Experimental investigation of coal tailing-derived nanoparticles for CO₂ foam stabilization

Carbon dioxide (CO₂) foams represent a highly promising method for CO₂ sequestration and enhanced oil recovery (EOR), yet their practical application is constrained by inherent instability arising from rapid bubble coarsening and lamella rupture. In this study, coal-tailing nanoparticles were synthesized and comprehensively characterized for their physicochemical properties. Their performance in stabilizing CO₂ foam was systematically evaluated and compared with commercial nanoparticles (hematite, calcite, hydrophilic and hydrophobic silica), while the effects of concentration, flow rate, temperature, salinity, pH, wettability, and zeta potential on foam generation, stability, and bubble characteristics were assessed using surface tension measurements and optical microscopy. The results demonstrate that coal-tailings-derived nanoparticles with amphiphilic surfaces, predominantly hydrophilic in character, significantly enhance the stability of CO₂ foams. Surface tension measurements identified optimal conditions at 0.05 wt% nanoparticles, 400 ppm SDBS, and 16000 ppm NaCl, corresponding to the lowest surface tension (∼27.4 mN/m) and the longest foam half-life (11.1 min, ≈178% improvement over surfactant-only foam). Moreover, foam stability was strongly influenced by pH, reaching a maximum at pH 10 due to increased negative zeta potential and enhanced electrostatic repulsion. Coal-tailing nanoparticles exhibited superior interfacial adsorption and dispersion compared with commercial nanoparticles due to their amphiphilic wettability, resulting in finer, more uniform bubbles and thicker lamellae (∼35.9 μm). This enhanced stability arises from the formation of a protective interfacial "armor" that reinforces lamellae, strengthens electrostatic and steric repulsion, and slows both liquid drainage and gas diffusion. These findings demonstrate that coal-tailing nanoparticles can enhance CO₂ foam performance, improving gas mobility and CO₂ storage while providing environmental benefits through waste valorization.