Thermodynamics, solubility and the separation of uranium

Journal of The ElectrochemicalSociety

Thermodynamics Solubility and the Separation of Uranium from Ceriumin Molten In3LiCl-2KCl SystemTo cite this article Minghui Xu et al 2020 J Electrochem Soc 167 136506

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Thermodynamics Solubility and the Separation of Uranium fromCerium in Molten In3LiCl-2KCl SystemMinghui Xu12 Valeri Smolenski134 Qi Liu1 Alena Novoselova134z Kewei Jiang12

Jing Yu1 Jingyuan Liu1 Rongrong Chen1 Hongsen Zhang1 Milin Zhang1 andJun Wang125z

1Key Laboratory of Superlight Material and Surface Technology Ministry of Education Harbin Engineering UniversityHarbin 150001 Peoplersquos Republic of China2College of Materials Science and Chemical Engineering Harbin Engineering University Harbin 150001 PeoplersquosRepublic of China3Institute of High-Temperature Electrochemistry UB RAS Ekaterinburg 620990 Russia4Department of Rare Metals and Nanomaterials Institute of Physics and Technology Ural Federal University Ekaterinburg620002 Russia5Harbin Engineering University Capital Management Co Ltd Harbin 150001 Peoplersquos Republic of China

The purpose of this work is to study the electrochemical behavior of uranium and cerium in fused In3LiCl-2KCl system in thetemperature range of 723ndash823 K by open-circuit potentiometry The apparent electrode potential of Ce3+Ce (U4+U) couples andapparent standard potential of Ce-In (U-In) alloys vs AgClAg reference electrode were established The principal thermodynamicproperties activity and solubility of cerium and uranium were determined The separation factor of uraniumcerium couple onliquid indium electrode was calculated The experimental results have been shown that a lower temperature should be moreeffective for the separation uranium from ceriumcopy 2020 The Electrochemical Society (ldquoECSrdquo) Published on behalf of ECS by IOP Publishing Limited [DOI 1011491945-7111abb7f2]

Manuscript submitted June 23 2020 revised manuscript received August 12 2020 Published September 22 2020

Nuclear power is one of the most environmentally friendlysources of electricity compared to existing ones that use coal andgas Today it plays an increasingly important role in the develop-ment of modern society The emergence of nuclear power gives usthe confidence when we talk about the replacing of organic fuel withnuclear fuel However the development of nuclear power will alsolead to the increasing of radioactive waste Currently the efficientreprocessing of spent nuclear fuel (SNF) is becoming the most actualproblem in the world1ndash3

At recent years electrolysis or extraction in molten salts has beenincreasingly used for reprocessing of nuclear waste Molten salts isused as a solvent during the high-temperature thermochemicaltreatment of SNF because of their good chemical and radiationstability Facts have proved that molten salts are feasible as areaction medium in the process of separating lanthanides (Ln) andactinides (An) which is also the most promising research plan forthe treatment of radioactive waste and spent nuclear fuel4ndash6 Todaythe most important issue for reprocessing of spent nuclear fuel is acreation of closed fuel cycle Therefore the separation and extrac-tion of nuclear fission products have become one of the mostimportant issues in the world nuclear industry today6ndash10

Currently high-temperature methods are being studied forreprocessing highly enriched SNF with a short holding time inliquid metal-molten salt systems For this it is necessary to study theelectrochemical properties and behavior of both rare earth elementsand basic fuel components (U Pu) The nature and the compositionof the studied molten system plays a determining role for theselectivity separation process of fission products8911ndash28

Understanding of the thermodynamic properties of fission elementsin SNF is critical to practical applicability in the actual separationprocess Cerium is one of the most dangerous elements of fissionproducts and in addition is a neutron poison The electrochemicaland thermodynamic properties of cerium chloride compounds inmolten 3LiCl-2KCl eutectic were investigated at different tempera-tures The data show one-step reduction reaction of Ce (III) ions tometal occurs on inert solid electrode Also it has been determinedone-step reduction process on active liquid electrodes by transientelectrochemical technique29ndash33 The electrochemical and

thermodynamic properties of uranium compounds in molten3LiCl-2KCl eutectic were studied1134ndash37 The mechanism ofcathodic reduction of uranium ions to metal and the influence ofvarious factors on this process has been investigated in these worksThe thermodynamic properties of the formation of An and Lnintermetallic compounds on liquid electrodes including the solubi-lity in the liquid metals the activity coefficients the separationfactor between the An and Ln and the Gibbs free energy changehave been studied Although the separation of fission elements onliquid electrodes is very effective and promising there have beenonly few studies on the separation by using liquid indiumelectrodes16172438ndash41

The goal of this manuscript is to study the principal thermo-dynamic properties of cerium and uranium in molten 3LiCl-2KCleutectic solubility of cerium in liquid indium and the separationfactor (SF) of UCe couple

Experimental

The whole electrochemical research process was carried out inIn3LiCl-2KCl matrix The mole ratio of molten lithiumpotassiumchlorides during the experiment was 32 Since lithium chloride is ahygroscopic salt and this fact was influenced at the accuracy of theexperiments the salt was placed in a vacuum drying furnace at atemperature 473 K for 12 h for removing the moisture of waterbefore the investigations Lithium chloride (gt997) and potassiumchloride (gt997) were purchased from Shanghai Zhan YunChemical Co Ltd Cerium chloride heptahydrate (AR 9999)was purchased from Aladdin Industrial Corporation Reagents CeCl3and UCl4 were prepared by reaction of carbochlorination34

