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 (CyMe4BTBP) and 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl)-1,10- phenanthroline (CyMe4BTPhen) into Amberlite XAD7 and Amberchrom CG300 polymer supports.
Trang 1Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/chroma
Joe Mahmouda, Matthew Higginsonb, Paul Thompsonb, Christopher Gilliganb,
Francis Livensa, Scott L Heathc, ∗
a Department of Chemistry, University of Manchester, M13 9PL, UK
b AWE, Aldermaston, Reading, RG7 4PR, UK
c Department of Earth and Environmental Sciences, University of Manchester, M13 9PL, UK
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
Several novel extraction chromatography resins (EXC) have been synthesised by solvent impregna-tion 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 (CyMe4BTBP) and 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl)-1,10-phenanthroline (CyMe4BTPhen) into Amberlite XAD7 and Amberchrom CG300 polymersupports The resinshavebeenphysicallycharacterisedbyasuiteofspectroscopic,analyticalandimagingtechniques Theresinshavealsobeenevaluatedintermsoftheirabilitytoselectivelyextractamericiumfrom com-plexmatricesintended tosimulatethosetypicalofspentnuclearfuelraffinate,environmentalsamples andnuclearforensicssamples.Theresinshavebeencomparedwithpreviouslyreportedattemptsto gen-erateEXCresinsbasedonCyMe4BTBPandCyMe4BTPhen.Previouslyreportedresinsallrelyoncomplex synthesisfortheformationofacovalentbondbetweenextractantandsupportbycontrastwiththe sim-plersolventimpregnationmethodreportedhere.TheAmberchromsupportedCyMe4BTBPresinachieved
aweightdistributionration(DAm)of170within60minandadecontaminationfactor(DF)of>1000for americiumoverlanthanidesbycolumnchromatography.TheAmberchromCyMe4BTPhenresinachieved
aDAmof540within30minandaDFforamericiumfromlanthanidesof60–160
© 2022TheAuthors.PublishedbyElsevierB.V ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/)
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 particu-
larly 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 partition-
ing of minor actinides, of which americium is one, from the fission
products This can be followed by transmutation of the minor ac-
tinides to radionuclides with shorter half-lives, i.e less hazardous,
by ‘burning’ the minor actinides as fuel in ‘Generation IV’ fast neu-
tron reactors [5]
∗ Corresponding author
E-mail address: scott.l.heath@manchester.ac.uk (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 ap- proach 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 produc- tion and the management of nuclear wastes [10] The key isotope
of interest is Am-241, which is generated by the decay of its par- ent isotope Pu-241 (t 1/214.3 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 environ- mental monitoring is that it can be used as an indicator of the presence of plutonium easily by rapid gamma counting of samples
https://doi.org/10.1016/j.chroma.2022.462950
0021-9673/© 2022 The Authors Published by Elsevier B.V This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
Trang 2If Am-241 is detected in samples those samples can be sent for
time consuming full radiochemical analysis for plutonium Environ-
mental 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 iso-
topic and elemental composition, macro- and microscopic struc-
ture, 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 dat-
ing of plutonium is of particular importance in nuclear forensics
since it can be used to distinguish legacy material from mate-
rial more recently produced Several parent-daughter pairs can be
exploited for the dating of plutonium, though most rely on plu-
tonium/uranium ratios that require larger sample sizes [11] and
can be more sensitive to environmental interferences [12] The Pu-
241/Am-241 pair can also be used to determine the age of a pluto-
nium sample and is less sensitive to environmental contaminants
allowing for more accurate age verification The use of Pu-241/Am-
241 isobars does however require more intensive chemical pre-
processing 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 ne-
gotiated 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 Peri-
