Investigation of Ternary Complexes in Combined

Organic Solvent for ALSEP

Alena Paulenova1, Brian J. GULLEKSON1, Artem V. Gelis2

1Oregon State University2Argonne National Laboratory

Acid+Neutral mixtures Reviewed in: V.A.Babain, “Extractant Mixtures” [Ion Exchange and Solvent Extraction: A Series of Advances, Volume 19,  Ed. BA Moyer, 2009].

The Universal Solvent Extraction (UNEX) Process. I. Development… VN Romanovskiy, IV Smirnov, VA Babain, TA Todd, RS Herbst, JD Law, KN Brewer, SExIEx (2001) 1‐21 

• BE Galkin et al (1988): "Extraction of cesium, Strontium, Rare Earths and Transplutonium Elements from Liquid Highly radioactive Wastes by Extraction based on Cobalt Dicarbollide,” ISEC 1988 Moscow, Russia.  

• Innovative/diamidic UNEX – based on using diamides of dipicolinic acid instead of CMPO • S.A. El‐Reefy, N.S. Awwad, H.F. Aly (1996): Liquid ‐ Liquid Extraction of Uranium from Phosphoric acid by 

HDEHP ‐ CYANEX 921 Mixture

• Dhami, P.S., Chitnis, R. R., Gopalakrishnan, V., Wattal, P.K., Ramanujam, A. & Bauri, A.K. (2001) Studies on the Partitioning of Actinides from High Level Waste Using a Mixture of HDEHP and CMPO as Extractant, Sep. Sci. Technol., vol. 36(2), 325–335. 

• G. Lumetta, A. Gelis, et al : The TRUSPEAK Concept: Combining CMPO and HDEHP for Separating Trivalent Lanthanides from the Transuranic Elements, SExIEx, 2013.

• A. Gelis, G. Lumetta: Actinide Lanthanide Separation Process  ALSEP, I&EC, 53, 2014, 1624‐1631

• Hérès, X., Nicol, C., Bisel, I., Baron, P. & Ramain, L.: PALADIN: A One Step Process for  Actinides(III)/Fission Products Separation, GLOBAL ’99 Proceedings, (1999) 585–591. 

• Innovative SANEX; DIAMEX‐SANEX based on HDEHP with TODGA and others (0.5M DMDOHEMA – 0.3M HDEHP – HTP; BTBP‐TODGA).

Extraction with Mixed Organic Solvents

3

Combine multiple ligands which extract metals from different aqueous conditions to simultaneously perform different separations

Neutral extractants require balancing the metal charge, allowing for use with high acidities

Cation exchange ligands need higher pH of aqueous phases allowing their deprotonation and exchange proton for metal

Structures of the Extractants

(A) HDEHP            (B) CMPO                        (C) HEH[EHP]                 (D) T2EHDGA             (E) TODGA

Selected Combinations

5

In combination with 1 M HDEHP and HEH[EHP] in n-dodecane, two, normal and branched, diglycolamides as neutral extractants were chosen:

TODGA and T2EHDGA Both extractants are reported to separate trivalent Ln and An from major

fission products – large working range of HNO3 concentration – good radiation stability

HDEHP –T2EHDGA showed sufficient SF of more than 20 in a wide range of pH conditions

HEH[EHP] 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexyl ester

T2EHDGAtetra‐2‐ethylhexyldiglycolamide

Distribution of Am and Eu

5

- 1M HDEHP - 1M HDEHP + 0.1M CMPO ► - 1M HDEHP + 20mM T2EHDGA - 0.75M HEH[EHP] + 50mM T2EHDGA - 0.75M HEH[EHP] + 50mM TODGA - Inset: 152Eu extraction from HNO3 by 50 mM T2EHDGA+0.75M EHE[EHP]

Gelis, A. V., Lumetta, G. J.; Actinide Lanthanide Separation Process – ALSEP, Ind. Eng. Chem. Res., 53 (4), 1624-1631, 2014

Am extraction from were drasticallyimproved when T2EHDGA or TODGAwere instead of CMPO.

D(Am) >10 at acidities >2 M with amixture with even low, 0.02MT2EHDGA in 1 M HDEHP, whereas 0.1M CMPO/(1 M HDEHP) mixture showsa decrease in D(Am) with increasingacidity.

