Thermogravimetric analysis of selected coal-bearing strata kaolinite

Two kinds of coal-bearing kaolinite from China were analysed by X-ray diffraction (XRD), Thermogravimetric analysis–mass spectrometry (TG–MS), infrared emission spectroscopy. Thermal decomposition occurs in a series of steps attributed to (a) desorption of water at 68 °C for Datong coal-bearing strata kaolinite and 56 °C for Xiaoxian with mass losses of 0.36% and 0.51%, (b) decarbonization at 456 °C for Datong coal-bearing strata kaolinite and 431 °C for Xiaoxian kaolinite, (c) dehydroxylation takes place in two steps at 589 and 633 °C for Datong coal-bearing strata kaolinite and at 507 and 579 °C for Xiaoxian kaolinite. This mineral was further characterised by infrared emission spectroscopy (IES). Well-defined hydroxyl stretching bands at around 3695, 3679, 3652 and 3625 cm−1 are observed. At 650 °C all intensity in these bands is lost in harmony with the thermal analysis results. Characteristic functional groups from coal are observed at 1918, 1724 and 1459 cm−1. The intensity of these bands decrease by thermal treatment and is lost by 700 °C.