Phase assemblage evolution and carbonation mechanism of ground granulated blast-furnace slag during enforced carbonation

Abstract

Many industrial solid wastes are dominated by amorphous glass phases with low intrinsic carbonation reactivity, which limits their carbonation efficiency and large-scale valorization. In this study, ground granulated blast-furnace slag (GGBS) was selected as a representative glass-rich model waste to systematically investigate the carbonation behavior and underlying mechanisms of aluminosilicate glass-dominated residues. An enhanced carbonation strategy incorporating mechanochemical input was applied to GGBS to reveal the kinetics and pathways of decalcification, carbonate formation and Si–Al network reconstruction. The results show that GGBS exhibited slow and progressive carbonation, reaching a CaCO3 content of 19.98% and a corresponding carbonation degree of 23.45% after 6 h of enforced carbonation. The carbonation includes three primary stages: (1) glass hydrolysis and Ca mobilization, (2) calcite precipitation coupled with Si–Al network reconstruction, and (3) further local condensation of the residual aluminosilicate structure. The limited early carbonate formation despite rapid Ca release is consistent with an induction period for calcite formation, while incomplete later carbonation suggests reduced accessibility of the remaining Ca. The combined Qn redistribution and persistent tetrahedral Al further support a proposed site-dependent Ca availability, with the results suggesting that Ca associated with low-connectivity environments may be more accessible for release than Ca retained in the evolving aluminosilicate structure. Overall, this study provides mechanistic insight into the CO2 mineralization of GGBS and establishes a basis for future investigation of other Ca-bearing aluminosilicate glasses.