth is thickened, filtered to remove excess water, and concentrates the gold minerals.
- Gravity Separation: Concentrated gold minerals undergo gravity separation using techniques like shaking tables or centrifugal concentrators. This separates heavy minerals from lighter ones, further concentrating the gold.
- Cyanide Leaching: The final concentrate, containing gold, undergoes cyanide leaching. Cyanide dissolves the gold, forming a gold-cyanide complex, while copper remains unaffected in the concentrate. The gold-cyanide complex is extracted from the solution using activated carbon or other methods.
- Refining: The refined gold undergoes further purification to remove impurities and obtain pure gold. The copper concentrate is smelted to eliminate impurities and produce pure copper.
This step-by-step process ensures the effective concentration of gold from a mixed ore type.
For ores containing both gold and copper, a mix of pyrometallurgical and hydrometallurgical techniques is employed. Pyrometallurgical processing involves roasting and smelting sulfide ore to produce matte, containing copper, iron, and sulfur. During smelting, some gold is captured in the matte. The matte undergoes an oxidizing step to produce blister copper, refined electrolytically for pure copper, with gold recovered as a byproduct. Hydrometallurgical processing uses leaching of oxide ore with dilute sulfuric acid, solvent extraction to separate copper, and electrowinning for pure copper. Any remaining gold is recovered through cyanide leaching of the residue.
Various gold-copper ore types include porphyry copper-gold, skarn-type gold-copper, and epithermal gold-copper ores. These ores are found in diverse geological settings such as porphyry deposits, skarns, and epithermal deposits. The processing methods and characteristics differ based on the specific ore type, ranging from low-grade bulk-minable deposits to high-grade, narrow veins of mineralization.