Effect of Sulfolane Demixing and Sorption on its Migration Through Model Fractured and Porous Media

Sulfolane is an emerging contaminant, miscible in pure water. The correlation between mixing behavior and transport of sulfolane with sulfate and chloride salts is not fully understood. Sulfate salts (e.g., Na₂SO₄) decrease the solubility of sulfolane in water. Specifically, solutions with 30wt% sulfolane separated into bulk phases with 130 g/kg Na₂SO₄ (2.4 mol% Na₂SO₄ relative to the total mixture) and emulsions formed with lower concentrations of Na₂SO₄ (41 g/kg or 0.7 mol% Na₂SO₄ relative to the total mixture). This is not observed with chlorides at these same concentrations. Na₂SO₄ enhanced sulfolane sorption onto montmorillonite clay, with 0.2 g sulfolane sorbed/g clay at high Na₂SO₄ concentrations (40.7 g Na₂SO₄/kg solution). As a result, Na₂SO₄ delayed sulfolane migration in model clayey fractures, compared to pure water. Sulfolane and co-contaminants such as toluene reciprocally influence their miscibility in water. Sulfolane emulsified toluene in pure water, while Na₂SO₄ supressed emulsification. In turn, sulfolane partitioned in toluene, and Na₂SO₄ enhanced this behavior by decreasing sulfolane miscibility in water. In flow tests conducted with 0.7 mol% Na₂SO₄ and 30wt% sulfolane (relative to water), the sulfolane concentration at the outlet is lower than that at the inlet for up to 80% of the total eluted volume. Therefore, in model sandy aquifers, the vertical migration of sulfolane was delayed with Na₂SO₄ and toluene, which floated on water and was trapped in soil pores due to capillary forces. Chloride salts had a less significant effect on toluene solubility in water and on its migration through model porous media.