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Cite this: Dalton Trans., 2014, 43,5252

Received 16th December 2013,Accepted 2nd January 2014

DOI: 10.1039/c3dt53529k

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Extraction and structural studies of an unexploredmonoamide, N,N’-dioctyl, α-hydroxy acetamidewith lanthanide(III) and actinide(III) ions†

Shanmugaperumal Kannan,*a Bal Govind Vats,a Illipparambil C. Pius,a

Donald M. Noronha,a Prem S. Dhami,b Prashant W. Naikb and Mukesh Kumarc

A monoamide, N,N’-dioctyl, α-hydroxy acetamide, shows unusual

extraction properties towards trivalent lanthanide and actinide

ions above 3 M HNO3. The extracted ions could be quantitatively

back extracted using 0.5 M HNO3. This amide shows negligible

extraction towards Sr(II) and Ru(III) ions, making it advantageous

over other reported extractants. The structures of Sm(III) and Eu(III)

nitrate compounds show that the metal ion is surrounded by three

of the ligands, one nitrate and one water molecule. The ligand acts

as a neutral bidentate ligand and bonds through the amido and

hydroxyl oxygen atoms.

The prior separation of long lived trivalent americium andcurium from the HLLW solution is an important step for thesafe disposal of waste by vitrification followed by burial underdeep geological repositories.1 This method of separation oflong-lived radionuclides followed by transmutation is beingconsidered by several countries.2 Due to the similarity inchemical properties, the selective extraction/separation of tri-valent actinides (Am(III) and Cm(III)) from HLLW solution con-taining a large excess of trivalent lanthanides is very difficult.Therefore, the co-extraction of An(III) and Ln(III) from HLLWsolution followed by group separation of actinides from lantha-nides is proposed3 (SANEX process). Several reagents were syn-thesized in the last two decades for this purpose and theirextraction properties with trivalent actinides and lanthanidesfrom HLLW solution were studied. Among them, the carba-moyl methyl phosphine oxides (TRUEX process),4 trialkylphosphine oxides (TRPO process),5 di-isodecyl phosphoricacid (DIDPA process),6 malonamides7 (DIAMEX process) andtetra-alkyl diglycolamide (TODGA or TEHDGA)8 have shown

excellent extraction properties for actinide and lanthanide ionsfrom the HNO3 medium.9 The major drawback of using organo-phosphorus extractants is the generation of solid residue thatresults upon their incineration at the end of their useful life inaddition to poor back extraction properties. The incinerablemalonamide based extractants7,9c show better extraction andback extraction properties, but the D values obtained for triva-lent lanthanide and actinide ions are relatively very low. Thediglycolamide based extractants8a,9d show better extractionproperties as compared to malonamide based extractants7,9c

due to their very high D values for Am(III) and Cm(III) from 3–4 MHNO3. The main disadvantage of these extractants is thatthey extract Sr(II) ions from the HLLW solution8a,10 alongwith An(III) and Ln(III) ions, and therefore needs additionalsteps during the stripping process. Several new extractantsfunctionalized with carbamoyl methyl phosphine oxides, mala-nomides and glycolamides have been explored11 in recentyears for the separation of lanthanide and actinide ions fromnitric acid medium. However, in most of the cases they showvery high D values even in lower acidities (<0.5 M) and there-fore need very low acidities for stripping (which is not advisa-ble in plant operation) or complexing agents. Though N,N-dioctyl, α-hydroxy acetamide is an important major radiationdegradation product12a as well as a synthetic precursor12b ofthe well known extractant tetra-octyl diglycolamide (TODGA),no work on the extraction and separation properties of thiscompound with trivalent actinides or lanthanides has beenreported so far. We report herein the extraction properties ofN,N′-dioctyl, α-hydroxy acetamide with Am(III), Eu(III), Sr(II),Cs(I), Pu(IV), Ru(III), Zr(IV) and U(VI) ions from HNO3 mediumand the structures of europium(III) and samarium(III) nitrateswith analogous N,N′-diisopropyl hydroxy acetamide ligands.

The ligands were prepared by the reaction of R2NCOCH2Clwith Et3NHOCOCH3 in 1,2-dichloroethane followed by hydro-lysis using NaOH in quantitative yield (Scheme S1; see theESI†). The IR spectra of ligands showed the presence ofhydroxo and carbamoyl groups. The 1H NMR spectra showedthe expected peaks for the desired compounds12 and the octylligand shows the presence of some un-reacted starting chloro

†Electronic supplementary information (ESI) available. CCDC 977001 and977002 for Eu and Sm compounds respectively. For ESI and crystallographicdata in CIF or other electronic format see DOI: 10.1039/c3dt53529k

aFuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.

