Recovery of sulphur from very high ash fuel and fine distributed pyritic sulphur containing coal using ferric sulphate

Studies on inorganic sulphur removal from (i) five high sulphur coals, where pyrite is highly disseminated in the organic matrix of coal and cannot be separated by a low-cost, simple and conventional-technology flotation process, from the northeastern (NE) region of India (viz., Ledo, Baragolai, Tipong, Dilli and Jeypore), (ii) two high sulphur coals from Wardha Valley coalfield of Central India (viz., Majri and Bellora), and (iii) five very high sulphur coal rejects from Taroda, Bellora, Rajur and New Majri (U/G) collieries in Wardha Valley coalfield, and recovery of sulphur in the form of ferric sulphate were carried out using aqueous ferric sulphate solution prepared from the ferric sulphate purchased from the market (for the first experiment). This was followed by three to four more similar experiments using the recovered ferric sulphate from the previous experiment. The objective was to see if the results are reproducible when the recovered, re-recovered and ferric sulphate was used for the subsequent experiments. It was found that the results were reproducible. ≥90% of the fine distributed as well as undisseminated (in organic matrix of coal) pyritic and sulphate sulphur were removed with recovery of ferric sulphate. The converted ferric sulphate from pyrite and sulphate sulphur was also recovered. It was established that the highly disseminated pyrite in coal was converted into ferric sulphate, hence removal of pyritic sulphur was achieved, which was otherwise not possible with the flotation technique, and the ferric sulphate recovered was successfully used again and again for the removal of inorganic sulphur from high sulphur coals/rejects. The process shows potential for use in utilizing very high ash and very high sulphur containing coal rejects, which otherwise cannot be used as high ash fuel in fluidized bed combustion unit, by way of recovering sulphur in the form of value-added product.