The Extraction of Silver and the Effect of Diluent,Ligand Side Group and Solvent Composition

Solvent extraction and the so called BTBP class of ligands can be used for the separation of the actinides from the rest of used nuclear fuel. One troublesome co-extracting element in this separation is silver.Therefore, two different BTBP molecules, having different side groups have been investigated. It was shown that the silver distribution ratio is higher using the CyMe4-BTBP than theC2 -BTBP ligand. In additional experiments, it was shown that no water soluble silver complex is formed in the CyMe4 system and that the complex is one ligand/metal. No effect of varying the diluent/solvent was proven.     

Interfacial activity of benzyloctadecyldimethyl ammonium chloride in a liquid/liquid extraction system

Interfacial tension and interfacial adsorption parameters for benzyloctadecyldimethyl ammonium chloride (BODMAC) in three organic diluents were determined and interpreted. The interfacial activity of BODMAC is affected by the type of the organic diluent and the composition of the aqueous phase. The general order of interfacial activity of BODMAC is n-heptane (5% isobutanol) > carbon tetrachloride > chloroform. The effectiveness of adsorption of BODMAC is not only dependent on the organic diluent, but also on the inorganic electrolytes in the aqueous phase.     

稀释剂极性对萃取动力学的影响 I: HEHEHP萃取Fe(Ⅲ)

考察了正辛烷等六种常用稀释剂中2-乙基己基膦酸单2-乙基己基酯从硝酸介质中萃取Fe(Ⅲ)的动力学行为。观察到稀释剂的极性不仅影响萃取速率的大小,而且会引起萃取过程控制模式的改变, 即随着稀释剂极性的增加, 萃取过程由界面化学反应和水相化学反应共同控制模式向单一的界面化学反应控制模式转变。     

Comparison of the effect of alpha and gamma radiolysis on the extraction of americium by C5-BTBP in cyclohexanone

Solvent extraction is a separation technique suitable for the treatment of used nuclear fuel. Two immiscible phases are contacted and the metals of interest are extracted from one phase into the other, most often using so called extractants. One group of extractants is the bis(triazine)-bipyridine (BTBP) type molecules. These molecules have been developed within EU research programs for the separation of actinides from lanthanides. During such an extraction process, the components of the two phases will be exposed to ionizing radiation, since the used fuel contains many highly radioactive species. Radiolytic reactions can alter the chemistry of the extracting system, and affect the metal extraction by degradation of the extractant and the formation of degradation products. In this paper the effect of irradiation with alpha particles and gamma rays, respectively, has been studied for one of the BTBP type molecules, C5-BTBP.     

Extraction separation of rare-earth ions via competitive ligand complexations between aqueous and ionic-liquid phases

The extraction separation of rare earth elements is one of the most challenging separation processes in hydrometallurgy and advanced nuclear fuel cycles. The TALSPEAK process (trivalent actinide lanthanide separations by phosphorus-reagent extraction from aqueous komplexes) is a prime example of these separation processes. The objective of this paper is to explore the use of ionic liquids (ILs) for the TALSPEAK-like process, to further enhance its extraction efficiencies for lanthanides, and to investigate the potential of using this modified TALSPEAK process for separation of lanthanides among themselves. Eight imidazolium ILs ([C(n)mim][NTf(2)] and [C(n)mim][BETI], n = 4,6,8,10) and one pyrrolidinium IL ([C(4)mPy][NTf(2)]) were investigated as diluents using di(2-ethylhexyl)phosphoric acid (HDEHP) as an extractant for the separation of lanthanide ions from aqueous solutions of 50 mM glycolic acid or citric acid and 5 mM diethylenetriamine pentaacetic acid (DTPA). The extraction efficiencies were studied in comparison with diisopropylbenzene (DIPB), an organic solvent used as a diluent for the conventional TALSPEAK extraction system. Excellent extraction efficiencies and selectivities were found for a number of lanthanide ions using HDEHP as an extractant in these ILs. The effects of different alkyl chain lengths in the cations of ILs and of different anions on extraction efficiencies and selectivities of lanthanide ions are also presented in this paper.     

