Unprecedented Inversion of Selectivity and Extraordinary Difference in the Complexation of Trivalent f Elements by Diastereomers of a Methylated Diglycolamide

When considering f elements, solvent extraction is primarily used for the removal of lanthanides from ore and their recycling, as well as for the separation of actinides from used nuclear fuel. Understanding the complexation mechanism of metal ions with organic extractants, particularly the influence of their molecular structure on complex formation is of fundamental importance. Herein, we report an extraordinary (up to two orders of magnitude) change in the extraction efficiency of f elements with two diastereomers of dimethyl tetraoctyl diglycolamide (Me₂-TODGA), which only differ in the orientation of a single methyl group. Solvent extraction techniques, extended X-ray absorption fine structure (EXAFS) measurements, and density functional theory (DFT) based ab initio calculations were used to understand their complex structures and to explain their complexation mechanism. We show that the huge differences observed in extraction selectivity results from a small change in the complexation of nitrate counter-ions caused by the different orientation of one methyl group in the backbone of the extractant. The obtained results give a significant new insight into metal–ligand complexation mechanisms, which will promote the development of more efficient separation techniques.     

二烃基二硫代膦酸萃取分离三价锕系与镧系元素研究

三价锕系与镧系元素的有效分离是实现“分离-嬗变”先进燃料循环的关键环节之一。然而,由于三价锕系与镧系元素的物理化学性质极为接近,其有效分离一直是分离领域的难题之一。在溶剂萃取分离法中,含S、N等软配体的萃取剂表现出良好的分离性能。1995年,商业试剂Cyanex 301被发现能够从常量镧系元素中有效分离三价锕系元素,随后发现其纯化产品二(2,4,4-三甲基戊基)二硫代膦酸对示踪量和常量的镧系元素中的三价锕系都具有非常好的萃取分离效果,并提出了分离工艺,进行了热实验验证。机理研究结果表明,二(2,4,4-三甲基戊基)二硫代膦与三价锕系或镧系元素形成的配合物中以八配位的立方体为主。烃基换成苯基或氯苯等基团之后,没有分离效果,但在磷酸三烃基酯等中性萃取剂协萃条件下,具有一定的分离效果。最近发现烃基换成o-三氟甲基苯基后,可以获得非常好的分离效果。虽然二烃基二硫代膦酸的稳定性还期望进一步提高,对其萃取分离机理的认识还有待深入,但是由于其卓越的分离性能,在三价锕系与镧系元素分离应用中具有良好的应用前景。     

含氮杂环化合物萃取分离三价锕系与镧系元素

乏燃料后处理中的三价锕系和镧系元素分离是“分离-嬗变”过程的主要环节,对于建立先进核燃料循环具有重要意义。然而,三价锕系和镧系元素结构与性质非常相似,实现二者的分离一直都是分离科学研究领域的难题。溶剂萃取法是三价锕系和镧系元素分离的基本方法之一,而运用含硫、氮等软配位原子的萃取剂则是实现分离的关键。在众多的萃取剂中,含氮杂环化合物因其优良的萃取分离能力,同时符合CHON原则而利于实现废物最小化,近年来引起了广泛的研究兴趣。本文综述了国内外研究报道的典型含氮杂环类三价锕系和镧系元素分离萃取剂,包括三联吡啶、TPTZ、BTP、BTBP以及以TPEN为代表的氮杂环取代胺类萃取剂,对其分离能力、稳定性等性能进行了比较,对萃取机理以及影响其萃取能力的因素等亦进行了说明,并对萃取剂的后续设计、改进提出了参考性建议。     

Highly Efficient Diglycolamide‐Based Task‐Specific Ionic Liquids: Synthesis,Unusual Extraction Behaviour,Irradiation, and Fluorescence Studies

Two new diglycolamide‐based task‐specific ionic liquids (DGA? TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA? TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am³⁺, and even higher extraction of the lanthanide ion, Eu³⁺ (about 5–10 fold). Dilution of the DGA? TSILs in an ionic liquid, C₄mim⁺ ? NTf₂^?, afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO₃^? anion, along with the participation of two DGA? TSIL molecules. Time‐resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner‐sphere water molecule in the Eu^III? DGA? TSIL complexes in the presence and absence of C₄mim⁺ ? NTf₂^? as the diluent. The very high radiolytic stability of DGA? TSIL 6 makes it one of the most‐efficient solvent systems for the extraction of actinides under acidic feed conditions.     

Solvent Extraction of Selenate and Chromate Using a Diaminocalix[4]arene

The extraction of Se(VI) and Cr(VI) using a diammoniumcalix[4]arene was investigated. A study of parameters such as ligand concentration, pH or diluent was carried out and allowed to specify the stoichiometry of the extracted species. It was shown that Se(VI) is extracted into CHCl₃ as (LH₂ ²⁺, Cl^-, HSeO₄ ^-) and ((LH₂ ²⁺)₂, 2Cl^-, SeO₄ ^2-)species at pH 2.6. An increase of pH or an addition of 5% or 10% decanol in CHCl₃ favors the extraction of SeO₄ ^2- over HSeO₄ ^- but leads to a drastic decrease of seleniumextraction. Cr(VI) was shown to be extracted as(LH₂ ²⁺, Cl^-, HCrO₄ ^-) at pH 2.6 and probably as (LH⁺, HCrO₄ ^-) for higher pH.     

