The water hydration and subsequent calcination (denoted as hydration-calcination) technique was used to modify the microstructure of lithium orthosilicate (Li4SiO4) prepared by solid-state reactions. The original and modified Li4SiO4 sorbents were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption, scanning electron microscopy, and thermogravimetric analysis. The cyclic capacity of these sorbents was further examined using a dual fixed-bed reactor. After treatment by water hydration, most of the Li4SiO4 transformed into LiOH and Li2SiO3. Moreover, following subsequent calcination, the sample exhibited a looser structure with a smaller particle size compared with the original Li4SiO4. This favorable structure was responsible for improved CO2 chemisorption properties, as measured by a higher capacity, faster absorption kinetics, and improved stability.