The experiments were carried out in a three-electrode quartzglass tube under a high-purity argon atmosphere at the temperaturerange of 723ndash823 K An inert solid molybdenum electrode and anactive liquid indium electrode were used as the working electrodesThe molybdenum electrode was a wire with a diameter of 05 mmThe high-purity indium was placed in a micro-crucible made fromcorundum The amount of indium was 2ndash4 g The referenceelectrode was made from a corundum tube the lower part of whichhad a thickness less than 01 mm This was provided the ionexchange between the standard and the test electrolytes The AgClcontent in standard molten salt was 00039 mf (10 wt)Recalculation of the obtained data vs to the chlorine referencezE-mail alena_novoselovalistru zhqw1888sohucom

Journal of The Electrochemical Society 2020 167 1365061945-71112020167(13)1365067$4000 copy 2020 The Electrochemical Society (ldquoECSrdquo) Published on behalf of ECS by IOP Publishing Limited

electrode was carried out The counter electrode for experiment wasmade of 3 mm vitreous carbon rod (SU-2000) All electrochemicaldata during the experiment were measured by using the PGSTAT302 N electrochemical workstation (Autolab Metrohm) controlledby Nova 18 software package The concentration of Ce and U inmolten 3LiCl-2KCl eutectic was about (20ndash30 wt) and less than05 wt in alloys The following primary battery were used formeasuring equilibrium electrode potentials of Ce3+Ce (U4+U)couples (1) and for the equilibrium electrode potentials of the alloys(2) by open-circuit chronopotentiometry (OCP)

-

+

+

+

Mo Ce U molten salt Ce

U molten salt AgCl Ag 1

s3

4

( ) ( )∣( )∣ ∣ ∣ ( ) [ ]

( )

-+

+

+

Ce U In molten salt Ce


3

4

( ) ( )∣( )∣ ∣ ∣ ( ) [ ]

Using the OCP method it is possible to minimize the appearance oftrivalent uranium ions in the melt due to the short duration of part ofthe experiment In this regard we can assume that the potential-timedependence corresponds to the quasi-equilibrium potential of the U(IV)U couple

After the experiments a small amount of the alloy and a sampleof solid salts were dissolved respectively in acid and in aqueoussolutions The concentration of cerium (uranium) in the samples wasdetermined by the ICP-MS test

Results and Discussion

The equilibrium electrode potential of the Men+Me couple(where Me = Ce U) was measured by OCP method Afterdeposition of a small amount of metal on the surface of inertmolybdenum electrode the value of horizontal plateau on thepotential-time dependence was fixed as the quasi-equilibriumpotential In order to calculate the principal thermodynamic proper-ties of MeCln in molten salts the values of the apparent standardpotentials were calculated by Nernst Eq 3 The AgClAg referenceelectrode was used at the measurement processes For thermody-namic calculations it is necessary to know the values of apparentelectrode potentials of Men+Me couple vs to the reference ClminusCl2electrode

= ++ + +E ERT

nFlnC 3Me Me Me Me Men n n [ ]

= ++ + +E ERT

nFlnf 4Me Me Me Me

0Men n n [ ]

= - + -+ + +E E

RT

3FlnC E vs Cl Cl

5

Ce Ce Ce Ce Ce AgCl Ag 23 3 3 ( )

[ ]

= - + -+ + +E E

RT

4FlnC E vs Cl Cl 6

U U U U U AgCl Ag 24 4 4 ( ) [ ]

where +EMe Men is the quasi-equilibrium electrode potential of thesystem V +EMe Men is the apparent electrode potential of thesystem V n is the number of the exchange electrons CCe

3+ CU4+ is

the concentration in the melt mf + +f fCe U3 4 is the activitycoefficient of cerium (uranium)

For recalculation data of the AgClAg reference electrode withthe molar fraction of AgCl 00039 (10 wt ) vs to ClminusCl2reference electrode the following equation was used42

= - -- -VE vs Cl Cl 10910 1855 10 T K 7AgCl Ag 24( ( ) ) middot ( ) [ ]

The variation between the apparent standard potential of thecouples Ce3+Ce and U4+U as a function of the temperature isshown in Fig 1 The obtained experimental data was fitted by usingsoftware Origin Pro 964

= - +

-

+E 3727 0007 840 023

10 T 0007 V 8

Ce Ce

4

3 ( ) ( )

middot [ ]

= - +

-

+E 3108 001 732 025

10 T 0004 V 9

U U

4

4 ( ) ( )

middot [ ]

When the concentration of metal ions in the molten salt does notexceed (3ndash5)middot10minus2 the activity coefficient of Men+ (Ce3+and U4+)can be regarded as a constant43 So the activity coefficient gMeCln

inthe studied molten 3LiCl-2KCl eutectic could be calculated bymeans of the equation

= D - D2303 RT log f G G 10MeCl MeCl MeCl0

n n n[ ]

where

D = G nFE 11MeCl MeCln n[ ]

The hypothetical supercooled liquid was chosen as the referencestate DGMeCl

0n

corresponds to the reaction between the purecompounds

+ =Men

2Cl MeCl 122 n [ ]

and was derived from Refs 44 45 The activity coefficient gives anidea of the cation complexation in molten chlorides Based on this itcan be predicted that the chlorine complexes formation will beformed according to the following reactions

+ =+ - -Ce 6Cl CeCl 13363 [ ]

+ =+ - -U 6Cl UCl 14462 [ ]

The activity coefficients of CeCl3 and UCl4 in molten 3LiCl-2KCleutectic vs the temperature were fitted to the expressions 15ndash16

= - - log f 0381022

T003 15CeCl3 [ ]