Isolation of a Star‐Shaped Uranium(V/VI) Cluster from the Anaerobic Photochemical Reduction of Uranyl(VI)

Actinide oxo clusters are an important class of compounds due to their impact on actinide migration in the environment. The photolytic reduction of uranyl(VI) has potential application in catalysis and spent nuclear fuel reprocessing, but the intermediate species involved in this reduction have not yet been elucidated. Here we show that the photolysis of partially hydrated uranyl(VI) in anaerobic conditions leads to the reduction of uranyl(VI), and to the incorporation of the resulting U^V species into the stable mixed‐valent star‐shaped U^VI/U^V oxo cluster [U(UO₂)₅(μ₃‐O)₅(PhCOO)₅(Py)₇] ( 1 ). This cluster is only the second example of a U^VI/U^V cluster and the first one associating uranyl groups to a non‐uranyl(V) center. The U^V center in 1 is stable, while the reaction of uranyl(V) iodide with potassium benzoate leads to immediate disproportionation and formation of the U₁₂^IVU₄^VO₂₄ cluster {[K(Py)₂]₂[K(Py)]₂[U₁₆O₂₄(PhCOO)₂₄(Py)₂]} ( 5 ).     

Selective extraction of toxic heavy metals and biological activity studies using pyrimidylthioamide functionalised calix[4]arene

The current study comprises synthesis of pyrimidylthioamide derivatized calix[4]arene (5), and its comparative liquid–liquid extraction properties with the compound 4 towards the selected transition metal ions (Cu²⁺, Co²⁺, Ni²⁺, Pb²⁺, Hg²⁺ and Cd²⁺) were investigated. Experimental results revealed that the compound 5 shows better efficiency and affinity for Pb²⁺ and Hg²⁺ ions as compared to compound 4. The antibacterial and antifungal effects of compound 5 were also investigated on various bacteria and fungi. It has been observed that compound 5 has some effects against Salmonella typhimurium NRRLB 4420, Bacillus cereus ATCC 11778, Staphylococcus aureus NRRL B767 and Bacillus subtilis NRS 744.     

Calix[4]arenes Bridged with Two Different Crown Ether Loops: Influence of Crown Size on Metal Ion Recognition

A series of calix[4]arene-bis-crownethers were synthesized in a fixed 1,3-alternateconformation with good yields by the reaction of amonocyclic calixcrown ether with multi-ethyleneglycoldi-p-toluenesulfonate in the presence of cesiumcarbonate. In the preparation of the monocycliccalixcrown ethers (1 and 2), the use ofpotassium carbonate as a base provided the best yieldregardless of the template concept. In two phaseextraction and competitive transport experiments forligand-metal complexation, calix[4]arene biscrown(5) provided the best selectivity for potassiumion. When a calixbiscrown ether (4) bearingdifferent sized crown ether loops coordinates to K⁺and Cs⁺, respectively, the changes of peak splittingpatterns and chemical shift on ¹H NMR spectra aredependent on the complexed metal ion species.     

Complexation of N-alkyl(aryl)- and N,N-dialkylcarbamoylmethylphosphine oxides with the f-elements

Complexation of N-alkyl(aryl)carbamoylmethylphosphine oxides (CMPO) and their N, N-dialkyl analogs in neutral media was studied. N-Alkyl derivatives react with praseodymium and europium nitrates both in solution and in the individual state to give 1: 2 and 1: 3 complexes, depending on the ratio of the starting reagents; for N-aryl amides, 1: 3 complexes were obtained only. With the uranyl cation, both N-alkyl and N,N-dialkyl derivatives of CMPO form various 1: 1 complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1862, September, 2008.     

Synthesis and Extraction Studies of a Versatile Calix[4]arene-Based “Proton-Switchable Extractant” for Toxic Metals and Dichromate Anions

The article describes the syntheses and extraction properties of a new calixarenebased extractant 5, which has been synthesized from5,11,17,23-tetra-tert-butyl-25,27-bis(chlorocarbonyl-methoxy)-26,28-dihydroxycalix[4]arene(4) by treatment with isoniazid (isonicotinic acid hydrazide) in the presence ofpyridine. The compound 5 was converted to its methyl iodide salt (6) by refluxing 5 with methyl iodide in acetonitrile. In this synthesis it was thought to explore the role of pyridinium sites in the extraction of HCr₂O ₇ ^- /Cr₂O ₇ ^2- anions. The complexing properties of 5 toward selected alkali/transition metal cationsand HCr₂O ₇ ^- /Cr₂O ₇ ² - anions are reported. It has been observed that receptor 5 does not extract alkali metal cations but shows an excellent selectivity toward transition metals. The protonated pyridinium form of 5 is an effective formfor transferring the HCr₂O ₇ ^- /Cr₂O ₇ ^2- anions from an aqueous into adichloromethane layer.     

Accomplishing Equilibrium in ALSEP: Demonstrations of Modified Process Chemistry on 3-D Printed Enhanced Annular Centrifugal Contactors

The major components of the modified ALSEP process have been demonstrated on a modified 2-cm annular centrifugal contactor with an enhanced mixing zone using stable fission products and radiotracers. The results show that by decreasing the pH of the minor actinide stripping solution, using HEDTA instead of DTPA, and increasing contact time, the process is very effective in separating americium from the lanthanides and the fission products.     

Surface tension of pure liquid lanthanide and early actinide metals

A systematic theoretical study of the surface tension of liquid rare earth metals and early actinides is performed. An equation, based on the theoretical considerations suggested by Eyring, enables one to calculate the surface tension of elementary substances in a wide temperature range from melting to boiling points. The results of temperature-dependent surface tension calculations of a pure liquid terbium (1629–1880?K) are fitted as γ?=?845?0.1 (T???T _m) (mJ?m²), where the surface tension decreases linearly with temperature. The surface tension was also calculated, at melting points, for all the liquid rare earth metals from La to Lu and for the first six metals of the actinide series from Ac to Pu. It is observed that the lanthanides may be divided into three groups in accordance with their electronic structure. Mostly, the calculated results agree well with available experimental data.