Electrochemical reduction of Gd(III) and Nd(III) on reactive cathode material in molten fluoride media

Abstract

The electrochemical reduction of two lanthanides (neodymium Nd and gadolinium Gd) was investigated in the 800-950°C temperature range on nickel and copper electrodes. These materials react with lanthanides (Ln) to form intermetallic compounds. The formation mechanism of the alloys was determined by coupling electrochemical techniques and Scanning Electron Microscopy (SEM) after electrolyses runs; this also allowed the identification of the binary compounds formed. In addition, from the electrochemical results, we calculated the Gibbs energies of Nd/Ni, Gd/Ni, Gd/Cu and Nd/Cu.

Neodymium and gadolinium extraction from molten fluorides by reduction on a reactive electrode

“…As reported in Ref. [11], the voltammogram peaks correspond to the formation of Ni 5 Nd, Cu 6 Nd, Ni 5 Gd and Cu 6 Gd, respectively. (ii) introduction of a EC into the bath for an electrolysis time of around 3 h to recover the alloy; this electrode was then removed from the experimental medium.…”

“…Reference [11] dealt with our results on the electrochemical behaviour of Nd(III) and Gd(III) on reactive nickel and copper electrodes. The study showed that Nd(III) and Gd(III) could be reduced by alloying with the cathodic material (Cu or Ni) at far more anodic potentials than on an inert cathode; this so-called 'depolarization effect'allows the theoretical extraction efficiency of these lanthanides to be enhanced up to 100%.…”

“…In a previous report dedicated to the extraction of Nd and Gd from a molten fluoride mixture by electrodeposition, Nourry et al demonstrated that (i) the equilibrium potential of Nd and Gd in the molten electrolyte is too close to that of solvent reduction to be able to expect complete extraction of each of the elements [11]. (ii) the use of a reactive cathode allows the reduction potential of Nd and Gd ions in alloys with the cathodic material, to be shifted towards more anodic values and consequently, the theoretical extraction efficiency to be close to 100% for these elements [11].…”

Thermodynamic reassessment of Gd–Ni system

“…Gibbs energies of formation of intermetallic compounds at 1113K were further calculated and compared with data measured by Nourry et al [40] in Fig. 5.…”

“…Using direct synthesis calorimetry, Guo and Kleppa [37,38] measured the standard enthalpies of formation of GdNi and GdNi 5 compounds. Nourry et al [40] measured experimentally the Gibbs energies of formation of some Gd-Ni intermetallic compounds. The predicted enthalpies of formation of Gd-Ni alloys from the semi-empirical model of Miedema et al [39] are also available in the literature.…”