Studies on Electrochemical Solvent Extraction of Metal Ions at Water/1,2-dichloroethane Interface

Abstract

Solvent extraction is one significant method to separate many kinds of metals. The solvent extraction involves the process by which a metal complex moves from aqueous phase to organic phase. The electrochemical study has been applied to the investigation of the interface between two immiscible electrolyte solutions (ITIES) because of the following advantages. An ionic transfer reaction rate at the interface can be controlled easily by the interfacial potential difference (or current). Therefore, it is possible to carry the metal complex across ITIES by the electrochemical driving force when the metal complex has an electrical charge. Freiser et al. [1][2][3][4][5] studied the transfer of the metallic ions which moved across the liquid/liquid interface by using voltammetry. investigated the ion transfer across the water/nitrobenzene interface by electrochemical methods, and discussed the reaction parameters for various cation transfers. Reymond et al. 10 developed an analytical method which used the half-wave potential, assuming that the diffusion coefficients are constant, and reported the complex stoichiometry (ratio of metallic ion to ligand) was related to concentrations of metallic ion and ligand. Furthermore, Reymond et al. 11 derived the theoretical expressions of the half-wave potential for transfer mechanisms by interfacial complexation/decomplexation (TIC/TID mechanism), by organic phase complexation (TOC mechanism) and by aqueous phase complexation (ACT mechanism). They reported that the complex of Pb(II) and 1,4,7,10-tetrathiacyclododecane (TTCD) had the multiple stoichiometries of 1:1 and 1:2 (metallic ion to ligand) in the transfer across water/1,2-dichloroethane (DCE) interface. Liu et al. 12 measured the voltammograms for transfer of Cd(II), Mg(II), Co(II), Zn(II), Cu(II) and Ni(II) across ITIES by using an ascending water electrode (AWE) and a stationary water electrode (SWE) system.Itagaki et al. 13 applied an electrochemical impedance spectroscopy (EIS) to the analysis of the solvent extraction of some metals. They examined the rate of solvent extraction and the correlation of the extraction rate and the distribution constant. The EIS discriminates the elementary steps in the solvent extraction, namely, the diffusion in aqueous and organic phases, and the charge transfer across ITIES. The authors 14 discussed the charge transfer mechanism of Mn(II) extracted by HQ into DCE by EIS, and showed that the measurement of EIS gave the rate constant and the interfacial capacitance. The authors 15,16 extended this method to analyses of the solvent extraction of Co(II) and Ni(II). In the previous work, 16 the Ni(II) species extracted by electrochemical driving force were confirmed by the in-situ determination of absorbance by spectrophotometry with an optical fiber system. Aprahamian et al. 17 and Watanabe et al. 18 measured rate constants of solvent extraction at the liquid/liquid interface by accelerating extraction rate with high-speed solvent stirring. Contrary to this, the rate constant at a stati...

Electrochemical Study of Solvent Extraction Based on Ion Transfer at the Aqueous/Organic Solution Interface

“…Itagaki et al [71][72][73] applied electrochemical impedance spectroscopy (EIS) to the study of the ion transfer mechanism involved in the solvent extraction of M 2+ ( M = Co, Ni, Zn, Mn and Fe ) with HQ.…”

Trapped in the coordination sphere: nitrate ion transfer driven by the cerium(iii/iv) redox couple

“…[1][2][3][4][5][6] In the latter, ions are separated between oil and water phases by changing the oxidation state, causing ions to migrate through the interface. [6][7][8][9][10][11][12] The electrochemistry underpinning such systems is complex as the ion transfer potential is inherently linked to the redox potential of the active species. [13][14][15] Because of this entanglement, there is lacking a fundamental strategy for designing redox-driven multiphasic ion transfer separation systems with potentials that are programmed at the molecular scale.…”

Development of high performance electrochemical solvent extraction method

“…One of the new solvent extraction techniques for which wide practical application is expected is a technique that has been called 'electrochemical extraction', 'electro-assisted solvent extraction', 'electrochemical solvent extraction', 'electrochemically assisted solvent extraction' or 'electrochemically modulated solvent extraction' [9][10][11][12][13][14]. The term 'electrochemical solvent extraction' will be adopted for use in this paper.…”

“…have been investigated widely based on VITIES during the last few decades [15][16][17][18][19][20]. The measurement of capacitance or impedance at the interface, together with VITIES, has offered information on the rate and mechanism of the ion transfer [12,16,[21][22][23][24]. VITIES has also been applied to the elucidation of the processes involved in solvent extraction, as well as membrane transport [9,[25][26][27][28][29].…”