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I.

INTRODUCTION

THEactivities of water and solutes in mixed aqueous solutions are important parameters in understanding the mechanism of reactions which are common in hydrometallurgical systems. The authors have applied an activity concept to the discussion of some hydrometallurgical reactions.L~-71 Cupric chloride is one of the most reactive leachants for leaching sulfide minerals in acidic chloride media, and cupric sulfate is also an important electrolyte in the copper electrolysis. Although studies on the acidic cupric chloride or cupric sulfate solution have important implications, only a few thermodynamic data of these solutions have been reported. Among many thermodynamic factors, activities of water and solutes are the most basic parameters in characterizing the aqueous solutions themselves. In this study, the activities of water in the solution systems of n2SOa-CuSO4-H20 and HC1-CuC12-H20 were measured at 298 K. The activities of H2SO 4 and H + in the solution system of H2SO4-CuSO4-H20 were also measured at 298 K by the emf method. On the other hand, the mean activity coefficients of solutes in both solution systems were determined at 298 K by the thermodynamical calculations based on the water activity data. This paper details the results obtained.

II.

EXPERIMENTAL PROCEDURES

A. Determination of Water Activities The water activities in the solution system of H2SO 4CuSO4-H20 were measured at 298 K by an isopiestic method, I8~ since both H2SO 4 and CuSO4 are nonvolatile, whereas those in the solution system of HC1-CuC12-H20

HIROSHI MAJIMA, Professor, and YASUHIROAWAKURA,Lecturer, are with the Department of Metallurgy, Kyoto University, Sakyo-ku, Kyoto 606, Japan. Manuscript submittedJune 3, 1987. METALLURGICALTRANSACTIONSB

were measured at the same temperature by a transpiration method t91 due to the volatile character of HC1. The experimental procedures of both methods were the same as those reported previously. I7~ All the chemicals used in this study were of reagent grade. Solutions were prepared with de-ionized water whose resistivity was above 5 x 106 ohm cm. The molalities of stock solutions of H2SO4, CuSO4, HC1, and CuC1 z were determined by the density measurement. Each test solution was prepared by mixing de-ionized water with these stock solutions and weighed just before each experiment. The molalities of the solutes in the test solutions were determined by calculation from the volume of deionized water added at 298 K.

B. Determination of Activity Coefficients of H2S04 and H + in the Solution System of H2SO4-fuSO4-n20 by the Emf Method The a(H2SO4) in the solution system of n2so4-CuSO 4H20 were determined at 298 K by the emf method using the following two cells: C1- ISE[0.01 mol kg -~ HCllGlass electrode

[1]

PbO2-PbSO 4 ITest soln. [ Glass electrode

[2]

where C1- ISE is a chloride ion selective electrode. Since cupric sulfate may affect the potential of a Pt-Pt black electrode, a glass electrode was employed as a hydrogen ion sensitive electrode in this study. The effect of asymmetric