Glycine-mediated leaching-mineralization cycle for CO2 sequestration and CaCO3 production from coal fly ash: Dual functions of glycine as a proton donor and receptor

Indirect aqueous carbonation of CaSO4·2H2O with aspartic acid as a recyclable additive

“…No characteristic peaks of calcite or aragonite phase were detected. The result was consistent with previous reported by Zheng et al 32 who proposed a glycine-mediated leaching-mineralization cycle from coal y ash. It seems that a relatively high content of amino acid can help the formation of vaterite phase.…”

Insights into the interaction between typical amines and alkaline minerals for improved CO2 absorption and mineralization

“…For MEA and DEA, carbamates (MEACOO − and DEACOO − ) can also participate in this process by decomposing to free amines and HCO 3 − via reaction 8. Therefore, the amine regeneration in the IAM process involved four key steps: alkaline earth metal (mainly Ca 2+ and Mg 2+ ) extraction and OH − releasing, neutralization of protonated amine, conversion of carbamate/HCO 3 − to CO 3 2− , and CaCO 3 /MgCO 3 formation 23,30 …”

“…This phenomenon could be explained by the interaction between the amino group of amines and Ca 2+ /Mg 2+ ions. On one hand, the amino group grabbed proton from the solution and produced an alkaline environment and increased pH value, which was not beneficial for Ca 2+ extraction 23 . Amine solution with a higher p K a value was more prone to the protonation of amino groups, 33 leading to an increase in alkalinity and the hindered the Ca 2+ /Mg 2+ extraction from Ca(OH) 2 /Mg(OH) 2 .…”

“…It is already known that the IAM process involved four key steps: alkaline earth metal (mainly Ca 2+ and Mg 2+ ) extraction and OH − releasing, neutralization of protonated amine, conversion of carbamate/HCO 3 − to CO 3 2− , and CaCO 3 /MgCO 3 formation 22 . In IAM process, amine serves not only as a CO 2 absorbent but even a metal‐ligand which was seriously neglected 23 . It was reported that free amines, protonated amines, and carbamates could spontaneously bind in the first coordination sphere of metal cations to form a complex, enhancing metal extraction potentially 24 .…”

“…Different metal extraction performances and mineralization performances of various amines may be due to their amino groups, which have different complexation constants when binding to Ca 2+ and Mg 2+ 25,26 . Furthermore, the amine solution was supposed to have a significant effect on the precipitation of CaCO 3 by offering different CO 2 ‐bearing species and varying solubility of Ca/Mg minerals 23 . In addition, the amine groups adsorbed on the CaCO 3 crystal surface can change the surface energy, thereby affect the growth and morphology of CaCO 3 crystal 27–29 .…”