Mixing Behavior and Electrical Conductivity of Diisopropyl Amine-Water Surfactantless Emulsions: Implications for the Electrokinetic Purification of Water

Abstract

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 10wt% DIPA when adding 2wt% Na2SO4 (relative to the mixture) to mixtures of 20wt%, 40wt% and 50wt% DIPA (relative to water). The same occurs when adding 2% NaCl to mixtures of 30wt%, 50wt% and 70wt% 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 30wt% DIPA could be reduced by ≈20wt% after 60mins treatment using a differential voltage = 12V. NaCl (0.25wt% relative to water) improved efficiency. After 15mins, the percent decrease in DIPA was ≈50wt%. 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.