Ion Exchange Equilibrium of Wood Pulp Dispersed in Electrolyte Solution

Abstract

In the system containing wood pulp and electrolyte solution, pulp behaves as weak acidic H-type cation exchanger owing to the presence of carboxyl groups. Investigation on the adsorption properties of pulp was carried out by the application of Donnan's membrane equilibrium theory to this system. Assuming that the change of hydrogen ion concentration of external solution after immersion of wood pulp is due to the exchange reaction between metal ion and hydrogen ion at carboxyl group, ion exchange isotherm and selectivity coefficient for ion exchange were obtained.Possible mechanism for ion adsorption in this system was discussed on the basis of the following two processes : (1) ion exchange reaction and (2) salt adsorption by forming ion pair. Concentration range covered were 1×10-51N. At lower concentration, ion exchange reaction primarily seems to occur and follows the isotherm of Freundlich type. On the other hand, at higher concentration, ion adsorption does not follow this isotherm. This is possibly due to the additional adsorption of ion by salt adsorption process at higher concentration. In this system hydrogen ion was liberated into external solution by ion exchange, but the simultaneous adsorption of hydrogen ion onto pulp surface also takes place. Change in accessibility of wood pulp without altering the amount of carboxyl group also affects the ion exchange equilibrium.At the present stage, because of insufficient establishment of the theory concerning the behavior of ion in concentrated electrolyte solution, the problem of ion adsorption to wood pulp in electrolyte solution of the range of higher concentration is left for future study.