Interfacial behavior of DEHEHP and the kinetics of cerium(IV) extraction in nitrate media

The effects of diluents, temperature, acidity, and ionic strength of the aqueous phase on the interfacial properties of DEHEHP have been extensively investigated using the Du Nouy ring method. In addition, the effect of cerium(IV) concentration loaded in the organic phase on the interfacial tension has also been studied. With the increase of DEHEHP concentration, the value of interfacial tension (gamma) decreases in the studied system, which shows that DEHEHP has interfacial activity as a kind of surfactant. The surface excess at the saturated interface (Gamma(max)) and the minimum bulk concentration of the extractant necessary to saturate the interface (C(min)) under the different conditions are calculated according to two adsorption equations such as the Gibbs and Szyszkowski functions to be presented in comprehensive tables and figures. The relationship between the interfacial activity of DEHEHP and cerium(IV) extraction kinetics by DEHEHP has been discussed by considering different factors such as the effects of diluents and temperature. However, the interfacial activity parameter of extractant only is a qualitative parameter, but cannot provide strong enough evidence to quantitatively explain the relationship between extraction kinetics and interfacial properties of an extractant.     

Development of normal phase-high performance liquid chromatography-atmospherical pressure chemical ionization-mass spectrometry method for the study of 6,6'-bis-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]-triazin-3-yl)-[2,2']-bipyridine hydrolytic degradation

In the field of nuclear waste management, the 6,6'-bis-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]-triazin-3-yl)-[2,2']-bipyridine (CyMe(4)BTBP) is a polycyclic N-based molecule eligible to remove actinides from spent nuclear fuel by liquid-liquid extraction processes. In such processes, the organic phase containing the extracting molecules will undergo hydrolysis and radiolysis, involving degradation products. The purpose of this work was to develop a normal phase chromatography (NP-HPLC) coupled to atmospherical pressure chemical ionisation-mass spectrometry (APCI-MS) method to separate and identify degradation products of CyMe(4)BTBP dissolved in octanol, submitted to HNO(3) hydrolysis. 1 mol L(-1) HNO(3) hydrolysis conditions were used regarding the selective actinides extraction (SANEX) process, while 3 mol L(-1) HNO(3) conditions were applied for the group actinide extraction (GANEX) process. The first step consisted in optimizing the chromatographic separation conditions using a diode array detection (DAD). Retention behavior of a non hydrolyzed mixture of N,N'-dimethyl-N,N'-dioctyl-hexyloxyethyl-malonamide (DMDOHEMA), a malonamide used in the SANEX process to increase the kinetic of extraction, and CyMe(4)BTBP were investigated on diol-, cyano-, and amino-bonded stationary phases using different mobile phase compositions. These latter were hexane with different polar modifiers, i.e. dioxane, isopropanol, ethanol and methylene chloride/methanol. The different retention processes in NP-HPLC were highlighted when using various stationary and mobile phases. The second step was the setting-up of the NP-HPLC-APCI-MS coupling and the use of the low-energy collision dissociation tandem mass spectrometry (CID-MS/MS) of the precursor protonated molecules that allowed the separation and the characterization of the main hydrolytic CyMe(4)BTBP degradation product under a 3 mol L(-1) HNO(3) concentration. Investigation of the CID-MS/MS fragmentation pattern was used to suggest the potential ways leading to this hydrolysis degradation product. This NP-HPLC-APCI-MS method development is described for the first time for the CyMe(4)BTBP and should provide separation methods regarding the analysis of polycyclic N-based extracting molecules and more generally for the investigation of the organic phase coming from liquid-liquid extraction processes used in nuclear fuel reprocessing.     

