Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 2, pp. 218−224.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.V. Novoselova, V.V. Smolenskii, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 2, pp. 229−235.
AND CORROSION PROTECTION OF METALS
Electrochemical Study of the Reduction of Tm(III) Ions
in a Molten NaCl–2CsCl Eutectic
A. V. Novoselova and V. V. Smolenskii
Institute of High-Temperature Electrochemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia
Received July 21, 2011
Abstract—Electrochemical behavior of TmCl
solutions in a NaCl–2CsCl eutectic melt at temperatures of 823–973
K on an inert Mo electrode was studied by cyclic and square-wave voltammetry and the method of electromotive
forces. The mechanism of the cathodic process was determined, kinetic parameters of the Tm(III) + e ' Tm(II)
reaction were found, and the temperature dependence of the diffusion coefﬁ cients of Tm(III) ions was calculated.
The conditional standard redox potential for the Tm(III)/Tm(II) pair was measured in the temperature range under
study. The basic thermodynamic characteristics of the Tm(III) + e ' Tm(II) redox reaction in a molten NaCl–2CsCl
eutectic mixture were determined.
The concept of partitioning and transmutation (P&T)
of ﬁ ssion products, presently considered an efﬁ cient
way to reduce the activity of radioactive waste, consists
in isolation of long-lived ﬁ ssion products from spent
nuclear fuel (SNF) and their incorporation into an inert
matrix (free of uranium) for subsequent transmutation in
appropriate reactors. Pyrochemical partitioning methods
have a number of advantages over hydrometallurgical
techniques, the main of which are the high radiation
hardness of salt solutions and possible regeneration of
SNF with short cooling time [1–3].
The goal of our study was to optimize the efﬁ ciency
of partitioning of minor actinides and to minimize
their content of ﬁ ssion products, primarily rare-earth
elements, which are neutron poisons. To tackle with this
problem, it is important to know the electrochemical and
thermodynamic properties of lanthanides and actinides
There is only scarce published evidence about
properties of thulium compounds in chloride melt.
In , the behavior of TmCl
solutions in a molten
LiCl–KCl eutectic was studied. The mechanism by
which trivalent thulium is reduced to the metal on
inert and active electrodes was described and data on
the diffusion coefﬁ cient of thulium(III) ions and on
the formation thermodynamics of TmCl
a melt were presented. In [19, 20], the redox potentials
of the Tm(III)/Tm(II) pair in a NaCl–KCl–CsCl eutectic
melt and CsCl relative to a chlorine reference electrode
and temperature dependences of E*
measured and thermodynamic characteristics of the
Tm(III) + e ' Tm(II) reaction were calculated.
In this study, we examined the electrochemical
properties of thulium compounds in a molten NaCl–
Sodium and cesium chlorides of chemically pure
grade were used. Preliminarily, these compounds were
subjected to prolonged drying in a vacuum at gradually
elevated temperature, puriﬁ ed by directed crystallization
, and then fused in a prescribed ratio .
Anhydrous thulium trichloride was prepared by
chlorination of TmCl
O (n = 4.5–5.0) crystal
hydrate, under heating in carbon tetrachloride vapor by
the method reported in . The crystal hydrate was
produced by dissolution of Tm
of OST (All-Union
Standard) 46-205–81 brand in hydrochloric acid to
pH 1–1.5, with subsequent evaporation of the solution