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

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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.