Evaluation of Calcium Ion Transport Number through a Cation Exchange Membrane By Chronopotentiometry

Abstract

In this research work, the transport properties of calcium ions (Ca2+) in a heterogeneous cation exchange membrane (IEM) MK-40 of Schekinoazot. Aqueous solutions of sodium chloride (NaCl) and calcium chloride (CaCl2) of 0.01 M and 0.02 M concentration, respectively, were used. The limit current density and transport numbers were evaluated by means of the chronopotentiometry technique, applying electric current pulses, obtaining electric potential differences, from which the chronopotentiograms were obtained. Then, plots of electric potential difference variation with respect to time were constructed to find the transition time. A linear fit of the transition time with the square of the inverse of the inverse of the electric current density was performed based on the modified Sand equation to determine the Ca2+ transport number. The results showed the Ca2+ transport numbers in the cation exchange membrane and in solution are 0.976 and 0.437, respectively. The limiting current density was also found for both membrane-solution systems. We conclude that chronopotentiometry is an accurate and fast technique for the determination of the ion transport number in systems consisting of ion exchange membranes and electrolyte solutions.