Figure 1 Variation of the apparent standard potentials +ECe Ce3

and +EU U4

vs ClminusCl2 as a function of the temperature in fused 3LiCl-2KCl eutecticThe concentration of CeCl3 in the solventmdash205 wt UCl4mdash187 wt

Journal of The Electrochemical Society 2020 167 136506

= - log f 3319892

T015 16UCl4 [ ]

The data obtained are in good agreement with those available in theliterature for cerium29

In order to calculate the apparent standard potential of Ce (In)and U(In) alloys the Nernst Eq 17 was applied

= ++a

aE E

RT

nFln 17Me In Me In

0 Me

Me In

n

[ ]( ) ( )( )

or

brvbarg

= ++ +

E ERT

nFln

C

x18Me In Me In

0 Me Me

Me In Me In

n nmiddotmiddot

[ ]( ) ( )( ) ( )

For the dilute dissolved metals in liquid indium the activitycoefficients of uranium and cerium are also constant38 Thereforethe apparent standard potential EMe In( ) of the alloy in the liquidcathode was described by the following expression

= ++

x

E ERT

nFln

C19Me In Me In

Me

Me In

n

[ ]( ) ( )( )

where Me = Ce or U EMe In( ) is the equilibrium potential of Me-Inalloy V EMe In( ) is an apparent standard potential of Me-In alloy Vn is the number of exchanged electrons +CMen is the concentrationof the metal ions in solvent in mole fraction xMe In( ) is theconcentration of the metal atoms in the alloy in atomic fraction

The equilibrium electrode potentials of the Me-In alloys (whereMe = Ce U) was measured by OCP method The dependences ofpotential-time 3LiCl-2KCl-UCl4 (24 wt) melt vs AgAgCl RE onthe liquid In WE (S = 038 cm2) after short polarization at inertatmosphere was presented as an example in Fig 2

The calculated values of apparent standard potentials of alloys infused 3LiCl-2KCl eutectic at different temperatures are presented inFig 3 The experimental data was fitted by using the software OriginPro 964

= - +

-

E 3025 0008 546 015

10 T 0004 V 20

Ce III Ce In

4

( ) ( )middot [ ]

( ) ( )

= - +

-

E 2612 0006 354 012

10 T 0004 V 21

U IV U In

4

( ) ( )middot [ ]

( ) ( )

The activity coefficients of solid Ce and U in the liquid indiumcan be determined by expression 2238

g = -+ nF

RTElog

23E 22Me In Me Me Me Inn( ) [ ]( ) ( )

The activity coefficients of solid Ce and U in liquid indium vs thetemperature were fitted by using software Origin Pro 964 andpresented in Fig 4

g = - log 51110682

T048 23Ce In [ ]( )

g = - log 2516365

T040 24U In [ ]( )

The calculated values of the activity coefficient are very smallThis fact indicates at a strong interaction between Ce and U metalswith liquid indium Figure 4 clearly shows that the increasing of thetemperature shifts the system towards more ideal behavior46 Theobtained results of the activity coefficients of cerium in liquidindium are satisfactorily fitted with the available data in literature

Figure 2 Dependences of potential-time 3LiCl-2KCl-UCl4 (24 wt) meltvs AgAgCl RE on the liquid In WE (S = 038 cm2) after short polarizationat inert atmosphere Currentmdash80 mA durationmdash20 s Temperature 1ndash7232ndash753 3ndash773 4ndash803 5ndash823 K

Figure 3 Variation of the apparent standard potential of the alloy ECe In( )and EU In( ) vs ClminusCl2 as a function of the temperature in molten 3KCl-2LiCleutectic The concentration of Ce in the alloymdash036 wt The concentrationof U in the alloymdash028 wt

Figure 4 Variation of the activity coefficients of solid U and Ce on liquidmetal (In) as a function of the temperature


expression 2547

g = -log 2418650

T25Ce In [ ]( )

The results of a comprehensive study of solutions of Lncompounds (4f elements) in molten salts48 indicate the proximityof their electrochemical properties This is due to the close values oftheir ion radiuses in the row from lanthanum (0122 nm) to lutetium(0099 nm) According to the theory of lanthanoid compression theproperties of 4f elements should be change monotonously49 Theavailable in the literature data for the cerium subgroup is shown inTable I The analysis of these results shows that the lanthanidescharacteristics of the cerium subgroup are also close to each otherwithin the limits of the experiment error which is confirmed by thetheory of lanthanoid compression

The relationship between the activity solubility and activitycoefficient are described by the following expression 2638

g= +alog log x log 26[ ]

In the above formula α is activity x is solubility and γ is activitycoefficient

For calculation of the activity of solid Ce in saturated Ce-Inalloys containing intermetallic compounds (CeIn3

54) the Eq 27 wasused

=D

alognF E

23RT27[ ]

where ΔE represents the difference between the equilibriumpotential of the couple +EMe Men( ) and the equilibrium potentialsof saturated alloy EMe In( )( ) in the above formula V n is the numberof exchanged electrons

The obtained results can be approximated by the Eq 28 in thestudied temperature range and are presented in Fig 5

= - alog 50912650

T065 28[ ]

The literature data (exp 29)50 of the activity of cerium in liquidindium are satisfactorily adapted with the results of this work

= -alog 39712230

T29[ ]

The solubility of cerium in the liquid indium was calculatedaccording to the expression 26 The results are presented byexpression 30 and in Fig 6 The obtained results are summarized inTable II

= - xlog 0282248

T005 30[ ]

The results obtained in this work are near to the literature one50

(exp 31)

= -xlog 1563580

T31[ ]

The partial excess Gibbs energy of uranium and cerium in theliquid indium was calculated according to Eq 33 which is describedby expressions 34 35

