A multi-faceted approach to probe organic phase composition in TODGA systems with 1-alcohol phase modifiers

The effect of varying 1-alcohol alkyl chain length on extraction of lanthanides (Lns), H₂O, and H⁺ was studied with tetraoctyl diglycolamide (TODGA) via solvent extraction coupled with FT-IR investigations. This multi-faceted approach provided understanding regarding the relationship between extracted Lns, H₂O and H⁺, 1-alcohol volume fraction, and 1-alcohol alkyl chain length. Under acidic conditions there is competition with 1-alcohols and their ability to solubilize aggregates and incidentally induce third phase formation by increasing the extraction of H₂O. At low 1-alcohol concentrations (5 vol%), the trend for 1-alcohol alkyl lengths in solubilizing the aggregates is 1-hexanol > 1-octanol > 1-decanol. Shorter alkyl chains suppress aggregation, ultimately resulting in lower H₂O concentrations and less available TODGA to hydrogen bond with H⁺. Increasing the 1-alcohol concentration to 30 vol% results in the opposite trend, with longer alkyl chains suppressing aggregation. These results suggest this approach is effective at probing trends in the organic phase micro-structure, and indicates trends across the Ln period with various 1-alcohol alkyl chain lengths are a function of outer-sphere coordination.

Extraction of Uranium in Nitric Media with Novel Asymmetric Tetra-Alkylcarbamide

The use of tetra-alkylcarbamides as novel ligands: N,N-butyl-N’,N’-hexylurea (L1: ABHU), and N,N-butyl-N’,N’-pentylurea (L2: ABPU), for the solvent extraction and complexation behaviors of uranium(VI) was synthesized and investigated in this study. The effects of HNO3 and NO3− concentrations in the aqueous phase on the distribution ratio of U(VI) were examined. Under 5 mol/L HNO3 concentration, DU reached 5.02 and 4.94 respectively without third-phase formation. During the extraction, slope measurements and IR spectral analysis revealed that the U(VI) complexes are a form of UO2(NO3)2·2L for both ligands. In addition, thermodynamic studies showed that the uranium extraction reaction was a spontaneous exothermic reaction. The deep structural analysis of the complexes was realized with DFT calculation. The bond length, bond properties, and topology of the complexes were discussed in detail to analyze the extraction behavior. This study enriches the coordination chemistry of U(VI) by tetra-alkylcarbamides, which may offer new clues for the design and synthesis of novel ligands for the separation, enrichment, and recovery of uranium in the nuclear fuel cycle.

Insights into the Coordination Behavior of Methyl-Substituted Phosphinic Acids with Actinides

The electronic structure and complexation behavior of methyl-substituted phosphinic acids with U(VI) and Pu(IV) were explored by applying quantum chemical methods. In contrast to Ingold's classification, our results indicate that the methyl group is electron-withdrawing, reducing the phosphoryl group electron density in substituted phosphinic acids. The magnitude of the computed complexation energy values increases along with the series, PA → MPA → DMPA, and MP → MMP → MDMP, implying an increasing complexation tendency upon methyl group substitution for both U(VI) and Pu(IV) complexes. One of the nitrate groups in UO₂(NO₃)₂•2L complexes (L = PA, MPA, and DMPA) is in monodentate coordination mode due to the additional stability gained from O₂N-O···H hydrogen bonding interactions with the acidic H atoms of respective ligands. The calculation indicates marginally stronger metal-ligand interactions in Pu(IV) complexes compared to that in U(VI), which is supported by the computed complexation energies, M-O_P bond lengths, ν(P═O), the extent of metal-ligand charge transfer, and properties of M-O_P bond critical points. The energy landscape of substituted phosphinic acid ligands is further analyzed within the framework of the activation strain model to explain the energetic preference of certain conformers.

l-cysteine intercalated layered double hydroxide for highly efficient capture of U(VI) from aqueous solutions

l-cysteine intercalated Mg/Al layered double hydroxide (Cys-LDH) composites were fabricated and applied for treating the U(VI) contaminated wastewater under various conditions. Interaction mechanisms and adsorption properties were investigated by using batch experiments with spectroscopy analysis. The adsorption isotherms and kinetics were fitted perfectly with the Langmuir isotherm and the pseudo-second-order model, respectively. The significant maximum adsorption capacity of Cys-LDH (211.58 mg/g) compared to LDH was attributed to the larger number of functional groups on Cys-LDH. The presence of humic acid (HA) decreased U(VI) elimination on Cys-LDH at high pH but increased U(VI) removal at low pH. Typically, the presence of various anions (such as NO₃^-, Cl^-, ClO₄^- and SO₄^2-) did not obviously affect U(VI) adsorption on Cys-LDH, while the coexisted CO₃^2- significantly affected U(VI) elimination. The predominate adsorption were determined to be the formation of Cys-U(VI)-Cys complexes with cysteine in the Cys-LDH interlayers. The results demonstrated that the Cys-LDH are promising adsorbents for efficient elimination and extraction of radionuclides in actual environmental contamination management.

Radiolysis products and degradation mechanism studies on tri-isoamyl phosphate (TiAP)

As an alternate extractant for spent fuel reprocessing, the radiolysis properties of TiAP should be systematically studied to evaluate the feasibility of using it in engineering scale. In this paper, the irradiation stability of TiAP was investigated by using the concept of radiolysis ratio and G value. It is found the extent of radiolysis would be increased with the increasing of absorbed doses, but decreased with the increasing of pre-equilibrium aqueous HNO3concentration. Furthermore, the radiolysis products were analyzed qualitatively and quantitatively with gas, liquid and ion chromatograph, based on which the possible radiolysis mechanism of TiAP was also concluded.

