An experimental investigation is presented of the continuous, single equilibrium stage foam fractionation of chromate (CrO42-) and of thiosulfate (S2O32-) from 0.4 to 3.0 × 10–4Maqueous solutions. The cationic surfactant, ethyl-hexadecyldimethylammonium bromide (EHDA-Br), is modeled as a soluble ion exchanger, considering the exchange of CrO42-and S2O32-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.