D = D - DG H T S 32Me Inex

Me In Me Inex [ ]( ) ( ) ( )

gD =G 2303RT log 33Me Inex

Me In [ ]( ) ( )

D = - + - -G 203965 9750 10 T 382 kJ mol 34Ce Inex 3 1middot [ ]( )

D = - + - -G 12638 5495 10 T 412 kJ mol 35U Inex 3 1middot [ ]( )

where DGex is the partial excess Gibbs free energy change kJmolminus1DH is a partial enthalpy change of mixing kJ molminus1DSex isa partial excess entropy change J molminus1middotKminus1

The obtained results show a slight difference in the data of thepartial enthalpy change of mixing and partial excess entropy changefor Ce-In alloy (DH = minus1658 kJ molminus1 DSex =minus461 J molminus1middotKminus1 38) which may be due to different conditionsof the experiments The comparison obtained data with U-In alloysalso indicates to the difference (DH = minus390 kJ molminus1 DSex =minus452 J molminus1middotKminus1 38)

The reaction of the alloy formation can be generally written as

+ + = +- -MeCl ne nIn Me In 6Cl 366n

n[ ] ( ) [ ]

In the study of the separation of lanthanides and actinides in thespent nuclear fuel the effectiveness of using electrochemicalseparation methods is usually described by the value of thedistribution or separation factor The value of the separation factoris described by Eq 37

Q =C X

C X372 1

1 2[ ]

where C1 and C2 is the concentrations of metals M1 and M2 in theelectrolyte and in the alloy (x1 x2) The separation factor of uraniumand cerium can be written as (exp 38)

Q =+

+

C X

C X38Ce U

U Ce

3

4[ ]

In the above expression XU XCe are the uranium and ceriumconcentration in the liquid indium in atomic fraction +C Ce3 +CU4

are the concentration of Ce3+ and U4+ ions in electrolyte in molefraction

The separation factor was calculated by using formula 3938 foruranium and cerium on the liquid indium

Q =- + -

logn m FE mFE nFE

23RT39

Ce In U In( )[ ]( ) ( )

where ECe In( ) is the apparent standard potential of cerium in alloy VEU In( ) is the apparent standard potential of uranium in alloy V m

and n are the number of the exchange electronsUsing the temperature dependence of the apparent standard

potentials of cerium (20) and uranium (21) in alloys the followingexpression for separation factor of uranium and cerium wasobtained

Q = - + log 2724892

T005 40[ ]

Table I Comparison of the experimental data on the activitycoefficients and solubility of lanthanides of the cerium subgroup inthe system ldquoliquid indiummdashmolten saltrdquo at 773 K

Element glog Ln In( ) xlog Ln In( ) References

La minus963 210 50Ce minus878 minus135 47Ce minus862 minus254 [this work]Pr minus960 minus210 51Nd minus921 minus232 52Sm minus962 minus198 53


The separation factor of the uranium-cerium couple in the molten3LiCl-2KCl eutectic calculated according to the above formulaindicates that cerium will be concentrated in the molten salt phaseand uranium will be deposited in the liquid metal phase The resultsof calculations show that the high values of SF can be achieved onlyat low temperatures Separation factor values decrease with theincreasing of the temperature due to the entropy factor The

obtained results are summarized in Fig 7 Table III The effect oflanthanoid compression on the separation of uranium from lantha-nides can be traced55 It can be seen that for the cerium subgroup oflanthanides a decrease of separation factor in the row from La to Ndis recorded

Figure 5 Variation of the activity of cerium in liquid indium as a function of the temperature 1mdashPresent work 2mdash42

Figure 6 Variation of the solubility of cerium in liquid indium as a function of the temperature 1mdashPresent work 2mdash42

Table II Experimental and calculated thermodynamic and solubility data of cerium in molten In3LiCl-2KCl system at different temperatures

TK +E VeqCe Ce

3 +E V

Ce Ce3 E Veq

Ce In( ) E VCe In( ) log γCe(In) log xCe(In)

723 minus3235 minus3122 minus2662 minus2636 minus967 minus284753 minus3208 minus3091 minus2639 minus2613 minus909 minus271773 minus3182 minus3070 minus2614 minus2598 minus862 minus254803 minus3175 minus3047 minus2589 minus2573 minus826 minus233823 minus3147 minus3021 minus2571 minus2554 minus784 minus217


Conclusions

The electrochemical behavior of uranium and cerium on solidinert molybdenum and liquid active indium electrodes in fused3LiCl-2KCl eutectic vs AgClAg reference electrode in the tem-perature range of 723ndash823 K at inert atmosphere by open-circuitpotentiometry was studied The principal thermodynamic propertiesactivity and solubility of cerium and uranium were calculated Theseparation factor of uraniumcerium couple on liquid indiumelectrodes was determined It has been found that a lower tempera-ture is more effective for separation actinides from lanthanidesAnalysis of experimental data shows that this system is interesting infuture innovative methods of nuclear waste disposal

ORCID

Valeri Smolenski httpsorcidorg0000-0002-8303-9626Alena Novoselova httpsorcidorg0000-0002-2338-0646Milin Zhang httpsorcidorg0000-0001-6161-8267

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6 J Zhang J Nucl Mater 447 271 (2014)7 H P Nawada and K Fukuda J Phys Chem Solids 66 647 (2005)8 M Iizuka T Koyama N Kondo R Fujita and H Tanaka J Nucl Mater 247

