Bioinspired controllable CaCO₃ synthesis from solid waste by an "all in one" amino acid-in strategy: Implication for CO₂ mineralization

CO2 mineralization suffers from extensive consumption of acidic/alkaline reagents due to the limited kinetics, which necessitates the development of an atom/energy-efficient process. An "all in one" reagent amino acid-based Ca2+ leaching-CO2 mineralization process inspired by biomineralization was proposed. This study explored the interactions between amino acids and Ca leaching, CaCO3 pre-nucleation, nucleation, and growth by investigating the evolution of Ca concentration, solution turbidity and CaCO3 morphology in complex CFA. Promising Ca2+ leaching efficiencies were observed, being 51.1 %, 34.2 %, and 21.0 % for glycine (Gly), L-alanine (Ala), and L-arginine (Arg), respectively, negatively correlated with their pI but positively correlated with their bonding energy with Ca2+. These amino acids ultimately led to a CaCO3 production of Gly (114.8 g/kg) > Ala (78.2 g/kg) > Arg (54.5 g/kg) from CFA. Gly leachate remained transparent (1.23 NTU) in the first 3 min of CO2 bubbling even though the solution was supersaturated and then got turbid suddenly (6508.75 NTU in 10 min) as continued CO2 bubbling, indicating the inhibition of Gly on CaCO3 nucleation. Observations using Cryo-SEM confirm the presence of abundant CaCO3 nanoparticles in the early stages of mineralization, which later assemble into vaterite crystal particles with a sub-structure and coalesce into larger particles in Gly and Ala. Meanwhile, Arg inhibited calcite growth along the C-axis, leading to the formation of thin, blocky-like particles. Furthermore, 0.010 similar to 0.027 mmol/g amino acids are occluded into the CaCO3, stabilizing the metastable vaterites and imparting thermal stability, which was believed to be associated with this multistep pathway involving a transient prenucleation cluster, nanoparticle precursor formation, and particle-particle coalescence.