Recent examples of high‐pressure organic reactions in (flow) glass microreactors of micrometer dimensions are described. Different types of reactions such as Diels‐Alder and nucleophilic aromatic ...substitution reactions performed in a capillary microreactor gave rate enhancements of 1.5–2.7 at 600 bar. Specifically designed flow glass microreactors, that withstand pressures of 140–690 bar, were used to study Diels‐Alder and oxidation reactions. The use of supercritical fluids gives rise to considerable rate enhancements, while the use of a transparent microreactor allows to visualize phase transitions.
Recent examples of high‐pressure organic reactions in (flow) glass microreactors of μm dimensions are reviewed. Diels‐Alder and oxidation reactions were studied by specifically designed flow glass microreactors that withstand pressures of 140–690 bar. The use of supercritical fluids leads to considerable rate enhancements, while a transparent microreactor allows visualizing phase transitions.
Extraction of Am super(3+) from acidic feed solutions was investigated using novel solvent systems containing a tripodal diglycolamide (T-DGA) in three room temperature ionic liquids (RTIL), viz.C ...sub(4)mimNTf sub(2 ), C sub(6)mimNTf sub(2) and C sub(8)mimNTf sub(2). Compared to the results obtained with N,N,N',N'-tetra-n-octyl diglycolamide (TODGA), T-DGA gave significantly higher distribution coefficients in these RTILs. The D sub(Am) values decreased with increasing carbon chain length in the RTILs, which was related to the solubility of the RTIL in the aqueous phase. The distribution studies included the effect of equilibration time, aqueous phase acid concentration variation and T-DGA concentration variation. In general, significantly higher equilibration times were observed for the extraction systems, which was partly due to the viscous RTIL phase and partly due to the slow conformational changes of the T-DGA ligand during complexation. Apart from Am super(3+), extraction of Pu super(4+), UO sub(2) super(2+), Eu super(3+), Sr super(2+) and Cs super(+) was also investigated, since they have significant implications in radioactive waste processing. Stripping studies indicated >99% stripping in three stages using 0.5 M EDTA or DTPA in 1 M guanidine carbonate. Slope analysis indicated the extraction of 1 : 1 complexed species of Am(iii) with T-DGA. Time resolved laser fluorescence spectroscopy (TRLFS) studies showed a strong complexation with no inner-sphere water molecules in the Eu(iii)-T-DGA complexes for C sub(4)mimNTf sub(2) as the diluent. Radiolytic degradation studies of the solvent systems containing T-DGA in the three RTILs were also carried out and while the D sub(Am) values decreased marginally when the solvents were exposed to 500 kGy absorbed dose, a relatively sharp decrease (60%) was seen when the solvents were exposed further to 1000 kGy absorbed dose, suggesting the possibility of recycling. Extraction studies were also carried out at varying temperatures and the thermodynamic parameters were calculated.
Diglycolamide (DGA)-functionalized poly(propyleneimine) diaminobutane dendrimers of the first (DGA-Den-I) or second (DGA-Den-II) generation and a room temperature ionic liquid (RTIL), viz., ...1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, based extraction chromatography resins were prepared for minor actinide separations from high level radioactive waste. The weight distribution coefficients (K d) of actinides on the two resins gave excellent and selective sorption of Am(III) and Pu(IV) over hexavalent uranyl ions, Sr(II) and Cs(I), over a wide range of acidity (0.01–6 M HNO3). The sorbed Am(III) and Pu(IV) could be efficiently desorbed with a buffered complexing solution of 1 M guanidine carbonate + 0.05 M EDTA. The sorption of metal ions on both the resins followed pseudo-second order rate kinetics and proceeded via a chemisorption phenomenon with a sorption energy of 13.4 ± 0.2 kJ/mol. The resin capacities were estimated to be 4.64 ± 0.18 and 4.19 ± 0.21 mg of Eu per g of DGA-Den-I and DGA-Den-II resins, respectively. The column loading of Eu(III) was about 85% of the theoretical value with a narrow elution profile using a buffered complexing solution. The resin affinity toward U(VI), Sr(II), and Cs(I) cations over Am(III) and Pu(IV) was poor, indicating the possible use of the resins for selective separation of Am(III) and Pu(IV) from other metal ions over a wide range of feed acidity.
•Extraction chromatographic resins were prepared using T-DGA and C4DGA.•The resin had Chromosorb W as the solid support and ionic liquid as solvent.•Uptake of actinide ions such as Am3+ was ...investigated.•Kinetic modeling of the uptake data was done.•Column studies were carried out for Am3+ separation.
