Integrated direct air capture and CO2 mineralization using amino acid salt solutions and alkaline solid wastes

Direct air capture (DAC) technologies are gaining growing attention for climate change mitigation but remain at a very early stage of large-scale deployment. This study proposes and comprehensively demonstrates a novel integrated DAC–mineralization process using five amino acid salt solutions as CO₂ liquid absorbents and cement kiln dust (CKD) as feedstocks for CO₂ mineralization and solvent regeneration. Upon DAC, sodium-based sarcosinate (Na-Sar), prolinate (Na-Pro), lysinate (Na-Lys) achieved desirable atmospheric CO₂ removal efficiencies above 92%, which outperformed sodium-based arginate (Na-Arg) and glycinate (Na-Gly). Solution alkalinity was identified as the key factor governing DAC, with a non-linear relationship observed between CO₂ removal efficiency and pH. At pH > 11.0, all liquid absorbents could maintain atmospheric CO₂ removal efficiencies above ∼60%, whereas a decrease in pH from 11.0 to 10.0 led to a pronounced decline in efficiency. In the integrated DAC–mineralization process, amino acid salt solutions and CKD were examined and characterized by FTIR, XRD, and TGA over six DAC–mineralization cycles. All liquid absorbents exhibited efficient recovery via mineralization, except for Na-Arg. XRD analysis revealed predominant calcite formation upon mineralization, while TGA indicated a CO₂ sequestration capacity of 92–172 g CO₂ kg −1 CKD. Overall, Na-Pro emerged as the most promising candidate for the DAC-mineralization technology. A simplified TEA analysis estimated the integrated process cost at 139–530 USD t −1 CO₂, approximately half that of conventional DAC technologies. For the scale-up of the technology, key technical and economic challenges were also identified and discussed in detail.