Surface oxidation mechanisms for selective separation of chalcopyrite and pyrite by hypochlorite at high altitude

Abstract

High-altitude areas possess abundant high-quality copper (Cu) resources, driving global mining development toward these areas. However, the low-pressure environment at high altitudes significantly reduced dissolved oxygen (DO) content in pulp (conventional low-altitude DO=8.2 mg/L), thereby altering the redox behavior at sulfide mineral interfaces and adversely affecting the flotation separation of chalcopyrite and pyrite. The study revealed that under a pH of 12.0, the DO content in high-altitude areas (4600 m, DO = 4.0 mg/L) inhibited the oxidative corrosion of pyrite, leading to a sharp decrease in calcium ion (Ca²⁺) adsorption (from 1.5 ×10⁻⁵ to 0.4 ×10⁻⁵ mol/g), thereby increasing the difficulty of its inhibition. Sodium hypochlorite exhibits stronger oxidizing capacity than oxygen, disrupting the surface structure of pyrite, exposing more hydroxylated iron and sulfate species. The enhanced Ca²⁺ adsorption capacity (0.7 ×10⁻⁵ mol/g) and reduced xanthate adsorption (from 2.9 ×10⁻⁷ to 2.6 ×10⁻⁷ mol/g) enhanced its inhibitory effect. By employing NaClO-enhanced oxidation and extended flotation time, the Cu grade of the concentrate from production samples in high-altitude areas increased from 18.86 % to 20.83 %, demonstrating improved separation efficiency. The enhanced oxidation process proposed in this study provided a theoretical foundation and engineering guidance for the development of Cu resources in high-altitude areas.