Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Evening Poster

S (Solid Earth Sciences) » S-MP Mineralogy & Petrology

[S-MP38] Physics and Chemistry of Minerals

Thu. May 24, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Hiroaki Ohfuji(Geodynamics Research Center, Ehime University), Seiji Kamada(Frontier Research Institute for Interdisciplinary Sciences, Tohoku University)

[SMP38-P02] Structure changes of hydromagnesite Mg5(CO3)4(OH)2・4H2O with temperature and pressure

*Gen-ichiro Yamamoto1, Atsushi Kyono1, Tomoya Tamura1, Sota Takagi1 (1.University of Tsukuba)

Keywords:CO2 geological storage, hydromagnesite Mg5(CO3)4(OH)2・4H2O, structure change, high-temperature XRD, high-pressure XRD

The global warming has become one of the most important environment problems in recent years. Geological storage of CO2 has great potential to eliminate atmospheric CO2 emitted by fossil fuel combustion (XUE and Nakao 2008). Regarding mineral CO2 sequestration, CO2 is chemically stored through mineral carbonation in solid carbonates. Magnesium and/or calcium carbonate minerals such as magnesite MgCO3, dolomite CaMg(CO3)2, calcite CaCO3, and aragonite CaCO3 have long been recognized as the best CO2 storage. Because hydrous magnesium carbonates can be directly precipitated from aqueous solution in a range between 0 and 200 oC (Cheng et al. 2009; Yamamoto et al. 2017), we consider that hydrous magnesium carbonates would be the best candidate for the CO2 storage process. The major hydrous magnesium carbonates formed from aqueous solution are nesquehonite MgCO3·3H2O and hydromagnesite Mg5(CO3)4(OH)2·4H2O. The physical properties of these minerals are critically important factors to assess environmental safety and phase stability over geological time scale, but they have not been fully investigated yet, especially of hydromagnesite. In this study, we performed investigated the structural behaviors of hydromagnesite under high temperature and high pressure using HT-XRD, TG-DTA, HP-XRD to reveal the physical properties and structural stability of hydromagnesite.
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.