Selective separation of dyes by colloidal gas aphrons: Conventional flotation vs countercurrent chromatography

Abstract

The present study investigates the use of Colloidal Gas Aphrons (CGA), which are surfactant stabilised microbubbles, to separate a mixture of dyes, in a batch mode and continuous mode. For this reason, CGA are applied in a flotation column and also for the first time here, in combination with countercurrent chromatography (CCC). The latter is used in order to explore an alternative scalable method to use CGA in a continuous mode. The mixture consisted of the anionic dye methyl orange and the cationic dye methylene blue which were separated with the positively charged CGA generated with a cationic surfactant. The selective separation of methyl orange (recovery 70.9\%) from the mixture of dyes clearly confirms the effect of electrostatic interactions on the separation. The optimum conditions of the CGA separation (volumetric ratio of CGA to feed equal to 6) established with the flotation column were applied to the CCC separation. First, different operating modes of the CCC were tested to determine the optimum stability of CGA in the centrifuge. Studies on the CCC behaviour of methyl orange in mixtures with the methylene blue showed that the separation values were slightly higher compared with the conventional separation in a flotation column. However, the selectivity of separation was higher for the flotation column (73.6 vs 13.3), which might be attributed to the observation that CGA collapsed easier in the CCC, whilst separation time was lower in the CCC (226 sec in CCC vs 600 s in the flotation column). This study shows that there is potential to use CCC as a scalable continuous separation of a mixture of dyes using CGA although overall, the best performance was obtained with the flotation column.