Extraction of curium and einsteinium by dibutyl,N,N,diethyl carbamyl phosphonate (DBDECP) from mineral acids

J. inorg,nucl.Chem., 1970,Vol. 32, pp. 3081 to 3089. PergamonPress. Printedin Great Britain

EXTRACTION OF CURIUM A N D EINSTEINIUM BY D I B U T Y L , N , N , D I E T H Y L CARBAMYL PHOSPHONATE (DBDECP) FROM MINERAL ACIDS H. F. ALY and R. M. LATIMER* Nuclear Chemistry Dept., Atomic Energy Establishment, U.A.R. (First received 18 November 1969: in revised form 20 January 1970)

A b s t r a c t - T h e extraction of curium and einsteinium by dibutyI,N,N,diethyl carbamyl phosphonate (DBDECP) from nitric, hydrochloric and perchloric acid solutions has been studied. A trisolvate is formed with the extracted species. A reaction mechanism is suggested in which the extracted complex takes the form MA3(DBDECP)3 and/or MA4 -1 . . . . . . +H30(DBDECP)~. S I D D A L L [ 1] s t u d i e d t h e e x t r a c t i v e p r o p e r t i e s o f a n u m b e r o f p h o s p h o n a t e s . A m o n g these, dibutyl,N,N,diethyl carbamyl phosphonate showed a high extractability for Ce, Pm, and Am from concentrated nitric acid solution. The extraction of Cm and Es from mineral acids has been studied and the synergistic effect of this solvent with HTTA tested. EXPERIMENTAL Materials. Purified dibutyl,N,N,diethyl carbamyl phosphonate (DBDECP) was obtained from Watree Chemical Company, Lugoff, South Carolina. Benzene, carbon tetrachloride and toluene were Baker, A.R. grade. Xylene was obtained from Allied Chemicals and isopropyl benzene from Mathson Coleman and Bell Company. All acids were Baker, A. R. grade and different concentrations were prepared by dilution and standardization with standard NaOH. Lithium chloride (Allied Chemicals) was purified by passing a saturated solution through an anion exchange column, Dowex I × 10, at 60°C. Different concentrations were prepared by dilution of the saturated solution. The final hydrogen concentration was adjusted using a Beckman pH meter. The organic phases were prepared by diluting D B D E C P with the appropriate diluent. For HTTA and D B D E C P mixtures, the desired molarity of HTTA was obtained by weight and that of D B D E C P by volume (density = 0.919 gm/cm s) and dilution with benzene to give a final total molarity of 1. The radiotracers 244Cm and 253Es were obtained from Lawrence Radiation Laboratory Heavy Production Group. Extraction procedure. To a 40 ml test tube containing a suitable amount of the tracer, known volumes of the aqueous and the pre-conditioned organic phases were added and vigrously stirred until equilibrium was attained (2 min for DB DEC P alone and 15 rain for HTTA alone or with DB DEC P). i n all cases, the aqueous phase contained 0.003M Ce ions to saturate any alkyl phosphoric acid impurities in the D B D E C P [1]. After equilibration, representitive samples from both phases were taken for radiometric assay using a 2~" proportional counter. When extracting from LiC1 solution, a separation was performed on the aqueous phase. This consisted of hydroxide precipitation with iron carrier, dissolution of the precipitate in 6MHCI and extraction of iron with methyl isobutyl ketone. The distribution coefficient Kd, was calculated using the expression

Kd = Aor. Va, Vor. Aaq *Lawrence Radiation Laboratory, Berkeley, California, U.S.A. I. T. H. Siddall, l l l , J , inorg, nucl. Chem. 26, 1991 (1964). 3081

3082

H.F.

ALY and R. M. L A T I M E R

where Aor and Aaq are the activities in the organic and aqueous phases, respectively, and Vor and Vaq are the volumes of the organic and aqueous phases, respectively. RESULTS

Effect of the diluent. The effect of the diluent on the extraction of curium from 12M HCI with 20% D B D E C P is shown in Table 1. It is clear that the diluent has a large effect on the extractability. For the diluents studied, the extraction coefficient decreases with increasing polarizability. Benzene was chosen as diluent for this study because of its high extractability. Table 1. Effect of diluent on the extraction of curium by D B D E C P *

Diluent Benzene Carbon tetrachloride Toluene Xylene Isopropyl benzene

Dielectric constant ~

Polarizabilityt P in cm s

Distribution coefficient Ka

2.284

26.634

I "253

2.234 2.379 2.404:[: 2.38

28. t 11 33.462 38.967 40.739

0.692 0.614 0.179 0-024

*The measurements were carried out using 20 per cent extractant in respective diluent from 12M hydrochloric acid solution. tPolarizability of the diluents was evaluated using the expression E--IM

~--2p where, M is the molecular weight of diluent and p the respective density. :[:Mean value for ortho, meta, and para xylene.

