Two novel extraction chromatography resins (ECRs) containing two diglycolamide (DGA) -functionalized calix[4]arenes with n-propyl and isopentyl substituents at the amide nitrogen atom, termed as ECR-1 and ECR-2, respectively, were evaluated for the uptake of Th(IV) from nitric acid feed solutions.
Journal of Chromatography A 1653 (2021) 462401 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Selective uptake of thorium(IV) from nitric acid medium using two extraction chromatographic resins based on diglycolamide-calix[4]arenes: Application to thorium-uranyl separation in an actual sample Rajesh B Gujar a, Prasanta K Mohapatra a, Mudassir Iqbal b, Jurriaan Huskens b, Willem Verboom b,∗ a b Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India Laboratory of Molecular Nanofabrication, MESA+ Institute for Nanotechnology, University of Twente, P O Box 217, 7500 AE Enschede, the Netherlands a r t i c l e i n f o Article history: Received 19 March 2021 Revised July 2021 Accepted July 2021 Available online July 2021 Keywords: Thorium(IV) Extraction chromatography Diglycolamide Calix[4]arene a b s t r a c t Two novel extraction chromatography resins (ECRs) containing two diglycolamide (DGA) -functionalized calix[4]arenes with n-propyl and isopentyl substituents at the amide nitrogen atom, termed as ECR-1 and ECR-2, respectively, were evaluated for the uptake of Th(IV) from nitric acid feed solutions While both the resins were having a quite high Th(IV) uptake ability (Kd >30 0 at M HNO3 ), the uptake was relatively lower with the resin containing the isopentyl DGA, which appeared magnified at lower nitric acid concentrations Kinetic modeling of the sorption data suggested fitting to the pseudo-second order model pointing to a chemical reaction during the uptake of the metal ion Sorption isotherm studies were carried out showing a good fitting to the Langmuir and D-R isotherm models, suggesting the uptake conforming to monolayer sorption and a chemisorption model Glass columns with a bed volume of ca 2.5 mL containing ca 0.5 g lots of the ECRs were used for studies to assess the possibility of actual applications of the ECRs Breakthrough profiles obtained with feed containing 0.7 g/L Th(NO3 )3 solution resulted in breakthrough volumes of and mL, respectively, for the ECR-1 and ECR-2 resins Near quantitative elution of the loaded metal ion was possible using a solution of oxalic acid and nitric acid A method for the separation of Th-234 from natural uranium was demonstrated for the possible application of ECR-1 © 2021 The Author(s) Published by Elsevier B.V This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Introduction Solid phase extraction is considered as an alternative separation method to solvent extraction and can alleviate some of the issues faced with the latter such as third phase formation, phase entrainment, phase disengagement limitations, etc Though solid phase extraction (SPE) involves sorbents for neutral molecules or ion exchange resins, there is a type of sorbents based on extraction chromatography (EC) where, the organic extractant is impregnated into an inert solid support material, is fast emerging as an efficient SPE technique with highly promising results [1–4] Furthermore, the extractant inventory can be very low in case of EC and hence, the cost of the separation method can be quite low This suggests that exotic extractants can be easily used in an EC method with- ∗ Corresponding author E-mail address: w.verboom@utwente.nl (W Verboom) out any significant cost consideration A variety of solid support materials have been used viz XAD-4 [5], XAD-7 [5], voltalef [6], Amberchrom – CG 71 [7], Chromosorb 102 [8], Chromosorb W [8], etc Out of these, Chromosorb W (dimethyl dichlorosilane treated acid washed celite diatomaceous silica) is quite interesting since the major constituent of this material is silica, which has good radiation stability and hence, can be easily used for radioactive feeds For the separation of actinide ions from acidic feeds, many extractants have been