Experimental and Molecular Simulation Research on the Effect of Metal Ions on the Stability of SDS Foam

The occurrence of metal ions in the form of inorganic minerals in coal is one of the main factors that affect the stability of surfactant foams. To explore the effect of metal ions in coal seams on the stability of anionic surfactant sodium dodecyl sulfate (SDS) foam, changes in the half-life of SDS foam under different base fluids were analyzed. The results showed that metal ions promoted the stability of SDS foam. When the Na+ concentration in the base fluid increased from 20 to 40 mg/L, the foam half-life increased by 67 s. When the Mg2+ concentration in the base fluid increased from 5 to 15 mg/L, the half-life of the foam increased by 148 s. The influence of divalent Mg2+ was more pronounced than that of monovalent Na+. A two-phase molecular dynamics model at the foam interface was constructed in Materials Studio molecular dynamics simulation software. The diffusion characteristics of H2O molecules in the foam walls and the hydration of metal ions in the foam walls were used to investigate how metal ions affected the stability of SDS foam. It was revealed that metal ions inhibited the diffusion of water molecules in the foam wall, thereby improving the stability of the foam. The inhibitory force of divalent Mg2+ was stronger than that of monovalent Na+.