183 (1997)9 K Uozumi K Kinoshita T Inoue S Fusselman D Grimmett J Roy T Storvick

C Krueger and C Nabelek J Nucl Sci Technol 38 36 (2001)10 K Kinoshita M Kurata and T Inoue J Nucl Sci Technol 37 75 (2000)11 G Y Kim D Yoon S Paek S H Kim T J Kim and D H Ahn J Electroanal

Chem 682 128 (2012)12 Y Sakamura T Inoue O Shirai T Iwai Y Arai and Y Suzuki Proceedings of

the International Conference on Future Nuclear Systems GLOBALrsquo99 (1999)

13 T Kato T Inoue T Iwai and Y Arai J Nucl Mater 357 105 (2006)14 T Koyama M Iizuka Y Shoji R Fujita H Tanaka T Kobayashi and

M Tokiwai J Nucl Sci Technol 34 384 (1997)15 T Murakami Y Sakamura N Akiyama S Kitawaki A Nakayoshi and

T Koyama Procedia Chemistry 7 798 (2012)16 V Smolenski A Novoselova A Osipenko and A Maershin Electrochim Acta

145 81 (2014)17 V Smolenski A Novoselova and V A Volkovich J Nucl Mater 495 285

(2017)18 V A Volkovich D S Maltsev L F Yamshchikov A V Chukin V

V Smolenski A V Novoselova and A G Osipenko J Nucl Mater 465 153(2015)

19 V Smolenski A Novoselova V Volkovich Y Lukrsquoyanova A OsipenkoA Bychkov and T R Griffiths J Radioanal Nucl Chem 311 687 (2017)

20 V Smolenski A Novoselova A Bychkov V Volkovich Y Lukrsquoyanova andA Osipenko InUraniummdashSafety Resources Separation and ThermodynamicCalculation (IntechOpen Rijeka) p 109 (2018)

21 K Yasuda S Kobayashi T Nohira and R Hagiwara Electrochim Acta 106 293(2013)

22 G De Coacuterdoba A Laplace O Conocar J Lacquement and C CaravacaElectrochim Acta 54 280 (2008)

23 V Smolenski and A Novoselova Electrochim Acta 63 179 (2012)24 A Novoselova and V Smolenski J Nucl Mater 509 313 (2018)25 A Novoselova V Smolenski V Volkovich and Y Lukrsquoyanova J Chem

Thermodyn 130 228 (2019)26 S A Kuznetsov H Hayashi K Minato and M Gaune-Escard Electrochim Acta

51 2463 (2006)27 K Serrano and P Taxil J Appl Electrochem 29 497 (1999)28 R B Prabhakara S Vandarkuzhali T Subramanian and P Venkatesh

Electrochim Acta 49 2471 (2004)29 Y Castrillejo M R Bermejo R Pardo and A M Martınez J Electroanal Chem

522 124 (2002)30 W Lu L Y Lan L Kui T S Ling and S W Qun Journal of Electrochemical

Society 162 179 (2015)31 L David C Seacuteverine B Gilles S Sylvie and P Geacuterard J Nucl Mater 341 131

(2015)32 M Zhang H Y Wang W Han M L Zhang Y N Li Y L Wang Y Xue F

Q Ma and X M Zhang Science China Chemistry 57 1477 (2014)33 K Liu Y-L Liu Z-F Chai and W-Q Shi Journal of Electrochemical Society

164 169 (2017)34 K Jiang V Smolenski A Novoselova M Zhao Q Liu H Zhang Y Shao

M Zhang and J Wang Electrochim Acta 318 194 (2019)35 C H Lee T-J Kim S Park S-J Lee S-W Paek D-H Ahn and S-K Cho

J Nucl Mater 488 210 (2017)36 D S Maltsev V A Volkovich B D Vasin and E N Vladykin ldquoAn

electrochemical study of uranium behaviour in LiCl-KCl-CsCl eutectic meltrdquoJ Nucl Mater 467 (2015)956

37 V Smolenski A Novoselova P Mushnikov and A Osipenko J Radioanal NuclChem 311 127 (2017)

38 V A Lebedev Selectivity of Liquid Metal Electrodes in Molten Halide(Metallurgiya Chelyabinsk) p 342 (1993) (in Russian)

39 V Smolenski A Novoselova A Osipenko M Kormilitsyn and Y LukrsquoyanovaElectrochim Acta 133 354 (2014)

40 Y Liu K Liu L Luo L Yuan and W Shi Electrochim Acta 275 100 (2018)41 S Y Melchakov D S Maltsev V A Volkovich L F Yamshchikov and A

G Osipenko ECS Trans 64 369 (2014)42 L Yang and R G Hudson J Electrochem Soc 106 986 (1959)43 M V Smirnov Electrode Potentials in Molten Chlorides (Nauka Moscow) p 247

(1973) (in Russian)44 J Barin and O Knacke (ed) Thermochemical Properties of Inorganic

Substances (Springer Berlin) (1973)45 HSC Chemistry 6 Software Outotec Research Oy Pori Finland46 G Kaptay Metallurgical and Materials Transactions 43 531 (2012)47 L F Yamshchikov V A Lebedev and I F Nichkov Nonferrous Metallurgy 5

50 (1980) (in Russian)48 A Plambeck James and A J Bard Encyclopedia of Electrochemistry of the

Elements (Marcel Dekker Inc New York and Basel)10 (1976)49 V Goldschmidt Geochemische Verteilungsgesetze Der Elemente Skrifter Norske

Videnskaps Akad (Oslo) (1925)

Figure 7 Variation of the separation factor of uranium from cerium onliquid metal indium as a function of the temperature

Table III Experimental and calculated data of uranium and separation factor CeU in molten In3LiCl-2KCl system at different temperatures

