CO2 capture properties of Li4SiO4 after aging in air at room temperature

Abstract

In this study, we evaluated the physicochemical stability of lithium orthosilicate (Li4SiO4) powders after aging in air. Thermogravimetric (TG) analysis in CO2 flow evidences that as-milled Li4SiO4 stored in a closed plastic container in air at Room Temperature (RT) suffers a time progressive CO2 absorption. This carbonation is clearly noticed in the samples with greater specific surface area and depends on two factors: the time of air exposure and the renewal of the air atmosphere in the plastic container, both of them modifying the CO2 capture capacity and kinetics of the material. Specific experiments to analyze the effect of water vapor and carbon dioxide atmospheres on the CO2 capture properties of Li4SiO4 were designed. TG, X-ray diffraction and spectroscopic studies demonstrate that the reaction between as-milled Li4SiO4 and CO2 present in air was promoted by exposure to humidity. In fact, LiOH and LiOH.H2O were formed at the surface of Li4SiO4 during water vapor exposure. These phases enhance the reaction with CO2 from the air to form Li2CO3 at RT before the first carbonation cycle. As a consequence, the CO2 capture capacity of Li4SiO4 in the first carbonation cycle was smaller than the one of Li4SiO4 without water vapor exposure. In opposition, negligible CO2 absorption occurred at RT under CO2 atmosphere. The original properties of Li4SiO4 powders with high specific surface area could be regenerated by heating at 700 °C. Consequently, the storage conditions of Li4SiO4 powders should be considered for their use in different applications.