Metal Extraction Driven By Galvani Potential at the Interface Between Two Immiscible Electrolyte Solutions

Abstract

In an immiscible water-oil system, potential determining salts can be applied to establish Galvani potential across the interface (ITIES). These salts contain a common ion in the both phases and, therefore, via a Nernstian equation, determine the Galvani potential difference that can be used to boost electron or ion transfer reactions across the ITIES [1,2]. The contribution of potential difference and potential determining salts to solvent extraction of various metals (Co, Cu, Ni, In) was investigated with cyclic voltammetry (CV) in a four-electrode cell and with shake-flask experiments; the extraction ratios were analyzed either by atomic absorption spectroscopy (AAS) or by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Di-2-(ethylhexyl)-phosphoric acid (D2EHPA) and diphenylthiocarbazone (Dithizone) were used as model ligands. While CV measurements showed ambiguous results - sometimes no ion transfer within the potential window was observed - shake-flask experiments showed clearly that the extraction ratio (co /cw ) of some metals is enhanced in the presence of potential determining salts (Fig. 1). Fig. 1. The contribution of the potential determining salt to the extraction ratio of Ni in pH 3 and 5. [1] P. Peljo, L. Murtomäki, T. Kallio, H.-J. Xu, M. Meyer, C. P. Claude, J.-M. Barbe, H. H. Girault, K. Laasonen, K. Kontturi, Biomimetic Oxygen Reduction by Cofacial Porphyrins at a Liquid-Liquid Interface, J. Am. Chem. Soc., 134, 5972-5984, 2012. [2] B. Su, R. Partovi-Nia, F. Li, M. Hojeij, M. Prudent, C. Corminboeuf, Z. Samec and H. H. Girault, H2O2 Generation by Decamethylferrocene at a Liquid|Liquid Interface, Angew. Chem., Int. Ed., 47, 2675-4678, 2008. Figure 1