Radiation stability of several polymeric supports used for radionuclide transport from nuclear wastes using liquid membranes

In an attempt to evaluate radiation stability of several polymeric materials used as the support in supported liquid membrane studies for the transport of radionuclides from nuclear waste, flat sheets made from polytetrafluoroethylene, polysulfone, polyether sulfone, polyacrylonitrile and polyvinylidenefluoride were irradiated to varying extents using a ⁶⁰Co gamma ray source and subsequently, the transport efficiency of the irradiated flat sheets were evaluated. The membrane integrity was assessed from the transport rates of Am³⁺ from a feed containing 3 M HNO₃ into a receiver phase containing 0.01 M HNO₃ as the strippant while 0.1 M TODGA (N,N,N′,N′-tetraoctyldiglycolamide) + 0.5 M DHOA (di-n-hexyloctanamide) in n-dodecane was used as the carrier extractant. The radiation stability of the membrane filters was evaluated after irradiating them up to 20 MRad absorbed dose in a gamma chamber.     

Effect of humic acid on the sorption of technetium on hematite colloids using <Superscript>95m</Superscript>Tc and <Superscript>96</Superscript>Tc as tracers

Sorption of technetium on hematite colloids, at varying pH (3–10), has been studied in absence and presence of humic acid using ^95mTc-⁹⁶Tc radiotracers. Technetium was found to be weakly sorbed on hematite at lower pH (<5) values, while no sorption was observed at higher pH values. Humic acid was found to have no effect on the sorption of technetium on hematite under aerobic conditions, while at lower pH values small reduction was observed which was attributed to the reduced zeta potential of the hematite colloids owing to the strong sorption of humic acid.     

Cation-exchange separation of uranium from thorium in nitric acid medium</p> </p>

Summary Sorption behavior of Th and U on cation-exchange resins was investigated from nitric acid medium by both batch and column methods. The cation-exchange studies involved the sorption of UO₂²⁺ and Th⁴⁺ and their cationic complexes onto Dowex 50Wx8 and Dowex 50Wx4 resins (50-100 mesh). The batch data yielded a separation factor (K_d,Th/K_d,U) value of >100 for the cation-exchanger, Dowex 50Wx4 at 1-2M HNO₃. Separation of uranium from thorium was also carried out by column method in nitric acid medium using cation-exchangers, Dowex 50Wx4 as well as Dowex 50Wx8. While uranium elution was possible at 1M HNO₃, Th could be eluted only at higher concentration of nitric acid (>6M). The stripped solution emanating from a mixer settler employing di-2-ethyl hexyl isobutyramide as extractant and feed solution similar to THOREX process comprising 350 mg/l U and 380 mg/l Th in 0.75M HNO₃ was loaded on the column and the decontamination factor value for U in the product was >1000.</p> </p>     

Performance of immobilized moss in the removal of 137Cs and 90Sr from actual low-level radioactive waste solutions

The efficiency of immobilized moss as a bio-sorbent for the removal of ¹³⁷Cs and ⁹⁰Sr radionuclides from actual low-level radioactive waste (LLW) solutions was investigated. Preliminary batch experiments with the moss (Funaria hygrometrica) for the sorption of Cs and Sr have shown a pH dependent binding trend from pH 1–13, with maximum binding between pH 5–10. Time dependence of the batch studies showed that a contact time of 30 minutes was sufficient to reach equilibrium. Column experiments for the sorption of Cs and Sr by moss after immobilizing in polymer silica matrix demonstrated that the sorbent is capable of removing considerable amounts of Cs and Sr from actual LLW solutions under constant flow conditions. The adsorption capacity was estimated to be 8.5 mg/g for Cs and 15 mg/g for Sr. These sorbed metal ions from the column could be leached out using 0.20M nitric acid. The regenerated sorbent exhibited relatively the same initial binding capacity of both Cs and Sr even after 3 cycles of reuse. This revised version was published online in July 2006 with corrections to the Cover Date.     

A pH dependent transport and back transport of americium(III) through the cellulose triacetate composite polymer membrane of cyanex-301 and TBP: role of H-bonding interactions

Transport of Am(III) was studied through the composite polymer membrane of Cyanex-301 [bis(2,4,4-trimethylpentyl)dithiophosphinic acid] and tri-n-butylphosphate (TBP). Depending on the pH of the strip solution containing alpha-hydroxyisobutyric acid (AHIBA), the transport behaviour of Am(III) was changed significantly. After approximately 70% of the Am(III) transported to the strip side, interestingly, back transport of Am(III) was observed at a pH of 3.5. The back transport phenomenon was not so significant at pH 1 and 5.7. The back transport of Am(III) was attributed to the transport of AHIBA from strip to the feed side due to its interaction with TBP in the membrane and the attainment of Donnan equilibrium because of the presence of Na(+) in the feed as the driving ion. The experimental observations were rationalized using the hydrogen bonding interaction energies obtained through ab initio molecular orbital and DFT calculations.     

Extraction of thorium(IV) by a mixture of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and tri-n-octyl phosphine oxide

The extraction behavior of Th(IV) from dilute nitric as well as perchloric acid medium using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and its mixture with tri-n-octyl phosphine oxide (TOPO) was investigated. The species of the type Th(X)(PMBP)₃·(HPMBP) and Th(X)(PMBP)₃·(TOPO) were extracted for the binary and ternary extraction systems, respectively, where X=NO₃− or ClO₄−. The presence of 1.25·10⁻⁵M Th carrier in the aqueous phase resulted in the extracted species of the type of Th(PMBP)₄ and Th(PMBP)₄·(TOPO), respectively. The extraction constant (logk _ex ) for the binary species Th(PMBP)₄ was found to be 6.89±0.01 while the overall extraction constant (logK) for the ternary species Th(PMBP)₄·(TOPO) was calculated to be 13.17±0.06.     

Preparation of High‐Loading Polymer Supports by Polymerization Reaction Useful for Oligonucleotide Synthesis

A simple protocol based on polymerization reactions has been developed for the preparation of high‐loading polymer supports, useful for large‐scale synthesis of oligonucleotides. Polymer supports of different pore sizes have been employed in the present investigation to improve the functional‐group density on them. A ten‐ to twelvefold increase in the loading of the functional groups, after the polymerization reaction, has been observed. The support was then used in the subsequent reaction to attach the leader nucleoside to obtain fully functionalized supports 6a – 6c by oligonucleotide synthesis in an automated DNA synthesizer. The aminoalkylated‐supports 5a – 5c were directly employed for the synthesis of oligonucleotide 3′‐phosphates. The oligonucleotides and oligonucleotide 3′‐phosphates synthesized on these supports were compared with the corresponding standard oligomers with respect to their retention time on HPLC. These were further characterized on MALDI‐TOF mass spectrometry.     

Development of tBu-phenyl Acetamide Appended Thiacalix[4]arene as “Turn-ON” Fluorescent Probe for Selective Recognition of Hg(II) Ions

Journal of Fluorescence - Herein, a novel N-(4-(tert-butyl)-phenyl)-2-chloroacetamide functionalized thiacalix[4]arene architecture, viz TCAN2PA has been synthesized and the sensing behaviour...