A new method for the preparation of high-purity CO₂-absorbing Li₃NaSiO₄ powder using lithium silicate and sodium carbonate

The starting materials and temperature for the preparation of Li₃NaSiO₄ powder, which has attracted attention as a CO₂ absorbent, were optimized in this study. Mixtures of Li₂CO₃, Na₂CO₃, and SiO₂ as well as Li₄SiO₄, Li₂SiO₃, and Na₂CO₃ were subjected to thermogravimetry-differential thermal analysis (TG-DTA) to elucidate their reaction mechanisms. The phase, morphology, specific surface area, and CO₂ absorption characteristics of the powder specimens that were obtained by heating the two mixtures were examined by X-ray diffraction (XRD), secondary electron microscopy (SEM), N₂ adsorption isotherm and isothermal TG-DTA. Melted LiNaCO₃ was generated via the heat treatment of the Li₂CO₃, Na₂CO₃, and SiO₂ powder mixture, yielding a low-purity bulk specimen with inhomogeneous particle size. However, the use of the Li₄SiO₄, Li₂SiO₃, and Na₂CO₃ mixture as a starting material ensured that no liquid phase was generated during heat treatment and successfully yielded Li₃NaSiO₄ powder which was purer than the product derived from the Li₂CO₃/Na₂CO₃/SiO₂ mixture, presumably because of the lower volatility of Li and Na in the solid phase than that in the liquid phase of LiNaCO₃. The Li₃NaSiO₄ powder derived from Li₄SiO₄, Li₂SiO₃, and Na₂CO₃ showed a slightly larger surface area with homogeneous particle size and almost identical CO₂ absorption kinetics compared to those of the product obtained from Li₂CO₃, Na₂CO₃, and SiO₂, in addition to absorbing a higher amount of CO₂ owing to its higher purity.