Extraction chromatography resins, prepared by impregnating two multi-podant diglycolamide ligands, viz. diglycolamide-functionalized calix4arene (C4DGA) and tripodal diglycolamide (T-DGA) dissolved in the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (RTIL: C4mimTf2N) on Chromosorb-W (an inert solid support), gave excellent results for the removal of trivalent actinides from acidic waste solutions. Distribution coefficient measurements on several metal ions showed selective sorption of Am(III) over hexavalent uranyl ions and other fission product elements such as strontium and cesium. The sorbed metal ions could be efficiently desorbed with a complexing solution containing guanidine carbonate and EDTA buffer. The sorption of Am(III) on both resins followed pseudo-second order rate kinetics with rate constants of 1.37×10−6 and 6.88×10−7g/cpmmin for T-DGA and C4DGA resins, respectively. The metal sorption on both resins indicated the Langmuir monolayer chemisorption phenomenon with Eu(III) sorption capacities of 4.83±0.21 and 0.52±0.05mg per g of T-DGA and C4DGA resins, respectively. The results of column studies show that these resins are of interest for a possible application for the recovery of hazardous trivalent actinides from dilute aqueous solutions.
Results about the kinetics of extraction of Eu(III) and Am(III) by extractants designed for the industrial reprocessing of nuclear wastes are reported. They were obtained using the rotating ...membrane cell (RMC) technique. Extraction and stripping kinetic rate constants were determined for various compositions of the aqueous and organic phases. The transfer was studied at liquid/liquid interfaces between an aqueous nitric acid solution and an organic solvent containing the diglycolamide extractant molecule N,N,N′,N′-tetra-n-octyl-diglycolamide (TODGA) or a mixture of the bipyridine molecule CyMe4BTBP with TODGA (the latter being used as a phase-transfer catalyst), dissolved in an aliphatic diluent. In some experiments, an aqueous ligand (a sulfonated bis triazinyl pyridine, SO3-Ph-BTP, or a PyTri-diol) was added to the aqueous phase as a stripping agent. The diffusion coefficients of Eu(III) and Am(III), which are key in the analysis of the kinetic data, were measured using the RMC and the closed capillary technique. Whenever possible, mechanisms are proposed to interpret the experimental results.
This review draws attention to information from the literature and our own observations supporting the view that higher plants and micro-organisms display an intrinsic capacity to be proactively ...involved in pedogenetic processes. 'Bioengineering' of this kind is deemed to be spearheaded by principal deep-rooted tree and shrub species and to result in optimisation of command and conservation of water and nutrients within an ecosystem. Specific examples discussed in the paper include, the formation of silicon- or iron-based linings of vertical channels and pores, binding of sand on roots, generation of organically derived hydrophobicity, development of clay-based hardpans and texture-contrast seals, precipitation of silcrete, calcrete and ferricrete pavements, effective accessing and conservation of P resources, including mining by microbes and the biological cycling of Si and Al via plants and micro-organisms. In each case, definitive roles and mechanisms are suggested for the organisms involved, particularly in relation to formative effects relating to secretion of organic acids, dispersing agents and other classes of exudate. We introduce the term 'phytotarium' to connote the collective outcomes of the above biotic influences in construction and maintenance of niches peculiar to specific vegetation types and then review the evidence of imprinting of soil profiles due to operation of phytotaria. Examples given relate to the lateral and vertical facies encountered in certain contemporary soil profiles and paleosols with which we are familiar and are described in a companion paper.
Ionic liquid-based solvent systems containing diglycolamide-functionalized calix4arenes (C4DGAs) are efficient for actinide ion extraction from nitric acid feeds. Therefore, the radiolytic stability ...of three C4DGAs (wide-rim, narrow-rim and both side DGA-functionalized calix4arenes) and TODGA (N,N,N′,N′-tetraoctyldiglycolamide) (used for comparison purpose), was evaluated by exposing their solutions in an ionic liquid as well as a 95:5 mixture of n-dodecane+isodecanol to gamma radiation up to an absorbed dose of 1000kGy. Liquid–liquid extraction studies were carried out using 241Am as a radiotracer. Apart from a decrease in the DAm values, ascribed to radiolytic degradation, FT-IR, EPR and GC–MS studies were carried out to characterize the degraded species. The different extractants are less sensitive to radiolytic degradation in the ionic liquid than in the molecular diluent.
