Lignite–water interactions studied by phase transition—differential scanning calorimetry

Differential Scanning Calorimetry measurements have been made over the temperature range 20 to −50 °C with a cooling rate of 5 °C/min for six raw Victorian lignites, and for some of these lignites after water washing or acid washing. Two small peaks were observed in the region −28 to −36 °C, as found by earlier workers, in addition to a major peak at −5±3 °C which was assigned to the freezing of free water. Solutions of sodium chloride showed a single peak at about −42 °C as well as the main water peak at approximately −20 °C. However, water or acid washing the lignites to remove cations gave samples which retained the small peaks in this region with little change in intensity so that an association between the small peaks and cations or dissolved salts is unlikely. Dry samples of the coals showed no peaks, confirming that these small peaks are associated with coal–water interactions and not with the coal structure or the presence of cations.