Study on the effect of electrolyte on surface tension of surfactant solution and wettability of coal dust

It is valuable to study the effect of electrolytes on the surface tension and wettability of surfactant solutions for industrial production. Surface tension test, coal dust sink test, and molecular dynamics simulation are employed to investigate the influence of four electrolytes (NaCl, NaAc, Na2CO3, MgCl2) on nonionic surfactant AEO-9 and anionic surfactant SDBS. The study showed that AEO-9 had a more extraordinary ability to reduce surface tension when the surfactant was applied alone. The surface tension achieved by SDBS solution was lower when compounded with electrolytes. The influence degree of electrolytes on the surface tension of SDBS solutions was shown as MgCl2>NaCl≈Na2CO3>NaAc. In contrast, the influence on the surface tension of AEO-9 solutions was insignificant. In addition, adding electrolytes to the low-concentration surfactant solution can markedly reduce the surface tension. When selecting the electrolytes compounded with anionic surfactants, the electrolyte cation is recommended to choose elements with a larger main groups number in the same periodic element from the periodic table and electrolyte anions that can form more hydrogen bonds with water molecules. The results of the coal dust sink test are different from the results of the surface tension measurement. Regardless of whether the electrolyte is added, the sink time of coal dust in the AEO-9 solution is shorter than that in the SDBS solution, and the wettability is better at the same concentration. The results of this study may guide the selection and design of dust suppression solutions.