Characterization and Washability of Pyrite in High Sulphur Coals from Tabas, Iran

Environmentally and technologically sulphur is a deleterious constitute in coal which makes it unsuitable for use in metallurgical industries unless the sulphur level can be reduced to the tolerable limit. Characterization of the various forms of sulphur and their associations in coal is an essential issue to find and propose a suitable desulphurization method. In this research, to evaluate sulphur washability characteristics and its removal potential of two high sulphur mines of Tabas region namely Mehr Azin and Takht Zeitoon was investigated using sink-float, microscopical and analytical analyses. The distribution, shape and concentrations of different forms of inorganic sulphur in the coals were studied using mineralogical analyses. Sink-float analyses were carried out using zinc chloride solutions having the densities of 1.3 to 1.8 g/cm in the size fractions of the Parvardeh Coal Washing Plant i.e. -0.5 mm (flotation feed) and 0.5-25 mm (heavy media cyclone feed). The concentration and forms of sulphur were also determined using chemical methods. Results showed that a significant part of the pyrite present in both Mehr Azin and Takht Zeitoon coals were in close association with the organic structure of coal and is difficult to be separated by physical methods. However, about 40% of Mehr Azin pyrite and 30% of Takht Zeitoon pyrite were liberated at the coarse fraction which might be eliminated easily by physical methods. Mineralogical studies revealed that pyrite occurs as finely disseminated, framboidal and coarse particles in the matrix of macerals for both Mehr Azin and Takht Zeitoon coal mines.