聚偏氟乙烯-稀释剂间介电常数差异对热致相分离法制膜微观结构的影响

采用1,4-丁内酯、邻苯二甲酸二甲酯、水杨酸甲酯、邻苯二甲酸二丁酯、三醋酸甘油酯和卡必醇醋酸酯作为稀释剂, 研究了在以热致相分离(TIPS)法制备聚偏氟乙烯(PVDF)微孔膜过程中, 聚偏氟乙烯-稀释剂间介电差异对PVDF膜微观结构的影响. 实验发现, PVDF-稀释剂间介电常数的差异与PVDF膜微观结构有一定关联. 当PVDF介电常数大于稀释剂的介电常数时, PVDF的分子间作用以引力为主导, PVDF分子易于聚集结晶, 形成松散球粒结构. 当PVDF介电常数与稀释剂的介电常数相近时, PVDF的分子间引力作用与斥力作用相均衡, 在淬冷条件下可形成近似双连续结构. 当PVDF介电常数小于稀释剂的介电常数时, PVDF分子间有一定的斥力效应, PVDF分子结晶困难.     

Interfacial activity of metal ion extractant

The interfacial activity of metal ion extractants is discussed. The interfacial tension isotherms are processed by matching the Szyszkowski equation, and estimation of selected parameters to discuss the interfacial activity of extractants. Results are presented in comprehensive tables and figures. The interfacial activity depends mainly on three different parameters; type of extractant, acidity of the aqueous phase and organic diluent. Strongly acidic extractants and protonated amine reagents exhibit the highest interfacial activity. The solvating reagents and non-protonated amines are on the opposite side of the scale, while the chelating reagents are somewhere in the middle. The acidity of the aqueous phase affects the interfacial activity of extractants, mainly by the ionisation (protonation and dissociation) of extractant molecules. Solvating diluents always decrease the interfacial activity of extractants.     

Basicity, complexation ability and interfacial behavior of BTBPs: a simulation study

BTBPs represent an important class of tetradentate heterocyclic ligands with N-donor binding sites that have been recently developed to separate trivalent actinides from lanthanides. We first investigate by QM calculations the conformational properties, basicity and complexation energies with Eu(NO(3))(3), comparing BTBP derivatives with alkyl substituents on the pyridinyl or triazinyl moieties to their conformationally cis-locked BTPhen analogues. The latter, preorganized for protonation and complexation, are found to be more basic and to afford more stable complexes. We next explore the interfacial behavior of CyMe(4)BTBP in its neutral versus protonated states and of 1:1 Eu(NO(3))(3)(CyMe(4)BTBP) complexes at the aqueous interface with an octanol-hexane mixture. The neutral BTBP ligand displays no visible surface activity, whereas protonated and complexed ligands are surface active. Taken together, the QM and MD results suggest that Eu(III) extraction by BTBPs occurs at the interface, via the protonated form of the ligand in acidic conditions, explaining why the extraction kinetics is slow and why BTPhen ligands are more efficient than BTBPs.     

Effect of electric fields on contact angle and surface tension of drops

Contact angles of sessile drops were experimentally investigated in the electric field. The experimental setup was designed such that the electric field was applied to all three interfaces. The advanced Automated Polynomial Fitting (APF) methodology was employed to measure contact angles with high accuracy. The significance of the observations and trends was examined by conducting statistical tests of hypothesis. It was found that contact angles of polar liquids such as alcohols increase in the electric field. However, no significant trend was observed for nonpolar liquids such as alkanes. The change in the contact angle was found to be stronger for liquids with longer molecules. It was shown that the polarity of the electric field is not an underlying factor in the observed trends. Using the equation of state for interfacial tensions, the observed shift in contact angles was translated into a corresponding change in surface tension of the liquids. The results suggest that the surface tension of alcohols increases by one to two percent (depending on the size of molecules) when an electric field of the order of magnitude of 10(6) V/m is applied.     