Diglycolamides (DGAs), and in particular
N
,
N
,
N
′,
N
′-tetraoctyl diglycolamide (TODGA), are well-known candidates for the co-extraction of trivalent actinides (An(
iii
)) and lanthanides (Ln(
iii
...)) from highly acidic aqueous solutions of nuclear waste. A derivative of TODGA, the so-called Me-TODGA with the addition of a methyl-substituent on the central part of the TODGA molecule, has been proposed to improve its stability properties and extraction behaviour. This work describes the stability and viability of Me-TODGA by studying the properties of its degradation compounds formed upon gamma irradiation. The main degradation products have been synthesised and studied individually. Particular attention has been paid to their quantification, as well as their complexation and extraction properties, for a better understanding of the degradation pathways and the behaviour of the solvents upon gamma irradiation. The extraction behaviour of irradiated Me-TODGA solvents and their degradation compounds have been studied toward the fission products and lanthanides present in a highly active raffinate (HAR) solution. Binding properties of parent molecules (TODGA and Me-TODGA) and their main degradation compounds with Ln(
iii
) have also been determined in a homogeneous phase. All the results obtained on degradation compounds are compared with those of the parent molecules in order to assess the effects of these compounds on the separation process. Among the radiolytic compounds, 2-hydroxyoctylamides are the most problematic compounds not only because of their high affinity for lanthanides but also for other fission products.
Understanding of ligand-metal interactions is crucial to develop new processes for nuclear waste treatment.
This paper reports a first-ever cyclic voltammetric study and the electrochemical characterization of Np(IV) complexes with task-specific ionic liquid with appended diglycolamide (DGA-TSIL) ligand ...dissolved in the room-temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C
4
mimNTf
2
). The results are compared with molecular entity,
N
,
N
,
N
′,
N
′-tetraoctyl diglycolamide (TODGA) dissolved in the same diluent. The diffusion coefficient (
D
) values were determined using the Randles–Ševcik equation. The standard rate constant (
k
s
) values were also computed for the Np(IV)/Np(III) electrode redox reaction. The activation energy for diffusion (
E
a
) and thermodynamic parameters for the redox reactions of the Np complexes were determined and compared.
► When DGA moiety was appended on to a tripodal framework, extraction of U(VI) decreased spectacularly while Am(III) and Pu(IV) extraction did not show much change. ► With the tripodal ligand 100 ...times less concentration of the reagent was required as compared to TODGA which make the observations quite extraordinary. ► The transport rates are dependent on the strippant used in the receiver phase and a 0.01
M EDTA solution (pH 3.0) was found to yield quantitative transport of Am
3+ using T-DGA. ► The transport efficiency of the carrier solvent system was Am
3+
>
Pu
4+
≫
Np
4+
>
UO
2
2+ which can be exploited for the separation of the actinide ions.
A novel tripodal diglycolamide (T-DGA) extractant in a diluent mixture (10:1
n-dodecane–
iso-decanol) was evaluated for the extraction of actinide ions such as UO
2
2+, Np(IV), Pu(IV), and Am(III) and fission product element ions such as Cs
+ and Sr
2+ from acidic feed solutions. Conditions for quantitative extraction and stripping were found out for the actinide ions other than UO
2
2+ which is poorly extracted. Solvent extraction studies were carried out at varying concentrations of the extractant and nitric acid using Am(III) and were compared with the results obtained with TODGA (
N,
N,
N′,
N′-tetraoctyldiglycolamide), a representative diglycolamide extractant proposed for actinide partitioning. The extracted species was found out to be Am(NO
3)
3·2T-DGA
(o) at higher T-DGA concentrations, while mixed 1:1 and 1:2 species were observed at lower T-DGA concentrations. The prevalence of 1:2 species in the present case as compared to the 1:1 species reported in a similar system was attributed to the low dielectric constant diluent medium used in the present study.
Supported liquid membrane studies were also carried out using the T-DGA under varying feed acidities, carrier extractant concentration and compared with TODGA under identical conditions. The transport rates are dependent on the strippant used in the receiver phase and a 0.01
M EDTA solution (pH 3.0) was found to yield quantitative transport of Am(III) using T-DGA as compared to dilute nitric acid, which was efficiently used for the TODGA system in an earlier study. The transport efficiency of the carrier solvent system was Am(III)
>
Pu(IV)
≫
Np(IV)
>
UO
2
2+. The diffusion parameters were calculated for the T-DGA system and compared with the experimentally determined parameters.
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