odic 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 separa-
tion 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 re-
moving americium at the start of these separation schemes
Extraction chromatography (EXC) is based upon the same prin-
ciples as solvent extraction (SX) but the separation is carried out
using a chromatographic column The extractant is physically ad-
sorbed 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:
• elimination of the requirement for mixing and phase separa-
tion and associated issues around ligand solubility and phase-
transfer 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
Fig 1 Molecular structures of CyMe 4 BTBP and CyMe 4 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 with- out the use of toxic thiocyanate reagents [18] EXC may represent the cleanest and simplest approach to rapid separations of ameri- cium from complex matrices provided that a suitably efficient and selective extractant can be devised
The efficacy of the triazine ligands CyMe 4BTBP (BTBP) and CyMe 4BTPhen (BTPhen) in selective solvent extractions of ameri- cium for its purification from lanthanides is well documented in the literature [19–22] with BTBP representing the current Euro- pean 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 how- ever all rely on the generation of a covalent bond between the ligand and support This work describes the synthesis and charac- terisation 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 CyMe 4BTPhen can be immobilised on silica-coated γ-Fe 2O 3 magnetic nanoparticles (MNPs) by a phenyl ether linkage to the C-5 of the phenanthroline unit [24] The func- tionalised MNPs were subsequently used for a solid-liquid extrac- tion of Am(III) from Eu(III) with SF Am/Eu= 1700 ± 300 in 4 M nitric acid [24], compared with SF Am/Eu=400 in comparable solvent ex- traction experiments [20]and also allowing the possibility of mag- netic collection
Generation of EXC resins by bonding the BTBP and BTPhen moi- eties 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 af- ter sonication and shaking in contact with Am-241 and Eu-152 tracers [25] The BTPhen resin was more successful, with maxi- mum measured weight distribution ratios of D Am=4900 ± 1000 in 0.1 M nitric acid and a maximum SF Am/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 op- posed to the 2:1 ligand to metal complexes found in the solvent extraction system, due to the short carbon-link chain length be- tween the silica particle and ligand [24, 25] The BTPhen EXC resin was tested in 0.001–4 M perchloric acid A significant drop in dis- tribution ratios for both metals was observed by comparison with
Trang 3the 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 Me 4BTPhen 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 simu-
late 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 D Am=780 ± 50 in 0.1 M nitric acid and a maximum
SF Am/Eu= 57 ± 4 in 4 M nitric acid The fibres also showed an ability
to extract curium with a maximum D Cm=440 ± 40 in 4 M nitric
acid
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 tem-
perature range 18–22 °C and were found to be within their stated
range All acid solutions were made from analytical grade concen-
trated 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 3 σ above the background count were consid-
ered significant
ICP-MS analysis was performed on an Agilent 7500cx spectrom-
eter 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 iso-
topes quantified by ICP-MS is 10% based on a standard uncertainty
multiplied by a coverage factor k = 2, providing a level of confi-
dence 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
2.2 Resin synthesis
Polymer (Amberlite XAD7/Amberchrom CG300) was pre-
treated according to the manufacturer’s instructions The re-
quired quantity of polymer was added to a solution of ligand
(CyMe 4BTBP/CyMe 4BTPhen) 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 re-
moved using a rotary evaporator
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 ap- plication of a mass correction in the weight distribution calcula- tion 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 radio- chemical 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 abun- dances
