Mechanism of enargite pressure leaching in the presence of pyrite

Hydrometallurgy is a promising alternative to treat copper concentrates that contain large amounts of enargite (Cu3AsS4). However, leaching of enargite is difficult due to its slow dissolution rate in acidic solutions. The pressure leaching of an enargite concentrate containing about 40% pyrite was carried out in sulfuric acid/oxygen at temperatures in the range of 160 to 200 °C and oxygen partial pressure of 345 to 1034 kPa. The results showed that the dissolution of enargite in the presence of pyrite was considerably faster than the dissolution of pure enargite. By leaching an enargite–pyrite concentrate sample of particle size −75 + 53 μm at 200 °C and 689 kPa O2, all the copper was extracted in 15 min. It was also found that temperature, oxygen partial pressure and particle size had a significant influence on the rate of enargite dissolution from the enargite–pyrite concentrate, while the sulfuric acid concentration had little effect. Ferric ions produced in the leaching were responsible for the enhanced dissolution of enargite in the presence of pyrite and pure enargite leaching was similarly enhanced by the addition of ferrous ions. Analysis of the data for the enargite–pyrite concentrate showed linear kinetics for the dissolution of pyrite, whilst the rate of dissolution of enargite increased substantially with time as ferric ions build up in solution.