Journal of Nuclear and Radiochemical Sciences, Vol. 18, pp. 13-15, 2018

Notes
Anion-exchange separation of americium and the lanthanides using a single column
Yutaka Miyamoto*, Kenichiro Yasuda
Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan

Received July 3, 2018; Accepted July 23, 2018: Published online July 25, 2018
A sequential separation technique using an anion-exchange column developed in the previous works has thepotential to completely separate picograms of Am from the lanthanides using mixtures of acetic acid, hydrochloric acid, and nitric acid as the eluents, without any functional ligands or special columns. This experimental
result implies that ultra-trace actinides, including Am, Pu, U, and Th in environmental samples can be sequentially separated by combination of these mixed-media eluents and an anion exchange column.

of Am in this separation system was investigated by separating an 243Am spike solution.

1. Introduction
Americium is an anthropogenic actinide produced innuclear power plants and from the explosion of Pu atomicbombs. Americium-241 can be produced as a decay product of241
Pu. The increase of 241 A m due to 241 Pu decay may
sig n i f ic a nt ly e n h a nc e t he a lph a - a c t iv it y level i n acontaminated area for a certain period of time1. Using the241
Am/241Pu ratio, the purification age, which is defined as thetime elapsed since the last chemical separation, can beestimated. The Pu purification age was accurately determinedby measuring the 241Am/241Pu ratio in a Pu-only sample and aU-Pu particle mixture synthesized from a reference sample2,3.
For the determination of 241Am and 241Pu by ICP-MS, it isnecessary to chemically separate these elements, because themass difference between these isobars (Δm = 2.3·10 -5 amu) is
too small to be separated by ICP-MS. Many analyticaltechniques based on ion chromatography and solvent extraction have been developed for the chemical separation of Amand Pu from matrix elements. Americium is a member of theactinides, whose chemical properties are very similar to thoseof the lanthanides. Ultra-trace levels of Am may co-exist withmicro-grams of lanthanides in environmental samples,including soils and sediments.
For these samples, chemical separation of Am from the lanthanides must be incorporated in separation process, as highconcentrations of lanthanides in the sample may interfere withthe accurate measurement of ultra-trace quantities of Am.
This interference occurs due to the matrix-effect, which leads
to a loss of sensitivity and deposition of salts on the orifice,sampling cone, and skimmer cone of the ICP-MS instrument.
Lanthanides and actinides can be effectively separated using
some selective ligands 4,5, including thiocyanate salts 6 andextractants on Eichorm resins, including DGA7 and TEVA8.
However, some of these acid-resistant ligands may elute withthe target elements, which is a severe issue for radiochemical
analyses, besides they may be very expensive compared withconventional ion-exchange resins. In some cases, several
tandem columns and/or systematic separation procedures arerequired to remove other matrix elements8. The sequential
anion-exchange separation of U, Pu, Th, Pb, and thelanthanides was successfully achieved by using a suitablecombination of acetic acid, nitric acid, hydrochloric acid, andthe hydrofluoric acid for selective elution of each element inour previous works9–11. In the current work, elution behavior*Corresponding author: E-mail: miyamoto.yutaka@jaea.go.jp

2. Experimental
The elements of interest were separated using a sequential
system known as the clean and automatic separation system
for ultra-trace analysis (CASSUAL)9–11. This system consistsof a small anion-exchange column, automatic inert valves, afraction collector, and Tef lon tubes. The eluents for thissequential separation were stored in the thick Teflon tubes,
and they were extruded using pressurized argon gas at 0.45
MPa. The eluent change and effluent collection were automatically controlled by a computer program. The flow rate of theeluents ranged from 0.03 to 0.07 mL/min, depending on theconcentration of the acid component. An anion-exchange
resin (MCI-GEL CA08S, resin size: 11 ± 2 μm, Mitsubishi
Chemical Corp., Japan) that was strongly basic (8% crosslinkage, Cl‒ form) was used for the separation. The MCI-GELproducts have been developed for high performance liquidchromatography (HPLC), and the resin size is well-controlled
to obtain high resolution of eluents with excellent reproducibility because the resins are essentially spherical and have acontrolled, narrow particle size distribution. This resin had
the same composition as Dowex 1×8 (Dow ChemicalCompany, USA). Some varieties of Dowex 1×8 in resin size
are available. Particle size is roughly controlled, and the particle size of the finest Dowex 1×8 resin ranges from 200 mesh to
400 mesh (equivalent to 38–75 μm). More fine resin such as
the CA08S in resin size isn't available from this company.
Fresh resin (dried weight: 72 mg) was packed into a PFA tube
(2 mm inner diameter) to make a 50-mm-long column (columnvolume (CV): 0.158 mL).
A solution containing 4 pg of 243Am (ORNL, USA) wasused to investigate the Am separation profile. Water wasdeionized and purified (resistivity: 18.2 MΩ·cm) using aMilli-Q water system (Millipore Corp., USA). Highly pure
HCl, HNO3, HF (TAMA-Pure AA-10 or AA-100 grade, Tama
Chemicals, Co. Ltd., Japan), acetic acid (ultra-pure grade;>99.9% purity, Kanto Chemical Co. Ltd., Japan), and hydrochloric hydroxylamine (NH 2OH·HCl) (guaranteed reagent(GR) grade; 99.0% purity, Merck Co., Germany) were usedwithout further purification. The 243Am spike solution waspipetted into a Teflon beaker, and dried with a hot-plate. The
residue after evaporation was dissolved in 500 μL of a mixtureof 16M acetic acid and 0.2M HNO3; the composition of thismixture was the same as that of the first eluent. The feed solu-© 2018 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 07/25/2018

