Study on the regulation of electrolyte on the wettability of anionic surfactant for bituminous coal: sodium dodecyl benzene sulfonate and sodium chloride as representatives

Constructing a molecular model of Baodian bituminous coal enables a microscopic investigation of electrolyte–surfactant regulatory mechanisms, advancing dust suppression technologies. This study examines the effect of electrolyte on the wettability of anionic surfactant on bituminous coal, using sodium dodecyl benzene sulfonate (SDBS) and sodium chloride (NaCl) as model compounds. A molecular model of Baodian bituminous coal was developed through material characterization, with a molecular formula of C193H137O11N3S and a molecular weight of 2706.29. Macroscopic wettability was assessed via surface tension tests, contact angle analysis, and coal dust sink tests. Molecular dynamics (MD) simulations were performed to construct and analyze the electrolyte/water/surfactant/coal quaternary system. Results show that NaCl enhances wettability by reducing electrostatic repulsion between SDBS headgroups via electrostatic shielding, disrupting the solvation layer, and strengthening SDBS adsorption onto the coal surface. Additionally, NaCl affects the aggregation dynamics of SDBS. At low concentrations, it promotes monolayer adsorption, whereas at high concentrations, it induces excessive aggregation, reducing the availability of free SDBS molecules for adsorption. Moreover, at SDBS concentrations below 4 × 10−8 mol/L, introducing NaCl increases surface tension due to hydrated ion formation. This study provides theoretical insights and technical guidance for the development of efficient and cost-effective dust suppressants.