Enhancing CO2 mitigation potential and mechanical properties of shotcrete in underground mining utilizing microbially induced calcium carbonate precipitation

Abstract

Achieving low-carbon development in the mining sector is fundamental for global carbon emissions abatement, especially considering the growing demand for mineral resources. Currently, the energy footprint of mines emerges as the main carbon contributor. While cleaner energy sources have the potential for reducing emissions, transitioning to these sources remains challenging. This study presents a practical CO₂ mitigation strategy for underground mining by integrating bacteria into shotcrete to enhance excavation. The findings demonstrate that bacteria can capture CO₂ from the atmosphere, thereby increasing the carbonation reactions. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis shows the captured CO₂ present in the forms of calcite, vaterite, and aragonite. The formed carbonates intermingled with the precipitated calcium-silicate-hydrate (C-S-H) at relatively low bacteria additions, densifying the cementitious matrix and improving the mechanical properties. However, high bacteria concentrations lead to excess carbonates that consume C-S-H precipitation, counteracting the benefits of carbonation and reducing mechanical strength. Optimal results were achieved with 0.3% bacteria by mass fraction, potentially mitigating 0.34 kg/m² of CO₂, which is approximately equivalent 567 g of CO₂ absorbed by 1 g of bacteria based on the effectiveness demonstrated in this study. These findings are crucial for advancing emissions control in mining and supporting climate goals outlined in the Paris Agreement.