Changes of pyrite and pyrrhotite in coal upon microwave treatment

Abstract

More stringent environmental regulations and the demand for higher quality final products require optimum sulphur removal from sulphur-containing ores. Microwave treatment is an emerging technique in minerals processing and may be used to reduce sulphur-containing minerals. In the present study two coal samples containing low and high amounts of sulphur, respectively, were subjected to microwave and caustic soda treatment with a view to desulphurization. In order to assess the microwave treatment, the same procedures were applied to a pyrite/pyrrhotite rock obtained from a coal mine. XRD and Mössbauer analyses were performed, before and after treatment in order to determine changes brought about in the structure and bonding. Following the treatment, both the low and high-sulphur coal samples showed a decrease in sulphur content of ≈ 40%, whilst the XRD and Mössbauer analyses did not detect the formation of new minerals or changes in structure. In the case of the pyrite / pyrrhotite rock sample the Mössbauer investigations showed the presence of pyrite (26%) and pyrrhotite (74%) After treatment the concentrations changed to 8% and 92% respectively, indicating a change in sulphur mineral composition during treatment, but no structural changes.