Electrochemistry of ytterbium (III) in molten alkali metal chlorides

The electrochemical behaviour of ytterbium ions was investigated in the eutectic LiCl-KCl at 723 K at the surface of tungsten, glassy carbon, aluminium and aluminium coated tungsten electrodes. On inert electrodes (W and GC) the electroreduction of Yb(III) to Yb(II) takes place in a quasi-reversible electrochemical mode within the electroactive window. The electrochemical system Yb(II)/Yb (0) is not observed because it is similar or more negative in potential than the Li(I)/Li(0) couple. As a result Yb metal in contact with the melt could react to give Li(0) according to the reaction:On the contrary, on reactive Al electrodes the electrochemical system Yb(II)/Yb(0) was observed within the electroactive range. The potential shift of the redox couple is caused by the decrease of Yb activity in the metal phase due to the formation of Yb-Al alloys at the interface. The formation mechanism of the alloys was determined in a melt containing both Yb(III) and Al(III) ions, using W, Al and Al coated tungsten electrodes. X-ray diffraction analysis and scanning electron microscopy (SEM) after potentiostatic electrolysis runs allowed the identification of Al 3 Yb and Al 2 Yb. Potentiometric titrations of Yb(III) solutions with oxide donors, using a ytria stabilized circonia membrane electrode "YSZME" as a pO 2À indicator electrode, have shown the formation of ytterbium oxychloride and ytterbium oxide and their solubility products have been determined at 723 K (pk s (Yb 2 O 3 ) = 7.6 AE 0.3 and pk s -(YbOCl) = 18.5 AE 0.7.

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“…The obtained value at 723 K is similar to those previously reported in the literature [37,38] (À0.648 and À0.629 vs. Ag j AgCl, respectively).…”

Section: Determination Of the Charge Transfer Kineticsupporting

confidence: 93%

Chemical and Electrochemical Extraction of Ytterbium from Molten Chlorides in Pyrochemical Processes

et al. 2010

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“…The activation energies have been calculated for each melt and the error between the two techniques for each temperature and eutectic composition is less than 10%, Table IV. The activation energy required for the diffusion of Eu 3+ in molten salt eutectic media has been attributed to the "hopping" mechanism by several authors. 20,25,41 The theory for the "hopping" mechanism is based on the hole theory of a liquid state by Fürth 42 which states that the motion of the holes determines the properties of the liquid and that the sizes of the holes are thermally distributed. Using this model the molten salt media can be seen as expanding and contracting within the solution.…”

Section: Resultsmentioning

confidence: 99%

“…12 Prior research has been performed using europium(III) chloride and evaluating its thermodynamic properties in different melts, such as LiCl, 13 KCl, [13][14][15][16] CsCl, [13][14][15][16][17] 3 LiCl -2 KCl, 18 NaCl -KCl, 13,15,16,[19][20][21] and LiF -CaF 2 . 22,23 A few investigations have also looked into the effects of changing the eutectic melt composition on the redox potential of some lanthanides such as Sm 3+/2+ , 13,17 Eu 3+/2+ , 13,14,17,19 Tm 3+/2+ , 24 and Yb 3+/2+ , 24,25 as well as the actinides Cm 3+/026 and U 3+/0 . 27,28 However, each study has used a different experimental design with varying temperatures and electrochemical techniques so the results cannot be easily compared.…”

mentioning

confidence: 99%

Electrochemistry of Europium(III) Chloride in 3 LiCl – NaCl, 3 LiCl – 2 KCl, LiCl – RbCl, and 3 LiCl – 2 CsCl Eutectics at Various Temperatures