used [9] However, diglycolamide (DGA) extractants such as TODGA (N,N,N’,N’-tetra-n-octyl diglycolamide) are quite promising [10] TODGA-based extraction chromatography resins (ECR) have been prepared by many researchers and used for the separation of trivalent actinide ions from acidic feeds [7,11,12] It has been reported that multiple DGA extractants such as the ones with a calix[4]arene scaffold display a much higher separation efficiency than TODGA [13–15] The DGA-functionalized calix[4]arenes (termed as C4DGAs) with a branched alkyl chain offer a better selectivity, albeit a lower extraction than a linear alkyl https://doi.org/10.1016/j.chroma.2021.462401 0021-9673/© 2021 The Author(s) Published by Elsevier B.V This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) R.B Gujar, P.K Mohapatra, M Iqbal et al Journal of Chromatography A 1653 (2021) 462401 2.2 Radiotracers 233 U was used from the laboratory stock after carrying out a fresh purification from its daughter products using a reported method [18] Carrier free 234 Th was obtained by freshly separating the radiotracer from an ‘aged’ solution of natural uranium in M HNO3 by extractive separation of the latter into a solution of Aliquat 336 in chloroform following a reported method [19] The aqueous phase contained predominantly the carrier free 234 Th tracer with 99% of the solvent, the ECRs were kept in a vacuum desiccator for drying overnight to yield free flowing materials for subsequent uptake studies The weight difference between the ECRs and the support material (Chromosorb W) suggested about 8% (w/w) ligand loading for both the resins 2.5 Characterization of the SPE resins The ECRs were characterized by thermogravimetry (TGA) for ligand loading and by SEM for the surface morphology; the results are given in a previous paper [21] The presence of the extractants inside the resin pores was characterized by FTIR recorded on a Bruker Alpha II ATR-FTIR spectrometer Experimental 2.6 Batch uptake studies 2.1 Chemicals The batch uptake studies involved acidic feeds containing Th(IV) and UO2 2+ ions For the batch studies, ca 10 mg of the ECR was taken in a stoppered Pyrex glass tube (10 mL capacity) containing the radiotracer spiked dilute nitric acid solution The tubes were agitated in a thermostated water bath at 25 ± 0.1 °C for about hour The time taken to attain equilibrium metal ion uptake values was much lower than the employed time which was done to ensure attainment of equilibrium The tubes were then rested for minutes and centrifuged at 30 0 rpm before removal of the samples for radiometric assay Usually, 100 μL aliquots were removed for assaying purpose using Eppendorf fixed volume micropipettes The weight distribution coefficient (Kd ) values of the metal ions were calculated using the following equation: The DGA-functionalized calix[4]arene (C4DGA) ligands LI and LII (Fig 1) have been described before [13] The same batch was used, again characterized by comparison of both the H NMR spectra (Fig S1) with the previous data and of the distribution coefficients for the extraction of Am(III) and Eu(III) using mM ligand solutions of 5% isodecanol and 95% n-dodecane at M HNO3 For ligand LI DAm and DEu values were obtained of 78±3.1 and 242±12 versus 79.5 and 225, respectively, in ref [13] For ligand LII the DAm and DEu values were 314±10 and 357±14 versus 325 and 370, respectively, in ref [13] Chromosorb-W (mesh size 60-80) was purchased from John Manville, USA and was cleaned and dried prior to use by rinsing with methanol and air drying at 70 °C Suprapur nitric acid (Merck) was used for the preparation of dilute nitric acid solutions for the uptake studies Thorium nitrate was purchased from Indian Rare Earths limited, while uranyl nitrate hexahydrate was obtained from Uranium Extraction Division, BARC All other chemicals were of AR grade Kd = (Co − C ) C · V , mL/g W (1) where Co and C are the initial and equilibrium concentrations of the metal ions, respectively, V is the aqueous phase volume (in R.B Gujar, P.K Mohapatra, M Iqbal et al