Rapid separation of americium from complex matrices using solvent impregnated triazine extraction chromatography resins

Journal of Chromatography A 1669 (2022) 462950

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Journal of Chromatography A
journal homepage: www.elsevier.com/locate/chroma

Rapid separation of americium from complex matrices using solvent
impregnated triazine extraction chromatography resins
Joe Mahmoud a, Matthew Higginson b, Paul Thompson b, Christopher Gilligan b,
Francis Livens a, Scott L. Heath c,∗
a
b
c

Department of Chemistry, University of Manchester, M13 9PL, UK
AWE, Aldermaston, Reading, RG7 4PR, UK
Department of Earth and Environmental Sciences, University of Manchester, M13 9PL, UK

a r t i c l e

i n f o

Article history:
Received 8 September 2021
Revised 6 March 2022
Accepted 7 March 2022
Available online 9 March 2022
Keywords:
Americium
Separation

Nuclear forensics
Extraction chromatography

a b s t r a c t
Several novel extraction chromatography resins (EXC) have been synthesised by solvent impregnation of the triazine ligands 6,6 -bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]triazin-3-yl)-2,2 bipyridine (CyMe4 BTBP) and 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl)-1,10phenanthroline (CyMe4 BTPhen) into Amberlite XAD7 and Amberchrom CG300 polymer supports. The
resins have been physically characterised by a suite of spectroscopic, analytical and imaging techniques.
The resins have also been evaluated in terms of their ability to selectively extract americium from complex matrices intended to simulate those typical of spent nuclear fuel raffinate, environmental samples
and nuclear forensics samples. The resins have been compared with previously reported attempts to generate EXC resins based on CyMe4 BTBP and CyMe4 BTPhen. Previously reported resins all rely on complex
synthesis for the formation of a covalent bond between extractant and support by contrast with the simpler solvent impregnation method reported here. The Amberchrom supported CyMe4 BTBP resin achieved
a weight distribution ration (DAm ) of 170 within 60 min and a decontamination factor (DF) of >10 0 0 for
americium over lanthanides by column chromatography. The Amberchrom CyMe4 BTPhen resin achieved
a DAm of 540 within 30 min and a DF for americium from lanthanides of 60–160.
© 2022 The Authors. Published by Elsevier B.V.
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1. Introduction
The purification of americium from complex matrices is a great
challenge in radiochemical separation science. Separation from the
chemically and physically similar lanthanide elements is particularly difficult [1]. The separation of americium from the lanthanide
elements has major applications in nuclear fuel reprocessing [2],
environmental monitoring [3] and nuclear forensics [4].
Two strategies currently exist for the long-term management of
spent nuclear fuel; the first is disposal in an underground facility,
and the second is reprocessing, which can include the partitioning of minor actinides, of which americium is one, from the fission
products. This can be followed by transmutation of the minor actinides to radionuclides with shorter half-lives, i.e. less hazardous,
by ‘burning’ the minor actinides as fuel in ‘Generation IV’ fast neutron reactors [5].

∗

Corresponding author.
E-mail address: (S.L. Heath).

The feasibility and safety of the first approach would be greatly
facilitated by the removal of americium from spent nuclear fuel
since total minor actinide content is typically about only 0.1% of
the total mass, yet americium alone contributes strongly to the
long-term associated heat and radiotoxicity [6,7]. The second approach is reliant on the effective partitioning of americium from
the fission products which occur as 5% of spent nuclear fuel, 1–2%
of which consist of lanthanides [8]. The lanthanides have a high
neutron absorption cross section and hence would act as a poison
in potential americium-based nuclear fuel [8,9].
Americium is also a key element of interest in environmental
monitoring to assess the environmental and ecological impact of
releases caused by nuclear weapons testing, nuclear power production and the management of nuclear wastes [10]. The key isotope
of interest is Am-241, which is generated by the decay of its parent isotope Pu-241 (t1/2 14.3 years) which is also an environmental
contaminant released by nuclear weapons testing and civil nuclear
operations. One reason for the importance of Am-241 for environmental monitoring is that it can be used as an indicator of the
presence of plutonium easily by rapid gamma counting of samples.

