Abstract
The development of efficient methods for the removal of organic dyes, which are considered to be toxic to the aquatic biota and therefore destroy the ecosystem, is required. In this study, the extraction of methylene blue (MB) from aqueous solution into DEHPA/isooctane solution was investigated. MB was hardly extracted at all from the aqueous to the organic phase at pH values below 5, and the extraction ratio of MB greatly increased with increasing pH in the range of 5-6 by the electrostatic attraction between dissociated DEHPA and MB. MB was not extracted to the organic phase at pH values above 6, since DEHPA leaked from the organic to the aqueous phase. The addition of 2-ethyl-1-hexanol suppressed the DEHPA leakage, and then MB was successfully extracted to the organic phase at pH values above 6. It was found that MB was solubilized as an MB-DEHPA complex in the organic phase in the pH range of 5-5.5, whereas MB would be entrapped in the waterpool of the reversed micelle at pH values above 5.5. The back extraction ratio of MB from the organic to the aqueous phase was about 100 % at pH values below 5 because of the destruction of the reversed micelles and the disappearance of the electrostatic attraction between DEHPA and MB.