Minimum for Am and Eu partitioning atabout ~0.5 M HNO3 for 0.05MT2EHDGA/0.75 M HEH[EHP]

The Am and Ln partitioning from weakHNO3 can be improved by:

• increasing the concentrations of bothHEH[EHP] and T2EHDGA (0.075MT2EHDGA/(1 M HEH[EHP])) or

• using TODGA instead of T2EHDGA asAm is better extracted with 0.05MTODGA /(0.75M HEH[EHP])

Non‐ideal D and SF have been shown in mixed extractant systems from 1−5M HNO3:

Expected

1

2HA ⇄ HA 1

In n-dodecane [J.Braley:• βdim(HDEHP) = 4.43• βdim(HEH[EHP]) = 4.03

M3+(aq) + 3(HA)2(org) + L(org) ↔ M(HA2)3·L(org) + 3H+(aq)

Intermolecular interaction, observed in comparable dual extractant systems, affect An/Ln separations.

Inter-ligand interactions: dimerization of acidic extractant + formation adducts

Non-ideal Ds and SFs in mixed extractant systems - investigations of the inter-ligand interactions must be investigated

Observed vs Expected (not)

Hydrogen bonding between phosphoryl group of CMPO and P−O−H group of HDEHP monomer: logβADD = 3.07 ± 0.05

Tkac, P; Vandegrift, GF; Lumetta, GJ; Gelis, AV: Study of the interaction between HDEHP and CMPO and its effect on the extraction of selected lanthanides. Ind. Eng. Chem. Res. 2012, 51, 10433.

TRUSPEAK: ALSEP:

.

HA DGA ⇄ HA ∙ DGA

Adducts in ALSEP organic phase

FTIR: Peak AssignmentsRegion (cm‐1) HDEHP/HEH[EHP] TODGA/T2EHDGA1700 ‐ 1600 ‐‐ C = O1300 – 1150 P = O ‐‐1150 ‐ 1100 ‐‐ C‒O‒C1100 ‐ 900 P‒O‒C ‐‐

TRUSPEAK: • FTIR (Tkac, 2012) and NMR (Lumetta, 2011)ALSEP:• NMR did not work (P, C, H): 0.25M DGA, 0‐2M HA• FTIR  on ATR diamond plate: (0.3M HA, 0‐0.5M DGA)

.

.P31

IR spectra of Ligand Combinations in n-Dodecane

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Significant spectral changes upon introduction of CMPO to HDEHP/HEH[EHP]• CMPO phosphoryl group (1650 cm‐1)• HDEHP/HEH[EHP] P‐O and P‐C bonds (1100 – 950 cm‐1)• New peaks introduced (1300 – 1100 cm‐1)

HDEHP mixed with DGAs also produce spectral changes• HDEHP P‐O bonds (1100 – 950 cm‐1)• New peaks introduced (1300 – 1100 cm‐1)

HEH[EHP] mixed with DGAs produces lesser spectral changes• HEH[EHP] P‐O bond and P‐C bonds (1100 – 950 cm‐1)• Fewer new peaks with less intensity introduced 

(1300 – 1100 cm‐1)

Observed vs Expected (not)

. 1 . 1

Log(β) of ligand interaction in n-dodecane

logβ CMPO T2EHDGA TODGA

HDEHP 3.29 2.33 2.64

HEH[EHP] 2.82 2.07 2.43

Agrees well with published data [3.4] by Tkac (2012), [3.07] by Lumetta, 2011.

Non-linear least squared regression fitting software used to determine adduct formation constants β :

Complexation of Am and Selected LN

13

Analysis of the observed extraction system (simpler, without nitrate)FIRST step: extraction of metal to organic phase: HCl ‐ negligible extraction  to the organic solvent containing only a cation 

exchange ligand in alkane diluent With no inorganic anions in organic phase, which could provide an alternate 

means of metal‐DGA complexation, metal charge in the extracted complex is balanced only with anions of the cation exchange extractant: 

3 ⇌ , 3 (1)

SECOND step: titration of the metal in the organic phase: Neutral extractant E (either TODGA or T2EHDGA) added in small increments, 

while concentration of HA is held constant.  Interaction of an adduct‐forming ligand with the metal complex preformed during 

the extraction can be described  without  other anions: ⇌ ∙ (2)

Metal,  Extracted with Titrant addedLigand:Ligandrange (mM)(mM) 1M Conc. (M) Extractant Conc. (mM)

