N.B. Ferapontov *, V.I. Gorshkov, L.R. Parbuzina,
N.L. Strusovskaya, A.N. Gagarin
M.V. Lomonosov Moscow State University, Department of Chemistry, Leninskie Gory, GSP-2, 119992 Moscow, Russian Federation
Received 18 March 2005; received in revised form 28 June 2006; accepted 19 August 2006
Available online 2 October 2006
Abstract
This work deals with thermodynamic description of equilibrium between an ion exchange resin and the solution of low
molecular weight electrolyte. The suggested approach allows calculating thermodynamic constant of ion exchange
equilibrium.
In order to calculate the activity of ion exchange groups in the resin having monoionic form we used published reference
data assuming that the activity of resin exchange sites and that of corresponding monomer are equal in the solutions with
equal concentrations. For ion exchange resin in mixed form in equilibrium with the mixed solution of corresponding low
molecular weight electrolytes the method of calculating each of ionic forms was also suggested. These activities were used
to determine the constant of ion exchange equilibrium.
 2006 Elsevier B.V. All rights reserved.
Keywords: Ion-exchange resin; Equilibrium; Theory

1. Introduction
A bead of ion exchange resin represents a threedimensional
polymeric matrix (network) with positively
or negatively charged functional groups. The
study of water and electrolyte sorption by ion
exchange resins was proceeding vigorously as far
back as 50–60th of the last century. These studies
were reviewed in many books; see for instance [1–
5]. The notions of these phenomena currently present
in physical chemistry of ion exchange resins are
based on the concept of quasi-homogeneity of swollen
resin. Moreover, the notions employed the
model of electrolyte Donnan distribution in which
the bead surface is likened to semi-permeable membrane
[6,7].
In practice, the distribution law followed from
the Donnan equation is not always fulfilled. To
explain the discrepancies Glueckauf and Watts [8]
supposed that both the functional sites and cross
linking bridges are distributed non-uniformly
throughout the entire volume of resin beads. Certain
shortcomings of this approach were reported
in [3, p. 31–32].
Davies and Yeoman [9] were the first to suggest
the idea of heterogeneous structure of ion exchange
1381-5148/$ — see front matter  2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.reactfunctpolym.2006.08.005
* Corresponding author. Tel.: +7 95 939 4019; fax: +7 95 939
0283.
E-mail address: nferapontov@mtu-net.ru (N.B. Ferapontov).
Reactive & Functional Polymers 66 (2006) 1749–1756
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