Electroextraction and thermochemistry of fission element gadolinium on plumbum electrode in molten salt

Abstract

• The results are vital to electroextraction and thermochemistry of Gd on Pb electrode. • Electrochemical parameters are meaningful to dry reprocessing of nuclear fuel. • Extraction raido of Gd on Pb electrode is about 99% by potentiostatic electrolysis. • The parameters were investigated by means of transient electrochemical techniques. • The results provide theoretical basis for extraction and separation of Lns and Ans. In order to electrolytically recover slivers of fission elements Gd from spent fuel, the electrochemical behavior of GdCl 3 and PbCl 2 on inert tungsten electrode in LiCl-KCl melts was systematically investigated by cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit chronopotentiometry (OCP). The kinetic and thermodynamic parameters of electrode process on Pb(II) and Gd(III) ions were also calculated by electrochemical methods. The results revealed that the diffusion activation energies ( E a ) of Gd(III) and Pb(II) are 31.81 kJ·mol −1 and 31.9 kJ·mol −1 ; the Δ G f ∗ 0 and Δ H f ∗ 0 of Gd(III) are −1035.87 kJ·mol −1 and −198.6 J·mol −1 ·K −1 , Pb(II) are −294.75 kJ·mol −1 and −60.5 J·mol −1 ·K −1 , respectively. The co-reduction behaviors of Gd(III) and Pb(II) ions were also studied, and three Gd x Pb y intermetallic compounds were detected by CV and OCP techniques. In order to study the deposition mechanism of Pb 3 Gd intermetallic compounds, its thermodynamic parameters were calculated. In addition, potentiostatic/galvanostatic electrolysis were carried out to extract Gd on plumbum membrane electrode. The results showed that the recovered Gd was in the form of Pb 3 Gd intermetallic compound at −1.75 V. The cathodic deposits of ion were characterized by X-ray and scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The results showed that Gd was extracted on plumbum membrane electrode with high extraction rate by ICP-AES analysis.