Nd, 8.64 mM HDEHP 1.00 TODGA 101.0 0 ‐ 42.9mM

HDEHP 1.00 T2EHDGA 101.9 0 ‐ 42.9mM

HEH[EHP] 1.00 TODGA 100.5 0 ‐ 42.9mM

HEH[EHP] 1.00 T2EHDGA 412.4 0 ‐ 117.8mM

Ho, 12.9 mM HDEHP 1.00 TODGA 125.1 0 ‐ 79.6mM

HDEHP 1.00 T2EHDGA 127.7 0 ‐ 63.8mM

HEH[EHP] 1.00 TODGA 210.6 0 ‐ 133.9mM

HEH[EHP] 1.00 T2EHDGA 276.3 0 ‐ 175.7mM

Am, 0.56 mM HDEHP 1.00 TODGA 100.6 0 ‐ 43.0mM

HDEHP 1.00 T2EHDGA 100.0 0 ‐ 42.8mM

HEH[EHP] 1.00 TODGA 100.0 0 ‐ 42.8mM

HEH[EHP] 1.00 T2EHDGA 101.6 0 ‐ 43.4mM

Experimental Conditions

NdNd[H(DEHP)2]3 + TODGA Nd[H(DEHP)2]3 +T2EHDGA

Nd(EH[EHP]2)3 + TODGA Nd(EH[EHP]2)3 +T2EHDGA

NdNd[H(DEHP)2]3 + TODGA Nd[H(DEHP)2]3 +T2EHDGA

⇌ ∙

UV‐Vis Spectra of Nd 4I9/2 → 4G5/2, 2G7/2 Transition for: 

HoHo[H(DEHP)2]3 + TODGA Ho[H(DEHP)2]3 +T2EHDGA

Ho(EH[EHP]2)3 + TODGA Ho(EH[EHP]2)3 +T2EHDGA

HoHo[H(DEHP)2]3 + TODGA Ho[H(DEHP)2]3 +T2EHDGA

⇌ ∙

Am Am[H(DEHP)2]3 + TODGA Am[H(DEHP)2]3 +T2EHDGA

Am(EH[EHP]2)3 + TODGA Am(EH[EHP]2)3 +T2EHDGA

AmAm[H(DEHP)2]3 + TODGA Am[H(DEHP)2]3 +T2EHDGA

⇌ ∙

Am -titrationAm[H(DEHP)2]3 + TODGA Am[H(DEHP)2]3 +T2EHDGA

Am(EH[EHP]2)3 + TODGA Am(EH[EHP]2)3 +T2EHDGA

Ternary Complexes of Metals (III) in mixed organic solvents:

I. Solvation of Extracted Complex with DGA

Nd TODGA T2EHDGA

HDEHP 2.33 ±0.01 2.01 ± 0.01

HEH[EHP] 1.39 ± 0.01

Ho  TODGA T2EHDGA

HDEHP 2.05 ± 0.01 1.62 ± 0.01

HEH[EHP] ± ±Am  TODGA T2EHDGA

HDEHP: L 2.86 ±HEH[EHP]

,

ON N

OO

ON N

OO

TODGA

T2EHDGA

The equilibrium constants for this metal complexations have been determined using HypSpec

Ternary Complexes of Metals (III) in mixed organic solvents:  I. Solvation of Extracted Complex with DGA

From Argonne NL:

22

1 10 1000.01

0.1

1

10

100

[TODGA], mM

D (E

u, A

m)

1M HDEHP varying TODGA conc. Extraction from 50 mM DTPA/1M NH4 Citrate pH 3.04.

10

20

30

40

50

60

70

SF(

Eu/

Am

)

Am

Eu

slope ~ 1

SeparationFactor

Conclusion

Fundamental chemistry of ALSEP

Radiatracer method to stability constant of extracted complexes

HA‐DGA adducts (dry/wet)  and extraction of acid

Adduct formation (FTIR, Ln‐NMR, TRFLS….)

Aggregation of extracted species ‐ SAXS 

XAFS investigation of the extracted complexes 

Translanthanide effect on complexation/separation behavior

Effect of nitric acid and ionic strength of aqueous phase on speciation of 

complexes formed in organic phase

Acknowledgment:This worked was performed  Brian J. Gullekson, a PhD candidate,   in the Laboratory of Transuranic Elements at  Oregon state University.  With:  Dr. Alena Paulenova,  Director of the OSU TRU LabDr. Art Gelis, Leader of the Radiochemistry Group at ANL

Acknowledgment:M. Alex Brown (PhD, OSU 2012,  ANL, Radiochemistry Group)Dr. P. Tkac (post‐doc at OSU, now  in ANL, Radiochemistry Group)Dr. J.L. Lapka (PhD, OSU 2013, postdoc WSU)

DOE $$uport:NEUP award   DE‐NE0000720