Effects of calcium ions on the streaming potentials of zirconium hydrous oxide-polyacrylate formed-in-place membranes

Abstract

The effects of calcium ions on the electrokinetic properties of a zirconium hydrous oxide-polyacrylate membrane were investigated by measuring streaming potentials of this membrane and its precursor substrate, a zirconium hydrous oxide membrane, in potassium and calcium chloride solutions. The streaming potential per unit of transmembrane flux was calculated and used as a parameter to characterize the electrokinetic properties of the membrane-electrolyte systems. This parameter for the zirconium hydrous oxide-polyacrylate membrane was more positive in the calcium chloride solutions over the pH range investigated, 3.5 to 8.5, than in the potassium chloride solutions. However, for the zirconium hydrous oxide membrane it was the same within experimental variation in both electrolyte solutions at pH greater than and including the common zero point of charge. These results imply that the effect of the calcium ion on the electrokinetic properties of the zirconium hydrous oxide-polyacrylate membrane in this pH range is constrained to an interaction with the polyacrylate, probably through site binding with the carboxylate groups of the polymer. At pH less than the zero point of charge, the parameter was more positive for the calcium chloride solution than for the potassium chloride solution for both types of membranes, which implies alteration of the surface of the zirconium hydrous oxide by the calcium.