Removal of ionic dyes with different charges by foam separation

Substances with an opposite charge to that of the ionic surfactant are preferentially removed during foam separation. The effect of charge on foam separation was studied using cationic surfactant dode-cyltrimethylammonium chloride (DTAC) and several anionic dyes with different numbers of anionic groups: Acid Blue 119 (mono-anion), Ethyl Orange (mono-anion), Xylene Fast Yellow 2G (di-anion), and Acid Yellow 23 (tri-anion). The negatively charged surfactant counterion chloride (Cl-) and the anionic dye (Acid Blue 119) were competitively removed during foam separation. The first-order rate constant (k) for the removal of the two types of anions was estimated to be 8 x 10(-4) min(-1) for Cl- and 2 x 10(-3) min(-1) for Acid Blue 119. The results indicated that the target material Acid Blue 119 was removed 2.5 times faster than the surfactant counterion Cl-. The k values of these dyes were determined using the DTAC at 298 K. The results showed that the removal rate increased with increasing number of anionic groups among the investigated anionic dyes: Acid Blue 119 < Ethyl Orange < Xylene Fast Yellow 2G < Acid Yellow 23. The increase in the number of anionic groups in the dye provided binding at multiple points to the adsorption monolayer of the surfactant and became stronger in the foam. In foam separation using an ionic surfactant, it was found that the number of ionic groups in the substance significantly affected the removal rate. (c) 2022 Elsevier B.V. All rights reserved.