Utilization of Bottom Ash From Power Plants as Backfill Material for Surface Coal Mines With Enhanced Carbon Dioxide Capture and Storage Capabilities

In response to the growing need for sustainable mine reclamation, this study investigates the use of bottom ash, a byproduct of coal or lignite combustion, as a component in backfill materials for surface mining. The study focuses on evaluating the CO₂ absorption capacity and mechanical strength properties of mixtures containing varying ratios of bottom ash and smectite. Composite backfill material strength was assessed through unconfined compressive strength (UCS) and direct shear tests. The mixture with a bottom ash to smectite ratio of 30:70 exhibited the highest UCS across all moisture levels, with a peak value of 139 kPa at 10% water content. At this condition, the mixture also showed a cohesion of 17.06 kPa, an internal friction angle of 31.2°, and a shear strength of 25.32 kPa. Based on these results, samples at 10% water content were selected for CO₂ absorption testing across different bottom ash–smectite ratios. The 10:90 ratio demonstrated the highest CO₂ absorption capacity at 3.16 mg/g, with a decreasing trend observed as the proportion of bottom ash increased. These findings suggest that bottom ash–smectite mixtures can be optimized to achieve both pit wall stability and enhanced carbon sequestration, supporting their use as sustainable backfill materials in mine reclamation.