Electrolytic reduction of Eu(III) to Eu(II) in acidic chloride solutions with titanium cathode

Abstract

The feasibility of a rare earth separation process by electrolytic reduction of Eu(III) with a titanium cathode was examined by cathodic polarization characteristics of Eu(III) on a titanium electrode and batch-type electrolytic reduction of Eu(III) using a bipolar electrolytic cell in acidic aqueous solutions of EuCl3. The reduction of Eu(III) started at a cathode potential of about −0.6 Vvs standard hydrogen electrode (SHE). The plateau current for the reduction of Eu(III) was observed at around −1.2 Vvs SHE, but a further decrease in cathodic potential resulted in a decrease in the reduction current, which was caused by the hydrolysis of Eu(III). The plateau current is a diffusion-limiting current in the reduction of Eu(III). In the batch-type electrolytic reduction of Eu(III) using a bipolar electrolytic cell, complete reduction of aqueous 0.1 kmol m−3 EuCl3 solution with a current efficiency of over 0.6 could be achieved by keeping the catholyte pH at 2, to avoid hydrolysis of Eu(III). The final percent Eu(III) reduction of the solution from an industrial europium purification process, which contained other rare earths, was lower than that of a synthetic EuCl3 single electrolyte solution probably because of a more significant hydrolysis of rare earth ions. However, the final percent reduction increased with decreasing reduction current, the concentration of rare earths, and the viscosity of solution.