Graphische Bestimmung der Gleichgewichtszusammensetzung im lonenaustausch

Abstract

If an ion exchanger is contacted with a dilute solution the amount of ions, adsorbed by the exchanger together with the co-ions, is negligible. In a stationary system (batch system) of determined amounts of the solid phase, the exchanger, and the liquid phase, the dilute solution, the momentary increasement of the absolute quantity of one ion, f.i. of the A-ion, in one of the phases is equal to the momentary decreasement of the absolute quantity of the same ion in the other phase. The relation between the changes of the equivalent ionic fractions in the phases is consequently reciprocal to the relation between the total ion contents of the phases. The total ion content of the exchanger is its total capacity, R C_R, that of the solution is L C_L. This relation is valid during the whole ion exchange reaction.

The coordinates in the usual ion exchange phase diagram are the equivalent ionic fractions in the phases. The composition of a certain system is represented by a point with the corresponding coordinates and the change of the composition by a line. As consequence of the relation above, in the present case this line is a straight one, the slope of which having the tangent equal to the relation between the ion content of the solution to the total capacity of the exchanger. To determine the equilibrium composition of a given system a straight line with the predetermined slope has to be drawn through the point, corresponding to the initial state of the system. This line cuts the exchange isotherm in the point, the coordinates of which are the equivalent ionic fractions in the equilibrium.

Unlike to the mathematical method of the determination of the equilibrium composition this graphical method is independent of the shape of the isotherm.