Effect of NaHCO₃ on the Magnesite Yield in Direct Aqueous Carbonation of Thermally-Activated Lizardite

The major aim of this research was to understand the effect of the addition of sodium bicarbonate (NaHCO₃) on the reaction yield and products in the direct aqueous mineral carbonation of heat-activated lizardite under single-step reaction conditions (130 bar, 150 °C) developed by the Albany Research Center. This was achieved by tracking the evolution of the aqueous and solid species produced over the duration of the reaction. Analysis of solid and liquid samples was performed using a variety of analytical techniques, including thermal gravimetric analysis mass spectrometry, inductively coupled plasma optical emission spectrometry, qualitative and semiquantitative X-ray diffraction analysis, and laser diffraction particle size analysis. Carbonation experiments were conducted with and without NaHCO₃ using heat-activated lizardite to study its effect on the reaction rate and overall yield. It was found that NaHCO₃ controlled the magnesium carbonate phase formed in the carbonation reaction [hydromagnesite or magnesite (MgCO₃)]. It can be concluded that NaHCO₃ elevates the concentration of carbonate ions (CO₃^2–), leading to a heightened level of supersaturation in the carbonate phase. This, in turn, contributes to an increased extent of MgCO₃ precipitation.