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 be- ing counted by gamma spectroscopy A small aliquot was removed and diluted for analysis of stable isotopes by ICP-MS
3 Results & discussion
The aim of this work was to produce an americium selective EXC resin based upon the solvent impregnation of BTBP and BT- Phen extractants into polymer supports This allows for a simpler, faster and cheaper method to produce the extraction chromatogra- phy material by comparison with the covalent bond forming meth- ods reviewed in Section1.1
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 sep- aration and quantification of Am-241 deliverable within one work- ing 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 compo- nent (interference) The principle is commonly used in radiochem- ical separations and is defined in Eq.(1):
DF=P f inal /P initial
I f inal /I initial
(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 distri- bution 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 extrac- tant 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
Trang 4Table 1
Calculated ligand loading based upon combustion analysis of EXC resins
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 ju-
dicious 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 BT-
Phen extractants which have been reviewed in Section1.1
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 Amber-
chrom materials [20] qualitatively confirming the presence of the
ligands on the supports
3.1.2 Elemental analysis
Elemental analysis for nitrogen was used to measure the extrac-
tant loadings on the polymer supports ( Table1)
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 lig-
and crystallised as platelets adhering to the surface of the poly-
mer 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 im-
ages whether this crystallised ligand was originally weakly bound
to the surface of the beads and dislodged during sample prepara- tion 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 ap- pear 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 Me 4BTPhen 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
3.2 Radiochemical separations 3.2.1 Batch experiments
The affinity of the resins for the metals to be extracted from so- lution has been characterised by the weight distribution ratio (D w) parameter ( Eq.(2)) The term A 0 represents the initial activity of the metal being extracted, A s 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 D wfor non-active metals has been calculated based upon mass in grams
D w= (A0− A s)
A0
mL
Eq.(2): Weight distribution ratio
This metric was chosen as it is commonplace in the litera- ture [17, 18, 25, 27, 36, 37–43] and thus provides a convenient point
of comparison between the resins examined here and those previ- ously reported elsewhere The weight distribution ratio is also eas-
Trang 5ily converted into other common measures of extraction capabil-
ity such as capacity factor ( k’) and free column volumes (FCV) for
comparison between batch experiment systems and column exper-
iments [44]
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 de-
scribed in Section2.2
The loading of 3.5% was chosen for these resins to closely re-
semble 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 the-
oretical 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 contain-
ing yttrium, europium and americium Nitric acid was chosen at
these concentrations as they represent the extraction and back-
extraction phases respectively for the analogous BTBP/BTPhen sol-
vent extraction (SX) system which consists of the BTBP/BTPhen lig-
and (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 con-
taminants that may be found in environmental/nuclear forensics
samples Europium is the commonly used test case for ameri-
cium/lanthanide separations in the literature, often being consid-
ered 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 re-
sults reported by Harwood [25] covered in Section 1.1 The anal-
ogous BTBP SX system however displays a D Am 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 D Am 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 sep-
