Electrodriven Selective Transport of Cs⁺ Using Chlorinated Cobalt Dicarbollide in Polymer Inclusion Membrane: A Novel Approach for Cesium Removal from Simulated Nuclear Waste Solution

The work describes a novel and cleaner approach of electrodriven selective transport of Cs from simulated nuclear waste solutions through cellulose tri acetate (CTA)/poly vinyl chloride (PVC) based polymer inclusion membrane. The electrodriven cation transport together with the use of highly Cs⁺ selective hexachlorinated derivative of cobalt bis dicarbollide, allows to achieve selective separation of Cs⁺ from high concentration of Na⁺ and other fission products in nuclear waste solutions. The transport selectivity has been studied using radiotracer technique as well as atomic emission spectroscopic technique. Transport studies using CTA based membrane have been carried out from neutral solution as well as 0.4 M HNO₃, while that with PVC based membrane has been carried out from 3 M HNO₃. High decontamination factor for Cs⁺ over Na⁺ has been obtained in all the cases. Experiment with simulated high level waste solution shows selective transport of Cs⁺ from most of other fission products also. Significantly fast Cs⁺ transport rate along with high selectivity is an interesting feature observed in this membrane. The current efficiency for Cs⁺ transport has been found to be ∼100%. The promising results show the possibility of using this kind of electrodriven membrane transport methods for nuclear waste treatment

Electrodriven Transport of Cs⁺ through Polymer Inclusion Membrane as “Solvent Separated Ions”

In our earlier work, we reported [<i>Env. Sci. Technol.</i> <b>2014</b>, <i>48</i>, 12994] a novel electrodialysis based selective separation of Cs⁺ from nuclear waste solution using chlorinated cobalt dicarbollide (HCCD) loaded polymer inclusion membrane (PIM). In continuation with that work, the mechanism of electrodriven transport of Cs⁺ through HCCD loaded polymer inclusion membranes has been explored. PIMs containing fixed amount of cellulose triacetate and nitrophenyl octyl ether (NPOE) but different concentrations of the carrier have been prepared. The experimental flux of Cs⁺ across the PIMs, for two different concentrations of the metal ion in the initial feed solution, has been measured using the radiotracer technique. On the basis of the Nernst–Planck equation, an attempt has been made to calculate the time dependence of concentration changes of the metal ion in the feed compartment. The experimental parameters of the membrane., viz., length, self-diffusion coefficient, distribution ratio, electrical resistance, and current, have been used in the calculation. The experimental results indicate that the transport of Cs⁺ by mobile carrier diffusion or fixed site jumping is not possible. It has been proposed that, under applied electric field, Cs⁺ is mostly transported as “solvent separated ions” through the polar lipophilic solvent NPOE. The proposed mechanism has been substantiated by comparing the experimental and the calculated results

Insight into the Complexation of Actinides and Lanthanides with Diglycolamide Derivatives: Experimental and Density Functional Theoretical Studies

Extraction of actinide (Pu⁴⁺, UO₂²⁺, Am³⁺) and lanthanide (Eu³⁺) ions was carried out using different diglycolamide (DGA) ligands with systematic increase in the alkyl chain length from <i>n</i>-pentyl to <i>n</i>-dodecyl. The results show a monotonous reduction in the metal ion extraction efficiency with increasing alkyl chain length and this reduction becomes even more prominent in case of the branched alkyl (2-ethylhexyl) substituted DGA (T2EHDGA) for all the metal ions studied. Steric hindrance provided by the alkyl groups has a strong influence in controlling the extraction behavior of the DGAs. The distribution ratio reduction factor, defined as the ratio of the distribution ratio values of different DGAs to that of T2EHDGA, in <i>n</i>-dodecane follows the order UO₂²⁺ > Pu⁴⁺ > Eu³⁺ > Am³⁺. Complexation of Nd³⁺ was carried out with the DGAs in methanol by carrying out UV–vis spectrophotometric titrations. The results indicate a significant enhancement in the complexation constants upon going from methyl to <i>n</i>-pentyl substituted DGAs. They decreased significantly for DGAs containing alkyl substituents beyond the <i>n</i>-pentyl group, which corresponds to the observed trend from the solvent extraction studies. DFT-based calculations were performed on the free and the Nd³⁺ complexes of the DGAs both in the gas and the solvent (methanol) phase and the results were compared the experimental observations. Luminescence spectroscopic investigations were carried out to understand the complexation of Eu³⁺ with the DGA ligands and to correlate the nature of the alkyl substituents on the photophysical properties of the Eu­(III)-DGA complexes. The monoexponential nature of the decay profiles of the complex revealed the predominant presence of single species, while no water molecules were present in the inner coordination sphere of the Eu³⁺ ion

Trivalent Actinide and Lanthanide Complexation of 5,6-Dialkyl-2,6-bis(1,2,4-triazin-3-yl)pyridine (RBTP; R = H, Me, Et) Derivatives: A Combined Experimental and First-Principles Study

