The water associated with a previously air-dried Yallourn brown coal has been studied using nuclear magnetic resonance pulse methods.
The intensity and the spin-spin relaxation of the magnetic resonance of the water protons of specimens containing a range of water contents were measured during temperature cycles between 300 and 220 K. The results show that in specimens containing up to about 26 kg water/100 kg dry coal all the water interacts with the coal. Water in excessof this freezes near 273 K indicating that it does not interact with the coal. There is no evidence to suggest that the water which interacts with the coal can be divided into physically discrete classes. Rather, the data are consistent with this water occupying a continuous distribution of states and comprising an interacting phase of molecules, the average properties of which vary with changes in water content.
The large quantities of water associated with brown coal deposits reduce the value of the coal as a fuel and are also relevant to its consolidation'.
The nature of the association of water with the coal and its importance in the development of methods of dewatering the coal have been the subject of several studies by Evans and co-workers1-4. Using gravimetric sorption techniques the)-estimated the proportions of the water contained as free water and that which interacts with the coal. They concluded that the interacting water consisted of water initially sorbed by interaction with specific sites -identified as polar residuesand water of capillary condensation sorbed at high watervapour pressures. The roles of the specific polar groups were quantitatively assessed in a study by Schafer'. Nuclear magnetic resonance (n.m.r.) studies have given useful information on the water of association in similar system&lo, and should be useful in providing additional insight into the nature of the interaction of brown coal with water. Whereas it is expected that the most useful information would be that obtained from n.m.r. studies of brown coal in the 'as mined' condition, the initial results reported here are on specimens of a previously air-dried Yallourn brown coal which had been prepared at different levels of water content in the laboratory.
Because of oxidation and other changes, the associated water in these specimens is significantly different from that in the 'as mined' condition.
However it is a simpler material to study and was chosen to enable a general insight into the n.m.r. properties of the system to be obtained more readily. Results of studies on 'as mined' coal will be reported later.