/>0021-9673/© 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license ( />

J. Mahmoud, M. Higginson, P. Thompson et al.

Journal of Chromatography A 1669 (2022) 462950

If Am-241 is detected in samples those samples can be sent for
time consuming full radiochemical analysis for plutonium. Environmental samples are typically comprised of soil and sediment which
are inherently complex matrices and usually contain approximately
200 ppm of lanthanides [10].
Nuclear Forensic Analysis (NFA) is a multidisciplinary science
that requires methodologies for the collection and analysis of

seized nuclear or radioactive material, or material that may be
contaminated with nuclear or radioactive material for the purpose
of informing criminal investigations. NFA utilises radio-analytical
chemistry and radiometric techniques in order to establish isotopic and elemental composition, macro- and microscopic structure, amongst other properties, in an attempt to elucidate the
provenance and intended use of interdicted nuclear or radioactive
material [4].
Nuclear forensic investigations may require an estimation of the
age of nuclear material, where age is defined as the time elapsed
since the last chemical processing of the material. The age dating of plutonium is of particular importance in nuclear forensics
since it can be used to distinguish legacy material from material more recently produced. Several parent-daughter pairs can be
exploited for the dating of plutonium, though most rely on plutonium/uranium ratios that require larger sample sizes [11] and
can be more sensitive to environmental interferences [12]. The Pu241/Am-241 pair can also be used to determine the age of a plutonium sample and is less sensitive to environmental contaminants
allowing for more accurate age verification. The use of Pu-241/Am241 isobars does however require more intensive chemical preprocessing for sufficient separation so as to allow for analysis by
mass spectrometry and alpha spectrometry [11–13].
Age dating information may be key to the enforcement of a negotiated Fissile Materials Cut-Off Treaty (FMCT) [11] which aims to
ban the production of fissile material for use in nuclear weapons
[14].
The applications discussed all typically require the separation of
very small quantities (fg-pg) of americium from complex matrices
that can contain many naturally occurring elements of the Periodic Table at greater than mg/g concentrations. Unfortunately, the
methods currently available for the purification of americium from
these interferences are typically very time-consuming, multi-stage
flowsheets of chemical operations that require the application of
complex chemistry and demand considerable skill on the part of
the operator and are dependant on a well characterised matrix for
efficient recovery of americium. A major drawback of most separation schemes is that collection of the purified americium fraction is
usually one of the last stages, meaning a lot of effort is expended
on removing all other elements to leave americium, rather than removing americium at the start of these separation schemes.
Extraction chromatography (EXC) is based upon the same principles as solvent extraction (SX) but the separation is carried out
using a chromatographic column. The extractant is physically adsorbed or covalently bound onto the surface of a porous support,

usually an organic polymer, consisting of bead-like particles [15].
Benefits of EXC over SX include:
•

•
•
•

•

Fig. 1. Molecular structures of CyMe4 BTBP and CyMe4 BTPhen.

multi-stage chromatographic techniques and ease of operation of
ion-exchange chromatography [16,17].
There are currently several EXC resins commercially available
that are commonly used in f-block element separations, but none
that are specifically selective for americium over lanthanides without the use of toxic thiocyanate reagents [18]. EXC may represent
the cleanest and simplest approach to rapid separations of americium from complex matrices provided that a suitably efficient and
selective extractant can be devised.
The efficacy of the triazine ligands CyMe4 BTBP (BTBP) and
CyMe4 BTPhen (BTPhen) in selective solvent extractions of americium for its purification from lanthanides is well documented in
the literature [19–22] with BTBP representing the current European reference ligand for actinide/lanthanide separations [23]. The
molecular structres of the ligands are shown in Fig. 1.
A handful of attempts have been made to immobilise BTBP and
BTPhen onto solid supports to generate an EXC resin capable of
selective americium extraction from aqueous media [24–27], and
these attempts are reviewed in Section 1.1. These methods however all rely on the generation of a covalent bond between the
ligand and support. This work describes the synthesis and characterisation of BTBP and BTPhen EXC resins produced by the solvent
impregnation method [28–35] which provides a simpler, faster and
cheaper synthetic route for the production of EXC material.