TK +E VUeq

U

4 +E VU U4

E VeqU In

( ) E VU In( ) log γU(In) log Θ(CeU)

723 minus2676 minus2550 minus2353 minus2328 minus619 401753 minus2653 minus2534 minus2339 minus2319 minus577 378773 minus2629 minus2516 minus2323 minus2305 minus553 361803 minus2611 minus2498 minus2308 minus2291 minus516 335823 minus2594 minus2482 minus2295 minus2280 minus495 318


50 V A Degtyar A P Boyanov V A Vnuchkova and V V Serebrennikov Metals4 149 (1971) (in Russian)

51 V A Degtyar A P Boyanov V A Vnuchkova and V V Serebrennikov J PhysChem 45 2401 (1976) (in Russian)

52 V I Kober I F Nichkov S P Raspopin and V M Kuzminikh Termodynamicsof Metal System (Nauka Alma-Ata) 72 (1979) (in Russian)

53 V A Lebedev V V Efremov and V I Kober Physical-Chemical Properties ofRare Earth Metal Alloys (Nauka Moscow) 96 (1975) (in Russian)

54 ASM Binary Phase Diagrams Software ASM International (1996)55 V Smolenski A Novoselova V Volkovich A Bychkov Y Lukrsquoyanova and

A Osipenko Proceedings of the International Conference on Fast Reactors andRelated Fuel Cycles Next Generation Nuclear Systems for SustainableDevelopment FR 17 CN 245ndash35 (2017)


Thermodynamics Solubility and the Separation of Uranium fromCerium in Molten In3LiCl-2KCl SystemMinghui Xu12 Valeri Smolenski134 Qi Liu1 Alena Novoselova134z Kewei Jiang12

Jing Yu1 Jingyuan Liu1 Rongrong Chen1 Hongsen Zhang1 Milin Zhang1 andJun Wang125z

1Key Laboratory of Superlight Material and Surface Technology Ministry of Education Harbin Engineering UniversityHarbin 150001 Peoplersquos Republic of China2College of Materials Science and Chemical Engineering Harbin Engineering University Harbin 150001 PeoplersquosRepublic of China3Institute of High-Temperature Electrochemistry UB RAS Ekaterinburg 620990 Russia4Department of Rare Metals and Nanomaterials Institute of Physics and Technology Ural Federal University Ekaterinburg620002 Russia5Harbin Engineering University Capital Management Co Ltd Harbin 150001 Peoplersquos Republic of China

The purpose of this work is to study the electrochemical behavior of uranium and cerium in fused In3LiCl-2KCl system in thetemperature range of 723ndash823 K by open-circuit potentiometry The apparent electrode potential of Ce3+Ce (U4+U) couples andapparent standard potential of Ce-In (U-In) alloys vs AgClAg reference electrode were established The principal thermodynamicproperties activity and solubility of cerium and uranium were determined The separation factor of uraniumcerium couple onliquid indium electrode was calculated The experimental results have been shown that a lower temperature should be moreeffective for the separation uranium from ceriumcopy 2020 The Electrochemical Society (ldquoECSrdquo) Published on behalf of ECS by IOP Publishing Limited [DOI 1011491945-7111abb7f2]

Manuscript submitted June 23 2020 revised manuscript received August 12 2020 Published September 22 2020

Nuclear power is one of the most environmentally friendlysources of electricity compared to existing ones that use coal andgas Today it plays an increasingly important role in the develop-ment of modern society The emergence of nuclear power gives usthe confidence when we talk about the replacing of organic fuel withnuclear fuel However the development of nuclear power will alsolead to the increasing of radioactive waste Currently the efficientreprocessing of spent nuclear fuel (SNF) is becoming the most actualproblem in the world1ndash3

At recent years electrolysis or extraction in molten salts has beenincreasingly used for reprocessing of nuclear waste Molten salts isused as a solvent during the high-temperature thermochemicaltreatment of SNF because of their good chemical and radiationstability Facts have proved that molten salts are feasible as areaction medium in the process of separating lanthanides (Ln) andactinides (An) which is also the most promising research plan forthe treatment of radioactive waste and spent nuclear fuel4ndash6 Todaythe most important issue for reprocessing of spent nuclear fuel is acreation of closed fuel cycle Therefore the separation and extrac-tion of nuclear fission products have become one of the mostimportant issues in the world nuclear industry today6ndash10

Currently high-temperature methods are being studied forreprocessing highly enriched SNF with a short holding time inliquid metal-molten salt systems For this it is necessary to study theelectrochemical properties and behavior of both rare earth elementsand basic fuel components (U Pu) The nature and the compositionof the studied molten system plays a determining role for theselectivity separation process of fission products8911ndash28

Understanding of the thermodynamic properties of fission elementsin SNF is critical to practical applicability in the actual separationprocess Cerium is one of the most dangerous elements of fissionproducts and in addition is a neutron poison The electrochemicaland thermodynamic properties of cerium chloride compounds inmolten 3LiCl-2KCl eutectic were investigated at different tempera-tures The data show one-step reduction reaction of Ce (III) ions tometal occurs on inert solid electrode Also it has been determinedone-step reduction process on active liquid electrodes by transientelectrochemical technique29ndash33 The electrochemical and

thermodynamic properties of uranium compounds in molten3LiCl-2KCl eutectic were studied1134ndash37 The mechanism ofcathodic reduction of uranium ions to metal and the influence ofvarious factors on this process has been investigated in these worksThe thermodynamic properties of the formation of An and Lnintermetallic compounds on liquid electrodes including the solubi-lity in the liquid metals the activity coefficients the separationfactor between the An and Ln and the Gibbs free energy changehave been studied Although the separation of fission elements onliquid electrodes is very effective and promising there have beenonly few studies on the separation by using liquid indiumelectrodes16172438ndash41

