Organometallic removal from contaminated soil by microemulsion technique

Abstract

This work demonstrated the feasibility of an organometallic compound removal from contaminated soil using microemulsion technique. Tetraethyl lead (TEL) was a well known substance used as an anti-knocking agent in gasoline. TEL is classified as a highly toxic substance causing a threat to human and environment. A contamination of TEL has been found in many areas, a robust remediation technique namely the surfactant enhanced aquifer remediation (SEAR) is a promising method to mitigate the contamination problem. Due to a harmfulness of TEL, the possibility to directly deal with this substance was very limited. As a consequence, the surrogate oil was required in order to investigate the capability of surfactant microemulsion formation to eliminate organometallic compound from contaminated soil. There are 4 main criteria for TEL surrogate selection: being an organomatallic substance, analogy in physical and chemical properties, less poisonous as compared to TEL, and able to be mixed well with other oils to obtain similar equivalent alkane carbon number (EACN) to TEL. In this study, the similarity of oil’s EACN was a main focus. Oils having similar EACN tend to form microemulsion using similar surfactant formulation. The EACN of TEL was successfully determined in a range of 6.04 to 7.23 using Salager’s equation. Thus, the TEL surrogate was selected to be a mixture of dibutyltin dichloride (DBTDC) and decane at molar ratio of 0.038:0.962. Three surfactant microemulsion solutions at total active surfactant(s) concentration of 4 wt%: pure sodium dihexyl sulfosuccinate (AMA), AMA/monoalkyl diphenyloxide disulfonates (Dowfax8390), and AMA/sorbitan monooleate (Tween80) were found to form microemulsion with this TEL surrogate, in which their supersolubilization regions were also identified. At those conditions, AMA/Dowfax839 yielded the highest surrogate oil solubilization followed by AMA and AMA/Tween80, respectively in batch experiments. The order of solubilization capacity of these surfactant systems was also discovered in the column study where the surfactant solutions were flushed to remove the residue saturated TEL surrogate from the contaminated soil. The removal efficiency was found in range of 86 to 98% within 40 pore volumes.