Phase transitions in the system MgO–CO2–H2O during CO2 degassing of Mg-bearing solutions

Carbonate mineral paragenesis and reaction kinetics in the system MgO–CaO–CO 2 –H 2 O in presence of chloride or nitrate ions at near surface ambient temperatures

“…Seeding also stimulates post-sparging hydromagnesite growth. Previous studies (e.g., Königsberger et al, 1999;Hopkinson et al, 2012) indicate that in all four experiments the system would have been simultaneously supersaturated with nesquehonite and…”

“…The latter mineral is interpreted to result from incongruent dissolution of nesquehonite. This further suggests that the length of the Mg5(CO3)4(OH)2·xH2O reaction pathway from nesquehonite to hydromagnesite may be a precise function of nesquehonite dissolution kinetics and/or conditions of synthesis, thereby accounting for the disparity in experimental results reported from independent investigations on the nesquehonite to hydromagnesite transition (e.g., Davies and Bubela 1973;Zhang et al, 2006;Hopkinson et al, 2008Hopkinson et al, , 2012). …”

“…XRD (Davies and Bubela, 1973) or eight and five waters of crystallization (Hopkinson et al, 2012). It is firmly established that the water content in MgCO3·xH2O phases are strongly affected by synthesis conditions, and that these phases may contain some bicarbonate (Zhang et al, 2006).…”

“…However, it is well documented that in near surface settings carbonate mineral assemblages do not conform to those predicted by equilibrium thermodynamics (e.g., Kazakov et al, 1959;Davies and Bubela 1973;Morse and Casey 1988). Instead, a variety of partially characterized temperature sensitive basic and hydrated magnesium carbonates exist, which in at least some experimental settings appear to be the product of parallel reaction pathways (e.g., Hopkinson et al, 2012). In association with these phases other studies show that the presence of magnesium in solution may suppress calcite formation, facilitate aragonite precipitation (e.g., Park et al, 2008;Hu et al, 2009) (Nishiyama et al, 2013).…”

“…The latter method is often accompanied by CO2 degassing induced by either increasing temperature and/or sonication (e.g. Hopkinson et al, 2012). Various combinations of the methods described above also exist including pH adjustments of the solutions (e.g., Ferrini et al, 2009;Ballirano et al, 2010).…”