Optimizing the rheology, microstructure and carbon sequestering performance of alkali activated material incorporating acetic acid modified fly ash

Abstract The integration of CO2 sequestration with alkali activated fly ash (FA) backfill slurry presents a promising strategy for simultaneous resource utilization of industrial waste and carbon capture. However, the efficiency of this process is often constrained by the inherently poor reactivity of FA and rheology of FA based slurry. This investigation applies acetic acid (AA) to modify FA in order to improve the CO2 sequestration and rheology properties of alkali activated FA based backfill (AFB) slurry. Results reveal that a non-monotonic relationship between AA dosage and CO2 sequestration capacity of AFB, characterized by an initial increase followed by a decline. At 1 wt.% AA, the material achieves its maximum CO2 uptake of 1.28% and peak yield stress (10.54 Pa). This improvement originates from AA-driven surface modification, resulting in finer particles and higher reactivity compared to that of the control group. Furthermore, AA adsorbs onto FA surface functions as a lubricant and dispersant, thereby improving slurry rheology. Carbon life cycle assessment indicates that AFB employing 1 wt.% AA modified FA reduces total emissions by 69.52 kg/t compared to that of the unmodified reference, underscoring the potential of this strategy for achieving negative carbon emissions in mining backfill applications.