Experimental Foam Fractionation Selectivity Coefficients for the Alkali (Group IA) Metals

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Abstract
An experimental investigation is presented of the continuous-flow foam fractionation of each of the colligends Li+, K+, Rb+, and Cs+ versus Na+, the counterion of the dodecylsulfate anion over the aqueous solution concentration range of 1.0 × 10−4 to 6.0 × 10−4 M. Initial experiments with K+ confirm the achievement of a single-equilibrium-stage separation. Surfactant selectivity coefficients, defined in terms of a colligend-surfactant counterion exchange model at the interfaces of the rising gas bubbles, are established. They represent the ratio of colligend to sodium in the interfacial “stream” to that in the residual steam and are Li+, 0.92; K+, 1.10; Rb+, 1.51; Cs+, 1.65. The selectivity sequence is compared to the sequence of absolute partial molal entropies of the cations in aqueous solution.