Probing coals for non-pyritic sulphur using sulphur-metabolizing mesophilic and hyperthermophilic bacteria

The presence of elemental sulphur in several coals from the midwestern US (Illinois No. 6, Indiana No. 5, and an Indiana refuse coal) as well as in an Australian brown coal was probed using specific microbial activity to this sulphur speciation. The objective of this work was to differentiate elemental sulphur from the apparent organic sulphur fraction in these coals. Two hyperthermophilic archaebacteria, Pyrodictium brockii and Pyrococcus furiosus, are known to specifically reduce elemental sulphur to sulphide seawater-based media. The eubacterium, Thiobacillus thiooxidans, is known to specifically oxidize elemental sulphur to sulphate. These biological activities were examined in aqueous solutions containing the above coal samples by comparing the biotic production of sulphide or sulphate with both the reduction of total coal sulphur content and the reduction in the sulphur extractable by carbon disulphide. Only the heavily weathered, refuse coal contained significant elemental sulphur (≈ 1%), by both biological assay and sulphur assay of carbon disulphide-extractable material. The elemental sulphur content of the refuse coal appeared as organic sulphur by conventional analytical methods (i.e., ASTM method for coal sulphur speciation). The results here point to the prospect of using biological probes for elemental sulphur determination in coals, thereby making organic sulphur content determination more specific.