不同稀释剂中HDEHP的界面性质研究

用滴体积法研究了HDEHP在不同稀释剂-0.05mol.dm^-^3(N2, Na2)SO4(pH=2.40)体系中的界面性质, 认为吸附于液-液界面的是单体HDEHP分子, 得到了各体系中HDEHP的Cmin, Tmax, Ai以及△Gad等界面吸附参数。HDEHP在不同稀释剂体系中的界面活性顺序为: 脂肪烃>芳香烃>氯仿>甲基异丁基酮, 这种变化主要是在体相中和界面上稀释剂与萃取剂、界面上的萃取剂及稀释剂与界面层水之间分子间相互作用的结果。同时讨论了HDEHP在不同稀释剂中的萃取动力学机理。     

The Chemistry of Separations Ligand Degradation by Organic Radical Cations

Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexants and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R^•+), carbon-centered radicals (R^•), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R^•+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with various ligands. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved.     

Interfacial behavior of Cyanex 302 and kinetics of lanthanum extraction

In this paper, interfacial tension of Cyanex 302 is measured by a Sigma-701 tensiometer and the adsorption parameters are calculated according to the Gibbs and Szyszkowski adsorption isotherms. The interfacial adsorbed behavior of Cyanex 302 is investigated. The results demonstrate that the dimer is the predominant species in the bulk organic phase; however, the monomer is adsorbed at the interface and more interfacially active. The effects of aqueous pH, ion strength, and temperature on the interfacial activity of Cyanex 302 in heptane are discussed and explained in detail. The lower interfacial activity of Cyanex 302 in aromatic hydrocarbon than in aliphatic hydrocarbon has also been determined. The values of interfacial excess at the saturated interface increase in the order n-heptane>cyclohexane>toluene>benzene, which is consistent with the order of extractability of lanthanum by Cyanex 302 in these diluents. The interfacial activity data are used to discuss the kinetic mechanism of lanthanum(III) extraction. It is shown that an interfacial mechanism is very probable, and the extraction limiting step is the reaction between the Cyanex 302 molecules in the organic phase sublayer and the adsorbed intermediate complex.     

Dependence of primary and secondary emulsion formation on the concentration of TBP,HNO3 and additives

Model studies on TBP—diluent—aqueous HNO₃ extraction systems were performed to establish the mechanism of emulsyfying during the reprocessing of spent reactor fuel with mixtures of TBP solutions. The systems of interest were emulsified under fixed conditions. The rate of separation of the primary emulsion as well as the turbidity of each phase were determined. The experiments were performed on mixtures of pure components of the extraction systems. Emulsion stability was investigated in terms of the influence of such factors as main products of TBP decay, the type of diluents, HNO₃ concentration and concentration of TBP in different diluents.     

Phase behavior of polymer/diluent/diluent mixtures and their application to control microporous membrane structure

Rechargeable battery separators containing controlled pores were fabricated via the thermally-induced phase separation (TIPS) process. Based on the idea that pores could be manipulated by controlling the liquid–liquid phase separation temperature in the TIPS process, phase boundaries of the polymer–diluent systems were controlled by using diluent mixtures. Phase behaviors of the polymer/diluent/diluent ternary blends consisting of polyethylene (PE) as polymer, and soybean oil (SBO) and dioctyl phthalate (DOP) as diluents were explored. PE/SBO and PE/DOP binary blends, and PE/SOB/DOP ternary blends exhibited typical upper critical solution temperature (UCST) type phase behaviors, and the phase separation temperatures of the PE/SBO blends were higher than those of the PE/DOP blends. When the mixing ratio of the polymer and diluent-mixture was fixed, the phase separation temperature of the PE/SBO/DOP blend initially increased with increasing SBO content in the diluent-mixture passing through a maximum centered at about 80 wt% SBO and decreased beyond this point. Furthermore, the phase separation temperature of the PE/diluent-mixture blend was always higher than that of the PE/SBO blend when the diluent-mixture contained more than or equal to 50 wt% SBO. To understand the observed phase behavior of the blends, thermodynamic analyses based on the lattice-fluid theory were performed. Larger pore membranes were fabricated from the blend when higher phase separation temperatures of the blend were exhibited.     