Journal of Chromatography A 1653 (2021) 462401 Table Various parameters for the column studies using the ECR-1 and ECR-2 resins Parameter Resin weight ECR-1 (n-propyl) 0.503 g ECR-2 (isopentyl) 0.501 g Bed height Bed volume Bed density Flow rate 20.5 cm 2.57 mL 0.022 g/cm3 0.05 mL per minute 20 cm 2.51 mL 0.022 g/cm3 0.05 mL per minute Fig Th(IV) uptake from M HNO3 as a function of equilibration time using the two C4DGA containing resins ECR-1 and ECR-2 the other hand, the C4DGA loaded resins show the >C=O bands at 1650 cm−1 indicating the presence of the carbonyl groups of the C4DGA ligands present in the pores of the ECRs For comparison purpose, the two ECRs were contacted with Th(IV) solution and the FTIR spectra of the Th(IV) loaded resins are also presented in Fig A clear shift in the >C=O stretching frequency to lower values (to ca 1610 cm−1 ) suggested binding of Th(IV) ions to the carbonyl groups present in the resins Fig FTIR spectra of the ECRs Top: Pristine Chromosorb W (green); Freshly made ECR-1 (black); Freshly made ECR-2 (red) Bottom: Th(IV) loaded ECR-1 (black); Th(IV) loaded ECR-2 (red) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 3.2 Batch uptake studies mL), and W the weight of the resin (in g) As radioactive solutions were used in the present study, the concentrations are conveniently expressed in terms of counts per unit time per unit volume All batch studies were carried out in duplicate and the mass balance was found to be within 5% The uptake of the metal ions was negligible (Kd values being ± 0.2 and ± 0.4, respectively, for U(VI) and Th(IV) at M HNO3 ) when pristine Chromosorb W (without any ligand loaded onto it) was used as the sorbent On the other hand, a very large increase in the Kd values was observed, especially for Th(IV), when the two ECRs were used at M HNO3 (vide infra) The Kd values of U(VI) were extremely low and were very close to the value obtained with bare Chromosorb W as the sorbent (vide infra), suggesting weak binding of the metal ion with the C4DGA ligands This is in line with the results obtained from the solvent extraction studies reported before [14] 2.7 Column studies The column studies were carried out using small glass columns of the dimension: 30 cm (length) × 0.4 cm (dia); bed volume ca 2.5 mL The columns were filled with a slurry containing the resins in distilled water and subsequently allowed to settle to get resin beds without any air bubble The top of the columns was fitted with a glass cup (10 mL), while the bottom part was fitted with flexible rubber tubing and pinch cocks for maintaining a constant flow rate The detailed column parameters are given in Table The columns were conditioned prior to the loading of the metal ions by passing 10 mL of HNO3 For the breakthrough studies, the column was loaded with a feed containing 0.7 g/L Th solution in M HNO3 The feed was spiked with 234 Th tracer for easy column data analysis After loading of the Th solution, the column was washed with M HNO3 prior to the elution of the loaded Th using a mixture of 0.5 M oxalic acid and 0.5 M HNO3 The loading of the uranium solution was performed in an identical manner, but as mentioned below the effect of the loading was quite insignificant 3.2.1 Time of equilibration For the column operations discussed below the time taken to attain equilibrium was determined Fig gives the plots of Kd vs time for both the resins for Th(IV), showing an equilibrium time of about 30 minutes U(IV) data are of less significance as the Kd values obtained were very low (in the range of to 30, which are about three orders of magnitude lower than the Kd values obtained with Th(IV)) The equilibrium Kd values for U(IV) were attained in ca 20 minutes but are not included in the plot Results and discussion 3.2.2 Effect of feed acid concentration It is well known from the solvent extraction data reported by Zhu et al [22] that the extraction of Th(IV) is highly favourable with DGA-based extractants such as TODGA The extraction of the metal ion increases sharply with the feed acid