Recycling CO2 from flue gas for CaCO3 nanoparticles production as cement filler: A Life Cycle Assessment

Abstract

CaCO3 nanoparticles as filler have received considerable attention for the mechanical improvement that they provide to cements. However, their life-cycle impact on the environment remains almost unexplored, even if the cement industry is considered one of the largest CO2 emitters. In this perspective, this research work assessed a novel method for using CO2 from cement flue gases to produce nanoCaCO3 as cement filler within the cradle to cradle thinking. For this purpose, two routes of CO2 capture were assessed followed by the study of the synthesis of CaCO3 through a mineral carbonation. Three scenarios for the synthesis of CaCO3 nanoparticles were assessed targeting the use of waste or by-products as raw materials and recirculation of them to reduce any kind of emission. The three scenarios were evaluated by means of the Life Cycle Assessment methodology. Once the best considered route for nanoCaCO3 production was determined, this research work examined the environmental effect of including 2 wt% of CaCO3 nanoparticles into the cement. Closing the loop follows a circular economy approach since the CO2 is captured within the same cement factory. The results were compared with conventional Portland cement. Regarding nanoCaCO3 results, the scenario with simultaneous production of NH4Cl, and using as calcium source CaCl2 deriving from the soda ash Solvay process, proved to be the best option. Moreover, when cement was filled with 2 wt% of this nanoCaCO3, the benefit in terms of emission reductions in the Climate Change category was higher than 60 % compared to the conventional Portland cement.