TODGA/HNO_3萃取La~(3+)的界面性质

利用滴体积法研究了La~(3+)/HNO_3/N,N,N',N'-四辛基-3-氧戊二酰胺(TODGA)/稀释剂体系的界面性质,考察了TODGA浓度、液滴形成时间、稀释剂种类、La~(3+)浓度、体系温度、离子强度和溶液酸度等因素对体系界面性质的影响.实验结果表明,体系达到界面饱和吸附时间约为120 s,可认为体系达到萃取平衡;TODGA浓度不同时,界面张力也不同,进而判定界面饱和吸附物种亦不相同;极性较小的稀释剂体系的界面张力降低较大,按照正辛烷环己烷苯甲苯次序降低;HNO_3对TODGA的质子化作用使其表面活性显著增强,故硝酸浓度增大导致界面张力降低;Na NO_3的存在降低了界面上游离萃取剂分子的浓度,致使界面张力增大.     

Effect of external factors on the increase in the extraction rate in a vibration treatment on the dynamic interfacial layer

Vibration treatment of a dynamic interfacial layer in the extraction system constituted by an aqueous solution of a salt of a rare-earth element and a solution of di-(2-ethylhexyl)phosphoric acid in heptane (toluene) results in an increase in the process rate. This increase is characterized by an acceleration coefficient defined as the ratio between the lanthanide concentrations in the organic phase after equal intervals of time in systems with and without vibrations. It is shown that the acceleration coefficient depends on the concentration of the extractive agent, initial concentration of an element being extracted, solution pH, and phase contact duration. The observed behavior is explained in terms of the process model suggested by the authors. According to this model, the effect depends on the relative contributions made by a number of interfacial phenomena accompanying the extraction of a lanthanide with solutions of di-(2-ethylhexyl)phosphoric acid in diluents and, in particular, by the spontaneous surface convection and structuring in the interfacial layer.     

Effect of organic diluents on the extraction of uranium from phosphoric acid

Phosphoorganic solvents such as OPPA, DEPA/TOPO and OPAP are commonly used to extract uranium from wet phosphoric acid. They are used in concentrations between 1–10% wt/wt in organic diluents. These inert organic substances serve to dilute the solvent, decrease its viscosity and secure a greater contact between the acid and the solvent. The diluents should also be cheap, readily available, immiscible with water and volatile at the temperature of the extraction which is from 30–50°C. They should not reduce the extraction coefficient of the solvent and separate well at the temperature of separation as an organic phase. This study was carried out to investigate the effect of various organic diluents in order to select the most suitable one. It is established that paraffinic diluents are better than aromatic ones. Since kerosene is cheap, available and not very volatile at the temperature of extraction, it is commonly used in extraction. However, the kerosene used should be treated to reduce the aromatic content to a minimum.     

Extraction of Nitric Acid and Np(IV) by some aliphatic ketones and alcohols

The extraction behaviour of HNO₃ and Np(IV) from aqueous nitrate solutions with some aliphatic alcohols and ketones using hexane, carbon tetrachloride, benzene and chloroform as diluents was studied. The acid concentration in the aqueous phase varied from 0.25 to 10 M and that of the extractant in the organic phase varied from 0.5 M to the undiluted fraction. In the alcohol systems, solutions of the same alcohol in the diluents CCl₄ and CHCl₃ showed similar capacity for acid extraction, and also in the same diluents, solutions of diisopropyl and diisobutyl alcohol showed similar capacity for extraction. Extraction of Np(IV) with the different ketones and alcohols used follow the same pattern as HNO₃.