aration factors of 4 ± 1 and 24 ± 1 The analogous BTPhen SX
system is reported to achieve D Am >10 0 0 within 15 min [20, 21]
and SF Am/Eu>400 [20]whilst the silica bonded covalent resin (10%
w/w) reported by Harwood is reported to achieve D Am >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 ex-
traction and it may be that the 560–710 μm particle size and cor-
responding 0.04 μm mean pore diameter of this support are not
conducive to providing this configuration with high enough avail-
ability at the loading of 3.5% (w/w) It is noted that Horwitz et
al reports pore diameter as a key consideration when immobil-
ising 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 lig-
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 ni- tric acid after 24 h contact time Given the poor uptake despite the change of support to a lower particle size and the now freely avail- able 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 capac- ity 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 proce- dure [47]
Batch experiments were utilised to probe the americium extrac- tion 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 solu- tion 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 D Am min =50 and a D Am max = 170, Resin 4 performed well by comparison to both its SX analogue which is reported to achieve only a D Am 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 con- centration [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 D Am >10 0 0 within 15 min [20, 21] and the silica bonded covalent resin (10% w/w) reported by Har- wood which is reported to achieve D Am >30 0 0 within 90 min in 0.1 M nitric acid [25] Despite this, the D Ammax =540 after 15 min contact time in 4 M nitric acid and D Am 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 D Amvalues in 0.01 M nitric acid im- ply 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 D Ammax =125 ± 11
The D w values for simulated matrix elements on Resin 5 for all of the elements included were in the range of D w= 10–30 ex- cept for cadmium and silver which had D Cd max =135 and D Ag max =340 after 30 min of contact time The affinity of BTPhen for cadmium and silver has been previously reported in solvent ex- traction studies using the ligand [22] The selectivity for ameri- cium 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]
Trang 6Fig 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 load-
ing 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 coelu-
tion 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 ameri-
cium 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 re- covery 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
Trang 7Fig 5 Elution profiles for americium and simulated matrix elements on Resin 6 columns
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 ele-
ments
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
4 Conclusion
Several extraction chromatography resins synthesised by the
solvent impregnation of CyMe 4BTBP and CyMe 4BTPhen into Am-
berlite XAD7 and Amberchrom CG300 have been reported The
prepared resins have been well characterised both for ligand load-
ing and homogeneity of distribution of ligand across the support
material by a suite of analytical techniques including IR spec-
troscopy, elemental (CHN) analysis, SEM imaging, and elemental
mapping
Resins of 3.5–5% (w/w) loading based on Amberlite and Amber-
chrom were found to be ineffective for americium extraction and
separation from lanthanides and other elements common in nu-
clear fuel, environmental, and nuclear forensics samples within the desired 24 hour timescale
A CyMe 4BTPhen 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 distribu- tion ratio (D Am) 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 CyMe 4BTBP resin (Resin 4) of 40% (w/w) loading on an Am- berchrom support achieved maximum also showed good extraction
of americium from nitric acid achieving a maximum weight distri- bution ratio (D Am) 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 method- ology 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 ap- plied to fundamental radiochemical studies to establish key per- formance metrics Future work will focus upon the optimisation of this method by further investigation into other promising ameri- cium/lanthanide selective ligands and the optimisation of separa- tion and recovery of americium by characterising the affinity of the resins with a greater range of acids and stripping phases
