CO ₂ absorption saturation threshold in carbonated coal-based solid waste backfill materials

A novel CO2-carbonated coal-based solid waste (CBSW) backfill material was developed to manage coal-based solid waste and sequester CO2. The absorption saturation threshold and reaction mechanisms of materials were investigated through mechanical tests and microscopic analysis. The maximum absorption capacity reached 2.485 mg-CO2/g-CBSW under 20-min ventilation, which enhanced the uniaxial compressive strength (UCS) by 116% post-carbonation. Microanalysis revealed that: 1) strength enhancement originated from CaCO3 and silica gel formation; 2) pore-filling by CaCO3 and C-A-S-H gel bonding occurred after saturation; 3) efficiency declined due to soluble Ca(HCO3)2 formation with excess CO2. The technology enables in-situ CBSW reuse and carbon sequestration.