Abstract
Samples of pyrite-rich brown coal from As Pontes and Meirama coalfields (Spain) were oxidized either by air at atmospheric pressure or by a cool oxygen plasma generated by radiofrequency activation. Despite the very different nature and characteristics of the oxidizing media, in both cases the RT Mössbauer spectra were easily fitted to two doublets, whose parameters matched those of pyrite and jarosite (hydrated iron (III) sulphate). The extent of pyrite oxidation to jarosite was monitored by the relative spectral areas of pyrite and jarosite doublets. Both, air and plasma, oxidized pyrite to the same extent and in a similar way, in contrast to coal organic matter, which was scarcely modified by air but completely oxidized by the plasma at the same temperature (ca. 423 K). The incomplete oxidation of pyrite by plasma is attributed to the action of a thin calcium sulphate layer which hinders the access of activated oxygen to small pyrite crystals.
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Gracia, M., Gancedo, J.R., Martínez-Alonso, A. et al. Comparative Mössbauer study of the oxidation of pyrite under different conditions. Hyperfine Interact 58, 2581–2587 (1990). https://doi.org/10.1007/BF02398380
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DOI: https://doi.org/10.1007/BF02398380