440
H. Matsuura et al. / Journal of Physics and Chemistry of Solids 66 (2005) 439–442
Fig. 1. A schematic view of the concept: reprocessing of spent hydrogen absorbing alloys.
Depending on the concentration and current density,
Tables 1 and 2, respectively. The geometry of electrodes
and a crucible is very similar to that previously reported [2].
separation of each rare earth would be possible. The
advantages of the suggested procedure are the compact
system, simplicity of the process, and the additional
possibility of reducing secondary wastes, resulting in
reduction of reprocessing cost and energy consumption.
The purpose of this study is several electrochemical
measurements under different operating conditions have
been performed to check the feasibility of processes (1)
and (3).
3
. Results and discussion
Cyclic voltammograms (CV) of LaCl , CeCl and NdCl
3
3
3
in LiCl–KCl eutectic at 793 K are shown in Fig. 2. In all
cathodic sweeps, shoulders are observed before electro-
deposition of melt bath component. They correspond to
electro-deposition of rare earths. Clear peaks are also
identified in all anodic sweeps. These peaks are due to
anodic dissolution of rare earths. With increasing scan rate,
the potential of the cathodic shoulders become negatively
larger, while the peak position of the anodic curves do not
change much, as shown in previous reports [2,3]. It is
conjectured that the cathodic reaction is quasi-reversible,
while the anodic reaction is almost reversible. In the
2
. Experimental
To avoid from contamination of moisture and oxygen, an
electrochemical cell were installed in a dry argon circulated
glove box (Miwa seisakusho Co. Ltd). Electrochemical
measurements have been performed by using a PC
controlled electrochemical analyzer (ALS). All anhydrous
chlorides have been purchased in ampoules with dry argon
atmosphere through AAPL and used for electrochemical
measurements without any further treatments. As the first
step, several electrochemical measurements have been
performed to confirm the difference of electro-deposition
potentials among rare earths. After that, electrolysis tests
have been carried out by using electrochemical conditions
previously optimized. Typical conditions for electrochemi-
cal measurement and electrolysis studies are listed in
cathodic sweeps of CVs containing LaCl
were observed which correspond to absorption and normal
peaks [2]. However, in CVs containing CeCl , only one
shoulder was appeared. The cathodic sweeps of CVs
containing NdCl have more complicated feature due to
, two shoulders
3
3
3
2
C
the possible existence of Nd
reactions.
during electrochemical
Electro-deposition and electro-dissolution potentials are
clearly determined by differential pulse voltammetry
(DPV). DPV obtained from the system containing rare
Table 1
Table 2
Experimental condition for electrochemical study
Experimental condition for electrolysis
Molten salt
59 mol%LiCl–41 mol%KCl w250 g
793 K
Molten salt
Temperature
Anode
59 mol%LiCl–41 mol%KCl w250 g
793 K
Temperature
Counter electrode
Working electrode
Composition
Glassy carbon (3 mmf!4 mm)
Molybdenum (1.5 mmf!2 mm)
La, Ce, Nd 0.5w/0
5
LaNi ingot (10 mm!w30 mm)
Low carbon steel (8 mmf!w20 mm)
La 5w/0
C
K1.90 V vs. Ag (0.1 w/0)/Ag
5300 C
Cathode
Composition
Electrolytic pot.
Transp. charge
Scan rate
0.01–0.5 V/s
C
0 to K2.2 V vs. Ag (0.1w/0)/Ag
Electrode potential
Matsuura