Acid effect. The extraction of Es and Cm from HCI, HNO3, and HCIO4 is shown in Fig. 1. The extraction behaviour for all acids is almost the same; a gradual increase in the extraction coefficient at low acid concentration followed by a rapid increase at high acidity. Using LiC1 solution at 0.1M[H ÷] concentration, a higher extraction for both Cm and Es was achieved than from HCI, Fig. 2. Extractant dependency. The extractant dependency from different acids is shown in Figs. 3-5. In general, the distribution coefficient is dependent on the third power of the D B D E C P concentration. This dependence was also obtained when using LiCI as salting agent. Synergism. Synergism was examined in the system D B D E C P - H T T A - b e n zene from nitric acid solution. With 1M nitric acid solution a maximium synergistic effect is noted at an organic composition of 0.84M H T T A ÷ 0.16M D B D E C P in benzene, the distribution coefficient increasing by factors of 24 and 52 for Cm and Es, respectively. The separation factor is increased from 0-94 to 1.95 (Fig. 6). For 0.1M HNO3 solution (Fig. 7), the synergistic effect was increased giving a maximium extraction at the composition, 0.67M H T T A ÷ 0 . 2 3 M DBDECP,

Extraction of curium and einsteinium

10 4

I

;

----O

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3083

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Fig. 1. Extraction of curium and einsteinium by 20% D B D E C P in benzene from mineral acids,

3084

H. F. ALY and R. M. L A T I M E R i0 ~'

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i

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Chloride

concentration

,M

Fig. 2. Extraction of curium and einsteinium by 20% D B D E C P in benzene from different chloride concentrations.

with an increase in the extraction coefficients of about 102 and 103 for Cm and Es, respectively. The separation factor increased from 0.51 to 4-78. DISCUSSION

From the results in Figs. 3-5, a trisolvate between the extracted species and D B D E C P could be proposed. This excludes the possibility of chelation as

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I

w e ~ e ~

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6' 2 M

8"6M

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' I00

Fig. 3. Effect of D B D E C P concentration on the extraction of curium and einsteinium from different perchloric acid concentrations.

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~A-

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12M HNO:j

Concentration of DBDECP in benzene , %

I

i

i

v

I

!

t

v

•

v

ioo

Fig. 4. Effect of D B D E C P concentration on the extraction of curium and einsteinium from different nitric acid concentrations.

10 -4

I0-~

iO-Z

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1.0

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R

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3.

3086

H . F . ALY and R. M. LATIMER

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,

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Concentration

50

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DBDECP

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benzene

I

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,%

Fig. 5. Effect of DBDECP concentration on the extraction of curium and einsteinium from different hydrochloric acid concentrations.

Extraction of curium and einsteinium

I

I

I

3087

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I 0.4

I 0"6

I 0"8

08

0"6

0.4

0.2

I'0 DBECP, M 0.0

Concentration ~ M

Fig. 6. Synergistic effect for the extraction of Cm and Es from 1.0M nitric acid medium.

3088

H.F.

i

ALY and R. M. L A T I M E R

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s

....

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1.0

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I

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0.4

0-6

0.8

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0.4

0.9'

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0.6 Concentration,

M

Fig. 7. Synergistic effect for the extraction of Cm and Es from 0- l M nitric acid medium.

Extraction of curium and einsteinium

3089

previously proposed, and confirms the data on trivalent lanthanides [1]. On spectroscopic evidence. Siddall and Prohaska[2] proposed that for D B D E C P a long O O \11 II / range effect exists on the grouping of the five atoms, P - - C - - N . This suggests / \ that the mobile electrons with an orbital over all the atoms have one centre for bonding. Accordingly, the extraction mechanism may be best explained by the reaction, M 3+ + (3 + x)A- + xH ++ 3 D B D E C P ~ Hx MA3+x (DBDECP)3 In the range greater than 5M acid concentration, the predominant species for trivalent actinides are of the types MAa and MA4-' [3, 4]. MAa could be extracted by formation of the complex MA3(DBDECP)a. On the other hand, the direct coordination of MA4-' with DBDECP is rather limited. Nevertheless, the latter anionic complex could be ionically bonded through a hydronium ion and the extracted complex may take the form DBDECP3(H30) + . . . . . . MA4-', as for TBP [5]. The order of the extraction from different acids could be generally explained on the basis of Lewis acid-Lewis base interaction, the size of the acid molecules and its energy of hydration [6]. However, this is subject to limitations dependent on the extraction behaviour of different acids. 2. T. H. Siddall, llI and C. A. Prohaska, Appl. Spectrosc. 21, 9 (1967). 3. E. P. Howritz, C. A. Bloomquist, L. J. Sauro and D. J. Henderson, J. inorg, nucl. Chem. 28, 2313 (1966). 4. G. R. Choppin and P. J. Unrein,J. inorg, nucl. Chem. 25, 387 (1963). 5. M. !. Tocher, D. C. Whitney and R. M. Diamond, J. phys. Chem. 68, 368 (1964). 6. K. N aito and T. Suzuki, J. phys. Chem. 66, 983 (1962).