Regenerable glycine induces selective preparation of vaterite CaCO3 by calcium leaching and CO2 mineralization from coal fly ash

Leaching-mineralization cycle (LMC) technology using amino acid as a multifunctional reagent meets the need for CO2 removal and alkaline industrial residues treatment while avoiding the heavy consumption of exogenous chemical reagents (e.g., leaching reagent, CO2 absorbent, and crystal inducer) in traditional CO2 mineralization. However, the technical feasibility in diverse conditions and underlying mechanisms of this technology are not fully explored and still lack direct evidence. The influence of key operating factors, including leaching time, glycine concentration, and coal fly ash (CFA) dosage on Ca leaching efficiency, mineralization efficiency, Ca utilization efficiency, and CaCO3 yield, were systemically investigated to obtain an optimal process performance. Results showed that the optimal CaCO3 yield of 98.8 g/kg-CFA, leaching efficiency of 38.7%, and mineralization efficiency of 74.4% were obtained at conditions of 1 h leaching time, 200 g/L CFA dosage, and 2 M glycine solution. FT-IR results of the mineralized solution depicted a decline of deprotonated glycine and an increase of glycine overtime during the mineralization step, implying a continued regeneration of glycine. Mineralogy and morphology analysis of the carbonated product revealed that vaterite with a narrow particle size distribution and uniform spherical shapes were induced selectively by glycine as its preferential binding of acidic residues to metal ions in inhibition of vaterite dissolution, and the feasibility of the selective vaterite preparation from CFA was confirmed in a broad range of conditions. There was a quandary between high yield and low particle because of the particle agglomeration caused by the high dosage of the substrate.