14J. Nucl. Radiochem. Sci., Vol. 18, 2018

Miyamototion was then loaded on the separation column via a sampleloop. The effluent was collected periodically in separate vials,and each fraction was dried using a hot-plate. The evaporation
residues were dissolved in 1 mL of 15M HNO3 and then dried
again. Finally, the evaporation residue was dissolved in 5 mLof 0.3M HNO3. The 243Am intensity in each elution fraction
was measured using sector-f ield ICP-MS (SF-ICP-MS)(ELEMENT-2, ThermoFisher Scientific Inc., Germany). The
recovery yield of Am was calculated from the ratio of theintensity of 243Am in the fraction of interest to the sum of theintensities of all fractions. The standard deviation of the Am
recovery yield was calculated from variation of the ion intensity in 5 repeats of ICP-MS measurement. All treatments werecarried out in clean rooms (ISO class 5 and 6) at the Clean
Laborator y for Environmental Analysis and Research(CLEAR) of Japan Atomic Energy Agency (JAEA)12.
3. Results and discussion
The calculated recovery yields of each fraction are summarized in Table 1. Americium was retained on the column inthe first two fractions, which were indicated as M-1 and M-2
fractions in the Table 1, and then gradually eluted in the fractions Ln-4 (Am recovery yield; 0.4%) and Ln-5 (1.1%) after
passing through the 11.6 CV of the eluent used for lanthanide
separation. By the end of this step, total Am loss was 1.7%.
All the remaining Am was eluted in the subsequent fractions
Th-1 (89.3%) and Th-2 (8.9%). In previous works9–11, alkaline
metals and alkaline earth metals were completely eluted in thefirst mixed-media equivalent to the M-1 and M-2 fractions,and then the lanthanides were completely eluted with the first
two fractions of the second eluent, which corresponds to thefirst 2 fractions (total 7.5 CV), Ln-1 and Ln-2 in this work.
These results imply that Am can be simply and sequentiallyseparated from lanthanides and also alkaline metals and alkaline earth metals, by only elution with this mixed acid.
Kimura et al.13 reported the calculated inner sphere hydration
number of Cm 3+ and several other lanthanide (III) species

decreased remarkably with increasing the mole fraction of thenon-aqueous component of the water/non-aqueous solvent
mixture, including the water/methanol mixture. Their experimental results showed that the hydration number of Cm3+ wassmaller than that of the lanthanide (III) species in the solvent
containing a greater amount of the non-aqueous component,
and also indicated that the H 2O molecules in the first coordination sphere of the ions were replaced to a considerable
degree by the non-aqueous molecules.
The mechanism by which Am eluted at a different position
than the lanthanides in this work might be explained by thedifference of their inner-sphere hydration number in the firstcoordination sphere in a water/non-aqueous solvent mixture.
In this scenario, acetic acid plays as the role of a polarized
non-aqueous solvent, similarly to methanol in their report. In
future works, sequential separation of Am, Pu, U, Th and thelanthanides using an anion-exchange column will be reported,and the chemical behavior of the lanthanides and Am in mixed
media composed of mineral acids and acetic acid mixed media
will be investigated.
Acknowledgements
The authors wish to express their thanks to Y. Takahashi
from the Japan Atomic Energy Agency (JAEA) for operating
the ICP-MS. This work was supported by financial aid from
the Ministry of Education, Culture, Sports, Science andTechnology (MEXT) of Japan (Scientific Research (C), Grant
No. 22550143, 25340078, 16K00592).
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TABLE 1: Recovery yields of Am by sequential anion-exchange separation using acetic acid-based mixed media
Fraction
No.
M-1
M-2
Ln-1
Ln-2
Ln-3
Ln-4
Ln-5
Th-1
Th-2
Th-3
Th-4
Th-5
PbFe
Pu
UTotalElution volume,[cumulative volume]*1 (CV)
9.1
[9.1]
11.1 [20.2]
3.7 [3.7]
3.8 [7.5]
4.1 [11.6]
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6.0 [21.8]
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3.6 [12.8]
6.5 [19.3]
14.5 [14.5]
3.0 [3.0]
14.8 [14.8]
11.8 [11.8]
105.4

Recovery yieldof 243Am (%)*2

Composition of theeluent

Eluted elementin the previous work*3

0.1 ± 0.1
0.0 ± 0.0
0.0 ± 0.0
0.1 ± 0.1
0.0 ± 0.0
0.4 ± 0.1
1.1 ± 0.1
89.3 ± 4.2
8.9 ± 0.6
0.0 ± 0.0
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0.0 ± 0.1
0.0 ± 0.1
0.0 ± 0.0
0.0 ± 0.1
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100.0 ± 4.3

16 M CH3COOH, and0.2 M HNO3

Mg. Rb. Sr, Cs, Ba, Be, Sc, Cr,Mn, Te

15 M CH3COOH,0.80 M HCl,0.9 M HNO3, and0.03 M NH2OH·HCl

Lanthanides, Y, Co

12 M CH3COOH, and2 M HCl, 0.1 M HF

Th

9M HCl8M HNO3
6M HCl, and 0.1M HF
0.2M HCl, and 1M HF

Pb, Cu, In, AgFe, Zn, Ga, CdU, Sn, Bi*1: Cumulative volume expressed in column volume (CV) unit of the fractions of interest. 1 CV is equivalent to 0.158 mL.
*2: The standard deviation of the recovery yields was calculated from variation of the ion intensity in 5 repeats of ICP-MS measurement.
*3: The elements which >50% of the total amount was eluted in the fraction of interest in the previous work11.

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