1.1. Review of Immobilised BTBP & BTPhen extractants
Few examples exist in the literature of the production of EXC
resins based on BTBP and BTPhen extractants but these examples
are reviewed here.
Harwood showed that CyMe4 BTPhen can be immobilised on
silica-coated γ -Fe2 O3 magnetic nanoparticles (MNPs) by a phenyl
ether linkage to the C-5 of the phenanthroline unit [24]. The functionalised MNPs were subsequently used for a solid-liquid extraction of Am(III) from Eu(III) with SFAm/Eu =1700 ± 300 in 4 M nitric
acid [24], compared with SFAm/Eu =400 in comparable solvent extraction experiments [20] and also allowing the possibility of magnetic collection.
Generation of EXC resins by bonding the BTBP and BTPhen moieties to silica gel gave 14% and 10% (w/w) loading respectively [25].
Batch experiments showed that the BTBP resin had poor affinity
for both Am(III) and Eu(III) in the 0.001–4 M nitric acid range and
poor separation factors with high uncertainties were observed after sonication and shaking in contact with Am-241 and Eu-152
tracers [25]. The BTPhen resin was more successful, with maximum measured weight distribution ratios of DAm =4900 ± 1000 in
0.1 M nitric acid and a maximum SFAm/Eu =140 in 4 M nitric acid.
Follow-up work suggested that the complex between the
surface-bound ligand and the metal forms a 1:1 complex with
a 10-coordinate metal ion, including three nitrate ligands, as opposed to the 2:1 ligand to metal complexes found in the solvent
extraction system, due to the short carbon-link chain length between the silica particle and ligand [24,25]. The BTPhen EXC resin
was tested in 0.001–4 M perchloric acid. A significant drop in distribution ratios for both metals was observed by comparison with

elimination of the requirement for mixing and phase separation and associated issues around ligand solubility and phasetransfer kinetics,
removal of the possibility of third phase formation,
allowance for variable elution profile,
the reduction, or total absence, of radioactive organic waste
streams,
the potential to recondition and reuse the resin and improve
cost effectiveness.

For these reasons EXC is often touted as offering both the high
selectivity of SX systems alongside the advantages associated with

2


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Journal of Chromatography A 1669 (2022) 462950

the nitric acid system at all concentrations except 0.001 M. This
was interpreted as highlighting the importance of the nitrate ion
in the extraction [36].
An EXC resin produced by the Heath group was formed
by covalently binding Me4 BTPhen via an aniline link to
poly(vinylbenzene) [26]. The resin gave americium recoveries
of greater than 95% and decontamination factors greater than
10 0 0. When applied to a complicated mixture, designed to simulate a nuclear forensic sample, americium recovery was unaffected
and only cadmium and praseodymium co-extracted [26].
The BTPhen ligand has also been electrospun into polystyrene
fibres [27] which showed reasonable distribution coefficients, with
a maximum DAm =780 ± 50 in 0.1 M nitric acid and a maximum
SFAm/Eu =57 ± 4 in 4 M nitric acid. The fibres also showed an ability
to extract curium with a maximum DCm =440 ± 40 in 4 M nitric
acid.

2.3. Batch experiments
Resin (100 mg) was soaked for a minimum of 6 h in >18 M
deionised water before being removed from the water and added
to a solution containing 50–100 Bq Am-241 in the stated acids and
vortex mixed at 20 0 0 rpm for 1–60 min. The acid solution was
drained and the resin and solution reweighed to allow for the application of a mass correction in the weight distribution calculation. The acid solution was transferred to a standard measurement
geometry and counted by gamma spectroscopy.

2.4. Column studies
A standard plastic column, with an internal diameter of 7 mm,
was packed to a 39 mm height using 0.6–0.7 g of resin. These
dimensions were chosen to emulate the size of many pre-loaded
commercially available EXC resin columns typically used in radiochemical separations.
The column was loaded with a minimum volume of solution
containing 50–100 Bq of Am-241 and 1 mg of stable Be(II), Sr(II),
Cd(II), Cs(I), Ba(II), Y(III), Mo(VI), Ce(III), Pr(III), Nd(III), Sm(III),
Tb(III) and Ag(I) generated from their nitrate/hydrochloride salts or
otherwise purchased as a certified standard from Essex Scientific
Laboratories Ltd, UK. All elements were at natural isotope abundances.
The column was eluted with the stated elution profiles with a
flow rate of 0.2 mL min−1 controlled using a vacuum box. Each
fraction was collected and made to a standard geometry before being counted by gamma spectroscopy. A small aliquot was removed
and diluted for analysis of stable isotopes by ICP-MS.

