Characterization of the Inorganic Constituents in Coal

Anticipating the environmental effects of utilization or disposal of coal combustion and conversion by-products requires proper characterization of the inorganic constituents in coal. Inorganic constituents include minerals as well as the organically associated inorganic elements. Characterization of these constituents should not be limited to the types and abundances of the minerals and elements, but should also include their modes of occurrence (Table I and Figures 1–4). Information on modes of occurrence should include the textural relationships of the minerals and the chemical form of the elements (i.e. organic/inorganic associations). This will enable us to predict better how the inorganic constituents will behave upon cleaning, combustion, conversion, or leaching of the coal. For example, chalocophile elements (As, Bi, Cd, Cu, Hg, Pb, Se, Sb, Tl, Zn) associated with secondary cleat (vertical breaks in the coal) or with vein filling sulfides will likely be removed during coal cleaning. In contrast, these elements, when associated with dispersed accessory sulfides and selenides [sphalerite (ZnS), clausthalite (PbSe), chalcopyrite (CuFeS2), galena (PbS)] are commonly concentrated in the cleaned coal. Calcium present in coal as a carbonate would respond to technological processes in a different way than calcium present in organic association or as calcium sulfate, phosphate or silicate.