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Lithium (Li)-bearing clays have become new types of Li resources, and it is found that the evolution of the mineral structure in Li-bearing clay greatly restricts the extraction of Li. Herein, a Li-bearing clay from Guizhou Province, China, was studied using in situ thermogravimetry–differential scanning calorimetry–mass spectrometry–Fourier transform infrared spectroscopy (TG–DSC–MS–FTIR) (evolved gases), 27Al and 1H magic-angle spinning nuclear magnetic resonance (MAS NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results showed that the Li-bearing clay contained illite, chlorite, kaolinite, pyrite, and anatase. The dehydroxylation reaction of the clay minerals occurred at 450 °C. CH2, CH4, C3H4, C6H5, and C8H9 evolved during the roasting process. The AlO4(OH)2 octahedra transformed to AlO4 tetrahedra due to the reaction between the reductive gases and the residual O in AlO5. The effect of dehydroxylation on the structural stability of different clay minerals differed. After dehydroxylation, kaolinite became amorphous, chlorite reacted with 20% H2SO4, and illite remained stable during the roasting-H2SO4 leaching process. The Li-leaching efficiency increased significantly after dehydroxylation and decreased sharply with the formation of mullite. [ABSTRACT FROM AUTHOR]

The thermal characteristic behaviors of two kaolinite samples selected from Qingshuihe region in Inner Mongolia in China were studied through thermogravimetry, derivative thermogravimetry, and differential scanning calorimetry (TG–DTG–DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The activation energies of dehydroxylation for the two kaolinite samples (determined as Kaol-1 and Kaol-2) were calculated based on KAS and FWO methods. The XRD results indicated that Kaol-1 and Kaol-2 both were determined as kaolinite, and a small amount of quartz, but the Kaol-2 presented many amorphous organic matters. The TG–DSC results displayed the adsorbed water desorption and dehydroxylation with the temperature increased from 200 to 1100 °C. The dehydroxylation is followed as the intensities decrease in the bands at 3690 cm−1, 3620 cm−1 and 914.0 cm−1 attributing to the stretching mode of inner surface hydroxyls, and which disappeared when the temperature reached at 600 °C. The endothermic peak temperature of dehydroxylation for Kaol-2 presented higher than that of Kaol-1, which may be attributed to present of amorphous organic matter and was in agreement with the XRD data. The maximum endothermic temperature of dehydroxylation increased both for Kaol-1 and Kaol-2 with the increase in heating rate, which was attributed to more sufficient decomposition as the decrease in heating rate. The thermal kinetic analysis indicated that the dehydroxylation reaction of Kaol-1 should be a single kinetic mechanism, but the E of Kaol-2 decreased as α increasing from 0.2 to 0.5 and then gradually increased with the increase of α. The average E of dehydroxylation for Kaol-2 both was lower than that of Kaol-1 based on Kissenger–Akahira–Sunose and Flynn–Wall–Ozawa methods, which was attributed to the relatively higher organic carbon content in Kaol-2. [ABSTRACT FROM AUTHOR]

The thermal behavior of coal gangue selected from Zhungeer, Inner Mongolia Autonomous Region of China, was investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry (TG), derivative thermogravimetry (DTG), and scanning electron microscope (SEM). The XRD data indicated that the mineral compositions of the coal gangue were kaolinite, boehmite, and quartz. The coal-gangue sample was considered as belonging to a typical mixture of kaolinite and boehmite. The XRD and FT-IR spectra clearly showed that the structural changes and dehydroxylation of coal gangue occurred with increased temperature from 100 to 900 °C. The reaction activity of coal gangue could be effectively improved by calcination. The calcined coal gangue contained considerable active amorphous AlO and SiO and had significant loss on ignition. The optimum activation temperature range of coal gangue was from 600 to 700 °C. The dissolution contents of SiO and AlO were 92.31 and 64.44 %, respectively, when the calcination temperature at 700 °C. [ABSTRACT FROM AUTHOR]

Abstract: Thermogravimetric analysis–mass spectrometry, X-ray diffraction and scanning electron microscopy (SEM) were used to characterize eight kaolinite samples from China. The results show that the thermal decomposition occurs in three main steps (a) desorption of water below 100°C, (b) dehydration at about 225°C and (c) well defined dehydroxylation at around 450°C. It is also found that decarbonization took place at 710°C due to the decomposition of calcite impurity in kaolin. The temperature of dehydroxylation of kaolinite is found to be influenced by the degree of disorder of the kaolinite structure and the gases evolved in the decomposition process can be various because of the different amount and kinds of impurities. It is evident by the mass-spectra that the interlayer carbonate from impurity of calcite and organic carbon is released as CO2 around 225, 350 and 710°C in the kaolinite samples. [ABSTRACT FROM AUTHOR]

Abstract: 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 3625cm−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 1459cm−1. The intensity of these bands decrease by thermal treatment and is lost by 700°C. [ABSTRACT FROM AUTHOR]