Impacts of biochar and slag on carbon sequestration potential and sustainability assessment of MgO-stabilized marine soils: insights from MIP analysis†

Mineral carbonation is a promising strategy for mitigating carbon emissions and combating climate change. This study investigates the efficacy and sustainability of MgO-based stabilization techniques for soft marine soils, incorporating supplementary cementitious materials (SCMs) such as biochar and slag. A combination of laboratory experiments and rigorous analyses was utilized to elucidate the complex interplay between the additives and their impacts on soil hydraulic characteristics, carbon sequestration potential, embodied energy, and economic viability. Mercury intrusion porosimetry (MIP) was employed to characterize pore structure changes induced by carbonation, while X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to correlate mineral formations. The results indicate that MgO–biochar-treated soils exhibit enhanced soil air content, pore connectivity, and carbon sequestration efficiency compared to MgO–slag-treated soils, exhibiting reduced pore volumes and limited CO₂ diffusion. Integrating biochar with MgO enhanced brucite and nesquehonite precipitation due to biochar's porous structure and functionalized surface area, facilitating gas diffusion and nucleation for mineral formation. Sustainability assessments highlight the environmental and economic trade-offs, positioning MgO–biochar and MgO–slag combinations as cost-effective and environmentally friendly alternatives. This research provides theoretical guidance for sustainable soil stabilization and efficient CO₂ mineralization, offering valuable insights for researchers, practitioners, and policymakers addressing climate change challenges.