Several methods (e.g., UV/H2O2 oxidation, adsorption, flocculation-precipitation) are normally employed to remove dye from water. A new technique based on liquid/liquid extraction using reverse micelles is proposed whereby recovery of solvent and reuse of dye is possible. Experiments were conducted by mixing a known quantity of dye in aqueous phase and solvent-containing surfactants in a simple mixer. The separation of solvent phase, containing encapsulated dye in reverse micelles, from aqueous phase due to gravity results in separation of dye from water. The removal of different ionic dyes (e.g., eosin yellow, methylene blue, malachite green, methyl orange, orange G) from aqueous phase in the presence of different cationic and anionic surfactants [e.g., sodium dodecylbenzene sulfonate, sodium bis(2-ethylhexyl) sulfosuccinate, hexadecyltrimethylammonium bromide, and cetyl pyridinium chloride] in different solvents (e.g., amyl alcohol, benzyl alcohol, methyl benzoate, and isooctane) were studied by conducting experiments. The percentage removal of dye from aqueous phase increases with the decrease in dye concentration or with the increase in surfactants concentration. Furthermore, the percentage COD removal of dye is increased with the increase in surfactant concentration. The nature of solvent has minimal effect on percentage removal of dye. The ratio of solventto aqueous phase volume required for the removal of dye decreases with the increase in surfactant concentration. It is possible to back-extract dye into aqueous phase and recover solvent by using counterionic surfactants. The separation of aqueous phase from the aqueous-phase solvent dispersion is faster for amyl alcohol as compared to benzyl alcohol and methyl benzoate. A theoretical model based on ion-exchange reaction between surfactants and dye is used to analyze the experimental data.

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Among the several methods, dye removal from water by solvent extraction using reverse micelles is promising in terms of the simplicity and efficiency of the process. The recovery of solvent and reuse of dye after its removal is related to the economic viability of the process. In the present study, backward extraction or recovery of dye into an aqueous phase from the solvent phase by using a counterionic surfactant after forward extraction is experimentally studied using a simple mixer and settler arrangement. The backward extraction of dye also resulted in the recovery of solvent. The effects of different parameters, such as the surfactant concentration, pH, and KCl concentration on the recovery of methyl orange and methylene blue dyes, are investigated. The percentage of both cationic and anionic dyes recovered increases with an increase in the counterionic surfactant concentration or with a decrease in the KCl concentration. The percentage of recovery of anionic methyl orange increases with a decrease in pH, whereas that for cationic methylene blue increases with an increase in pH. Selective removal of dye from a cationic and anionic dye mixture was experimentally studied by treating the dye mixture with reverse micelles of anionic and cationic surfactants in a stepwise manner. The results obtained are explained based on electrostatic interaction between the surfactant and dye.