Laboratory of Advanced Technologies in Non-ferrous and Ferrous Metals Raw Materials Processing at the Institute of New Materials and Technologies, Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia:

E. A. Kuzas, Senior Researcher, Candidate of Technical Sciences, e-mail: e.kuzas@ya.ru
K. A. Karimov, Senior Researcher, Candidate of Technical Sciences
D. A. Rogozhnikov, Head of the Laboratory, Doctor of Technical Sciences

Current concentration plants are dealing with great amounts of low-grade sulphide ores containing gold and other noble metals. Because noble metals are often found encapsulated in the main sulphide minerals (such as pyrite and arsenopyrite), such ores cannot be processed using conventional processes (e.g. cyaniding). Nitric acid leaching offers one of the innovative techniques for loosening sulphide minerals. That’s why one believes it to be of relevance to look at the dissolution kinetics of sulphide minerals in nitric acid solutions. The authors consider using the full factorial design model to study the leaching kinetics of iron being a part of arsenopyrite. The process involves the use of a rotating disk in HNO₃ solutions with the concentrations of 3 and 5 mol/dm³ at the temperatures of 303 and 333 K and the rotary speeds of 3.3 and 10 RPS. The kinetic equations obtained describe the dissolution process with a high degree of accuracy. Temperature and HNO₃ concentration were found to produce the most positive effect on the iron dissolution rate when iron comes as part of arsenopyrite. Agitation does not appear to produce any noticeable effect. This is confirmed by low orders of reaction with respect to the disk rotation frequency, which vary in the range of –0.13 to 0.20. The high apparent activation energy (60.8–69.6 kJ/mol) calculated can be attributed to a significant influence of the temperature on the iron dissolution rate when iron comes as part of arsenopyrite. High reaction orders with respect to the concentration of nitric acid for iron (3.9–4.7) were observed when a sample arsenopyrite disk was dissolved. It may be attributed to a passivating film that formed on the disk surface, the presence of which is indicative of a possible transition into a state in which internal diffusion serves as a limiting stage.
Support for this research was provided by the Ministry of Science and Higher Education of the Russian Federation under the Development Programme of the Ural Federal University named after the First President of Russia B. N. Yeltsin and in line with the Strategic Academic Leadership Programme Prioritet-2030.

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