2. Materials and methods
2.1. General
All radionuclides used were provided from calibrated stocks in
the School of Chemistry, University of Manchester. Micropipettes of
10–10 0 μL, 20–20 0 μL, 0.1–1 mL and 2–10 μL were calibrated on a
4 decimal place balance with >18 M deionised water in the temperature range 18–22 °C and were found to be within their stated
range. All acid solutions were made from analytical grade concentrated solutions and were diluted with >18 M deionised water.
Gamma counting was performed using a Canberra 2020 coaxial
HPGe gamma spectrometer with an Ortec DSPEC-50 multi-channel
analyser energy and efficiency calibrated for the geometry used.
Gamma spectroscopy was performed against a standard of known
activity counted in the same geometry and Am-241 was quantified
using the diagnostic photon energy of Am-241 (59.5 keV). Limits of
detection were calculated by the GammaVision software. Peaks of

values greater than 3σ above the background count were considered significant.
ICP-MS analysis was performed on an Agilent 7500cx spectrometer. Multiple standards for each element in the range 1–100 ppb
were used for ICP-MS quantification. All reagents and solvents used
were of standard analytical grade.
The estimated uncertainty on the measurements of stable isotopes quantified by ICP-MS is 10% based on a standard uncertainty
multiplied by a coverage factor k = 2, providing a level of confidence of approximately 95%.
Infrared Spectrometry was performed using a Bruker Invenio-S
infrared spectrometer.
Scanning electron microscope images were produced using a
FEI Quanta 650 FEG ESEM equipped with a Bruker XFlash® 6 |30
silicon drift detector (SDD) instrument. Samples were prepared
with a gold coating.

3. Results & discussion
The aim of this work was to produce an americium selective
EXC resin based upon the solvent impregnation of BTBP and BTPhen extractants into polymer supports. This allows for a simpler,
faster and cheaper method to produce the extraction chromatography material by comparison with the covalent bond forming methods reviewed in Section 1.1.
The benchmark for a successful extractant was considered to be
a material that could achieve a selective americium extraction with
a decontamination factor of >10 0 0 over lanthanides with both separation and quantification of Am-241 deliverable within one working day. These criteria were chosen as they represent the standard
achieved by the covalently bound BTPhen resin previously reported
[26].
A decontamination factor is a measure of the purification of the
component that is to be extracted (product) from another component (interference). The principle is commonly used in radiochemical separations and is defined in Eq. (1):

DF =

Pf inal /Pinitial
I f inal /Iinitial

(1)

Decontamination factor Eq. (1) where P represents the Product
and I the Interference, both of which are commonly expressed in
units of activity in the case of radioactive isotopes or alternatively
in units of concentration The term ‘separation factor’ (SF) is also
commonly used to quantify separations. In the context of the work
reviewed and presented here SF is taken to be the ratio of distribution coefficients of the target material to be extracted and the
interference, as is common in the literature.
The EXC resins produced have also been characterised in terms
of extractant loading, homogeneity of distribution of the extractant across the support and the accuracy and reproducibility of the
production method. Methods for determination of the extraction
capabilities of EXC resins are common in the literature, although

2.2. Resin synthesis
Polymer (Amberlite XAD7/Amberchrom CG300) was pretreated according to the manufacturer’s instructions. The required quantity of polymer was added to a solution of ligand
(CyMe4 BTBP/CyMe4 BTPhen) that had been dissolved in acetone
with stirring at 45 °C. The ratio of polymer to ligand was chosen
to meet the target loading on the resin, i.e. 1 g of 40% (w/w) resin
consisted of 1 g of pre-treated polymer added to 0.4 g of ligand
dissolved in acetone. The resulting slurry was left being stirred at
room temperature for 1 hour before the excess acetone was removed using a rotary evaporator.
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Journal of Chromatography A 1669 (2022) 462950

Table 1

Calculated ligand loading based upon combustion analysis of EXC resins.
ID
Resin
Resin
Resin
Resin
Resin
Resin
Resin
Resin

1
2
3
4
5
6
7
8

Ligand

Substrate

Target Loading /% (w/w)

Measured Loading /% (w/w)

RSD /%

CyMe4 BTBP
CyMe4 BTPhen
CyMe4 BTPhen
CyMe4 BTBP
CyMe4 BTBP
CyMe4 BTPhen
CyMe4 BTPhen
Me4 BTPhen