E-mail: skannan@barc.gov.in; Tel: +91-22-25594576/0643bFuel Reprocessing Division, Bhabha Atomic Research Centre, Mumbai, 400085,

IndiacSolid State Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085,

India

5252 | Dalton Trans., 2014, 43, 5252–5255 This journal is © The Royal Society of Chemistry 2014

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compound (<2–3%). The ESI-MS spectrum of octyl ligandsshows the peaks at m/z values of 300 (LH+, 100%), 322 (L + Na,22%), and 621 (2L + Na, 18%), indicating that the compoundis more than 98% pure (see the ESI†). The extraction studieswith 0.2 M starting chloro compound (C8H17)2NCOCH2Cl indodecane showed negligible extraction for Am(III), Eu(III) andSr(II) ions from nitric acid under the conditions studied. There-fore, all extraction studies were carried out without any furtherpurification or separation of the synthesized ligand.

The time of equilibration for Am(III) and Pu(IV) ions from4 M HNO3 using 0.2 M of (C8H17)2NCOCH2OH in dodecanewas studied (Fig. S1, see the ESI†). This study shows clearlythat the extraction process is completed in less than10 minutes in both cases. Therefore, all other experimentswere carried out by allowing the extraction for about30 minutes of contact time.

The extraction studies of Am(III), Pu(IV), U(VI), Eu(III), Sr(II),and Cs(I) ions from different concentrations of HNO3 using0.2 M solution of N,N′-dioctyl, α-hydroxy acetamide indodecane diluent were carried out. The data on DM vs. [HNO3]are shown in Fig. 1. These graphs show clearly that the data onDM follow the order: DPu ≫ DAm > DEu ≫ DU above 3 M HNO3

(DSr and DCs are negligible at all acidities studied and aretherefore not included in the figure). The observed D valuesfor Am(III) and Eu(III) are higher than the values reported forany of the monoamides and malonamides7,9b and lower thanthat of tetra-alkyl diglycolamide.8,9d The D value for uranium isvery low and comparable to that of the values obtained withthe diglycolamide based extractants. The interesting obser-vation is that the D value for Sr(II) ion is negligible (<10−4) ascompared to that observed for diglycolamide basedextractants.8a,10

Stripping studies on the extracted metal ions were per-formed using 0.5 M HNO3 solution. The Am(III), Eu(III) andU(VI) ions could be back extracted quantitatively (99.0%) fromthe loaded organic phase in a single contact. The Pu(IV) couldbe back extracted quantitatively using a mixture of 0.5 M HNO3

and 0.2 M oxalic acid.

In order to find out the nature of the species extractedduring the extraction of Am(III) (as a tracer) the DAm wasmeasured as a function of amide concentrations at a constantHNO3 concentration. The log DAm vs. log [amide] plot shows astraight line with a slope closer to 6 (see the ESI†). This indi-cates that there are six molecules of amide involved in theextraction process. Similarly, the log DAm vs. log [NO3

−] plotshows a straight line closer to 3 (see the ESI†), indicating thatthere are three molecules of NO3 involved in the extractionprocess.

From these studies, the nature of the species extractedduring the extraction process could be written as [Am-(NO3)3L6]. In order to find out the nature of the bondingbetween the ligand and the metal, the compounds of La(III),Eu(III) and Sm(III) nitrates with N,N-diisopropyl hydroxy amidewere synthesized and characterized. The structures for Sm(III)(Fig. S2, see the ESI†) and Eu(III) (Fig. 2) show that both areiso-structural with the metal ion surrounded by three of theligands, one nitrate and one water molecule, to give a distortedtricapped trigonal prismatic geometry. Two of the nitrates areoutside the primary coordination and hydrogen bonded to thewater molecule and the ligand. The ligand acts as a neutralbidentate chelating ligand and bonds through the hydroxyland carbamoyl oxygen atoms to a metal center similar to thatreported in the literature.13 It is worth noting here that there isalways a difference between the number of ligands involvedduring the solvent extraction process (tracer) and that involvedin solid state compounds (bulk). The number of ligandsinvolved during the extraction of Ln(III) with carbamoyl methylphosphine oxides, malonamides and tetra-alkyl diglycolamideare three, three and four, respectively. However, the solid statestructures show two, two and three ligands, respectively, forcarbamoyl methyl phosphine oxides,14a,b malonamides14c andtetra-alkyl diglycolamide.14d

Fig. 1 Distribution ratios for Pu(IV), Am(III), Eu(III) and U(VI) versus [HNO3].

Fig. 2 Molecular structure of [EuL3(NO3)(H2O)](NO3)2. Selected bonddistances [Å] angles [°]: Eu–O1 2.422(5), Eu–O2 2.380(4), Eu–O32.451(4), Eu–O4 2.368(5), Eu–O5 2.514(5), Eu–O6 2.457(5), Eu–O72.400(5), Eu–O8 2.500(5), Eu–O9 2.531(5), O9–Eu–O8 50.2(2), O2–Eu–O3 63.2(2), O4–Eu–O5 62.4(2), O6–Eu–O7 62.6(2).

