Preliminary studies of XANES and DFT calculation of Ru extraction by imino-diacetamide and related compounds.

We connected three research fields on Ru extraction, XANES, and DFT calculation and elucidate the sequence of distribution ratio (D) and their reactions. The magnitude order of the distribution ratio, D(Ru), from acids, HCl > H2SO4 > HNO3 > HClO4, by IDOA indicates to extract readily the stable Ru-Cl ions. The XANES signals, which suggests the electrical charge of Ru(III) extracted into the organic phase, supports the ion-pairing extraction of the anionic Ru-Cl complex with an extractant protonated. Ru(III) in other acids might be extracted by solvation of extractant, thus ion-pair extraction is stronger than solvation in Ru extraction. According to the D(Ru), the same extractant trend, NTAamide > MIDOA > IDOA, as the energy gap of HOMO and LUMO by DFT calculation is found, which suggests that DFT calculation can give the relative magnitude of each D(M) value when extractant and metal in an extraction are determined.

Sr(ii) extraction by crown ether in HFC: entropy driven mechanism through H2PFTOUD.

The solvent extraction of Sr(ii) was carried out using dicyclohexano-18-crown-6 (DCH18C6) and two HFC mixed solvents MS1 and MS2, where MS1 was composed of 30/60 (w/w)% trans-1,2-dichloroethylene/HFC-43 (HFC-43: 1,1,1,2,2,3,4,5,5,5-decafluoropentane) and MS2 was 5/95 (w/w)% heptane/HFC-43. Nitric acid and perfuruoro-3-6-9-trioxaundecane-1,11-dioic acid (H2PFTOUD) were used to study the effect of acid on the extraction. The maximum distribution ratio of Sr(ii) (D Sr) observed for H2PFTOUD conditions was ∼180, and >10 times larger than aqueous nitric acid conditions. The D Sr value was influenced by concentrations of the DCH18C6, Sr(ii), and acid, and by temperature. The composition of extracted complexes was estimated using slope analysis as an Sr(ii)-anion-DCH18C6 ratio of ∼1 : 2 : 1. From the extended X-ray absorption fine structure (EXAFS) measurements of Sr(ii) in the aqueous and organic phases, it is inferred that regardless of the acid used, DCH18C6 coordinates to the first coordination sphere of the Sr(ii) extracted complexes and Sr(ii) is hydrated (complexation with H2PFTOUD cannot be distinguished) in the aqueous phase. Thermodynamic data were significantly changed by choice of acid, i.e., both enthalpy and entropy values were negative for nitric acid conditions, on the other hand, entropy values were large and positive for H2PFTOUD conditions. These results have demonstrated that the combination of HFC solvent and crown ether is applicable for metal extraction.

Hydrothermal-treatment desorption of cesium from clay minerals: The roles of organic acids and implications for soil decontamination.

The adsorption and desorption of cesium (Cs) on clays of contaminated soil in a rhizosphere zone can be greatly affected by various biogeochemical processes, the timespans of which are usually months to years. Herein, we present several representative scenarios of the binding of Cs on diverse sites of vermiculitized biotite by controlled Cs adsorption to particles of different sizes. We investigated whether and how the fixed Cs in the different scenarios is desorbed by ambient and hydrothermal treatments with several low-molecular-weight organic acids (LMWOAs). The results showed that the sorbed Cs was discriminatively retained in the un-collapsed, partially collapsed, and thoroughly collapsed structures of vermiculites. The desorption of the sorbed Cs by hydrothermal LMWOAs extractions was easily realized in the un-collapsed structure, but was limited or minimal in the partially collapsed and thoroughly collapsed structures. The Cs desorption varied in accord with the LMWOA species applied and increased with the acid concentration, temperature, and number of treating cycles. The analysis of Cs-desorbed specimens confirmed their partial destruction and interlayer expansion, suggesting that the underlying mechanism of Cs removal by LMWOAs involves not only acid dissolution and complexation but also the accelerated weathering of clays within a short time under hydrothermal conditions. Our findings contribute novel insights into the mobility, bioavailability, and fate of Cs in contaminated soils and its removal from these soils for environmental restorations.

Effects of Diluents on the Separation of Minor Actinides from Lanthanides with Tetradodecyl-1,10-phenanthroline-2,9-diamide from Nitric Acid Medium.

To investigate the effective separation of actinides (Ans) from lanthanides (Lns), single-stage batch extraction experiments were performed with a novel extractant, tetradodecyl-1,10-phenanthroline-2,9-diamide (TDdPTDA) with various diluents such as 3-nitrobenzotrifluoride (F-3), nitrobenzene, and n-dodecane for Am, Cm, and Lns. The extraction kinetics with TDdPTDA was rapid enough to perform continuous extraction experiments using mixer-settler extractors. The slopes of the distribution ratio versus the TDdPTDA concentration and the distribution ratio versus the nitric acid concentration were similar for F-3 and nitrobenzene systems, but different from the n-dodecane system. These differences were attributed to the characteristics of the diluents. This study revealed high distribution ratios of Am (DAm) and Cm (DCm) for TDdPTDA, with the high separation factors (SFs) of Am from Lns enough for their separation.

Thermodynamic, Spectroscopic, and Computational Studies of f-Element Complexation by N-Hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic Acid.

Potentiometric and spectroscopic techniques were combined with DFT calculations to probe the coordination environment and determine thermodynamic features of trivalent f-element complexation by N-hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic acid, HEDTTA. Ligand protonation constants and lanthanide stability constants were determined using potentiometry. Five protonation constants were accessible in I = 2.0 M (H+/Na+)ClO4. UV-vis spectroscopy was used to determine stability constants for Nd3+ and Am3+ complexation with HEDTTA. Luminescence spectroscopy indicates two water molecules in the inner coordination sphere of the Eu/HEDTTA complex, suggesting HEDTTA is heptadentate. Luminescence data was supported by DFT calculations, which demonstrate that substitution of the acetate pendant arm by a N-hydroxyethyl group weakens the metal-nitrogen bond. This bond elongation is reflected in HEDTTA's ability to differentiate trivalent actinides from trivalent lanthanides. The trans-lanthanide Ln/HEDTTA complex stability trend is analogous to Ln/DTPA complexation; however, the loss of one chelate ring resulting from structural substitution weakens the complexation by ∼3 orders of magnitude. Successful separation of trivalent americium from trivalent lanthanides was demonstrated when HEDTTA was utilized as aqueous holdback complexant in a liquid-liquid system. Time-dependent extraction studies for HEDTTA were compared to diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA) and N-hydroxyethyl-ethylenediamine-N,N',N'-triacetic acid (HEDTA). The results indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.