Role of Elemental Sulphur in Stage B Self-Heating of Sulphide Minerals, and the Potential Role of Polysulphides

Abstract

Sulphide minerals undergo numerous stages of mineral processing to extract the desired metal. When they are exposed to certain environmental conditions, some sulphide minerals can spontaneously heat up, a process called self-heating (SH), which, if left unchecked, can be a major hazard. Self-heating occurs in three distinct temperature stages, termed Stage A (temperature below 100 °C), Stage B (temperature range of 100 °C–350 °C), and Stage C (above 350 °C). Historically, it was understood that elemental sulphur generated in Stage A fuels Stage B reactions; however, the full extent of this behaviour is still unknown. The aim of this study is to understand the role of elemental sulphur in Stage B reactions. The results have demonstrated that elemental sulphur is incapable of fueling Stage B self-heating on its own, and it needs to interact with sulphide minerals in ambient temperatures in the presence of moisture and air. This interaction seems to be unique to pyrrhotite, as it failed to demonstrate stage B self-heating with other sulphide minerals. Previous works in surface chemistry suggest that this interaction leads to the formation of polysulphides.