Synergistic and inhibitory mechanisms of CO2 mineralization in fly ash–tailings backfill under different conditions

The global rise in greenhouse gas emissions has emerged as a critical driver of ecological disruption and an accelerant of ongoing climate change. In this study, a carbon-negative backfill strategy utilizing industrial solid wastes has been proposed. The feasibility of using fly ash-based cementitious materials and mine tailings as backfill media in metal mines was demonstrated through multi-condition experiments. Systematic experiments revealed that under high-pressure dynamic conditions (0.5 MPa), the addition of NaHCO 3 enhanced the carbon sequestration ratio (K) to 2.211% by intensifying HCO 3 - mass transfer. This performance surpassed the results achieved with NaCl and NH 4 Cl under same conditions. In the absence of any additives, the peak carbon sequestration ratio ( K ) reached 1.421%, synchronizes with the maximum pH 6.63 under a pressure of 0.5 MPa. However, further increases in pressure induced H + -driven passivation, limiting the sequestration efficiency. Extended grinding duration from 25 to 50 min boosts K by 52%, while prolonging the mineralization time from 0.5 to 1.0 h resulted in a 25-fold gain. Hybrid systems composed of 80% tailings and 20% cement exhibited ambient-condition synergy, achieving a carbon sequestration ratio (K) of 1.304% through Ca 2+ release and CO 3 2- ion-bridge formation. However, under high-pressure conditions, an anti-synergistic effect was observed, necessitating the use of staged mineralization protocols. XRD and SEM–EDS analyses confirmed the formation of Ca- and Mg-carbonates as well as surface passivation phenomena, while TG–DTG results established the relative efficacy of additives in the order: NaHCO 3 > NaCl > NH 4 Cl. This study introduces a novel carbon-negative backfilling approach supported by a quantitative dataset, offering new guidance for integrating carbonation-based valorization into sustainable mine tailings management. • NaHCO 3 enhanced the carbon sequestration ratio by intensifying HCO 3 - mass transfer. • In the absence of additives, pressure increases limit the sequestration efficiency. • Hybrid systems exhibited ambient-condition synergy. • Carbon sequestration efficacy with additives in the order: NaHCO 3 > NaCl > NH 4 Cl.