Mixing behavior and electrical conductivity of diisopropyl amine-water surfactantless emulsions: Implications for the electrokinetic purification of water

The water pollutant diisopropylamine (DIPA) creates surfactantless emulsions in water. DIPA droplets bear a negative electrostatic charge, as demonstrated by electrophoretic measurements. Sodium salts (NaCl and Na₂SO₄) decrease their charge, leading to droplet coalescence and separation into bulk layers, depending on the salt and DIPA percentages. Attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR) show that the DIPA concentration in the water rich phase is below 10 wt% DIPA when adding 2 wt% Na₂SO₄ (relative to the mixture) to mixtures of 20 wt%, 40 wt% and 50 wt% DIPA (relative to water). The same occurs when adding 2% NaCl to mixtures of 30 wt%, 50 wt% and 70 wt% DIPA (relative to water). DIPA-water mixtures are electrically conductive and can be separated by subjecting them to an electric field (electrokinetic separation). Without salts, the concentration of DIPA in 30 wt% DIPA could be reduced by ≈ 20 wt% after 60 mins treatment using a differential voltage = 12 V. NaCl (0.25 wt% relative to water) improved efficiency. After 15 mins, the percent decrease in DIPA was ≈ 50 wt%. Electrokinetic treatment targets exclusively contaminants dispersed in water. DIPA sorbs onto clay, alumina and iron oxide minerals, whereas it does not sorb onto gypsum and limestone. Therefore, the in situ electrokinetic separation of DIPA can be most successfully applied in aquifers where the dominant minerals are gypsum and limestone.