Thermogravimetric analysis–mass spectrometry (TGA–MS) of hydromagnesite from Dujiali Lake in Tibet, China

• Published in: Journal of thermal analysis and calorimetry 2018-09, Vol.133 (3), p.1429-1437
• Main Authors: Lin, Yongjie, Zheng, Mianping, Ye, Chuanyong, Power, Ian M.
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Basic magnesium carbonate; Carbon dioxide; Carbonates; Chemistry; Chemistry and Materials Science; Crystal structure; Crystallization; Decarbonation; Decomposition; Endothermic reactions; Fourier transforms; Heating rate; Helium; Hydrogen; Hydrogen bonds; Infrared spectroscopy; Inorganic Chemistry; Magnesite; Magnesium carbonate; Magnesium compounds; Mass spectrometry; Measurement Science and Instrumentation; Partial pressure; Physical Chemistry; Polymer Sciences; Scanning electron microscopy; Scientific imaging; Thermal decomposition; Thermogravimetric analysis; X-ray diffraction
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-018-7197-8

Thermogravimetric analysis–mass spectrometry, in situ X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize hydromagnesite [Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O] from Dujiali Lake in Tibet, China. This study describes the variations in the thermal decomposition mechanisms of hydromagnesite at varying heating rates and under either helium (He) or carbon dioxide (CO 2 ) atmospheres. In a He atmosphere, only two decomposition stages were observed; the loss of the crystalline water followed by the combined dehydroxylation and decarbonation. However, under a CO 2 atmosphere, the dehydroxylation and decarbonation occur separately as the inert CO 2 gas prevents the decomposition of the MgCO 3 component of hydromagnesite. Overall, the thermal decomposition is an endothermic process. A distinctly exothermic process occurs at about 540 °C under conditions of high partial pressure of CO 2 or high heating rate and implies the crystallization of magnesite (MgCO 3 ). We propose that the release of H 2 O and CO 2 at different stages likely results from the complicated hydrogen bonds and different carbonate groups in the crystal structure of hydromagnesite.