A new method for the preparation of high-purity CO 2 -absorbing Li 3 NaSiO 4 powder using lithium silicate and sodium carbonate.

The starting materials and temperature for the preparation of Li ₃ NaSiO ₄ powder, which has attracted attention as a CO ₂ absorbent, were optimized in this study. Mixtures of Li ₂ CO ₃ , Na ₂ CO ₃ , and SiO ₂ as well as Li ₄ SiO ₄ , Li ₂ SiO ₃ , and Na ₂ CO ₃ were subjected to thermogravimetry-differential thermal analysis (TG-DTA) to elucidate their reaction mechanisms. The phase, morphology, specific surface area, and CO ₂ 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), N ₂ adsorption isotherm and isothermal TG-DTA. Melted LiNaCO ₃ was generated via the heat treatment of the Li ₂ CO ₃ , Na ₂ CO ₃ , and SiO ₂ powder mixture, yielding a low-purity bulk specimen with inhomogeneous particle size. However, the use of the Li ₄ SiO ₄ , Li ₂ SiO ₃ , and Na ₂ CO ₃ mixture as a starting material ensured that no liquid phase was generated during heat treatment and successfully yielded Li ₃ NaSiO ₄ powder which was purer than the product derived from the Li ₂ CO ₃ /Na ₂ CO ₃ /SiO ₂ mixture, presumably because of the lower volatility of Li and Na in the solid phase than that in the liquid phase of LiNaCO ₃ . The Li ₃ NaSiO ₄ powder derived from Li ₄ SiO ₄ , Li ₂ SiO ₃ , and Na ₂ CO ₃ showed a slightly larger surface area with homogeneous particle size and almost identical CO ₂ absorption kinetics compared to those of the product obtained from Li ₂ CO ₃ , Na ₂ CO ₃ , and SiO ₂ , in addition to absorbing a higher amount of CO ₂ owing to its higher purity.