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A very high level of extraction of trivalent lanthanideand actinide ions from 3–4 M HNO3 and quantitative backextraction by 0.5 M HNO3 showed the potential nature of thisnovel monoamide extractant (which is ideally suited for thereal HLLW solution). This is the first monoamide which showssuch an unusual and interesting extraction property withhigh D values for trivalent lanthanide and actinide ionsfrom 3–4 HNO3 medium.7c Poor extraction for Sr(II) ion from3–4 M HNO3 reduces one extra step needed during the backextraction process.

An extraction study using 0.2 M of compound (C8H17)2NCO-CH2OH in dodecane with 100 times diluted HLLW solu-tion from 4 M HNO3 was carried out. The preliminary resultsof this study are given in Table 1. This result shows that morethan 99% of α, 64% of β and 47% of γ activities could beextracted in a single contact. The Cs(I) and Ru(III) ions showeither negligible or poor extraction under the conditionsstudied. The extracted activities (α, β, and γ) could be backextracted using 0.5 M HNO3 or a mixture of 0.2 M oxalic acidand 0.5 M HNO3 quantitatively (see the ESI†). The extractionstudy of Zr(IV) ion from 100 times diluted HLLW solutionfrom 4 M HNO3 (see the ESI†) shows that around 88% of theion could be extracted in a single contact and the same couldbe back extracted using 0.2 M oxalic acid containing 0.5 MHNO3.

Conclusions

In conclusion, the high level of extraction of trivalent lanthanideand actinide ions above 3 M HNO3 and quantitative backextraction by 0.5 M HNO3 showed the potential nature of thisnovel monoamide extractant. Poor extraction of Sr(II) ion from3–4 M HNO3 and Ru(III) from HLLW solution makes itadvantageous over other extractants by reducing the extra stepsneeded during the back extraction process. The structure ofthe Eu(III) and Sm(III) nitrates shows that the ligand acts as aneutral bidentate chelating ligand and bonds through thehydroxy and carbamoyl oxygen atoms to a metal center.

Acknowledgements

The authors wish to thank Dr K. L. Ramakumar, Director,RC&I Group, Dr S. K. Aggarwal, AD, RC&I Group, Head,Fuel Chemistry Division and Shri. P. M. Gandhi, Head, Fuelreprocessing Division for their encouragement and support.

Notes and references

1 P. A. Baisden and G. R. Choppin, Nuclear Waste Manage-ment and Nuclear Fuel Cycle, in Radiochemistry andNuclear Chemistry, ed. S. Nagyl, Encyclopedia of LifeSupport Systems (EOLLS), EOLLS Publishers, Oxford, U.K.,2007.

2 (a) Actinide and Fission Product Partitioning and Transmuta-tion: Status and Assessment report, OECD/NEA, Paris, 1999;(b) Potential Benefits and Impacts of Advanced Nuclear FuelCycles with Actinide Partitioning and Transmutation, inNuclear Science, OECD/NEA, Paris, 2011.

3 (a) Z. Kolarik, U. Müllich and F. Gassner, Solvent Extr. IonExch., 1999, 17, 23; (b) C. Madic, M. J. Hudson,J. O. Liljenzin, J.-P. Glatz, R. Nannicini, A. Facchini,Z. Kolarik and R. Odoj, New Partitioning Techniques forMinor Actinides, Project report EUR 19149 EN, EuropeanCommission, Luxembourg, 2000; (c) H. H. Dam,D. N. Reinhoudt and W. Verboom, Chem. Soc. Rev., 2007,36, 367.

4 E. P. Horwitz and W. W. Schulz, The TRUEX process: Avitaltoll for disposal of US defense nuclear waste, Elsevier,London, 1991, pp. 21.

5 Y. Zhu and R. Jiao, Nucl. Technol., 1994, 108, 361.6 Y. Morita, J. P. Glatz, M. Kubota, L. Koch, G. Pagliosa,

K. Roemer and A. Nicholl, Solvent Extr. Ion Exch., 1996, 14,385.

7 (a) C. Musikas and H. Hubert, Solvent Extr. Ion Exch., 1987,5, 877; (b) D. S. Purroy, P. Baron, B. Christiansen,J. P. Glatz, C. Madic, R. Malmbeck and G. Modolo, Sep.Purif. Technol., 2005, 45, 157; (c) C. Musikas, Inorg. Chim.Acta, 1987, 140, 197.

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Table 1 Extraction data for fission products and alpha emitters by 0.2 M (C8H17)2NCOCH2OH in dodecane from 4.0 M HNO3 having 100 timesdiluted high level active waste

Alpha α/mg L−1

Beta β/mCi L−1

Gamma γ/mCi L−1

144Ce/mCi L−1

106Ru/mCi L−1

137Cs/mCi L−1

125Sb/μCi L−1

95Nb/μCi L−1

Feed 98.95 57.71 20.15 10.21 5.66 8.43 2.45 13.78Raffinate (aqueous) <0.2 20.83 10.43 22.00 µCi L−1 5.58 8.40 — —Loaded organic 98.7 36.84 9.57 10.2 214 µCi L−1 — 1.94 11.4

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