concentration as per the following equation: 3.1 Characterization of the extraction chromatography resins Th4+ aq + n TODGAorg + NO3 − aq = Th(NO3 )4 •nTODGAorg The FTIR spectra of the resins were recorded (Fig S2) However, for the sake of checking C4DGA loading in the resins, the FTIR bands in the range of 1700 – 1550 cm−1 are magnified and given in Fig Pristine Chromosorn W has no bands in this region On where the subscripts ‘aq’ and ‘org’ refer to the species present in the aqueous and the organic phases, respectively, and n is 3.39 for TODGA On the other hand, the extractant dependence for the C4DGA ligands LI and LII is not known Since there are four DGA (2) R.B Gujar, P.K Mohapatra, M Iqbal et al Journal of Chromatography A 1653 (2021) 462401 Fig Th(IV) and U(VI) uptake profiles as a function of aqueous feed nitric acid concentration using the C4DGA-containing resins ECR-1 and ECR-2 The separation factor (SF) data are also presented Table Bach extraction of Th(IV) using various stripping solutions from ECR-1 and ECR-2 resins moieties present in the C4DGA ligands, the value of n could be Consequently, Eq (1) can be extended to the following equation when the ligand is impregnated in the ECR Th4+ aq + C4DGAR + NO3 − aq = Th(NO3 )4 C4DGAR (3) where the subscript ‘R’ represents species in the resin phase It is clear from the above equations that the extraction of Th(IV) ion has a positive dependence with the acid concentration of the feed and hence, should increase with the feed acid concentration The Th(IV) uptake data (quantified in terms of Kd ) as a function of the feed HNO3 concentration (in the range of 0.5 M – M) are presented in Fig The Kd values for U(VI), obtained under identical experimental conditions, are also plotted in the same figure Uptake data were not obtained at nitric acid concentrations < 0.5 M due to the possibility of hydrolysis of the tetravalent metal ion at these conditions As shown in Fig 4, the Kd values for Th(IV) increase steeply at lower acid concentrations and reach a plateau at nitric acid concentrations > M On the other hand, U(VI) uptake shows a steady increase in the entire range of nitric acid concentrations The separation factor (SF = Kd,Th /Kd,U ) values were calculated and plotted in the same figure for a better impression of the results The SF values exhibit a rapid rise at lower acid concentrations and a sharp decline at higher acidities However, at M HNO3 , which is the acid concentration of interest in most radioactive wastes, SF values of >100 suggest that the resins can be employed for the separation of Th(IV) from U(VI), which has relevance in THOREX type feeds [23] for application in AHWR Finally, comparing the efficiency of the two resins, ECR-1 is superior to ECR-2, the reason being a less efficient extraction of the metal ions with C4DGA ligand LII containing branched alkyl chains, as discussed before [15] Stripping solution % Stripping (ECR-1) % Stripping (ECR-2) 0.5 M oxalic acid 0.5 M oxalic acid + 0.5 M nitric acid 0.05 M HEDTA + 0.05 M nitric acid 84.7 86.5 87.1 84.4 86.1 86.3 Fig Reusability of the ECRs based on the Th(IV) uptake data after regeneration using stripping conditions of 0.5 M HNO3 and 0.5 M oxalic acid Though HEDTA was marginally better as a stripping agent as compared to the mixture of oxalic acid and nitric acid, we have used the latter in view of some previous reports where the stripping mixture has been successfully used In our previous studies involving tetravalent ions such as Np(IV) and Th(IV), stripping was achieved using oxalic acid or a mixture of it with nitric acid [24,25] This is due to the rather strong complexation of these tetravalent ions with oxalate anion [26] Subsequently, the reusability of the resin was studied by carrying out repeated uptake and stripping for five cycles (Fig 5) ECR-1 resin showed almost no change in the Kd values even after about four cycles, though a clear deterioration was seen after the fourth cycle Even the Kd value obtained after four cycles of uptake and stripping was 3.2.3 Back