Complexations of lanthanide ions with 5,6-dialkyl-2,6-bis­(1,2,4-triazin-3-yl)­pyridine [RBTP; R = H (HBTP), methyl (MeBTP), ethyl (EtBTP)] derivatives have been studied in the acetonitrile medium by electrospray ionization mass spectrometry, time-resolved laser-induced fluorescence spectroscopy, and UV–vis spectrophotometric titration. These studies were carried out in the absence and presence of a nitrate ion in order to understand the effect of the nitrate ion on their complexation behavior, particularly in the poor solvating acetonitrile medium where strong nitrate complexation of hard lanthanide ions is expected. Consistent results from all three techniques undoubtedly show the formation of lower stoichiometric complexes in the presence of excess nitrate ion. This kind of nitrate ion effect on the speciation of Ln³⁺ complexes of RBTP ligands has not so far been reported in the literature. Different Am³⁺ and Ln³⁺ complexes were observed with RBTP ligands in the presence of 0.01 M tetramethylammonium nitrate, and their stability constant values are determined using UV–vis spectrophotometric titrations. The formation of higher stoichiometric complexes and higher stability constants for Am³⁺ compared to Ln³⁺ ions indicates the selectivity of these classes of ligands. A single-crystal X-ray diffraction (XRD) study of europium­(III) complexes shows the formation of a dimeric complex with HBTP and a monomeric complex with EtBTP, whereas MeBTP forms both the dimeric and monomeric complexes. Density functional theory calculations confirm the findings from single-crystal XRD and also predict the structures of Eu³⁺ and Am³⁺ complexes observed experimentally

Trivalent Actinide and Lanthanide Complexation of 5,6-Dialkyl-2,6-bis(1,2,4-triazin-3-yl)pyridine (RBTP; R = H, Me, Et) Derivatives: A Combined Experimental and First-Principles Study

Complexations of lanthanide ions with 5,6-dialkyl-2,6-bis­(1,2,4-triazin-3-yl)­pyridine [RBTP; R = H (HBTP), methyl (MeBTP), ethyl (EtBTP)] derivatives have been studied in the acetonitrile medium by electrospray ionization mass spectrometry, time-resolved laser-induced fluorescence spectroscopy, and UV–vis spectrophotometric titration. These studies were carried out in the absence and presence of a nitrate ion in order to understand the effect of the nitrate ion on their complexation behavior, particularly in the poor solvating acetonitrile medium where strong nitrate complexation of hard lanthanide ions is expected. Consistent results from all three techniques undoubtedly show the formation of lower stoichiometric complexes in the presence of excess nitrate ion. This kind of nitrate ion effect on the speciation of Ln³⁺ complexes of RBTP ligands has not so far been reported in the literature. Different Am³⁺ and Ln³⁺ complexes were observed with RBTP ligands in the presence of 0.01 M tetramethylammonium nitrate, and their stability constant values are determined using UV–vis spectrophotometric titrations. The formation of higher stoichiometric complexes and higher stability constants for Am³⁺ compared to Ln³⁺ ions indicates the selectivity of these classes of ligands. A single-crystal X-ray diffraction (XRD) study of europium­(III) complexes shows the formation of a dimeric complex with HBTP and a monomeric complex with EtBTP, whereas MeBTP forms both the dimeric and monomeric complexes. Density functional theory calculations confirm the findings from single-crystal XRD and also predict the structures of Eu³⁺ and Am³⁺ complexes observed experimentally

First Report on the Separation of Trivalent Lanthanides from Trivalent Actinides Using an Aqueous Soluble Multiple N‑Donor Ligand, 2,6-bis(1<i>H</i>‑tetrazol-5-yl)pyridine: Extraction, Spectroscopic, Structural, and Computational Studies

A terdentate multiple N donor ligand, 2,6-bis­(1<i>H</i>-tetrazol-5-yl)­pyridine (H₂BTzP), was synthesized, and its complexation with trivalent americium, neodymium, and europium was studied using single-crystal X-ray diffraction, attenuated total reflectance-fourrier transform infrared spectroscopy, time-resolved fluorescence spectroscopy, UV–vis absorption spectrophotometry. Higher complexation strength of BTzP toward trivalent actinide over lanthanides as observed from UV–vis spectrophotometric study resulted in an effective separation of Am³⁺ and Eu³⁺ in liquid–liquid extraction studies employing <i>N,N,<i>N</i>′,N′</i>-tetra-<i>n</i>-octyl diglycolamide in the presence of BTzP as the aqueous complexant. The selectivity of BTzP toward Am³⁺ over Eu³⁺ was further investigated by DFT computations, which indicated higher metal–ligand overlap in the Am³⁺ complex as indicated from the metal–nitrogen bond order and frontier molecular orbital analysis of the BTzP complexes of Am³⁺ and Eu³⁺