A cationic surfactant as a soluble ion exchanger in the continuous foam fractionation of nitrate; iodide, and bromide

An experimental investigation is presented of the continuous foam fractionation of NO₃⁻ versus Br⁻ and of T⁻ versus Br⁻ with a quaternary ammonium surfactant at concentrations of the order 1.8 × 10⁻⁴M. An equation is derived to enable the computation of anion selectivity coefficients from foam fractionation data. The key assumptions of the derivation are verified experimentally. The selectivity coefficient for NO₃ versus Br⁻ is 1.56 ± 0.28 and for I⁻ versus Br⁻ is 5.85 ± 1.81, established from 40 continuous‐flow experiments. Precipitation of EHDA‐I is indicated at the highest ratios of the bulk solution concentrations of I⁻ and Br⁻. significantly, both selectivity coefficients are independent of the fraction of the exchanger occupied by the preferred ion, indicating an exchanger activity coefficient ratio of unity, and are independent of ionic strength. The counterion present markedly influences the surfactant distribution coefficient.