extraction and reusability The back extraction (stripping) of the loaded Th(IV) was attempted by three stripping solutions, viz a) 0.5 M oxalic acid; b) 0.5 M oxalic acid + 0.5 M nitric acid; c) 0.05 M HEDTA (N-(2hydroxyethyl)ethylenediamine triacetic acid) + 0.05 M nitric acid The back extraction of the loaded metal ion was done by first loading the resin (ca 20 mg) with 234 Th radiotracer from M HNO3 followed by careful removal of the aqueous phase completely from the tube After this, the stripping solution was added (0.5 mL) to the tube and aqueous phase samples were removed after hour of equilibration The results of the back extraction are given in Table R.B Gujar, P.K Mohapatra, M Iqbal et al Journal of Chromatography A 1653 (2021) 462401 Fig Kinetic modeling of the Th(IV) uptake data as fitted to (a) pseudo-first and (b) pseudo-second order models Table Parameters obtained from the straight-line plots obtained by data fitting to Eqs (4) and (5) ca 20 0, which is quite high for metal ion uptake On the other hand, the ECR-2 resin appeared stable (based on the Kd values) only up to two cycles of uptake and stripping runs The Kd values with ECR-2 fall sharply from ca 2400 in the second cycle to ca 750 in the fifth cycle, suggesting clear degradation which is attributed to the leaching of the extractant from the resin pores Pseudo-first order kinetic model Resin k1 (min−1 ) ECR-1 0.018 ± 0.005 ECR-2 0.014 ± 0.005 Pseudo-second order kinetic model Resin k2 (g/cpm.min) ECR-1 (2.67 ± 0.01) × 10−6 ECR-2 (3.48 ± 0.01) × 10−6 3.3 Kinetic modeling of the uptake data To understand the mechanism of sorption, kinetic modeling of the Th4+ ion uptake data was done Uptake studies were carried out at different time intervals (for 3-4 hours) using the two extraction chromatographic resins, where the feed contained 700 mg/L Th in M HNO3 and 234 Th radiotracer for easy assaying by radiometry (vide supra) The uptake data were fitted using the following equations: Pseudo first-order kinetic model: ln (qe − qt ) = ln qe − k1 · t R2 0.999 0.999 Table Linearized form of different sorption isotherm models.a (4) Pseudo second-order kinetic model: t/ = 1/ t qt k2 qe + /qe R2 0.7228 0.6967 Model Linearized form model equation Langmuir Freundlich D-R Temkin Ce qe [1] b·qmax Ce qmax + = log qe = log K f + 1n log Ce ln qe = ln qmax − βε qe = BT ln AT + BT ln Ce Plot [Ref] Ce qe [31] [32] [33,34] [35] vs · Ce log qe vs · log Ce ln qe vs · ε qe vs · ln Ce a qe is the concentration of metal ion sorbed per gram of the solid at equilibrium; Ce is the equilibrium concentration of the metal ion in the aqueous phase; qmax and Kf are the maximum sorbed mass of Th(IV) at saturation and the Freundlich constant, respectively; β and ε represent the D-R constant and Polanyi potential, respectively; BT and AT are the Temkin constants (5) where qe and qt are the mass of the metal ion retained per unit mass of the resin at equilibrium and at time ‘t’, respectively The pseudo-first order and pseudo-second order rate constants are denoted as k1 and k2 , respectively The pseudo first-order kinetic model or the Lagergren model [27] is operating if the Ln (qe -qt ) vs t plot should conform to straight-line fits with negative slopes to give the pseudo-first order rate constant (Fig 6a) On the other hand, when t/qt vs t plots conform to straight-line fits, it is presumed that the data obey the Ho’s pseudo second-order model [28] From Fig it is clear that the fit to the Lagergren model is very poor (R2 = 0.72 and 0.70, for ECR-1 and ECR-2, respectively), while near perfect straight-line fits are obtained for the pseudo second-order kinetic model, suggesting chemisorption as the rate-limiting step [29] i.e., a chemical reaction controls the uptake mechanism This is only logical as the uptake reaction mainly involves the extraction of the metal ion as per Eq (2) The rate constants obtained from the kinetic modeling along with the fitting parameters are listed in Table As indicated from the square of the correlation coefficient (R2 ) values, the pseudo