Transport studies of nickel arsenate membrane

The membrane potentials of inorganic membrane were measured with uni-univalent electrolytes solution using saturated calomel electrodes. Theories for the salt concentration dependence of uni-univalent potentials, proposed by (a) Teorell–Meyer–Sievers and (b) Kobatake method have been compared in order to obtain a relationship for the theoretical values of uni-univalent potentials. The order of fixed charge density for electrolytes used is found to be KCl > NaCl > LiCl. The conductance values have been found to increase with increase in concentration as well as with temperature. The specific conductance values of electrolytes follow the sequence for the cations: K+ > Na+ > Li+. The membrane pores reduce the conductance of small ions, which are much hydrated. An increase in conductance with increase in temperature may be due to the state of hydration, which implies that the energy of activation for the ionic transport across the membrane follows the sequence of crystallographic radii of ions accordingly. Negative ΔS∗ values are considered to indicate either formation of a covalent bond between the permeating species and the membrane material or that the permeation through the membrane may not be the rate determining step. The structure of the membrane was observed with the aid of a scanning electron microscope.