[SMP38-P02] Structure changes of hydromagnesite Mg5(CO3)4(OH)2・4H2O with temperature and pressure
Keywords:CO2 geological storage, hydromagnesite Mg5(CO3)4(OH)2・4H2O, structure change, high-temperature XRD, high-pressure XRD
The results of in-situ high-temperature XRD showed that, no significant change was observed up to 170 oC. With increasing temperature, however, the intensities started to decrease at 200 oC, and all peaks disappeared at 290 oC. Above the decomposition temperature a few peaks corresponding to periclase appeared. The results of TG-DTA clearly showed two weight loss steps in the temperature range from 200 to 340 oC and from 340 to 500 oC, which correspond to the dehydration and decarbonation of hydromagnesite, respectively. Therefore, hydromagnesite decomposes into periclase, carbon dioxide, and water as following reaction: Mg5(CO3)4(OH)2・4H2O → 5MgO + 4CO2 + 5H2O. No magnesite is formed from hydromagnesite with temperature. The results of in-situ high-pressure XRD showed that the intensities gradually decreased with compression, and then most of peaks disappeared above 6.4 GPa. After decompessing to 4.2 GPa, however, the hydromagnsite reappeared. It suggests that no dehydration occurs below at least 6.4 GPa. The amorphousization of hydromagnesite with compression would be caused by disordered arrangements of MgO6 octahedra and CO3 triangles in the structure.