Comparative evaluation of two substituted diglycolamide extractants for ‘actinide partitioning’

Extraction behaviour of actinides, lanthanides, fission products and structural elements has been studied with the two diglycolamide extractants, namely N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (T2EHDGA) and N,N,N′,N′-tetraoctyl diglycolamide (TODGA). The acid extraction studies suggested that T2EHDGA (K_H: 1.8) is less basic as compared to its linear homologue, TODGA (K_H: 4.1). The distribution ratio of Am(III) by 0.1 M diglycolamides followed the order: TODGA > T2EHDGA. The number of ligand molecules present in the stoichiometry of the extracted species of Am(III) was found to be three and four for T2EHDGA and TODGA, respectively. Thermodynamics studies suggested that the extraction of Am(III) by both the extractants is exothermic in nature. The radiolytic stability of TODGA and T2EHDGA solutions in n-dodecane has been investigated. Due to lower distribution ratio of Am by T2EHDGA, 0.2 M of its solution has been used as compared to 0.1 M solution of TODGA. The distribution behaviour of various metal ions, viz. Am, Nd, Fe, Mo, Cr, Sr and Cs has been studied from nitric acid as well as from simulated high level waste solution.     

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.     

Thermodynamics of U(VI) complexation by succinate at variable temperatures

Complexation of U(VI) by succinate has been studied at various temperatures in the range of (298 to 338) K by potentiometry and isothermal titration calorimetry at constant ionic strength (1.0 M). The potentiometric titrations revealed the formation of 1:1 uranyl succinate complex in the pH range of 1.5 to 4.5. The stability constant of uranyl succinate complex was found to increase with temperature. Similar trend was observed in the case of enthalpy of complex formation. However, the increase in entropy with temperature over-compensated the increase in enthalpy, thereby favouring the complexation reaction at higher temperatures. The linear increase of enthalpy of complexation with temperature indicates constancy of the change in heat capacity during complexation. The temperature dependence of stability constant data was well explained with the help of Born equation for electrostatic interaction between the metal ion and the ligand. The data have been compared with those for uranyl complexes with malonate and oxalate to study the effect of ligand size and hydrophobicity on the temperature dependence of thermodynamic quantities.     

Preconcentration and separation of trace amounts of palladium using dithiooxamide functionalized chelating resin followed by its determination using radiotracer technique

The work describes a procedure of preconcentration and separation of trace amounts of Pd(II) by solid phase extraction of the metal ion by dithiooxamide groups incorporated into a matrix of polystyrene-divinylbenzene whereas the determination of palladium has been carried out by radiotracer technique using ¹⁰⁹Pd (T _1/2 = 13.43 hr, E _γ = 311, 647 keV). The experiments were carried out using both batch method and column operation. Parameters such as the amount of resin, effect of pH, equilibration rate, sorption and desorption of metal ions have been studied. The maximum sorption capacity for palladium was found to be 0.10 mmol·g⁻¹ at pH 6.0. The method is rapid, has a good accuracy and can be used routinely.     

Evaluation of a calix[4]-bis-crown-6 ionophore-based supported liquid membrane system for selective Cs transport from acidic solutions

Facilitated transport of Cs(I) from aqueous nitrate feed solutions to a receiver solution containing distilled water through a supported liquid membrane (SLM) containing calix[4]-bis-2,3-naphtho-crown-6 (CNC) in 0.45 μm PTFE (polytetrafluoroethylene) membranes was investigated. The carrier solution usually consisted of CNC dissolved in a mixture of 80% 2-nitrophenyl octyl ether and 20% n-dodecane. The transport rates were found to be influenced by the mobile carrier concentration, cesium concentration as well as the feed acidity. The extracted species conformed to a stoichiometry of 1:1 metal to ligand ratio suggesting the extraction of an organophilic mono-Cs-crown complex. Fission products obtained from an irradiated natural uranium target were found to be poorly transported while Cs-137 got significantly transported suggesting the possible application of the separation method for the removal of bulk Cs-137 from radioactive waste solutions. Durability/chemical stability of the membrane was remarkably good when tested over 20 days of continuous operation.     

Certain Results Concerning the Iterative Function System

Invention of wavelets and fractals have revolutionized several areas of emerging technologies, especially image processing and scientific computing. The iterated function system [2-4,13,17,18,20,25,26,29], inverse problem of images [5,14-16] and wavelet-based numerical methods [6,7,10,19,22,23] are basic in-gredients of these exciting developments. The iterated function system and the collage theorem are among the basic mathematical tools which are consequences of the Banach contraction fixed point theorem. In one of the sections of this paper we have generalized these two theorems applying a generalization of the Banach contraction fixed point theorem due to Edelstein [11]. In the other section we have studied the inverse problem of images by the iterative function system with grey-level in the context of Besov space, extending a result of Forte and Vrscay [16].     

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.