Direct CO₂ Mineralization of Steel Slag Accelerated by Sporosarcina pasteurii

The microbially induced carbonate precipitation (MICP) process, particularly that using Sporosarcina pasteurii, is recognized for its environmental sustainability and cost-efficiency. This method has demonstrated significant potential in geological reinforcement, concrete restoration, and heavy metal pollution control. Through high urease activity, S. pasteurii converts urea into CO32– within cells, which subsequently binds with metal ions such as Ca2+ adsorbed on the cell surface to form CaCO3 precipitates. However, current engineering applications typically rely on an external supply of urea and Ca2+, while studies exploring this technology for direct CO2 capture from air or industrial flue gas remain limited. This study investigates S. pasteurii for direct mineralization using calcium from steel slag and CO2, aiming to achieve CO2 capture and simultaneous removal of free calcium oxide (f-CaO) from steel slag at a low temperature (30 °C) and atmospheric pressure. Experimental results indicate that under a 10% CO2 concentration, the CO2 uptake rate of steel slag can reach 8% within 30 min, attributed to accelerated dissolution of CO2 and subsequent precipitation of CaCO3 on the highly negatively charged surface of S. pasteurii. Under 100% CO2 conditions, after 60 min of mineralization treatment, the carbonation degree of steel slag by S. pasteurii reaches up to 49%, significantly outperforming Bacillus subtilis and Escherichia coli. SEM observations reveal the formation of abundant CaCO3 clusters on the surface of steel slag postmineralization, with deposition increasing markedly over time. Moreover, the content of f-CaO in the steel slag was reduced from an initial 5.9 to 0.5%, fully meeting building material standards and demonstrating its potential application value in the construction industry. This study not only verifies the high efficiency and technical feasibility of S. pasteurii in the CO2 mineralization of steel slag but also paves a new path for achieving net-zero CO2 emissions and waste resource utilization in the steel industry.