Physical–chemical parameters promoting phase changes in non-ionic environmental-friendly microemulsions

Abstract

A series of influencing parameters (water/oil ratio, cosolvent, temperature, surfactant concentration, metallic salt and dye concentration) on the phase transitions in Water/polyoxietilen(4)laurylether/Ethyl acetate ternary system have been studied in order to optimize the extraction of pollutants (metallic cations and dyes) from aqueous media by non-ionic microemulsions. This system presents a phase inversion temperature (PIT) around 15°C, corresponding for WI to WII phase transition. While there is an extending tendency of WII areas with increasing temperature over 40°C, the opposite effect is noticed by adding Ni(II) and Crystal Violet dye into the water phase. No effect was registered at small amounts of Crystal Violet dye addition. Based on evaluation of distribution coefficient in liquid–liquid Ni(II) extraction system and the load capacity of microemulsion with the two pollutants (Ni(II) and Crystal Violet dye), the optimum extraction conditions for this system would correspond to water/microemulsion volumetric ratio, F=8, no added co-solvent, and surfactant concentration around 20% (w/w), resulting in extraction efficiencies around 90%. The pollutants extraction from an aqueous phase by WII microemulsions is based on their diffusion from diluted water phase in the interfacial film of surfactant (CV dye) or into the micelles (Ni(II)) according to the equilibrium constant and rate constant data. By a simple control of surfactant concentration, the non-ionic microemulsions Water/polyoxietilen(4)laurylether (Brij 30)/Ethyl acetate (EtOAc) system can be an efficient solution for extraction of hydrophilic pollutants sensitive to heat from aqueous media at environment temperature.