Mechanism of nonoxidizing and oxidative pyrrhotite leaching

Pyrrhotite is one of the main components of sulfide ores. As a result, its behavior has a significant influence on the course of metallurgical processes and on the extraction of nonferrous metals. There is no definitive description of the mechanism of the chemical reactions that occur during nonstoichiometric iron sulfide dissolution. In some studies on pyrrhotite dissolution, pyrite formation is assumed; in others, elemental sulfur is assumed to form. The aim of this study is to clarify the mechanism of the chemical reactions of pyrrhotite dissolution in nonoxidizing acids during oxidative bacterial leaching. In this work, different methods of analysis have been used: scanning electron microscopy, micro X-ray spectral, X-ray diffraction, Mossbauer and IR-spectroscopy analysis. It has been established that acid pyrrhotite dissolution in nonoxidative conditions proceeds in stages, beginning with low-sulfur pyrrhotite dissolution. This occurs with the transition of iron ions to solution and to hydrogen sulfide, with the simultaneous formation of sulfur-rich iron sulfide in the residue from the leaching. Pyrrhotite oxidative bacterial leaching proceeds in two stages. In the first stage, the pyrrhotites are enriched with iron and then, in the second stage, the low-sulfur sulfides dissolve with the formation of iron sulfate (Fe2+). This study proposes a mechanism for sulfide oxidative bacterial leaching that can predict the parameters and the results of the process. Minerals & Metallurgical Processing, 2012, Vol. 29, No. 3, pp. 159-164. An official publication of the Society for Mining, Metallurgy, and Exploration, Inc.