Determination of Water and Solute Activities in H<SUB>2</SUB>SO<SUB>4</SUB>&ndash;In<SUB>2</SUB>(SO<SUB>4</SUB>)<SUB>3</SUB>&ndash;H<SUB>2</SUB>O System

Abstract

The activities of water of the system H2SO4-In2(SO4)3-H2O are determined by using the isopiestic method at 298 K. The results obtained satisfactorily obey the Zdanovskii's empirical rule. From the water activities determined isopiestically, the mean ionic activity coefficients of the solutes are calculated by applying the Mckay-Perring method. Furthermore, the applicability of the Meissner's empirical procedure to estimation of the mean ionic activity coefficient of indium sulfate and that of the RobinsonBower equation to evaluate the water activity to the present solution system are also discussed. (Received October 16, 1986) Keywords: water activity, mean ionic activity coefficient, sulfuric acid, indium sulfate, isopiestic method, electrolyte aqueous solution. ‡T . Introduction Most of the valuable metals utilized as functional materials are frequently recovered as byproducts from the production processes of mass-produced metals. In this case, the separation between them may be made occasionally by precipitation operation by neutralization of the leaching solution containing sulfuric acid and metal sulfates. As a theoretical background for the precipitation operation, we commonly refer to the ion activity-pH diagrams of simple metal-H2O systems. It is, however, questionable whether such a simple theory can be applied to more complicated systems containing sulfate ions, which have a strong tendency to form sulfato-complexes with metal ions.From this viewpoint a series of investigations have been made by the authors on the pH-dependence of the solubility of IIIb-metal hydroxysalts(1)-(3). However, to analyse the experimental results obtained, some thermodynamic information about the systems H2SO4-M2(SO4)3-H2O (M:Ga,In) was needed. The objective of this paper is, therefore, to present information on the water and solute activities in the system H2SO4-In2(SO4)3-H2O, being not available yet.