Amberlite
Amberlite
Amberchrom
Amberchrom
Amberchrom
Amberchrom
Amberchrom
PVB

3.5
3.5
5
40
40
40
40
5

3.5
3.6
5

31
52
42
42

6
6
0.5
3
3
4
4

Fig. 2. SEM images of Amberchrom CG300 starting material and Resins 4–8.

detailed physical characterisation of EXC resins is less so. A robust
method for the cheap and easy synthesis of a selective EXC resin
could theoretically be generalised to extraction of any metal by judicious choice of ligand. Such a method could provide a powerful
tool for radiochemical separation procedures.
The materials synthesised in this work have been compared
with previous attempts to produce EXC resins using BTBP and BTPhen extractants which have been reviewed in Section 1.1.

to the surface of the beads and dislodged during sample preparation or whether the material consists of both surface bound ligand
and unbound crystalised ligand.
The BTPhen ligand presents a different morphology (Resin 6
and Resin 7). The longer, thinner crystals of the BTPhen ligand appear to be less homogenously distributed about the support than
in the case of the BTBP and perhaps less strongly closely associated
with the surface of the polymer.
Resin 8 is a covalently bound resin previously synthesised [26].
The Me4 BTPhen ligand appears to be more evenly distributed

across the Amberlite polymer beads in this resin by comparison
with the solvent impregnated resins. There is a total absence of
unbound ligand in the interstitials which is to be expected given
the covalent bond between the ligand and the support.

3.1. Physical characterisation of resins
3.1.1. IR spectroscopy
IR spectroscopy showed phenanthroline stretches, diagnostic of
the BTBP and BTPhen ligands in both the Amberlite and Amberchrom materials [20] qualitatively confirming the presence of the
ligands on the supports.

3.2. Radiochemical separations
3.2.1. Batch experiments
The affinity of the resins for the metals to be extracted from solution has been characterised by the weight distribution ratio (Dw )
parameter (Eq. (2)). The term A0 represents the initial activity of
the metal being extracted, As the activity remaining in solution
post extraction, mL the volume of solvent used in the extraction
and g the grams of resin. Units of concentration or mass may also
be used rather than activity in the case of non-active metals. In
this work Dw for non-active metals has been calculated based upon
mass in grams.

3.1.2. Elemental analysis
Elemental analysis for nitrogen was used to measure the extractant loadings on the polymer supports (Table 1).
3.1.3. Scanning electron microscopy
Scanning electron microscope (SEM) images were taken of the
starting and ligand-loaded materials, except for resins 1–3 which
showed no americium extraction capability. The images of the
starting material and ligand-loaded resins are shown in Fig. 2.
The BTBP loaded resins (Resin 4 and Resin 5) have the ligand crystallised as platelets adhering to the surface of the polymer support. Nitrogen mapping is consistent with localisation of

the BTBP ligand in these features. The ligand is evenly distributed
on the individual polymer bead shown, although unbound ligand
is also seen in the interstitial space. It is unclear from these images whether this crystallised ligand was originally weakly bound

Dw =

(A0 − As ) mL
A0

g

(2)

Eq. (2): Weight distribution ratio.
This metric was chosen as it is commonplace in the literature [17,18,25,27,36,37–43] and thus provides a convenient point
of comparison between the resins examined here and those previously reported elsewhere. The weight distribution ratio is also eas4


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Journal of Chromatography A 1669 (2022) 462950

ily converted into other common measures of extraction capability such as capacity factor (k’) and free column volumes (FCV) for
comparison between batch experiment systems and column experiments [44].

and bound by aniline linkage with free rotation around the carbon
bonds would not be expected to be hindered in this way.
3.2.1.2. Amberchrom supported resins. Due to the poor americium
extraction capabilities displayed by the Amberlite based resins the
polymer support was switched to Amberchrom CG300 which has