second-order kinetics has a better fitting and hence, should be valid for the present case the different isotherm models used for data analysis are given in Table The Th(IV) uptake studies were carried out using a 234 Th tracer spiked carrier solution containing 1.2 g/L Th in M HNO3 The feed acid concentration was chosen since most of the radioactive waste feeds contain ca 3-4 M HNO3 [30] The sorption isotherm data when fitted to the Langmuir adsorption isotherm equation (Table 4) by plotting Ce /qe vs Ce yielded straight lines (Fig 7a) with very good correlation coefficient values of >0.99 (Table 5) This indicates that the uptake of Th(IV) by both the ECRs conform to the monolayer model The qmax values for ECR-1 and ECR-2 were found to be 12.4 ± 1.3 and 5.1 ± 1.1 mg, respectively, as against the experimentally determined saturation Th(IV) uptake values of 13.2 ± 1.4 and 5.8 ± 1.2 mg, showing a reasonably good agreement The intercept of the straight-line plots yield ‘b’, which is related to a dimensionless equilibrium constant RL (also known as the separation factor [36]) as given by: RL = 1/(1 + bC ) o (6) where a value of RL > suggests an unfavourable sorption On the other hand, a favourable sorption process is considered where RL falls in between and 1, while RL = points to an irreversible uptake process The experimentally obtained b values were found to be 0.21 and 0.95, respectively, for ECR-1 and ECR-2, which when 3.4 Sorption isotherms To understand the nature of the interaction of the metal ion (Th(IV)) with the ligands present in the resin pores, it was imperative to carry out sorption isotherm studies The linear forms of R.B Gujar, P.K Mohapatra, M Iqbal et al Journal of Chromatography A 1653 (2021) 462401 Fig Th(IV) uptake data fitted to the linearized forms of (a) Langmuir, (b) Freundlich, (c) D-R, and (d) Temkin sorption isotherms Table Parameters calculated from Langmuir, Freundlich, D-R, and Temkin isotherm models for the sorption of Th(IV) onto the extraction chromatographic resins ECR-1 and ECR-2; Aqueous phase: 25 mg/L to 300 mg/L Th(IV) solution in M HNO3 Isotherms Parameters Values at 25 °C ECR-1 ECR-2 Langmuir b (mL/mg) qmax (mg/g) R2 Kf (mg/g) n R2 Xm (mmol/g) E (kJ/mole) RT2 A BT R2 0.21 ± 0.01 12.4 ± 1.3 (13.2 ± 1.4)a 0.999 3.18 ± 0.05 2.95 ± 0.06 0.829 0.089 ± 0.010 17.9 ± 1.7 0.996 6.05 ± 0.31 1.85 ± 0.10 0.980 0.95 ± 0.02 5.1 ± 1.1 (5.8 ± 1.2)a 0.996 2.49 ± 0.04 4.82 ± 0.03 0.839 0.024 ± 0.018 54.2 ± 1.8 0.981 3.94 ± 0.4 0.66 ± 0.13 0.816 Freundlich D-R Temkin a Values in parentheses refer to the experimental values Fig Breakthrough profiles for the Th(IV) uptake columns containing ECR-1 and ECR-2 resins Feed contained a 234 Th tracer spiked solution of M HNO3 containing 0.7 g/L Th used in Eq (6) resulted in RL values of 0.799 and 0.467, respectively, and suggest a favourable uptake of the metal ion into the resins When the uptake data were fitted to the Freundlich isotherm model [32] by plotting log qe vs log Ce , the scatter (Fig 7b) could not be fitted well to a linear regression line, the correlation coefficient (R2 ) values being very poor (Table 5) This suggests the absence of the multilayer sorption phenomenon for the Th(IV) uptake in case of both resins On the other hand, the linear fitting of the sorption data to the D-R isotherm model [34] by plotting ln qt vs ε gave reasonably good correlation coefficients (0.996 for ECR-1 and 0.981 for ECR-2; Table 5; Fig 7c) Other parameters of the fitting of the sorption data to the D-R model are also listed in Table The slope gives the quantity β which can be correlated to E (mean sorption energy), which is defined as the free energy needed to transfer one mole of the Th(IV) ions from infinity to the surface of the ECRs [35] and is given as: E = 1/ −2β (7) Depending on the value of E one can get a rough idea about the mechanism of sorption, such as chemisorption (E >8 kJ/mol) or physisorption (E 105 ; Kd value of U(VI) ~ 102 Use of 90% glacial acetic acid is needed for loading Apparently simple method DF ~ 500 DF values