Insights into dual functions of amino acid salts as CO2 carriers and CaCO3 regulators for integrated CO2 absorption and mineralisation

Abstract Integrated CO2 absorption and mineralisation (IAM) is a promising technology for rapidly CO2 absorption and sequestration. However, the traditional IAM using alkanolamines as CO2 solvents and solid wastes as carbonation feedstocks still suffers from the utilization difficulty of low value products and environmental risks of amine degradation. In this study, the green solvent, amino acid salts (AAS), including potassium l -argininate (ArgK), potassium glycinate, potassium sarcosinate, potassium l -alaninate, potassium β-alaninate, were selected for IAM using rejected brine as the carbonation feedstock. Results shows that compared to amines (monoethanolamine, diethanolamine, N-methyldiethanolamine, triethanolamine, piperazine, 2-amino-2-methy-1-propanol), the selected AASs in IAM were not only more effective CO2 carriers that passed CO2 to calcium ions to form CaCO3, but also better CaCO3 growth regulators to tune morphology properties of products. CO2 desorption efficiencies in CO2-loaded AASs (nearly 100 %) were much higher than those of in CO2-loaded amines especially than in MEA (38 %). ArgK stood out in regulating the morphology of crystal with smallest particle size. Then ArgK was selected for optimization experiments at various conditions (temperature, Ca2+/CO2 ratio, reactant concentration and chelating agent) to further investigate effects of operating conditions on CaCO3 properties and to provide some basic information for the polymorph and morphology regulation of CaCO3. Ethylene diamine tetraacetic acid (EDTA) as a chelating agent was found a notable influence on controlling the polymorph of CaCO3, where the amorphous CaCO3 and new structures of calcite appeared. However, the effect of EDTA on CO2 absorption step was not clear and required further investigation.