Preparation of Li4SiO4-based adsorbents with coal slag for high temperature cyclic CO2 capture

Abstract SiO32- was separated from coal slag (CS), one of the largest annual solid waste emissions, by an alkali extraction method and converted into SiO2 by the reaction with HAc. The prepared SiO2 was mixed with LiAc by an immersion method and calcinated to form Li4SiO4 adsorbents (LAS). The LAS prepared exhibited the close saturated CO2 adsorption capacity of 367 mg/g at 650 °C in 1 h. The influences of calcination temperature, calcination time, and heating rate on the CO2 adsorption capacity of the LAS were systemically investigated and the preparation conditions were optimized. To improve the cyclic stability of the LAS, 10 wt% activated CS (ACS) was doped into LAS. The ACS doping significantly improves the cyclic stability of LAS with the CO2 adsorption capacity 76.43 % higher than that without doping in 20 cycles. Further investigation suggests that the Si in ACS can react with Li2CO3 to form Li4SiO4 and Li2SiO3, which promotes the transformation of Li+ and CO2. In all, our work has provided a new approach to the preparation of Li4SiO4-based adsorbents from CS waste.