VARIATION IN ELEMENTAL COMPOSITION OF MACERALS - AN EXAMPLE OF THE APPLICATION OF ELECTRON-MICROPROBE TO COAL STUDIES

Elemental composition of macerals in lignite, sub-bituminous, high-volatile bituminous, medium-volatile bituminous and anthracitic rank coals have been investigated using the electron microprobe technique. The concentration of C, 0, N, S, Fe, Si, and Al have been measured directly and hydrogen was calculated by difference. The chemical composition was compared to reflectance values and whole coal chemistry. In lignite, the sequence: ulminite (66.27% C), porigelinite (67.32% C), micrinite (67.92% C) corpocollinite (68.21% C), macrinite (70.24% C) and fusinite (73.03% C) represents a series with increasing carbon content. Sulphur concentration is the highest in porigelinite (2.95%) and the lowest in fusinite (0.21%) whereas nitrogen is the highest in corpocollinite (3.12%) and the lowest in micrinite and porigelinite. In sub-bituminous coal, the sequence of decreasing carbon content is as follows: macrinite (80.01% C), sporinite (73.00% C), semifusinite (72.76% C) and telocollinite (67.49% C). Sulphur content is the highest in telocollinite (3.29%). In high-volatile bituminous coal, carbon content is highest in fusinite (93.68%) and lowest in cutinite (82.82). Vitrinite macerals have the highest sulphur content and fusinite has the lowest. In medium-volatile bituminous coal, a sequence of decreasing carbon and increasing oxygen content: fusinite (90.02% C), semifusinite (89.73% C) and vitrinite (88.56% C) is detectable but differences in carbon and oxygen content between macerals are small. In anthracite, no statistical differences in carbon and oxygen content between vitrinite and inertinite macerals exist (about 94% C and 1% O for both macerals). Comparison of reflectance values to carbon and oxygen contents for individual macerals demonstrates that vitrinite and sporinite enter a common coalification path at 88.5% C and a reflectance of 1.25%. Semifusinite joins the path at about 89% C and a reflectance of 1.8-2.0%. More data are needed to determine the relationship between reflectance and elemental composition for other macerals.