a much smaller particle size range of 50–100 μm and lower mean
pore diameter of 0.03 μm The loading was increased to 5% (w/w)
for Resin 3 since the ligand was no longer in limited supply and
this loading better approximated Resin 8.
Resin 3 also displayed poor uptake of americium from 4 M nitric acid after 24 h contact time. Given the poor uptake despite the
change of support to a lower particle size and the now freely available ligand it was decided to prepare resins of 40% (w/w) loading
on the Amberchrom support. The 40% (w/w) loading was chosen
to bring the triazine based resins in line with the standard 40%
(w/w) loading for commercially available EXC resins typically used
in actinide separations such as TEVA, UTEVA, LN resin, Actinide
Resin etc. [47]. This loading was found to be the maximum capacity for the various organic ligands on Amberchrom used in these
EXC resins with further loading leading to significant leaching of
ligand from the support into solution during the extraction procedure [47].
Batch experiments were utilised to probe the americium extraction capabilities of the 40% (w/w) loaded resins. The resins were
vortex mixed for 1–60 min with 4 M and 0.01 M nitric acid solution containing 50–100 Bq Am-241. Nitric acid was chosen at these
concentrations for the reasons previously discussed.
As can be seen in Fig. 3, with a DAm min=50 and a DAm
max=170, Resin 4 performed well by comparison to both its SX
analogue which is reported to achieve only a DAm on the order of
10 after 60 min contact time and also with a covalently bound 14%
(w/w) BTBP-silica resin reported by Harwood which did not show
any americium extraction from nitric acid in the 0.001–4 M concentration [25]. The uncertainties graphed represent the calculated
RSD based upon triplicate studies.
Resin 6 did not perform as well as the BTPhen SX counterpart
which is reported to achieve DAm >10 0 0 within 15 min [20,21]
and the silica bonded covalent resin (10% w/w) reported by Harwood which is reported to achieve DAm >30 0 0 within 90 min in
0.1 M nitric acid [25]. Despite this, the DAm max=540 after 15 min
contact time in 4 M nitric acid and DAm max=460 after 15 min in
0.01 M nitric acid still represent good extraction of americium with
>94% of americium was extracted from solution within 10 min and

>99% within 60 min. The high DAm values in 0.01 M nitric acid imply that this would not constitute an appropriate back-extraction
phase as is the case in the BTPhen SX system.
The americium extraction capability of Resin 6 was also tested
in 4 M and 0.1 M hydrochloric acid and was not competitive with
the nitric acid system achieving DAm max=125 ± 11.
The Dw values for simulated matrix elements on Resin 5 for
all of the elements included were in the range of Dw =10–30 except for cadmium and silver which had DCd max=135 and DAg
max=340 after 30 min of contact time. The affinity of BTPhen for
cadmium and silver has been previously reported in solvent extraction studies using the ligand [22]. The selectivity for americium over lanthanides displayed by the soft N-donor ligands BTBP
and BTPhen is commonly attributed to the greater covalency of
the 5f orbitals by comparison with the 4f orbitals [20,48,49]. Care
must be taken with the definition of covalency in this context since
early actinides display greater covalency due to the relative radial
extension of the 5f valence orbitals. The valence orbitals of the
minor actinides such as americium however are more contracted
and computational calculations suggest that selectivity for An(III)
over Ln(III) by soft N-donor ligands is likely due to a better energy
match between metal and ligand orbitals [50].

3.2.1.1. Amberlite supported resins. The first resins synthesised in
this work were based upon the impregnation of BTBP and BTPhen
into high purity Amberlite XAD7 at a loading of 3.5% (w/w) as described in Section 2.2.
The loading of 3.5% was chosen for these resins to closely resemble the loading of the covalently bound resin that has been
previously reported by the Heath group [26] (Resin 8). Resin 8 had
a nominal loading of 5% but this was lowered to 3.5% due to the
limited availability of ligand at the time of this study. The slight
deviation in ligand loadings was not considered to be of detriment
to the comparison since the ligand loading represented a large theoretical excess of ligand to americium used in these separations.
The Amberlite substrate represents a commonly used polymer
support in the production of EXC resins [28,31,33,35,45] and has

