Low-temperature microemulsions for the in situ extraction of contaminants from soil

Abstract

A complex microemulsion system using rape oil–methyl ester as the oil component, anionic and non-ionic surfactants and brine was developed for the in situ extraction of hydrophobic contaminants at temperatures of about 10°C. The phase behaviour at different compositions of quaternary, quinary and hexanary systems was studied. The behaviour was governed by the anionic surfactant. The concentration of brine strongly influences the phase behaviour. In addition, increasing the salt concentration leads to the suppression of liquid crystals. The addition of a third, very bulky surfactant further suppresses the formation of liquid crystals for equal mass fractions of oil and brine. Equal amounts of oil and water are necessary to avoid the formation of liquid crystals. A system with low surfactant concentration was chosen to determine the viscosity and surface tension. First column experiments were performed in order to determine the flow behaviour and the amounts of microemulsion components adsorbed onto soil. In a batch experiment, the extraction efficiency of the microemulsion system was investigated at 10°C for polychlorinated biphenyls from a doped soil. It was better than the efficiency of the toluene extraction. Microemulsion systems seem to be excellent media for the in situ remediation of hydrophobic contaminants from soil.