Inhibitory characteristics of a surfactant-enhanced sodium salt inhibitor for coal spontaneous combustion

Sodium-salt-based physical inhibitors reduce coal–oxygen interactions through moisture absorption and retention in the prevention of coal spontaneous combustion, but their wetting and spreading performance on coal surfaces can be further improved. To enhance the overall inhibition performance of sodium-salt-based inhibitors, the anionic surfactant sodium dodecyl sulfate (SDS) was introduced to modify the sodium chloride (NaCl) inhibition system, and the optimal composite inhibitor formulation was selected through experimental characterization and comprehensive evaluation using the entropy weight method. The results showed that SDS further enhanced the moisture-regulation capacity of the NaCl system. The coal sample treated with 20% NaCl + 0.15% SDS exhibited an average water absorption of 15.45 g and an average mass loss of 4.76 g during the moisture desorption stage, representing a 99% increase and a 59% decrease, respectively, compared with the sample treated with 20% NaCl alone. Meanwhile, oxygen consumption and CO generation were effectively reduced and suppressed, respectively. Contact-angle and FTIR results showed that SDS improved coal–liquid interfacial wettability, while different inhibitor treatments altered the relative functional-group composition and chemical environment of coal. SDS promoted the wetting, spreading, and effective contact of the NaCl solution on coal surfaces, while the hygroscopic and hydration effects of NaCl enhanced moisture retention, thereby weakening coal–oxygen interactions and retarding low-temperature oxidation. Comprehensive evaluation using the entropy weight method identified 20% NaCl + 0.15% SDS as the optimal formulation. These results provide a reference for formulation optimization and parameter design of surfactant-enhanced sodium-salt inhibitors.