Construction and performance evaluation of preparation method of fly ash deamination and carbon fixation coupling paste material

To simultaneously address ammonia emission during paste backfill application and strength degradation caused by poor stability of fly ash, this study designed an experimental protocol integrating flue gas stripping of fly ash slurry and subsequent preparation of backfill materials. The effects of free CaO(f-CaO) content, solid-liquid ratio (S/L), gas-liquid ratio (G/L), and alkali dosage on ammonia removal and CO₂ sequestration efficiency were systematically investigated during simulated flue gas stripping. Microstructural and mineralogical evolution of fly ash before and after treatment was characterized via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The feasibility of utilizing stripped slurry for paste backfill preparation was further evaluated. Results demonstrated that under optimal conditions (S/L=0.2 kg/L, G/L=800 L/m³, alkali dosage=0.5%, 30-min stripping), CO₂ in flue gas was effectively mineralized by f-CaO, achieving over 80% of theoretical CO₂ sequestration capacity across three fly ash types, with a maximum sequestration of 90.52 g/kg. SEM and XRD analyses revealed that Ca(OH)₂ was converted to CaCO₃ during stripping, predominantly forming crystalline aggregates adhered to fly ash particles. Although ammonia removal efficiency reached only 30%, the pH of fly ash slurry decreased to neutrality due to CO₂ mineralization, significantly suppressing ammonia release (about 70% reduction) during curing of backfill materials. The 28-day compressive strength of backfill specimens prepared from treated slurry reached 6.62, 7.91 and 8.34 MPa, exhibiting substantial improvements compared to untreated controls. While rheological properties slightly declined, all pastes met engineering specifications. This integrated flue gas stripping-carbonation activation strategy provides a systematic solution for large-scale utilization of industrial solid wastes (e.g., ammonia-rich high-f-CaO fly ash), enabling dual benefits of pollutant control and resource recovery while advancing sustainable practices in coal-fired power and chemical industries.