Measurement of the activity of electrolytes and the application of activity to hydrometallurgical studies

Abstract

The activity of HC1 in solutions of HCl-NaCl, and the approximate values of the activities of H+ and Cl− in solutions of HC1, HC1O4, HCl-NaCl, HClO4-NaClO4 and HC1O4-NaCl were determined at 25 ° by measuring the electromotive force of a cell consisting of a Pt-Pt black electrode and an Ag-AgCl electrode. The liquid junction potential, estimated by using Henderson’s equation as a first approximation, was subtracted from the measured electromotive force of the cell. Some hydrometallurgical problems which were difficult to understand with the concept of concentration were re-examined, using the activity values thus determined. These problems were the rate of non-oxidative leaching of galena and sphalerite, the acid dissolution rate of cupric oxide, and the rate of oxidation of Fe(II) with molecular dissolved oxygen. Although the dependence of the dissolution rates of galena, sphalerite and cupric oxide upon acid concentration appeared to be rather complicated, the dissolution rates of these minerals were found to be of first order with respect to aH+. It was also possible to elucidate the role of Cl− ions by using thea Cl-values. A rate equation obtained experimentally for the autoxidation of Fe(II) in HC1 solutions was found to generally explain the experimental results of previous researchers, which seemed to be inconsistent with each other.