The problems of phase equilibrium, the equilibrium distribution of a component between phases are considered, and the distribution coefficient is determined in two versions. A formula for determining the selectivity coefficient is obtained, equations relating the compositions of coexisting phases, by equating the activities in these phases, Margules constants are found. Based on the given content of the components, the numerical values of (Margules constant for A component in solvent S) and (Margules constant for S component in solvent A) were found Using the Margules equation for ternary systems, the activity coefficients of components A and B are determined in two phases. The experimentally obtained values of the molar fractions of each of the three components, responsible to different points of the binodal curve, the corresponding activity coefficients of component B, and also calculated on these coefficients of the activity values

doi.org/10.32737/0005-2531-2020-4-17-21

**Keywords :**equilibrium, coefficient, extraction, component, equation, activity, selectivity