Kinetics and mechanism of arsenopyrite leaching in nitric acid solutions in the presence of pyrite and Fe(III) ions

Abstract

The main sulphide minerals that serve as gold carriers in low-grade raw materials are pyrite and arsenopyrite. Traditional methods of processing such refractory raw materials rely on high-pressure or pyrometallurgical oxidisation, which destroys the crystal lattice of sulphides and releases gold particles. An alternative method of oxidation is leaching with nitric acid. The study examined the kinetics and oxidation mechanism of the natural mineral arsenopyrite in nitric acid media, along with the effect of pyrite on the kinetic characteristics of dissolution. Using the shrinking core model (SCM), it was shown that during the first 5 min of the process, the kinetic of the reaction is controlled by the chemical reaction. Further in the course of the process, the mode changes, which is confirmed by the new shrinking core model. During the period from 5 to 60 min the model was fitted according to diffusion through a product layer and interfacial transfer. The addition of Fe(III) ions and an increase in the concentration of nitric acid have a similar effect on the nitric acid leaching of arsenopyrite, which is associated with an increase in the oxidation potential of the system. The influence of pyrite on the leaching of arsenopyrite is probably associated with its catalytic action in the early stage of the process, which is due to the role of an alternative surface for the reduction of nitrate ions in electrochemical contact with arsenopyrite. The difference in the mechanisms of arsenopyrite oxidation in the presence of Fe(III) ions and pyrite was confirmed by the SEM-EDX analysis.