Structural investigations on uranium(vi) and thorium(iv) complexation with TBP and DHOA: a spectroscopic study

Spectroscopic studies were carried out to understand the complexation of U(vi) and Th(iv) with tri-butyl phosphate (TBP) and N,N-dihexyl octanamide (DHOA) in different non-aqueous solvents.

Determination of the Structures of Uranyl-Tri-n-butyl-Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

The complex structure of a plutonium uranium refining by extraction (PUREX) process organic phase was characterized by combining results from experiments and molecular dynamics simulations. For the first time, the molecular interactions between tri-n-butyl phosphate (TBP) and the extracted solutes, as well as TBP aggregation after the extraction of water and/or uranyl nitrate, were described and analyzed concomitantly. Coupling molecular dynamics simulations with small- and wide-angle X-ray scattering (SWAXS) experiments can lead to simulated organic solutions that are representative of the experimental ones, even for high extractant and solute concentrations. Furthermore, this coupling is well adapted for the interpretation of SWAXS experiments without preliminary hypothesis on the size or shape of aggregates. The results link together previous literature studies obtained for each level of depiction separately (complexation or aggregation). Without uranium, or at low metal concentration, almost no aggregation was observed. At high uranium concentration, organic phases contain small [UO₂ (NO₃ )₂ (TBP)₂ ]_n polymetallic aggregates (with n=2 to 4), in which the 1:2 U/TBP stoichiometry is preserved.

The recovery of gallic acid from wastewater by extraction with tributyl phosphate/4-methyl-2-pentanone/n-hexane, tributyl phosphate/n-octanol/n-hexane and n-hexanol

Gallic acid recovery was investigated using two extraction solvent systems. The three most influential parameters obtained through univariate experiments were further optimized by BBD resulting in an enhancement of the extraction rate.

Spectroscopic study of the uranyl-acetohydroxamate adduct with tributyl phosphate

The ultraviolet-visible (UV-Vis) and Fourier transform infrared (FT-IR) spectroscopic studies carried out for the system UO2(NO3)/AHA/TBP (uranyl-acetohydroxamate-tributyl phosphate) confirmed the presence of the adduct of UO2(NO3)(AHA) 2TBP with 1:1 stoichiometry for UO2:AHA (acetohydroxamic acid). The spectrum of this complex is identical to the infrared spectrum of the organic phase formed in the uranium distribution experiments with 30% TBP/n-dodecane and AHA present in aqueous phase. Disappearance of the hydroxyl stretching band and a shift in the position of the carbonyl band in the infrared spectra revealed that both the hydroxyl and the carbonyl group of acetohydroxamic acid are involved in the chelate ring with uranium. Also, acetic acid, accrued after acidic hydrolysis of acetohydroxamic acid, was identified in the extraction organic phase.

Structural study of trivalent lanthanide and actinide complexes formed upon solvent extraction

The coordination of the trivalent 4f ions, Ln = Nd3+, Eu3+ and Yb3+, as well as the trivalent 5f ion, Am3+, with diamide and dialkylphosphoric acid extractants, individually and in combination, was studied by use of X-ray absorption spectroscopy. These studies provide metrical information about the interatomic interactions between the f-ions (M3+) and the ligands, dihexylphosphoric acid (HDHP) and N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA), that is of practical relevance to the control of metal-ligand binding in liquid-liquid extraction systems for the separation of trivalent actinide ions, An3+, from trivalent lanthanide ions, Ln3+. Through systematic variations of extraction conditions and extractant combinations, we have found that the HDHP complexes with M3+ involve MO6 coordination and distant M...P interactions, whereas the DMDOHEMA complexes with M3+ involve MO8 coordination. The combination of the EXAFS results with ancillary extraction data and IR results facilitates descriptions of the stoichiometries and structures of the molecular species formed in solution upon liquid-liquid extraction and leads to a new understanding of the binary extraction systems in terms of the strength and selectivity of An3+- vs. Ln3+-ligand interactions. This fundamental structure information affords insight into solvent extraction processes that are of contemporary and practical importance in heavy element chemistry and to environmentally related issues arising from the separation and disposal of radioactive materials, particularly actinides and selected fission products, in the field of nuclear waste reprocessing research.

Extraction of inorganic acids with neutral phosphorus extractants based on a reverse micelle/microemulsion mechanism

The extraction of inorganic acids such as HCl, HNO(3), H(2)SO(4), and HClO(4) has been investigated in three neutral phosphorus compound systems, i.e., tri-n-butyl phosphate (TBP), di-isoamylmethyl phosphonate (DiAMP), and trialkylphosphine oxide (TRPO, C(6)-C(8)), using n-heptane as a diluent. The techniques of electrical conductivity, Fourier transform infrared (FTIR) spectroscopy, 1H NMR, and dynamic laser scattering (DLS) were selected to characterize the organic phases. The results indicate that the interaction between acids and neutral phosphorus compounds follows a molecule-ion combination mechanism. When the acid in the organic phase reaches a certain concentration, the molecular-ion species have a tendency to self-assemble and form reverse micelles/microemulsions (W/O). The further increase of the acid concentration leads the organic phase to split into two layers. Extractants and acids are mainly located in the down layer, in which aggregations are formed. The tendency to form microemulsions follows TRPO > DiAMP > TBP.