Schroll

Chatterjee

Levitskaia

et al. 2017

J. Electrochem. Soc.

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Here we report the effect of changing the eutectic melt composition on the electrochemical properties of europium(III) chloride under pyroprocessing conditions. Stoichiometry of electron-transfer, redox potentials and diffusion coefficients were determined using various electrochemical and spectroelectrochemical techniques in four different eutectic mixtures (3 LiCl -NaCl, 3 LiCl -2 KCl, LiCl -RbCl, and 3 LiCl -2 CsCl) while varying the temperature of the melt. It was determined that Eu 3+ undergoes a one electron reduction to Eu 2+ in each melt at all temperatures evaluated. Within each of the melts a positive shift in the redox potential as well as an increase in the diffusion coefficient for Eu 3+ was observed as the temperature increased. Also observed was a positive shift in the redox potential and increase in the diffusion coefficient for Eu 3+ as the weighted average of the cationic radii the melt composition decreased. Pyroprocessing is one of the newest techniques for spent nuclear fuel reprocessing in which the separation is accomplished electrochemically in molten salt media at temperatures of >500• C. 1-3 Some of the advantages of pyroprocessing over the more traditional liquidliquid extraction techniques are that there is no organic solvent that is susceptible to radiolysis, 4,5 lack of pure plutonium product which provides less likelihood for proliferation, 6 generation of the U-Pu alloy product is ready for immediate fabrication into new fuel rods 7 and the ability to do a group separation of all actinides.8 There are also engineering related advantages such as amenability to scaling to the needs of the facility 9 and making the refinement vessel more compact. 10,11The most important information needed to understand pyroprocessing is accurate thermodynamic data for each of the analytes that may be found in used nuclear fuel in each of the possible eutectic melt compositions. We have chosen to investigate europium(III) chloride because it is a non-radioactive analog to the actinides which makes it safer to work with, it has the least negative redox potential of the lanthanides, and it undergoes a change in its absorption spectrum when it is reduced from Eu 3+ to Eu 2+ . 12 Prior research has been performed using europium(III) chloride and evaluating its thermodynamic properties in different melts, such as LiCl, 13 In this work we systematically evaluated the redox potentials and diffusion coefficients for europium(III) chloride using differential pulse voltammetry and cyclic voltammetry in three different eutectic salt compositions over a range of temperatures. The experiments were performed from 673 K to 1173 K in 3 LiCl -NaCl, LiCl -RbCl and 3 LiCl -2 CsCl. This data along with the results from our previous * Electrochemical Society Member.z E-mail: heinemwr@ucmail.uc.edu; sam.bryan@pnl.gov reports (Electrochemistry of Europium in 3 LiCl -2 KCl from 643 to 1123 K 29 and Spectroelectrochemistry of Europium in 3 LiCl -NaCl, 3 LiCl -2 KCl, LiCl -RbCl, and 3 LiCl −2 CsCl at 873 K 30 ) were analyzed ...

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“…In most of the studies, measurements have been made simply by visual determination of the immersion depth, 4,14,17,[22][23][24][25][26][27][28]32,33,39,42,[49][50][51][52][53]58 which has an error associated with capillary effects and wetting between the electrode and the salt at different temperatures. Several studies used wires encased in alumina or other insulating material tubes with a known apparent surface area.…”

Section: Resultsmentioning

confidence: 99%

Method Development for Quantitative Analysis of Actinides in Molten Salts

Tylka

Willit

Prakash

et al. 2015

J. Electrochem. Soc.

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This paper describes how electrochemical techniques have been used to develop a method for high-precision, real-time quantitative measurements of the concentration of actinides, present in in molten salts as actinide chlorides, for pyrochemical process monitoring applications. Possible reasons for discrepancies between reported measurements obtained with electrochemical techniques have been investigated and a combination of methods to improve their precision has been established. The combination of methods consists of selecting a suitable electroanalytical measurement technique, experimentally verifying assumptions used in its theoretical analysis, ensuring reproducible conditions at the electrode/electrolyte interface, and using an improved method to eliminate the need to know the electrode surface area. By following the developed procedures and refining both experimental techniques and data analysis methods, precise and reproducible measurements were obtained for U and Pu in LiCl/KCl eutectic at 773 K. Preliminary results showed that cyclic voltammetry, along with a method of standard area addition, are very promising tools for in situ quantitative measurements with a degree of precision comparable to destructive analysis techniques. Electrorefining is the main step in pyrochemical reprocessing. During this process, actinides are separated from the bulk of the fission product elements by electrochemical dissolution and electrotransport onto a solid or liquid cathode. The goal of the process is to maximize the separation and recovery of actinides from chlorinated fission products so that minimal amounts of actinides are lost to the process waste stream. [1][2][3][4][5] In addition to efficient actinide recovery, there is a need to address the safeguarding the recycle system. 5 Highprecision, real-time concentration measurements of actinides, present as actinide chlorides, in molten salts are required for process monitoring and control and could be used to support traditional material control and accountability techniques. Development of these measurements is essential to implement and operate a commercial fuel reprocessing facility. [6][7][8][9][10] Electrochemical techniques are well suited for in situ monitoring because they allow rapid, real-time measurements, are compatible with remote handling operations, and do not require the use of standards. Also, the equipment is not affected by the high radiation field present in a fuel processing operation.9,10 Unlike offline destructive analysis techniques, in situ methods do not require representative sample collection and preparation, and therefore avoid problems with sample contamination and degradation. In addition, analytical results can be received in a relatively short period (for example, less than 2 minutes).In an electrochemical cell, the measured potential (E), current (i), or charge (Q) is related to the quantity of the analyte in the solution; therefore, it can serve as an analytical signal for concentration measurements. 11,12 Depending on the applied...

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Electrochemistry of ytterbium (III) in molten alkali metal chlorides

Cited by 62 publications

References 11 publications

Chemical and Electrochemical Extraction of Ytterbium from Molten Chlorides in Pyrochemical Processes

Chemical and Electrochemical Extraction of Ytterbium from Molten Chlorides in Pyrochemical Processes

Electrochemistry of Europium(III) Chloride in 3 LiCl – NaCl, 3 LiCl – 2 KCl, LiCl – RbCl, and 3 LiCl – 2 CsCl Eutectics at Various Temperatures

Method Development for Quantitative Analysis of Actinides in Molten Salts

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