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It is very important to develop the recycle process for rare earth metals from the standpoint of environmental friendly and saving energy. We have already demonstrated that an economic recycle process of the rare earths from the waste of neodymium based magnets. This study in rare earths recycle process was focused on the separation of the iron group metal and the recovery of the rare earths using a novel ionic liquid. In addition, this phosphonium based ionic liquid was adaptable as an electrodeposition media for the recycle process because this kind of ionic liquid is unique physicochemical properties such as low viscosity and high electrochemical stability. The electrochemical and the diffusive properties of the iron complex were investigated from linear sweep voltammetry and chronoamperometry. The diffusion coefficient of Fe() was estimated to be the order of 10 -11 m 2 s -1 at 100°C. It was also revealed that the nucleation process of Fe() was proceeded on the instantaneous nucleation from Scharifker model. The overpotential of the nucleation process for Fe() was decreasing with elevating the bath temperature of the ionic liquid. Moreover, the selective separation of the iron metal was effectively possible for the electrodeposition at the constant potential. Furthermore, the electrodeposition in ionic liquid bath was allowed us to recover the neodymium metal at highly efficient.

Cerium­(IV) is often employed as a surrogate for plutonium­(IV) in investigations involving the processing of spent nuclear fuel and is an important oxidant in organic synthetic reactions. Surprisingly little is known about the chemistry and electrochemistry of cerium­(IV) complexed as [CeCl6]2– in the hydrophobic green ionic liquids that are proposed for these applications such as those based on the bis­(trifluoromethylsulfonyl)­imide (Tf2N–) anion. Of particular interest is its stability in these ionic liquids in the presence of unbound Cl–. Therefore, the homogeneous pseudo-first-order kinetics of the reaction between [CeCl6]2– and Cl– was investigated in the 1-(1-butyl)-1-methylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide (BuMePyroTf2N) ionic liquid as a function of temperature. These measurements revealed that [CeCl6]2– is surprisingly stable, even at elevated temperatures with a half-life of 44 min at 398 K. Although classed as an outer sphere electron transfer process, the [CeCl6]2–/3– redox reaction exhibits mixed control in this ionic liquid. In order to elucidate the origin of this behavior, detailed measurements of the heterogeneous rate of this reaction were carried out in BuMePyroTf2N and in five additional ionic liquids based on the Tf2N– anion with structurally and chemically distinct cations, including 1-(1-butyl)-3-methylimidazolium (BuMeIm+), tri­(1-butyl)­methylammonium (Bu3MeN+), 1-butyltrimethylammonium (BuMe3N+), 1-(1-butyl)­pyridinium (BuPy+), and 1-ethyl-3-methylimidazolium (EtMeIm+) by using electrochemical impedance spectroscopy (EIS). The heterogeneous rate constants of the [CeCl6]2–/3– reaction at a glassy carbon electrode were found to exhibit a near linear dependence on the absolute viscosity of these ionic liquids, indicating that the rate of this reaction may be controlled by solvent reorganization dynamics in these highly viscous ionic liquids in accordance with contemporary predictions of the Marcus theory of electron transfer. Furthermore, the choice of the organic cation can be used to tune the redox potential of the [CeCl6]2–/3– electrode reaction.

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