Influence of Quartz, Kaolin, and Organic Matter on the Critical Micelle Concentration of Tween Surfactants and their Application in Diesel‐Contaminated Soil Washing

Abstract

Surfactant solutions are commonly used for the remediation of petroleum-contaminated soil due to their good petroleum removal performance, time-saving capability, and cost effectiveness. However, applying surfactants in excess concentrations could make oil recovery difficult. Moreover, residual surfactants in soil are toxic to microorganisms and plants. Thus, it is crucial to identify a suitable surfactant concentration for soil washing applications. The main objective of this study was to evaluate the effect of soil minerals (quartz and kaolin) and organic matter (OM) on the critical micelle concentration (CMC) of polyethoxylated sorbitan ester surfactants (Tween 20, 40, 60, and 80) and its effect on diesel removal from dieselcontaminated soil by soil washing. The results showed that Tween surfactants with shorter carbon chain lengths required higher CMC for diesel removal from quartz, while those with longer chains needed higher CMC for kaolin cleanup. FTIR results illustrated that oxygenated functional groups of Tween surfactants played an important role in their adsorption on quartz, while alkyl chains of Tween surfactants were responsible for their adsorption on kaolin. At a certain OM concentration, quartz and OM exhibited antagonistic effects, resulting in CMC reduction. In soil washing application, maximum diesel removal could be achieved from kaolin, in the presence of which surfactants exhibited the highest CMC. Based on FTIR results, the adsorbed surfactant could reduce the hydrophobicity of the kaolin surface, thus preventing the re-deposition of detached diesel.

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“…Hydrogen bonds between the ethoxylate group of TW80 and the surface of the particulate matter might be responsible for this phenomenon. Moreover, the double bond in the TW80 hydrophobic tail group provides a strong adsorption site for TW80 on the surface of organic matter [ 24 ]. Due to surfactant adsorption, the concentration of surfactant must be greater than its CMC to ensure good extraction performance [ 25 ].…”