Work

Mineral Carbonation of Red Mud Using CO2 Microbubbles under Ambient Conditions

Year: 2025

Type: article

Abstract: This study investigated the mineral carbonation and neutralization behavior of red mud (RM) using CO2 microbubbles (CO2 MBs) under ambient temperature and pressure conditions, and further assessed the feasibility of utilizing carbonated RM as a cement substitute. Batch experiments were conducted at various solid-to-liquid ratios (S/L=0.001–1.0), monitoring pH, electrical conductivity (EC), and aqueous carbonic acid (H2CO3(aq)) concentrations. In the RM–CO2 MBs system, pH initially dropped sharply and then recovered to the buffering zone (pH 7–8.5), while EC exhibited a rapid rise followed by gradual decline, indicating sequential ion release and carbonate precipitation. The H2CO3(aq) concentration decreased over time due to both carbonation consumption and pH-induced speciation shift. In continuous experiments (reactor dimensions: D=14.6cm, H=34 cm, S/L=0.025), both powdered (RM-P) and sludge-type (RM-S) samples achieved neutralization (pH=7) within 4 minutes, accompanied by a characteristic EC decrease–rebound pattern. The total inorganic carbon (TIC)-based CO2 uptake of RM-S reached 8.87g-CO2/kg-RM, corresponding to approximately 84% of the theoretical maximum carbonation potential (TMCP). Mortar specimens incorporating carbonated RM as a partial cement replacement (0–15 wt%) exhibited decreasing compressive strength with increasing substitution ratio, yet 5 wt% replacement maintained adequate strength for non-structural construction materials. These results demonstrate that CO2 MBs enable rapid (≤2 min), high-efficiency carbonation and neutralization of RM under ambient conditions without pressurized systems. The proposed process provides a low-energy, environmentally friendly pathway for simultaneous CO2 sequestration and red mud valorization, contributing to sustainable carbon-neutral technology.

Source: 대한환경공학회지

DOI: 10.4491/ksee.2025.47.11.748