The goal of this manuscript is to study the principal thermo-dynamic properties of cerium and uranium in molten 3LiCl-2KCleutectic solubility of cerium in liquid indium and the separationfactor (SF) of UCe couple

Experimental

The whole electrochemical research process was carried out inIn3LiCl-2KCl matrix The mole ratio of molten lithiumpotassiumchlorides during the experiment was 32 Since lithium chloride is ahygroscopic salt and this fact was influenced at the accuracy of theexperiments the salt was placed in a vacuum drying furnace at atemperature 473 K for 12 h for removing the moisture of waterbefore the investigations Lithium chloride (gt997) and potassiumchloride (gt997) were purchased from Shanghai Zhan YunChemical Co Ltd Cerium chloride heptahydrate (AR 9999)was purchased from Aladdin Industrial Corporation Reagents CeCl3and UCl4 were prepared by reaction of carbochlorination34

The experiments were carried out in a three-electrode quartzglass tube under a high-purity argon atmosphere at the temperaturerange of 723ndash823 K An inert solid molybdenum electrode and anactive liquid indium electrode were used as the working electrodesThe molybdenum electrode was a wire with a diameter of 05 mmThe high-purity indium was placed in a micro-crucible made fromcorundum The amount of indium was 2ndash4 g The referenceelectrode was made from a corundum tube the lower part of whichhad a thickness less than 01 mm This was provided the ionexchange between the standard and the test electrolytes The AgClcontent in standard molten salt was 00039 mf (10 wt)Recalculation of the obtained data vs to the chlorine referencezE-mail alena_novoselovalistru zhqw1888sohucom

Journal of The Electrochemical Society 2020 167 1365061945-71112020167(13)1365067$4000 copy 2020 The Electrochemical Society (ldquoECSrdquo) Published on behalf of ECS by IOP Publishing Limited


-

+

+

+



s3

4

( ) ( )∣( )∣ ∣ ∣ ( ) [ ]

( )

-+

+

+



3

4

( ) ( )∣( )∣ ∣ ∣ ( ) [ ]





= ++ + +E ERT


= ++ + +E ERT

nFlnf 4Me Me Me Me

0Men n n [ ]

= - + -+ + +E E

RT

3FlnC E vs Cl Cl

5


[ ]

= - + -+ + +E E

RT

4FlnC E vs Cl Cl 6

U U U U U AgCl Ag 24 4 4 ( ) [ ]


3+ CU4+ is





= - +

-

+E 3727 0007 840 023

10 T 0007 V 8

Ce Ce

4

3 ( ) ( )

middot [ ]

= - +

-

+E 3108 001 732 025

10 T 0004 V 9

U U

4

4 ( ) ( )

middot [ ]




n n n[ ]

where



0n


+ =Men

2Cl MeCl 122 n [ ]


+ =+ - -Ce 6Cl CeCl 13363 [ ]

+ =+ - -U 6Cl UCl 14462 [ ]


= - - log f 0381022

T003 15CeCl3 [ ]


and +EU U4



= - log f 3319892

T015 16UCl4 [ ]



= ++a

aE E

RT

nFln 17Me In Me In

0 Me

Me In

n

[ ]( ) ( )( )

or

brvbarg

= ++ +

E ERT

nFln

C

x18Me In Me In

0 Me Me

Me In Me In

n nmiddotmiddot

[ ]( ) ( )( ) ( )


= ++

x

E ERT

nFln

C19Me In Me In

Me

Me In

n

[ ]( ) ( )( )




= - +

-

E 3025 0008 546 015

10 T 0004 V 20

Ce III Ce In

4

( ) ( )middot [ ]

( ) ( )

= - +

-

E 2612 0006 354 012

10 T 0004 V 21

U IV U In

4

( ) ( )middot [ ]

( ) ( )


g = -+ nF

RTElog

23E 22Me In Me Me Me Inn( ) [ ]( ) ( )


g = - log 51110682

T048 23Ce In [ ]( )

g = - log 2516365

T040 24U In [ ]( )






expression 2547

g = -log 2418650

T25Ce In [ ]( )







=D

alognF E

23RT27[ ]



= - alog 50912650

T065 28[ ]


= -alog 39712230

T29[ ]


= - xlog 0282248

T005 30[ ]


(exp 31)

= -xlog 1563580

T31[ ]



Me In Me Inex [ ]( ) ( ) ( )


Me In [ ]( ) ( )







n[ ] ( ) [ ]


Q =C X

C X372 1

1 2[ ]


Q =+

+

C X

C X38Ce U

U Ce

3

4[ ]




Q =- + -

logn m FE mFE nFE

23RT39

Ce In U In( )[ ]( ) ( )




Q = - + log 2724892

T005 40[ ]










TK +E VeqCe Ce

3 +E V

Ce Ce3 E Veq




Conclusions


ORCID


References











































TK +E VUeq

U

4 +E VU U4

E VeqU In












-

+

+

+



s3

4

( ) ( )∣( )∣ ∣ ∣ ( ) [ ]

( )

-+

+

+



3

4

( ) ( )∣( )∣ ∣ ∣ ( ) [ ]





= ++ + +E ERT


= ++ + +E ERT

nFlnf 4Me Me Me Me

0Men n n [ ]

= - + -+ + +E E

RT

3FlnC E vs Cl Cl

5


[ ]

= - + -+ + +E E

RT

4FlnC E vs Cl Cl 6

U U U U U AgCl Ag 24 4 4 ( ) [ ]


