Pyrite Occurrences in Telkwa and Quinsam Coal Seams

Sulphur in coil1 is il major environmental concern. The use of coal for combustion requires the control of sulphur dioxide emissions. To reduce these emissions, the total solphur content in c~ial product ~must he decreased. This can he accomplished by using low-sulphur coal. cleaning coal prior to combustion. retaining sulphw during wmhustion. or hy treatment of tlur gases after combustion. The use of low-sulphur coal is I?mitcd to the areas where such coals are available, and retaining the sulphur during combustion is a process in the expel-imcntal stage. The remaining alternatives are to clean co;11 before combustion or reduce sulphur dioxide emissions by blur gas desulphu~i/ation. Physical cleaning before combustion, however. is still the nmost economical option. Sulphur is found in coal in both inorganic and organic forms. The inorgamc sulphur occurs: as iron disulphide, either pyrite (cubic) or marcasite (ortborhomhic): as a sulphatr, chiefly gypsum and iron sulphate: and iis clcmental sulphur. Elemental ,sulphur and sulphlrte ire usually found in very small concentrations. generally lest than 0.2 per cent and 0.1 per cent, rcspcctively (Greer. IY7Y). The organic sulphur is hound to the coal structure. Pyritic and organic sulphur, however. account for most of the sulphur in will. Conventional cleaning is not adeqwte for the removal of organic sulphur, and chemical cleaning would he more appropriate. Pyritic :rulphur is the only sulphur form which can hc removed hy physical methods. Therefore attention is usually focused on the forms of pyrite. For physical sulphur wnoval to hc successful it is necessxy to understand the nilt~re and OCCUITC~~~S of pyrite in the coal. The sulphur contents of most British Columbia coals are considered to he low (<I%). The two major coalfields. the Northeast and Southeast. product coids with sulphur contents in the range 0.30 to 0.60 per cent. Coals from the Telkwa, Bouron River and Comox coalfields. have, <,n average, sulphur v;~lues greater than I per cent. and are exceptions. British Columbia low-sulphur coal seams contain prrdominantly organic sulphur, Table 5-L35lfa) shows the distrihution of sulphur forms in low-sulphur seams. Total sulphur mnpes from II.23 to 0.69 per cent and the organic sulphur comprises from 55.4 to 96.5 per cent of the total. A decrease in the proportion of organic sulphur is usually accompanied hy an increase in pyritic sulphur. Organic sulphur is assumed to he part of the organic coal structure. and it is convenient to express it on a dry ash-free basis, to emphasize this aswziation. Coals from the Comox, Telkwa and Bowron River coulfields generally average between 0.5 and I .6 per cent sulphur. Compared with sub-bituminous c nls, ther na coals from these are;,s arc relatively high rank (higher k:al.’ kg), and therefore the elevetcd sulphur co! tent in ~;tcsc: seams will have much less effect on the po1 sihle sulphtu dioxide emissions. In coals with higher sulphur content an im rease of t:Gil sulphur content is mainly due to an incrr: se in p:y.iti<. sulphur (,WP pan h of Table :i-Ii-l). The xoporticn o‘ organic sulphur decreases drastically and ma! hc as low a!. 4.5 per cent of the total sulphur in some case. The orgxnir: sulphur content. as calculated on a dry a ,h-free besis, however, appears to he much higher then th’: organic WI.. phur in the low-sulphur co& For Telkwa s :ams, org;mi(: sulphur is as much as I.81 per cent of organ c matter. I;o’ Quinsam No. 2 seam and No. I -Rider seam t ranges f:um 0.80 to 0.87 per cent. whrr:as, for Iuw-s rlphur ccids. organic sulphur on a dry ash-free hasis averrges 0.56 pe’cent. The objective of this study is 1:” investigate pyrite oc~:w races in Telkwa and Quinsam coals. as thse coalii<:ld:; produce higher sulphur coal. Pyrite occuv :nces will he discussed in terms of six and association vith maceral; (microlithotypes) with a view to assessing :heir poxihlc influence on the cleaning processes.