Experimental measurement of portlandite carbonation kinetics with supercritical CO2

A series of experiments was performed to observe and quantify the reactivity of portlandite with supercritical CO2. The experiments were carried out in a batch reactor under different conditions: pressure of 160 bar, temperatures of 80, 120, and 200 °C, presence or absence of liquid water. Initial reaction rates are proposed, based on two independent techniques: measurements of the advancement of reaction by X-ray diffractometry (i.e. quantification of newly formed mineral assemblage), and monitoring of volume of CO2 injected into the batch reactor to compensate for pressure drop during the experiment (CO2 consumption, exsolution of secondary H2O).The scanning electron microscopy observations show two different behaviours: in the presence of liquid water, the reaction leads to the complete carbonation of the portlandite into calcite. On the other hand, in the absence of a liquid phase, partial carbonation leads to the passivation of the portlandite surface by precipitation of a coating of tiny calcite crystals, and an incomplete weathering reaction of the portlandite.