Geochemistry of coals in Panian Coalfield, Semirara Island, Philippines

Panian coalfield of Semirara Island is the largest producing coal mine in the Philippines and accounts for 93% of the annual domestic coal production. The coals from Panian have consistently shown a high tendency for slagging and fouling despite the relatively low average ash content, and it is the aim of this study to understand why. Thirty one representative samples of seams 22, 32/33 and 42 were analyzed to characterize the geochemistry of the coal seams in Panian coalfield. Proximate analyses and vitrinite reflectance measurements designate the rank of the seams as lignite to sub-bituminous, based on the ASTM coal classification. H/C versus O/C ratios indicate that the seams are made up largely of huminite, denoting early stages of coalification of woody plants. Chemical analysis of the ash reveals high contents of Na, Mg, Fe, Ca, Ba and Sr which show strongly negative correlation with ash yield, denoting organic affinity for the major elements of the seam. Na has shown a tendency to increase its concentration with depth while Mg, Fe, Ca and Sr are observed to diminish. The determined amounts of potentially hazardous trace elements As, Pb, Cr, Cu, Ni, V, Zn, Cl, Ba, Mn, Sr and Th in the seams are within acceptable levels when compared with world-Traded coals. Owing to the enrichment in alkali and alkali-earth elements, slagging and fouling indices indicate that the seam has medium to high propensity for slagging and a severe tendency for fouling. The detrimental characteristics of coal feedstock from Panian mine is mitigated by blending with coals imported from Indonesia, China and Australia.