a particle size of 560–710 μm which matches the particle size of
Resin 8 [26]. Amberlite is also chemically inert and stable in the
systems of interest.
The extraction and separation capabilities of Resin 1 and Resin
2 were tested by vortex mixing experiments in which 100 mg of
resin was contacted with 4 M and 0.01 M nitric acid containing yttrium, europium and americium. Nitric acid was chosen at
these concentrations as they represent the extraction and backextraction phases respectively for the analogous BTBP/BTPhen solvent extraction (SX) system which consists of the BTBP/BTPhen ligand (0.01 M) in a 1-octanol diluent [20–22].
Yttrium and europium were chosen as they are commercially
available radiotracers for the elements that can be conveniently
counted by gamma spectroscopy, and they represent realistic contaminants that may be found in environmental/nuclear forensics
samples. Europium is the commonly used test case for americium/lanthanide separations in the literature, often being considered the lanthanide ‘analogue’ of americium due to europium’s
similar electronic configuration and ionic radii [46].
Resin 1 showed no affinity for americium even after 24 h of
contact time at either acid concentration. This agrees with the results reported by Harwood [25] covered in Section 1.1. The analogous BTBP SX system however displays a DAm of ca. 10 after
60 min of contact time [25] meaning that the BTBP Amberlite resin
underperformed by comparison.
Resin 2 showed some affinity for americium within the same
period with a DAm value of 42 ± 2 and 94 ± 5 in 4 M and
0.01 M and nitric acid respectively however in both cases there
was significant co-extraction of europium resulting in modest separation factors of 4 ± 1 and 24 ± 1. The analogous BTPhen SX
system is reported to achieve DAm >10 0 0 within 15 min [20,21]
and SFAm/Eu >400 [20] whilst the silica bonded covalent resin (10%
w/w) reported by Harwood is reported to achieve DAm >30 0 0
within 90 min in 0.1 M nitric acid [25].
The poor extraction kinetics observed in the case of the BTPhen
Amberlite resin, despite the large theoretical excess of ligand to
metal, may be caused by sub-optimal orientation of the adsorbed
ligand onto the Amberlite support. Only ligands that present the
binding pocket to the solution are likely to be capable of metal extraction and it may be that the 560–710 μm particle size and corresponding 0.04 μm mean pore diameter of this support are not
conducive to providing this configuration with high enough availability at the loading of 3.5% (w/w). It is noted that Horwitz et

al. reports pore diameter as a key consideration when immobilising an extractant across similar polymer supports [17]. Resin 8,
which successfully extracted americium under similar conditions
despite its 5% (w/w) loading, supports this conclusion as the lig5


J. Mahmoud, M. Higginson, P. Thompson et al.

Journal of Chromatography A 1669 (2022) 462950

Fig. 3. Weight distribution ratios as a function of contact time for americium and simulated matrix elements.

Fig. 4. Elution profiles for americium and simulated matrix elements on Resin 4 columns.

3.2.2. Column studies
A column separation of americium from the simulated matrix
was performed using Resin 4 and the elution profile of the column
is displayed in Fig. 4a.
Significant amounts (46–54%) of simulated matrix elements
passed straight through the column in the loading fraction with
the exception of cadmium and silver which were strongly retained
on the column whilst 27.6% of the americium eluted in the loading fraction. The americium on the column was strongly retained
until a small amount (ca. 3%) was eluted across fractions 16–18
by 0.1 M HCl. Elution with 15 mM TBP solution stripped 5.5% of
the bound americium from the column across fractions 19–21. The
DF for americium from simulated matrix elements in the highest
americium containing fraction (fraction 20) which contained 2.7%
of the americium initially loaded onto the column fell short of the
target of DF > 10 0 0 for americium over lanthanides at DF =60.
This was driven by the poor recovery of americium and high coelution of lanthanides by the use of the TBP stripping agent.
Total americium recovery from the column was 38.9%. Gamma

spectroscopy of the column confirmed that the remainder of the
americium was retained on the column.
An alternative elution profile shown in Fig. 4b maintained the
loading fraction at 4 M nitric acid before 11 fractions of 2 M HCl
were used to elute the lanthanides from the column. Americium
was retained on the column during these elutions. The column
was rinsed with 15 mM TEDGA solution and 52% of the americium initially added to the column was recovered across 6 frac-

tions. The calculated DF for americium based on fraction 13, which
contained the highest proportion of americium, (28%) are shown
in Fig. 6. This method produced DF values that were in line with
or greater than the target value of DF >10 0 0 for americium over
lanthanides.
Fig. 5a displays the elution profile for an americium separation
from simulated matrix elements based upon a column separation
using Resin 6.
There was 100% retention of americium on the column in the
loading fraction whilst 50–53% of beryllium, strontium, caesium,
barium and yttrium passed straight through the column with a
further 16–22% of these elements eluted cumulatively across the
elution profile. Lanthanides were strongly retained on the column
until the application of 0.1 M HCl. Terbium was an exception as
11% passed straight through in the loading fraction. Elution of 15–
31% of lanthanides was observed across the 6 elutions with 0.1 M
HCl. A small amount of americium coelution was observed across
the 0.1 M HCl fractions with a total of 7% americium eluted across
the 6 fractions.
Application of 15 mM TBP eluent led to a total americium recovery of 89% of the total americium applied to the column across
10 fractions. The DF for americium from lanthanides achieved by
this column separation was insufficient at DF =10–20.

