Extraction Kinetics of Methylene Blue by AOT and DEHPA Reversed Micellar Solution

Water pollution in China, Southeast Asia and other developing countries is a major problem, one of which is synthetic dyes contained in industrial wastewater. In this study, we focused on reversed micellar extraction which is promising from the viewpoint of both costs and energy saving, and examined the extraction rate of methylene blue (MB) using sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and di(2-ethylhexyl)phosphate (DEHPA). In the AOT/isooctane system, the overall mass transfer coefficient of the MB extraction, KW, decreased with increasing NaCl or KCl concentration. In contrast, in the AOT/2-ethyl-1-hexanol (EHA) and DEHPA/EHA systems, the effect of the KCl concentration was smaller. For the AOT/(isooctane + EHA) and DEHPA/(isooctane + EHA) systems, the KW value increased with increasing EHA concentration. However, the dissolution of MB in the organic solvent cannot be ignored at higher EHA concentrations. At the same concentrations of salt and EHA, the KW values of the AOT and DEHPA systems were almost the same. The dissociation state of DEHPA changed with pH, and the KW value decreased with decreasing pH. It was confirmed that the KW value for MB extraction was determined by the dissociated DEHPA concentration.