Removal and concentration of pyrene from contaminated soil using a phase separation of mixed cationic and anionic surfactants solution

Abstract

A new approach using mixed cationic surfactant (DTAB) and anionic surfactant (DOWFAX) for pyrene removal from contaminated soil was proposed. In this study, surfactant adsorption onto soil and pyrene solubilization by pure DTAB, pure DOWFAX and mixtures of DTAB:DOWFAX at molar ratios of 1.5:1, 1:1, 1:1.5, and 1:2 were investigated. The results showed that DTAB adsorption onto soil increases with concentration, while DOWFAX does not adsorb onto soil. The DTAB:DOWFAX at all studied molar ratios showed the greater pyrene solubilization over those of DTAB and DOWFAX alone. From the surfactant adsorption and pyrene solubilization results, the DTAB:DOWFAX at 1:1 molar ratio was selected for further use to investigate the effects of total surfactants concentration and additives (CaCl2 and lipophilic linkers) addition on pyrene removal from contaminated soil. The results showed that the optimal surfactant formulation is DTAB:DOWFAX at 1:1 molar ratio with 20 mM total surfactants concentration, 0.025%wt CaCl2, and 1 mM dodecanol, where the highest pyrene removal of 87.5% was achieved. These surfactant systems with and without each additive were later on adjusted the molar ratio of DTAB:DOWFAX to induce the aqueous surfactant two-phase (ASTP) system to investigate the preconcentration ability. The results showed that the ASTP system formed by DTAB:DOWFAX at 2:1 molar ratio and 0.025%wt CaCl2 exhibited the best preconcentration ability, where most of pyrene and surfactants accumulate in a small volume of the surfactant-rich phase, and the pyrene and surfactant partition ratios were as high as 3,200.