Transport Studies of Divalent Ions through Nafion-117 Ion Exchange Membrane in the Presence of Polyacrylate

The effect of binding of divalent ions (Mg2+ and Ba2+) with a polyacrylate anion on the Donnan membrane equilibrium distribution and the transport kinetics have been studied using Nafion-117 membrane. The extent of association of the divalent counterions with polyacrylate has been ascertained from the deviation from Donnan membrane equilibrium condition. The equilibrium concentrations of ions in polyacrylate compartment have been found to be in excess of expected equilibrium concentrations obtained from Donnan membrane equilibrium condition. This has been attributed to higher electrostatic interactions of divalent ions with the polyacrylate backbone compared to the monovalent ions. The strength of binding has been found to depend on the nature of divalent ion. Precipitation has been observed for Ba2+, thereby changing the total salt concentration of the polyacrylate compartment. Also, the strength of counterion binding has been found to depend on salt concentrations of the two compartments. The rate of transport of the ions with polyacrylate in the receiver solution has been calculated based on modified NernstPlanck (NP) approach. The calculated transport kinetics have been found to agree with the experimental transport kinetics.