The effect of mineral matter on the moisture-binding capacity of samples from two Australian
bituminous coal seams was investigated by gravimetric sorption and nuclear magnetic resonance
(NMR) techniques. The water uptake contributions from the mineral matter (predominantly
clay) and organic components of the coal samples were determined from precise isothermal
sorption measurements at relative pressures up to 0.9 using a Hiden intelligent gravimetric
analyzer. Also, water interacting with the coal samples, such that it is unfrozen at −3 °C during
heating, was quantified using a proton NMR technique. Water uptake (per unit mass of dry
solids) at a relative pressure of 0.9 by the mineral matter in the coal samples studied was assessed
to be 2.3−2.8 times the uptake by the organic material. Coal mineral matter containing 26 wt
% of montmorillinite, a swelling type clay, had more than twice the water uptake per unit surface
area when compared to mineral matter in which clay was present only as kaolinite. For two
coal samples from the same seam differing in both mineral-matter content and maceral
composition, the differences in water uptake at relative pressures up to 0.9 could be accounted
for completely by the mineral-matter content. This indicates that the large difference in maceral
composition between these two samples had no effect on the moisture-holding capacity. The
NMR results for the amount of water in the coal samples that was unfrozen at −3 °C support
the findings of the water sorption measurements.