Ambient, Two-Step CO2-to-CaCO3 Conversion: Alkali-Activated H2O2-Promoted Carbonate CO2 Capture and Direct Calcite Mineralization

Abstract

We demonstrate an ambient-temperature two-step CO2-to-CaCO3 conversion in which alkali-activated H2O2 accelerates carbonate CO2 capture, followed by calcite mineralization upon CaCl2 addition, without thermal stripping of the capture liquor. Alkali activation generates transient reactive oxygen species (ROS) that promote rapid CO2 absorption at 30°C into aqueous Na2CO3 and K2CO3 without persistent promoters, yielding bicarbonate-rich liquors that are directly mineralized to phase-pure calcite and release a CO2 stream free of O2. Single-reactor screening identified concentration windows that maximize capacity while maintaining homogeneity, with Na2CO3 optimal near 7-10 wt% and K2CO3 near 20-25 wt%. Multi-reactor staging prolonged cycle duration and moderated the trade-off between outlet CO2-removal specification and first-stage carbonate-to-bicarbonate conversion, with K2CO3 formulations showing the smallest penalty at stricter cutoffs. The CaCO3 products were identified as calcite by XRD and ATR-FTIR, with SEM/EDS results consistent with rhombohedral CaCO3 and no detectable secondary elements. A consumables-only techno-economic analysis using four geography-specific reagent price decks shows that LCOC is reagent-dominated, with carbonate utilization emerging as the principal cost lever through its effect on stoichiometric make-up demand. Overall, the results establish an ambient-temperature capture-to-mineralization route in which alkali-activated H2O2-derived ROS accelerate carbonate capture and direct mineralization avoids thermal regeneration.