Declaration of Competing Interest
The authors declare that they have no known competing finan- cial interests or personal relationships that could have appeared to influence the work reported in this paper
CRediT authorship contribution statement Joe Mahmoud: Conceptualization, Methodology, Formal anal- ysis, Investigation, Data curation, Writing – original draft, Writ- ing – review & editing, Visualization Matthew Higginson: Con- ceptualization, Validation, Investigation, Data curation, Writing – review & editing, Supervision, Project administration, Funding ac- quisition Paul Thompson: Conceptualization, Writing – review & editing, Supervision, Project administration, Funding acquisition
Christopher Gilligan: Conceptualization, Methodology, Investiga- tion, Validation, Data curation Francis Livens: Resources, Writing – review & editing, Supervision, Project administration, Funding ac- quisition Scott L Heath: Conceptualization, Resources, Data cura- tion, Writing – review & editing, Supervision, Project administra- tion, Funding acquisition
Trang 8Acknowledgement
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
References
[1] K.L Nash, C Madic, J.N Mathur, J Lacquement, Actinide separation science and
technology, Chem Actinide Transactinide Element (2010) 2622–2798, doi: 10
1007/978- 94- 007- 0211- 0 _ 24
[2] T Kooyman, Current state of partitioning and transmutation studies for ad-
vanced nuclear fuel cycles, Ann Nucl Energy 157 (2021) 108239, doi: 10.1016/
j.anucene.2021.108239
[3] F.R Livens, Evaluation of methods for the radiometric measurement of
Americium-241 in environmental samples, Analyst 114 (1989) 1097–1101,
doi: 10.1017/CBO9781107415324.004
[4] K.J Moody , I.D Hutcheon , P.M Grant , Nuclear Forensic Analysis, 2nd ed., CRC
Press, 2014
[5] E.M González-Romero, Impact of partitioning and transmutation
on the high level waste management, 241 (2011) 3436–34 4 4
https://doi.org/10.1016/j.nucengdes.2011.03.030
[6] M Salvatores, Nuclear fuel cycle strategies including partitioning and transmu-
tation, 235 (2005) 805–816 https://doi.org/10.1016/j.nucengdes.2004.10.009
[7] M Nilsson, K.L Nash, A review of the development and operational charac-
teristics of the TALSPEAK process, Solvent Extract Ion Exchange 6299 (2007)
665–701, doi: 10.1080/07366290701634636
[8] J Veliscek-Carolan, Separation of actinides from spent nuclear fuel: a review,
J Hazard Mater 318 (2016) 266–281, doi: 10.1016/j.jhazmat.2016.07.027
[9] J Magill, V Berthou, D Haas, J Galy, R Schenkel, H.W Wiese, G Heusener,
J Tommasi, G Youinou, Impact limits of partitioning and transmutation sce-
narios on the radiotoxicity of actinides in radioactive waste, Nucl Energy 42
(2003) 263–277, doi: 10.1680/nuen.42.5.263.37622
[10] P.E Warwick, I.W Croudace, R Carpenter, Review of analytical techniques for
the determination of Americium-241 in soils and sediments, Appl Radiat Isot
47 (1996) 627–642, doi: 10.1016/0969-8043(96)0 0 023-1
[11] Y Chen, Z Chang, Y Zhao, J Zhang, J Li, F Shu, Studies on the age de-
termination of trace plutonium, J Radioanal Nucl Chem (2009) 675–678,
doi: 10.1007/s10967- 009- 0056- 0
[12] U Nygren, H Ramebäck, C Nilsson, Age determination of plutonium us-
ing inductively coupled plasma mass spectrometry, 272 (2007) 45–51
https://doi.org/10.1007/s10967-006-6780-9
[13] B.H.T Zhang, F.R Zhu, J Xu, Y.H Dai, D.M Li, X.W Yi, L.X Zhang,
Y.G Zhao, Age determination of plutonium material by alpha spectrom-
etry and thermal ionization mass spectrometry, 331 (2008) 327–331
https://doi.org/10.1524/ract.2008.1499
[14] F.M.C Treaty, N Treaty, Verification of a fissile Material Cut-Off treaty, (1997)
[15] J Lehto , X Hou , Radionuclides in the Environment Nuclear and Radiochem-
istry, Wiley-VCH, 2011
[16] S Siekierski , Theoretical aspects of extraction chromatography, J Chromatogr
Lib 2 (1975) 1–16
[17] E.P Horwitz, D.R Mcalister, M.L Dietz, E.P Horwitz, D.R Mcalister, M.L.D Ex-
