Surface chemistry controlled carbonation of amorphous calcium (alumino) silicate slags in aqueous solutions

Amorphous calcium (alumino)silicates in industrial solid wastes are key determinants of their reactivity towards CO 2 . However, the carbonation mechanisms governing the reaction kinetics of these phases remain insufficiently understood. This study systematically investigates the aqueous carbonation reaction and its enhancement for phosphorus slag (PS) and blast furnace slag (SG). Comparative analysis of aqueous carbonation in pure H₂O-CO₂ and NaHCO₃ systems revealed significant differences in the dissolution-carbonation kinetics of PS and SG. Notably, in the NaHCO₃ system, the CO 2 uptake of PS increased by more than an order of magnitude within 30 min, whereas SG exhibited only a marginal increase (∼2 ×) even after 6 h of carbonation. Surface chemistry analysis indicated that these disparities coincide with the formation of a surface alumina-silica gel layer on SG during carbonation. The enhancing effect of NaHCO₃ is attributed to the increased (bi-)carbonate concentration at higher pH. Enhanced carbonation in the NaHCO₃ system was confined to the early stages, before rapid formation of surface precipitates slowed the carbonation progress. • Present the distinct dissolution-carbonation behaviors between PS and SG over a range of variables including solution chemistry, carbonation time and temperature. • Explain the effect of glass composition on the carbonation mechanism, and the formation of a protective alumina-silica gel layer enhanced by the higher aluminum availability. • Demonstrate the enhancement of aqueous carbonation in NaHCO 3 solutions, clearly demonstrating CO 2 uptake increase of PS by more than an order of magnitude within 30 min.