ABSTRACT
When solid particles are immersed in liquid medium, solid-liquid interfacial interactions will
cause the formation of an adsorption layer on their surface. The material content of the
adsorption layer is the adsorption capacity of the solid adsorbent, which may be determined
in binary liquid mixtures if the so-called adsorption excess isotherm is known. Due to
adsorption, the initial composition of the liquid mixture, x01, changes to the equilibrium
concentration x1, where n s ¼ ns1 þ ns2, the mass content of the interfacial phase (e.g.,
mmol=g). This change, x01 x1 ¼ Dx1, can be determined by simple analytical methods. The relationship between the reduced adsorption excess amount calculated from the change in
concentration, n sðnÞ 1 ¼ n0ðx01 x1Þ, and the material content of the interfacial layer is given by the
Ostwald-de Izaguirre equation [1-5]. In the case of purely physical adsorption of binary
mixtures, the material content of the adsorption layer ðns ¼ n0 nÞ for component 1 is illustrated by the following material balance (see Fig. 1):
n0x01 ¼ ns1 þ ðn0 nsÞx1 ð1Þ ns1 ¼ n0ðx0i xiÞ ¼ n0Dxi ði ¼ 1; 2; . . .Þ ð2Þ
where n0 is the total quantity of liquid mixture referred to unit mass of the adsorbent (e.g.,
mmol=g adsorbent), x01 is the mole fraction of the ith component before adsorption, and x1 is that in the equilibrium homogeneous liquid phase. The adsorption excess isotherms ns1 ¼ f ðxiÞ calculated in accordance with Eq. (2) can be classified into five basic types by the Schay-Nagy
isotherms classification [2-4].
