Redox potential characteristics of cupric chloride solutions

Abstract

The nature of the redox potential in concentrated cupric chloride solutions where [NaCl] = 280 g/L and [Cu 2+] = 10–40 g/L was studied at temperatures 25–85 °C for 49 days. The redox potential of the solution was studied as a function of solution storage time, temperature and initial cupric chloride concentration. Measured redox potential values varied in the range 0.56–0.75 V vs. Ag/AgCl, increasing with increasing total copper concentration and temperature. The rate of reduction of cupric to cuprous species was highest in the most concentrated solution and occurred in 5 days, with the concentration of copper species 40 g/L. The solutions having initial copper concentrations of 30, 20 and 10 g/L reached steady state after 20, 26 and 26 days, respectively. The standard electrode potential, E o, in concentrated cupric chloride solution was determined using the Nernst equation. The form of cuprous complex was proposed on the basis of the value of E o, since the cupric/cuprous standard electrode potentials divide clearly in two groups. The E o for redox couples, with cuprous present as a chloro-complex form, is a minimum of 0.3 V higher than the E o for redox pairs with uncomplexed cuprous ions. E o value for the redox pair existing in a HydroCopper ® type environment was calculated to be − 0.039 (± 0.121) V vs. Ag/AgCl. This suggests that in a very concentrated cupric chloride solution without any additives, not all cuprous ions present are complexed with chlorides.