Flotation processes are essential methods for separating copper and gold from copper-gold ores. Depending on the characteristics of the ore, these processes primarily include the flotation of sulfide copper ores and the flotation of oxide copper ores. Common primary oxide copper minerals include malachite (CuCO3-Cu(OH)2, containing 57.4% copper) and azurite (2CuCO3·Cu(OH)2, containing 55.2% copper), followed by chrysocolla (CuSiO3·2H2O, containing 36.2% copper) and cuprite (Cu2O, containing 88.8% copper).
The sulfidation method is the most common flotation method for oxide copper ores. It is suitable for most oxidized copper ores that can be sulfidized. Sulfidized oxide ores exhibit properties of sulfide ores and can be floated using xanthate.
Usage of Sulfidizing Agents: Sodium sulfide is used at a dosage of 1-2 kg/t (of raw ore). Sodium sulfide and other sulfidizing agents oxidize easily, have short action times, and the formed sulfide films are unstable and can easily detach under intense agitation. Therefore, it should be added in batches directly into the first flotation cell.
Pulp pH Control: The sulfidation rate increases as the pulp pH decreases. The pH is usually maintained around 9, and lime can be added if necessary.
Collectors: Butyl xanthate or a mixture of black and yellow collectors is commonly used.
Dispersants: When there is a high amount of slime, a dispersant such as water glass is used.
Organic acids and their soaps can effectively float malachite and azurite. However, this method is less selective when the gangue contains a large amount of carbonate minerals, making it difficult to improve the concentrate grade.
Applicability: Suitable for ores where the gangue minerals are not carbonate. The flotation performance deteriorates when the gangue contains a significant amount of floatable iron and manganese minerals.
Auxiliary Reagents: Sodium carbonate, water glass, and phosphates are typically added as gangue inhibitors and pulp regulators.
When neither the sulfidation nor the organic acid methods achieve satisfactory results, the leaching-precipitation-flotation method is used.
Process Flow: The oxide copper ore is first leached with sulfuric acid, then copper is precipitated using iron powder, and the precipitated copper is subsequently floated.
Leaching Conditions: The leach solution is a 0.5%-3% dilute sulfuric acid solution, with acid consumption varying between 2.3-45 kg/t (of raw ore) depending on the ore's properties. For refractory ores, leaching can be performed at elevated temperatures (45-70°C).
Flotation Conditions: Flotation is carried out in an acidic medium using cresol black or double xanthate as collectors.
This method is suitable for ores with a high content of alkaline gangue, where acid leaching would be too costly.
Process Flow: After fine grinding, the ore is treated with sulfur powder and ammonia leaching. The copper ions in the oxide copper ore form complexes with NH3 and CO2 while being precipitated by sulfur ions into new sulfide copper particles. Ammonia is then evaporated and recovered, followed by sulfide copper flotation.
Pulp pH Control: The pulp pH is maintained between 6.5 and 7.5.
Flotation Reagents: Standard flotation reagents for sulfide copper ores are used.
This method is used for refractory oxide copper ores, particularly those with a high slime content and combined copper accounting for more than 30% of total copper.
Process Flow: The appropriately sized ore is mixed with 2%-3% coal powder and 1%-2% salt, then subjected to chloridizing reduction roasting at 700-800°C. The resulting copper chloride volatilizes from the ore and is reduced to metallic copper within the furnace, which is then adsorbed onto coal particles. These particles are subsequently separated from the gangue via flotation.
Applicability: Suitable for ores with high chrysocolla and cuprite content. This method is advantageous for comprehensive recovery of gold, silver, and other rare metals compared to the leaching-flotation method.
Drawbacks: High energy consumption and costs.
The flotation process for mixed copper ores should be determined based on experimental results. The process can either involve simultaneous flotation of sulfide and oxide copper minerals after sulfidation or sequential flotation where sulfide minerals are floated first, followed by sulfidation and flotation of oxide minerals. The amounts of collectors and sulfidizing agents should be adjusted according to the oxide content in the ore.
The choice of flotation process for copper-gold ores depends primarily on the specific characteristics and mineral composition of the ore. The sulfidation method is suitable for most oxide copper ores, while the organic acid method is preferable for ores without carbonate gangue minerals. The leaching-precipitation-flotation method is used when other methods are ineffective. The ammonia leaching-sulfide precipitation-flotation method is suitable for ores with high alkaline gangue content, and the segregation-flotation method is applicable for refractory oxide copper ores. Optimizing the flotation process and reagent regime through testing can achieve the best recovery rates and economic benefits.
