Abstract
High-resolution 27Al and 29Si NMR were employed to characterize layered silicates in the suite of eight Argonne Premium coals. Analyses were performed on native coals directly, or fractions isolated by sink−float techniques. Mineral phases of kaolinite, quartz, and illite−montmorillinite clays could readily be distinguished nonquantitatively by 29Si NMR techniques using direct detection or cross polarization. 27Al NMR was used to determine quantitatively the amounts of tetrahedral and octahedral aluminum forms present. The 27Al NMR results were consistent with mineralogical analyses by XRD, showing that increases in tetrahedral content paralleled illitization of the clay minerals. A remarkably good relationship also was found between the total amount of tetrahedral aluminum associated with the mineral matter and degree of maturation of the organic matter in the coal. The data suggest that illitization of the clays can be used as a mineralogical thermal maturity indicator for Type II kerogens, as demonstra...
Published Version
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