New Classification of Inorganic Matter in Coal Using ~(27)AI MQMAS NMR at High Magnetic Field (16.4 T)

摘要

Structural analysis of inorganic matter in coal is very important, from the viewpoint of both geology and coal utilization. However, it is often difficult to assign the inorganic matter from conventional techniques such as XRD, because some inorganic matter, i.e. clay mineral, in coal has low crystallinity. On the other hand, solid-state NMR techniques are well suited for the analysis of noncrystalline solids such as inorganic matter in coal. Several kinds of minerals were estimated from the percentage of tetrahedral Al species that was determined by ~(270AI MAS NMR. However, because the ~(27)AI MAS method can't average out the second-order quadrupolar interaction, detailed chemical structures of inorganic matter in coal are hardly obtained. In this study, we successfully developed the method for characterization of four minerals (kaolin, montmorillonite, muscovite, and alumina) in coal by virtue of the combination of a high magnetic field (16.4 T) and a MQMAS (Multiple Quantum Magic Angle Spinning) technique that is capable of canceling the second-order quadrupolar broadening. As a result of structural analysis of Al-containing inorganic matter in 26 natural coal samples, 6 groups could be classified according to types of minerals.