Surfactant enhanced solubilization for organometallic compound removal

Abstract

To find the approach to clean up the contaminated site by surfactant flushing technique based on the solubilization mechanism. Even tetraethyl lead (TEL) is a focused contamination in this study, TEL surrogate was needed to be identified and used instead of TEL due to its toxicity and troublesome handling. The equivalent alkane carbon number (EACN) of TEL was determined and found to be about 6.04 to 7.68. This EACN value had been used as one of criteria for proper surrogate selection. Dibutyltin dichloride (DBT) was selected based on designed criteria of being organometallic compound. The surrogate oils were then prepared as the mixture of DBT and decane at the molar ratio of 0.038:0.962 and mixture of DBT and perchloroethylene (PCE) at the same ratio. Various surfactants systems were tested to form a microemulsion with these surrogate oils. The selected surfactant solution was 3.6 wt.% sodium dihexyl sulfosuccinate and 0.4 wt.% monoalkyl diphenyloxide disulfonates. The solubilization study revealed that PCE and decane were solubilized into the core of these surfactant micelles in both single and mixed oil systems. The solubilization isotherm of DBT suggested that DBT solubilizes near the surface of the micelles in a single oil system. The DBT solubilization was increased if mixed with PCE or decane indicating that those oils may help facilitating the DBT into the core of micelles. It may be concluded that the DBT behaves like a polar organic compound. The solubilization of PCE and decane were quantified from the effluent stream in the column experiment and compared the result to their solubilization capacity. The mechanism of solubilization of PCE and decane can be explained following the behavior found in batch study. However not for the case of DBT that the solubilization was found extremely low. Moreover, the gradient technique could not enhance the solubilization of DBT. The adsorption of DBT onto sand surface was a major cause to limit DBT solubilization. The adsorption of DBT could be minimized by altering pH of surfactant solution to the very acidic condition (pH 1), where the DBT is a cationic form and the surface of sand possesses positively charges but this strong acidic condition is not applicable in an actual site remediation. At pH 4 and pH 9, the DBT removal efficiency was not promising. Thus, the removal of DBT-PCE mixture by solubilization was improper to be applied if the media naturally possess negative surface charge such as sand and silicon oxide.