Sulphur release from pyrites in relation to coal pyrolysis

Abstract

In a study of the fixation of coal sulphur in the coke-char formed during heat treatment, the role of the mineral/inorganic sulphur and the influence of subsequent high temperature treatment on the release of the sulphur were examined with carbon/ferrous sulphide systems prepared by mixing pyrites with organic materials prior to carbonization and by heating mixtures of pyrites and graphitic and non-graphitic carbons. These carbon/ferrous sulphide systems and a series of commercial cokes were heated up to 2000 °C and the residues were analysed for total sulphur and sulphide sulphur. The carbonization of organics mixed with pyrites gave carbon residues with 3–5 wt% sulphur and in the non-graphitic poly(vinylidene chloride) carbon some 40% of this was present in organic form. The sulphur was progressively released by heat treatment above 1000 °C until at 1800 °C there was less than 0.1 wt% in the residual carbon. Heating non-graphic carbons with pyrites again led to the fixation of some organic sulphur in the carbon and such materials tended to retain their sulphur to higher temperatures than the carbon/ferrous sulphide systems based on graphitic carbons. It is concluded that the presence of carbon facilitates the thermal decomposition of ferrous sulphide. The fixation of sulphur by the carbon is, however, to some extent dependent on the nature of the carbon. Such ‘organic’ sulphur is more resistant to high temperature decomposition than the inorganic/mineral sulphur.