THE CHEMICAL-STRUCTURE OF SECONDARY SULFUR IN ASSAM COAL

The nature of secondary sulfur in high sulfur Assam coal was investigated by thermal treatment in air at 180-degrees-C. Two types of sulfur: one oxidized sulfur, soluble in warm dilute HCI and the other reduced sulfur which is oxidized and soluble in warm dilute HNO3 were considered for the coal and the samples collected at 100, 200, 300 and 350 h. The increase of oxidized sulfur at the expense of reduced sulfur should give a decreased amount of the latter in the 100 hour sample, but instead its content increases. This reveals that an unknown form of reduced sulfur, in addition to pyrite, must be present in the coal which was released during thermal treatment. This type of sulfur is considered as secondary sulfur having Fe-S moieties associated with the coal organic matter. Infrared study further lends support for the existence of such moieties in the coal sample. The author presumes that the formation of iron disulfide may be possible from the breakdown of the secondary sulfur, i.e. Fe-S, moieties during later developments of the coalification process.