Selectivity Coefficients for Divalent Oxyanions from the Continuous Foam Fractionation of a Quaternary Ammonium Surfactant

Abstract

An experimental investigation is presented of the continuous, single equilibrium stage foam fractionation of chromate (CrO₄ ^2-) and of thiosulfate (S₂O₃ ^2-) from 0.4 to 3.0 × 10–⁴ M aqueous solutions. The cationic surfactant, ethyl-hexadecyldimethylammonium bromide (EHDA-Br), is modeled as a soluble ion exchanger, considering the exchange of CrO₄ ^2- and S₂O₃ ^2- or EHDA-CrO₄ ^? and EHDA-S₂O₂ ^? for Br^?. The data indicate that EHDA-CrO₄ ^? or EHDA- S₂O₃ ^? is exchanged with Br^?. The selectivity coefficient for chromate is 3.90 and that for thiosulfate is 16.8.