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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 presence and formation of hydroxy-interlayered minerals in the Holocene paleosol at the Wugong profile on the southernmost Chinese Loess Plateau were investigated by examining the < 1 μm and 1–2 μm clay fractions of the 50–150 cm horizon by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Prior to the analyses free Al and Fe phases were removed by dithionite-citric-bicarbonate (DCB) extraction. XRD patterns were obtained with air-dried, Mg-saturated, Mg-saturated with glycerol solvation (Mg-glycerol) and K-saturated and heated at 110, 250, 350, 450 and 550 °C samples both before and after hydroxy-interlayered materials removal by sodium citrate extraction. The absorption bands at 3699 and 3430 cm − 1 in the FTIR spectra of both sub-fractions indicated the presence of hydroxy-interlayered minerals. The K-saturated and heated XRD patterns confirmed this by the progressive collapse of the 1.4 nm reflection to a 1.0 nm reflection. After removal of the hydroxy-interlayered materials no obvious increase of the relative XRD intensity of the 1.8 nm reflection in Mg-glycerol pattern was observed and the 1.4 nm reflection exhibited a stronger collapse to 1.0 nm after K-saturation and increasing temperature treatment. This indicated that the hydroxy-interlayered minerals in the Holocene paleosol were mainly composed of hydroxyl-interlayer vermiculite. The hydroxyl-interlayer vermiculite was formed by the polymerization of Al/Fe-hydroxy materials within the interlayer space of vermiculite. Shoulder-like reflection at 1.2 nm in the K-550 °C pattern of the 1–2 μm fraction indicated a higher degree of Al/Fe-hydroxylation in the coarse fraction than in the fine fraction, which was consistent with the lower extractable Al and Fe in the coarse fraction. The reflection at 1.38 nm in the K-550 °C pattern could be interpreted as pedogenic chlorite. Thus, transformation of vermiculite into hydroxy-interlayered vermiculite and finally into a chlorite-like mineral (pedogenic chlorite) has occurred in the Holocene paleosol on the southernmost Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]