As may have been expected from the weight distribution ratios
observed in the batch experiments both cadmium and silver were
both strongly retained on the column, with a total eluted recovery
of only 3.6% and 8.2% respectively demonstrating that the BTPhen
6


J. Mahmoud, M. Higginson, P. Thompson et al.

Journal of Chromatography A 1669 (2022) 462950

Fig. 5. Elution profiles for americium and simulated matrix elements on Resin 6 columns.

clear fuel, environmental, and nuclear forensics samples within the
desired 24 hour timescale.
A CyMe4 BTPhen resin (Resin 6) of 40% (w/w) loading with
an Amberchrom support showed good extraction of americium
from nitric acid solutions achieving a maximum weight distribution ratio (DAm ) of 540 within 15 min of contact time. The same
resin achieved decontamination factors in the range of 60–160 for
americium over lanthanides by column chromatography.
A CyMe4 BTBP resin (Resin 4) of 40% (w/w) loading on an Amberchrom support achieved maximum also showed good extraction
of americium from nitric acid achieving a maximum weight distribution ratio (DAm ) of 170 within 60 min. Decontamination factors
of >10 0 0 were attained for several interferences including many
lanthanides by column chromatography.
This work has demonstrated a rapid, cheap and easy methodology for the generation of extraction chromatography resins from
commercially available, relevant extractants and support materials.
Resins can be easily prepared on inert supports and the process
controlled using analytical techniques. The resins can then be applied to fundamental radiochemical studies to establish key performance metrics. Future work will focus upon the optimisation of
this method by further investigation into other promising americium/lanthanide selective ligands and the optimisation of separation and recovery of americium by characterising the affinity of the
resins with a greater range of acids and stripping phases.

Fig. 6. Decontamination factors for americium from lanthanides on Resin 4 and
Resin 6 columns.

resin may be valuable as a rapid filtration method for these elements.
Fig. 5b shows the elution profile based upon repeated HCl
washes for the alternative column separation scheme using Resin
6 as detailed above. The strategy of removing the lanthanides by
repeated HCl washes prior to stripping the americium with TBP
dramatically improved the DF of americium over most elements as
is shown in Fig. 6. The lanthanide elements however did not meet
the target of DF >10 0 0.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to
influence the work reported in this paper.
CRediT authorship contribution statement

4. Conclusion

Joe Mahmoud: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Matthew Higginson: Conceptualization, Validation, Investigation, Data curation, Writing –
review & editing, Supervision, Project administration, Funding acquisition. Paul Thompson: Conceptualization, Writing – review &
editing, Supervision, Project administration, Funding acquisition.
Christopher Gilligan: Conceptualization, Methodology, Investigation, Validation, Data curation. Francis Livens: Resources, Writing
– review & editing, Supervision, Project administration, Funding acquisition. Scott L. Heath: Conceptualization, Resources, Data curation, Writing – review & editing, Supervision, Project administration, Funding acquisition.

Several extraction chromatography resins synthesised by the
solvent impregnation of CyMe4 BTBP and CyMe4 BTPhen into Amberlite XAD7 and Amberchrom CG300 have been reported. The
prepared resins have been well characterised both for ligand loading and homogeneity of distribution of ligand across the support
material by a suite of analytical techniques including IR spectroscopy, elemental (CHN) analysis, SEM imaging, and elemental

mapping.
Resins of 3.5–5% (w/w) loading based on Amberlite and Amberchrom were found to be ineffective for americium extraction and
separation from lanthanides and other elements common in nu7


J. Mahmoud, M. Higginson, P. Thompson et al.

Journal of Chromatography A 1669 (2022) 462950

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Funding for this project was provided by AWE and EPSRC via a
studentship to JM through the Next Generation Nuclear Centre for
Doctoral Training, The University of Manchester.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.chroma.2022.462950.
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9