In this work several Li4SiO4-based sorbents from fly ashes for CO2 capture at high temperatures have been developed. Three fly ash samples were collected and subjected to calcination at 950 °C in the presence of Li2CO3. Both pure Li4SiO4 and fly ash-based sorbents were characterised and tested for CO2 sorption at different temperatures between 400 and 650 °C and adding different amounts of K2CO3 (0–40 mol%). To examine the sorbents performance, multiple CO2 sorption/desorption cycles were carried out. The temperature and the presence of K2CO3 strongly affect the CO2 sorption capacity for the sorbents prepared from fly ashes. When the sorption temperature increases by up to 600 °C both the CO2 sorption capacity and the sorption rate increase significantly. Moreover when the amount of K2CO3 increases, the CO2 sorption capacity also increases. At optimal experimental conditions (600 °C and 40 mol% K2CO3), the maximum CO2 sorption capacity for the sorbent derived from fly ash was 107 mg CO2/g sorbent. The Li4SiO4-based sorbents can maintain its original capacity during 10 cycle processes and reach the plateau of maximum capture capacity in less than 15 min, while pure Li4SiO4 presents a continual upward tendency for the 15 min of the capture step and attains no equilibrium capacity.