3+ CU4+ is





= - +

-

+E 3727 0007 840 023

10 T 0007 V 8

Ce Ce

4

3 ( ) ( )

middot [ ]

= - +

-

+E 3108 001 732 025

10 T 0004 V 9

U U

4

4 ( ) ( )

middot [ ]




n n n[ ]

where



0n


+ =Men

2Cl MeCl 122 n [ ]


+ =+ - -Ce 6Cl CeCl 13363 [ ]

+ =+ - -U 6Cl UCl 14462 [ ]


= - - log f 0381022

T003 15CeCl3 [ ]


and +EU U4



= - log f 3319892

T015 16UCl4 [ ]



= ++a

aE E

RT

nFln 17Me In Me In

0 Me

Me In

n

[ ]( ) ( )( )

or

brvbarg

= ++ +

E ERT

nFln

C

x18Me In Me In

0 Me Me

Me In Me In

n nmiddotmiddot

[ ]( ) ( )( ) ( )


= ++

x

E ERT

nFln

C19Me In Me In

Me

Me In

n

[ ]( ) ( )( )




= - +

-

E 3025 0008 546 015

10 T 0004 V 20

Ce III Ce In

4

( ) ( )middot [ ]

( ) ( )

= - +

-

E 2612 0006 354 012

10 T 0004 V 21

U IV U In

4

( ) ( )middot [ ]

( ) ( )


g = -+ nF

RTElog

23E 22Me In Me Me Me Inn( ) [ ]( ) ( )


g = - log 51110682

T048 23Ce In [ ]( )

g = - log 2516365

T040 24U In [ ]( )






expression 2547

g = -log 2418650

T25Ce In [ ]( )







=D

alognF E

23RT27[ ]



= - alog 50912650

T065 28[ ]


= -alog 39712230

T29[ ]


= - xlog 0282248

T005 30[ ]


(exp 31)

= -xlog 1563580

T31[ ]



Me In Me Inex [ ]( ) ( ) ( )


Me In [ ]( ) ( )







n[ ] ( ) [ ]


Q =C X

C X372 1

1 2[ ]


Q =+

+

C X

C X38Ce U

U Ce

3

4[ ]




Q =- + -

logn m FE mFE nFE

23RT39

Ce In U In( )[ ]( ) ( )




Q = - + log 2724892

T005 40[ ]










TK +E VeqCe Ce

3 +E V

Ce Ce3 E Veq




Conclusions


ORCID


References











































TK +E VUeq

U

4 +E VU U4

E VeqU In











= - log f 3319892

T015 16UCl4 [ ]



= ++a

aE E

RT

nFln 17Me In Me In

0 Me

Me In

n

[ ]( ) ( )( )

or

brvbarg

= ++ +

E ERT

nFln

C

x18Me In Me In

0 Me Me

Me In Me In

n nmiddotmiddot

[ ]( ) ( )( ) ( )


= ++

x

E ERT

nFln

C19Me In Me In

Me

Me In

n

[ ]( ) ( )( )




= - +

-

E 3025 0008 546 015

10 T 0004 V 20

Ce III Ce In

4

( ) ( )middot [ ]

( ) ( )

= - +

-

E 2612 0006 354 012

10 T 0004 V 21

U IV U In

4

( ) ( )middot [ ]

( ) ( )


g = -+ nF

RTElog

23E 22Me In Me Me Me Inn( ) [ ]( ) ( )


g = - log 51110682

T048 23Ce In [ ]( )

g = - log 2516365

T040 24U In [ ]( )






expression 2547

g = -log 2418650

T25Ce In [ ]( )







=D

alognF E

23RT27[ ]



= - alog 50912650

T065 28[ ]


= -alog 39712230

T29[ ]


= - xlog 0282248

T005 30[ ]


(exp 31)

= -xlog 1563580

T31[ ]



Me In Me Inex [ ]( ) ( ) ( )


Me In [ ]( ) ( )







n[ ] ( ) [ ]


Q =C X

C X372 1

1 2[ ]


Q =+

+

C X

C X38Ce U

U Ce

3

4[ ]




Q =- + -

logn m FE mFE nFE

23RT39

Ce In U In( )[ ]( ) ( )




Q = - + log 2724892

T005 40[ ]










TK +E VeqCe Ce

3 +E V

Ce Ce3 E Veq




Conclusions


ORCID


References











































TK +E VUeq

U

4 +E VU U4

E VeqU In











expression 2547

g = -log 2418650

T25Ce In [ ]( )







=D

alognF E

23RT27[ ]



= - alog 50912650

T065 28[ ]


= -alog 39712230

T29[ ]


= - xlog 0282248

T005 30[ ]


(exp 31)

= -xlog 1563580

T31[ ]



Me In Me Inex [ ]( ) ( ) ( )


Me In [ ]( ) ( )







n[ ] ( ) [ ]


Q =C X

C X372 1

1 2[ ]


Q =+

+

C X

C X38Ce U

U Ce

3

4[ ]




Q =- + -

logn m FE mFE nFE

23RT39

Ce In U In( )[ ]( ) ( )




Q = - + log 2724892

T005 40[ ]










TK +E VeqCe Ce

3 +E V

Ce Ce3 E Veq




Conclusions


ORCID


References











































TK +E VUeq

U

4 +E VU U4

E VeqU In
















TK +E VeqCe Ce

3 +E V

Ce Ce3 E Veq




Conclusions


ORCID


References











































TK +E VUeq

U

4 +E VU U4

E VeqU In











Conclusions


ORCID


References











































TK +E VUeq

U

4 +E VU U4

E VeqU In


















Documents

Thermodynamics, solubility and the separation of uranium