Chemical and electrochemical behaviour of copper ions in the ZnCl2-2NaCl mixture at 450 °C

✍ Scribed by Y. Castrillejo; C. Abejón; M. Vega; R. Pardo; E. Barrado

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 986 KB
• Volume: 42
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/s0013-4686(96)00306-4

✦ Synopsis

To

investigate the possibility of selective chlorination to separate copper traces from zinc matrixes, we have determined redox and oxoacidobasic properties of the copper in the molten ZnClrZNaCl.

In this way, the stability of copper chlorides and oxides as well as the electrochemical behaviour of Cu(I) have been studied by using voltammetric, chronopotentiometric, chronoamperometric and potentiometric techniques. The experiments were performed in a controlled argon atmosphere cell with safety features. Copper oxidation states I and II have been shown to exist in the mixture and the stability of metallic copper has been confirmed. The standard potential of the redox couple Cu(II)/Cu(I) and Cu(I)/Cu(O) have been determined by voltammetry (/!&l,,~c.,,, = -0.135 f 0.016 V vs Cl&-)

and by potentiometry (,!&,~~cu,O, = -1.129 f 0.030 V vs Cl2/Cll), respectively, finding that Cu(I1) ion can oxidize, under certain conditions, the chloride ion of the melt. Moreover, the stability of both Cu(I) and Cu(I1) oxides was investigated and the solubility product of CuO was determined, whereas CUZO was found to be a hard oxide donor. These results have allowed the construction of E-p02-equilibrium diagram. On the other hand, the kinetics of copper electrodeposition and electrocrystallization at a tungsten electrode were studied, and it was demonstrated that the process is quasi-reversible. In the same way, the Cu(II)/Cu(I) exchange was found to be quasi-reversible. The values of the kinetic parameters, K" and t(, were obtained for both reactions. Mass transport towards the electrode is a simple diffusion process, and the diffusion coefficient has been calculated. Chronoamperometric studies indicated instantaneous and three dimensional nucleation and crystal growth of copper.