Kinetics of enhanced magnesium carbonate formation for CO2 storage via mineralization at 200 °C

Abstract

The precipitation of carbonate minerals through chemical reaction between injected CO2 and reactive basaltic rocks can enable a long-term carbon storage solution (carbon mineralization). Magnesite is one of the most stable carbonate precipitates that can contribute to addressing the challenge of long-term carbon storage, and the chemical mechanism that can catalyze its formation is of great interest and practical significance. Here, using batch reactor experiments at 200 ºC and mineralogical characterization, we explore magnesite precipitation kinetics in injected fluids whereby the chemical impact of fluid pH, NaCl, and MgO nanoparticles is investigated. The results show that an alkaline or a saline environment significantly accelerates magnesite formation by enhanced phase transition of hydrated metastable magnesium carbonate to magnesite. Raised CO32− activity in an alkaline environment may promote the transformation of hydromagnesite to magnesite. Competition for hydration water between background ions and magnesite building ions in the presence of NaCl can promote Mg dehydration and magnesite mineralization. Although MgO hydrophilic surfaces may retard magnesite formation at the early stage of the reaction, an alkaline pH environment can subsequently accelerate magnesite growth by enhanced replacement of hydromagnesite. This research provides new insights into the mechanism and kinetics of magnesite precipitation at mineral-fluid interfaces in a range of conditions, and can facilitate the deployment of carbon storage technologies and support defining strategies to accelerate underground CO2 mineralization in deep basalt reservoirs.