Arsenic not only significantly affects the quality of gold concentrate but also causes environmental pollution. In gold ores, arsenic usually exists in the gangue mineral arsenopyrite and is often closely associated with gold minerals, making separation difficult. Among the methods for reducing arsenic content in concentrates, common approaches include the soda ash method, lime method, and oxidation method. The oxidation method is particularly effective and widely applied.
The main principle of this method is to use an oxidant to increase the free oxygen content in the aqueous solution, leading to the surface oxidation of arsenic minerals and thereby achieving the depression of arsenic minerals. Building on this suppression effect, the free oxygen content in the water can be increased and the floatability of arsenic minerals reduced by adjusting the pH value and temperature, thereby lowering the arsenic content in the gold concentrate. Typically, arsenic minerals exhibit good floatability under weakly acidic conditions, while their floatability decreases under neutral to weakly alkaline conditions. Gold minerals, however, maintain relatively good floatability under these conditions. A pH value around 8 is generally adopted as the flotation condition for arsenic-bearing gold ores.
For different types of arsenic-bearing gold ores, the specific oxidant, pH value, and temperature range all vary. Determining suitable conditioning factors through beneficiation tests is a scientific and reasonable approach.
The core of treating arsenic-bearing gold ores lies in effectively removing or immobilizing arsenic while extracting gold, thereby avoiding environmental pollution. Common treatment methods mainly fall into the following categories:
Pre-treatment Arsenic Removal Methods: These involve treating the ore beforehand to reduce arsenic content before gold extraction.
Roasting De-arsenification: At high temperatures (500–800°C), arsenic compounds (e.g., arsenopyrite) in the ore are oxidized into volatile As₂O₃, achieving separation from gold. This is suitable for high-arsenic gold ores.
Pressure Oxidation Method: Under high pressure, high temperature (150–220°C), and acidic conditions, oxygen is used to oxidize arsenic compounds into soluble arsenate ions. This method both removes arsenic and exposes gold particles for subsequent extraction.
Bacterial Oxidation Method: This utilizes microorganisms such as Acidithiobacillus ferrooxidans to oxidize and decompose arsenic compounds. It is environmentally friendly and has lower costs, making it suitable for low-grade arsenic-bearing gold ores.
Direct Gold Extraction Methods (Combined with Arsenic Removal)
Cyanidation Method (Improved): Traditional cyanidation is easily hindered by arsenic. Interference can be reduced by controlling pH, adding oxidants (e.g., hydrogen peroxide), or employing combined pre-treatment and cyanidation processes.
Non-cyanide Gold Extraction Methods: These use thiourea, thiosulfate, etc., as substitutes for cyanide. They minimize environmental pollution while reducing arsenic interference and are suitable for scenarios with high environmental requirements.
During the treatment process, special attention must be paid to the recovery and harmless treatment of arsenic to prevent its release into the environment. The selection of a specific method should be comprehensively determined based on ore properties, grade, and environmental requirements.