traction, M.L Dietz, Separation science and technology extraction chromatog-
raphy versus solvent extraction: how similar are they? Separat Sci Technol
41 (2007) 2163–2182, doi: 10.1080/014 9639060074284 9
[18] E.P Horwitz, M.L Dietz, R Chiarizia, H Diamond, S.L Maxwell, M.R Nelson,
Separation and preconcentration of actinides by extraction chromatography
using a supported liquid anion exchanger: application to the characterization
of high-level nuclear waste solutions, ACTA Anal Chimica Acta 310 (1995) 63–
78, doi: 10.1016/0 0 03-2670(95)0 0144-O
[19] M Nilsson, S Andersson, F Drouet, C Ekberg, M Foreman, M Hudson, J.O Lil-
jenzin, D Magnusson, G Skarnemark, Extraction properties of 6,6 -Bis-(5,6-
dipentyl-[1,2,4] triazin-3-yl)-[2,20]bipyridinyl (C5-BTBP), Solvent Extr Ion Exch
24 (2006) 299–318, doi: 10.1080/07366290600646947
[20] F.W Lewis, L.M Harwood, M.J Hudson, M.G.B Drew, J.F Desreux, G Vidick,
N Bouslimani, G Modolo, A Wilden, M Sypula, T.H Vu, J.P Simonin, Highly
efficient separation of actinides from lanthanides by a Phenanthroline-Derived
Bis-triazine ligand, J Am Chem Soc 133 (2011) 13093–13102, doi: 10.1021/
ja203378m
[21] F.W Lewis, L.M Harwood, M.J Hudson, M.G.B Drew, A Wilden, M Sypula,
G Modolo, T.-.H Vu, J.-.P Simonin, G Vidick, N Bouslimani, J.F Desreux, From
BTBPs to BTPhens: the effect of ligand pre-organization on the extraction prop-
erties of quadridentate Bis-Triazine ligands, Procedia Chem 7 (2012) 231–238,
doi: 10.1016/j.proche.2012.10.038
[22] M.A Higginson, P Thompson, O.J Marsden, F.R Livens, L.M Harwood,
F.W Lewis, M.J Hudson, S.L Heath, Rapid selective separation of ameri-
cium/curium from simulated nuclear forensic matrices using triazine ligands,
Radiochim Acta 103 (2015) 687–694, doi: 10.1515/ract- 2015- 2403
[23] A Geist, C Hill, G Modolo, M.R.S.J Foreman, M Weigl, K Gompper, M.J Hudson, [2, 2 ] bipyridine, an effective extracting agent for the separa- tion of Americium (III) and Curium (III) from the Lanthanides, 6299 (2007) https://doi.org/10.1080/07366290600761936
[24] A Afsar, L.M Harwood, M.J Hudson, P Distler, J John, Effective separation of Am(iii) and Eu(iii) from HNO3 solutions using CyMe4-BTPhen-functionalized silica-coated magnetic nanoparticles, Chem Commun (2014) 15082–15085, doi: 10.1039/c4cc07478e
[25] A Afsar, P Distler, L.M Harwood, J John, J Westwood, Extraction of mi- nor actinides, lanthanides and other fission products by silica-immobilized BTBP/BTPhen ligands, Chem Commun 53 (2017) 4010–4013, doi: 10.1039/ c7cc01286a
[26] M.A Higginson, O.J Marsden, P Thompson, F.R Livens, S.L Heath, Separation
of americium from complex radioactive mixtures using a BTPhen extraction chromatography resin, React Funct Polym 91–92 (2015) 93–99, doi: 10.1016/j reactfunctpolym.2015.05.002
[27] A Afsar, J Westwood, P Distler, L.M Harwood, S Mohan, J John, F.J Davis, Separation of Am(III), Cm(III) and Eu(III) by electro-spun polystyrene- immobilized CyMe4-BTPhen, Tetrahedron 74 (2018) 5258–5262, doi: 10.1016/ j.tet.2018.04.037
[28] A.G Strikovsky, K Je ˇrábek, J.L Cortina, A.M Sastre, A Warshawsky, Solvent impregnated resin (SIR) containing dialkyl dithiophosphoric acid on Amber- lite XAD-2: extraction of copper and comparison to the liquid-liquid extrac-
[29] J.L Cortina, A Warshawsky, Developments in solid-liquid extraction by solvent-impregnated resins, ChemInform (2010) 28, doi: 10.1002/chin
199752337 [30] N Kabay, J Luis, A Trochimczuk, M Streat, Reactive & functional poly- mers solvent-impregnated resins (SIRs) – Methods of preparation and their applications, React Funct Polymers 70 (2010) 4 84–4 96, doi: 10.1016/j reactfunctpolym.2010.01.005
[31] J.L Cortina , N Miralles , A.M Sastre , M Aguilar , A Profumo , M Pesavento , Sol- vent-impregnated resins containing di-(2,4,4-trimethylpentyl) phosphinic acid Study of the distribution equilibria of Zn (II), Cu(II) and Cd(II), Reactive Poly- mers 21 (1993) 103–116
[32] P Taylor, M.S Hosseini, M Hosseini, A Hosseini, Solvent Impregnated Resins containing Quinizarin : preparation and Application to Batch - mode Separa- tion of Cd (II), Cu (II), Ni (II), and Zn (II) in aqueous media prior to the de- termination by flame atomic absorption spectrometry, Sep Sci Technol 42 (2007) 3465–3480, doi: 10.1080/01496390701626552
