Electrochemical extraction of metallic Y using solid and liquid double cathodes

Abstract

To select proper electrode material for the extraction of rare earth elements and purification of salt, double cathode electrolysis cell was designed to compare the extraction of Y on solid and liquid electrodes. The electrode process kinetic and thermodynamic data of Y(III) on liquid Zn electrode and solid Cu electrode were studied employing cyclic voltammetry (CV), open-circuit chronopotentiometry (OCP) and linear polarization (LP), respectively. The thermodynamic results indicated that the reduction peak potentials of (Y–Zn)solution and Zn-rich Y–Zn compound are more positive than that of Cu-richest Y–Cu compound, and the standard molar Gibbs energy of formation for (Y–Zn)solution is smaller than those for Y–Cu compounds, which meant (Y–Zn)solution formed easily. Furthermore, the dynamic properties, such as exchange current densities and charge-transfer resistances of Y(III)/Cu7Y and Y(III)/(Y–Zn)solution couples, were determined employing LP technique. The reaction activation energies for the two couples were also estimated according to the relationship of exchange current density and temperature, which showed the reaction activation energy for Y(III)/Cu7Y couple is larger than that for Y(III)/(Y–Zn)solution couple. To compare to the extraction rate and efficiency, the electrochemical extracting Y on single cathode (solid Cu or liquid Zn) and double cathodes (solid Cu and liquid Zn) was executed by constant current electrolysis under same conditions. The results displayed that the extraction rate and efficiency of metallic Y is higher on liquid Zn electrode in the first 6 h, and only a small amount of metallic Y was deposited on solid Cu electrode in double cathode system.