of 178 and 165 are obtained [40] Nitric acid / HCl Nitric acid / acetic acid Nitric acid M HNO3 Dowex × (nitrate form) Aliquat 336-based ECR ECR-1 and ECR-2 [41] [42] [25] This work was attempted and DF (Th/U) values of 178 and 165 were obtained with the ECR-1 and ECR-2 resins, respectively Declaration of Competing Interest The authors have no conflict of interest to declare CRediT authorship contribution statement Rajesh B Gujar: Formal analysis, Investigation Prasanta K Mohapatra: Conceptualization, Methodology, Writing – original draft Mudassir Iqbal: Investigation Jurriaan Huskens: Methodology, Supervision Willem Verboom: Methodology Acknowledgement The authors (RBG and PKM) thank Dr P.K Pujari, Head, Radiochemistry Division, Bhabha Atomic Research Centre for his constant encouragement Supplementary materials Fig 11 Separation of U(VI) from Th(IV) as measured from their gamma ray spectra (a) Natural uranium solution in the feed; (b) Eluted fraction from the ECR-1 column; (c) Eluted fraction from the ECR-2 column Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.chroma.2021.462401 References Conclusions [1] O.B Mokhodoeva, G.V Myasoedova, E.A Zakharchenko, Solid-phase extractants for radionuclide pre-concentration and separation New possibilities, Radiochemistry 53 (2011) 35–43 [2] I Akaza, Extraction Chromatography, Elsevier, NY, 1975, p 17 [3] S Risticevic, V.H Niri, D Vuckovic, J Pawliszyn, Recent developments in solid-phase micro-extraction, 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extraction chromatography resins containing two DGA-functionalized calix[4]arene ligands (ECR-1 and ECR-2) using 234 Th radiotracer for easy radiometric assay The Kd values for Th(IV) were found to be significantly higher than those obtained for U(VI) in the entire range of acid concentrations studied In view of the very low ligand loading into the ECRs (ca 8%), the resins are quite efficient for Th(IV) ion uptake These resins are far superior to the known ECRs reported in the literature A previously reported Aliquat 336-based resin displayed much lower (about 10 to 20 times) Kd values at M HNO3 demonstrating that the present set of resins are much more superior On the other hand, the uptake of U(VI) was negligible suggesting that the resins can be used for the separation of 234 Th tracer from natural U for possible applications as a radiotracer Kinetic modeling of the Th(IV) uptake data pointed to pseudosecond order kinetics, which is the possible mode for chemical interactions The batch uptake data were fitted to various isotherms and conformed both to the Langmuir isotherm, suggesting a monolayer adsoption mechanism, and to the D-R isotherm, indicating chemisorption The column studies were carried out by loading Th(IV) in a feed containing M HNO3 and the breakthrough profiles showed much better loading with ECR-1 than with ECR-2 Sharp elution peaks were obtained while using an eluent mixture of 0.5 M oxalic acid and 0.5 M nitric acid The separation of 234 Th R.B Gujar, P.K Mohapatra, M Iqbal et al Journal of Chromatography A 1653 (2021) 462401 [14] A Sengupta, P.K Mohapatra, M Iqbal, J Huskens, W Verboom, A highly efficient solvent system containing functionalized diglycolamides and an ionic liquid for americium recovery from radioactive wastes, Dalton Trans 41 (2012) 6970–6979 [15] R.B Gujar, P.K Verma, P.K Mohapatra, M Iqbal, J Huskens, W Verboom, Extraction of tetra- and hexavalent actinide ions from nitric acid solutions using some diglycolamide 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extraction chromatography resins containing two DGA-functionalized calix[4]arene... such as TODGA The extraction of the metal ion increases sharply with the feed acid concentration as per the following equation: 3.1 Characterization of the extraction chromatography resins Th4+... 3-phenyl-4-benzoyl-5-isoxazolone and neutral donors from nitric acid medium, Talanta 43 (1996) 1305–1312 [20] A Bhattacharyya, P.K Mohapatra, V.K Manchanda, Solvent extraction and extraction chromatographic separation of