[33] J.L Cortina, N Miralles, A Sastre, M Aguilar, A Profumo, M Pesavento, Solvent impregnated resins containing Cyanex 272 Preparation and application to the extraction and separation of divalent metals, 18 (1992) 67–75
[34] Y Tang, S Bao, Y Zhang, L Liang, Effect of support properties on prepa- ration process and adsorption performances of solvent impregnated resins, React Funct Polym 113 (2017) 50–57, doi: 10.1016/j.reactfunctpolym.2017.02
006 [35] J.L Cortina, N Miralles, M Aguilar, A.M Sastre, Solvent impregnated resins containing Di-(2-Ethylhexyl) phosphoric acid - preparation and study of the retention and distribution of the extractant on the resin, Solvent Extr Ion Exch
6299 (2007) 349–369, doi: 10.1080/07366299408918214 [36] A Afsar, P Distler, L.M Harwood, J John, J.S Babra, Z Selfe, J Cowell, J.S Babra, Z.Y Selfe, J Westwood, Separation of minor actinides from lanthanides using immobilized ligand systems: the role of the Counterion, Heterocycles 99 (2018) 3–10, doi: 10.3987/com- 18- s(f)71
[37] E.R Bertelsen, J.A Jackson, J.C Shafer, E.R Bertelsen, J.A Jackson, J.C Shafer,
A Survey, A survey of extraction chromatographic f -element separations de- veloped by E P Horwitz, Solvent Extr Ion Exch 38 (2020) 1–39, doi: 10.1080/ 07366299.2020.1720958
[38] M.L Dietz , E.P Horwitz , A.H Bond , Extraction Chromatography : Progress and Opportunities, Chemistry Division, Argonne National Laboratory, 1997 [39] F.W.E Strelow, R Rethemeyer, C.J.C Bothma, Ion exchange selectivity scales for cations in nitric acid and sulfuric acid media with a sulfonated polystyrene resin, Anal Chem 37 (1965) 106–111, doi: 10.1021/ac60220a027
[40] D.R Mcalister, E.P Horwitz, Characterization of extraction of chromatographic materials containing Bis (2-ethyl-1-hexyl) phosphoric acid, and Bis (2,4,4- Trimethyl-1-Pentyl) phosphinic acid, Solvent Extr Ion Exch 6299 (2007) 757–
769, doi: 10.1080/07366290701634594 [41] N Gharibyan, A Dailey, D.R McLain, E.M Bond, W.A Moody, S Happel, R Su- dowe, A Walter, Extraction behavior of americium and curium on selected extraction chromatography resins from pure acidic matrices, Solvent Extr Ion Exch 32 (2014) 391–407, doi: 10.1080/07366299.2014.884888
[42] A Afsar, J Cowell, P Distler, L.M Harwood, J John, J Westwood, Synthe- sis of Novel BTPhen-Functionalized Silica-Coated magnetic nanoparticles for separating trivalent actinides and lanthanides, Synlett 28 (2017) 2795–2799, doi: 10.1055/s- 0036- 1590865
[43] M.L Dietz , E.P Horwitz , L.R Sajdak , R Chiarizia , An improved extraction chro- matographic resin for the separation of uranium from acidic nitrate media, Ta- lanta 54 (2001) 1173–1184
[44] D.C Harris , C.A Lucy , Quantitative Chemical Analysis, 9th ed., WH Freeman,
2015 [45] E.P Horwitz, M.L Dietz, R Chiarizia, H Diamond, A.M Essling, D Graczyk, Sep- aration and preconcentration of uranium from acidic media by extraction chro- matography, Anal Chim Acta 266 (1992) 25–37, doi: 10.1016/0 0 03-2670(92) 85276-C
Trang 9[46] N Vajda, CK Kim, Determination of 241 Am isotope: a review of analyti-
cal methodology, J Radioanal Nucl Chem 284 (2010) 341–366, doi: 10.1007/
s10967-010-0475-y
[47] C Pin, J Rodriguez, Separation Methods Based on Liquid-Liquid Extraction, Ex-
traction Chromatography, and Other Miscellaneous Solid Phase Extraction Pro-
cesses, 2nd ed., Elsevier Ltd., 2013, doi: 10.1016/B978- 0- 08- 095975- 7.01409- 1
[48] F.W Lewis, L.M Harwood, M.J Hudson, M.G.B Drew, V Videva,
V.Véronique Hubscher-Bruder, BTBPs versus BTPhens: some reasons for
their differences in properties concerning the partitioning of minor ac-
tinides and the advantages of BTPhens, Inorg Chem 52 (2013) 4993–5005, doi: 10.1021/ic3026842
[49] M.J Hudson, L.M Harwood, D.M Laventine, F.W Lewis, Use of soft heterocyclic N-donor ligands to separate actinides and lanthanides, Inorg Chem 52 (2013) 3414–3428, doi: 10.1021/ic3008848
[50] N Kaltsoyannis, Does covalency increase or decrease across the actinide se- ries? Implications for minor actinide partitioning, Inorg Chem 52 (2013) 3407–3413, doi: 10.1021/ic3006025