Distribution of Inorganic Constituents in the Coals from Panian Coalfield, Semirara Island, Philippines
Stella Marris Limos-Martinez1, Koichiro Watanabe1
1Dept. of Earth Resources Engineering, Graduate School of Engineering, Kyushu University,
6-10-1 Hakozaki, Higashi-ku 8128581, Fukuoka, Japan
Abstract
Panian coalfield of Semirara Island is the largest producing coal mine in the Philippines that accounted for 93% of the local coal production in 2004. The coals of Panian coalfield are characterized by low contents of sulfur and ash that are relatively enriched in Na, Ca, Mg, and Fe and relatively depleted in silica and alumina content. Geostatistical analyses revealed strongly negative correlation between Na, Ca, and Mg against ash yield, indicating organic affinity, while Fe indicated intermediate to strongly negative correlation with the ash yield. Calculated slagging and fouling indices indicate that the Panian seams have medium to high tendency for slagging and a severe propensity for fouling.
Sequential leaching of composite samples from seams 22, 32/33 and 42 showed that a considerable fraction of Ca and Mg are present as exchangeable ions organically bound to the carboxylates. About 90% of Na in the shallower seam 22 and 30% Na in seam 32/33 and 42 occur as ions dissolved in the coal’s pore waters. The remaining 70% Na in seams 32/33 and 42 is ion-exchangeable and organically bound to the carboxylates and similar functional groups in the coals. In all samples, Fe occurs in the acid-soluble form, indicating its presence as chelates, carbonates and other acid-soluble compounds. Considering that the larger proportion of major inorganic elements comprising the Panian coal seams are closely associated with the organic fraction, beneficiation of the coals by ordinary washing and mechanical separation may not be economically feasible. Other than the more expensive chemical treatment or combustion of these coals using more technologically advanced methods, blending of the Panian coals with coal feedstocks containing less amounts of alkali elements may be the most efficient way to undermine the slagging and fouling tendencies of this coal feedstock. |