Phase Transfer Kinetics Research Articles

Determination of Crystal Growth Rates in Multi-Component Solutions

Many solid forming processes involve crystallization from multi-component solutions. In order to predict final phase assemblages, multi-component phase transfer kinetics must be known. It is not sufficient to have the kinetics of only one crystallizing component in the presence of other entities; the kinetics of concurrent crystallizing components are of interest as well. However, methods for their determination are currently lacking. We propose a new method comprising desupersaturation measurements of a 150 µm film of supersaturated solution in contact with a planar crystalline substrate. We show that concentration measurement at a single point in the film is sufficient to retrieve the phase transfer kinetics. For this, we use a confocal micro-Raman spectroscope, which is able to distinguish between different components and has a high spatial resolution. We chose crystallization of Na2SO4 and Na2CO3 decahydrate from aqueous solution as our model system because of its well-known phase equilibrium. In binary experiments, we demonstrate the mode of operation and its ability to reproduce known kinetics from the literature. In ternary experiments, we successfully distinguish two courses of crystallization, the first of which is a preferential crystallization of one component and the second a simultaneous crystallization of both crystallizing components. In both cases, the parameters for simple power law kinetics are determined. If sodium carbonate decahydrate crystallizes while sodium sulfate remains in solution, the mean mass transfer coefficient is revealed to be kg,CO3=6×10−7ms−1, which is about an order of magnitude lower compared to binary crystallization. If sodium carbonate decahydrate crystallizes concurrently with sodium sulfate decahydrate, the crystallization kinetics are similar to binary cases. The other component tends to be significantly slower compared to its binary crystallization.

Transport Modeling of Kinetically Limited Microscale Extraction Systems: Droplet and Supported Liquid Membrane Separations

Microfluidic droplet extraction devices can be used to efficiently measure solute phase transfer kinetics in liquid–liquid extraction systems. In this work, a droplet extraction apparatus was const...

Evaluation of phase transfer kinetics and thermodynamic equilibria of Reactive Orange 16 sorption onto chemically improved Arachis hypogaea pod powder

Biosorbent from pods of Arachis hypogaea (AhP) were inducted with sulphuric acid treatment and then the activated materials were employed to sequester a sulphonated textile dye; Reactive Orange 16 (RO16) from water system. The characteristic features of the surface functionalized AhP (Ct-AhP) were analysed using instrumentation techniques. The biosorption influencing variables like operating pH, agitating time, initial RO16 concentration and temperature effects were investigated. One-factor optimization revealed that 0.5 g Ct-AhP was sufficient to achieve maximum removal of RO16 (20–120 mg/L) within 180 min agitation at 150 rpm. The isotherm data were applied to non-linear isotherms viz., Freundlich, Langmuir and Temkin models as well as rate limiting steps were elucidated using kinetic models. Freundlich isotherm showed good fit and pseudo-second order kinetic data explained RO16 removal by Ct-AhP followed chemisorption. The outcome of thermodynamic parametric values infer that RO16 biosorption was spontaneous, feasible and involved exothermic type of heat. Elovich and intraparticle diffusion revealed the biosorption mechanisms. The maximum RO16 biosorption (56.48 mg/g) by 0.5 g Ct-AhP were witnessed in the system containing 120 mg/L RO16 agitated at 150 rpm operating at pH 7.0, 303 K for a span of 180 min. Thus, the Ct-AhP is considered to be a promising biosorbent which can be employed in treating the textile effluents.

Functionalized Dipicolinic Acid Derivatives as TALSPEAK-MME Stripping Agents

ABSTRACT This work describes the results of an assessment of two derivatives of dipicolinic acid (DPA) as the actinide-selective stripping reagents in the combined HEH[EHP]/Cyanex-923 system, TALSPEAK-MME (mixed monofunctional extractants). One purpose of this investigation is to demonstrate probable advantages derived in phase-transfer kinetics by deploying dipicolinates as preorganized aminopolycarboxylate complexants in TALSPEAK-derived separation systems. The investigation is focused on the behavior of the lanthanides, Am, and selected transition metals (Zr, Mo, Pd, Ru, and Rh) in the extraction, solvent conditioning, and stripping steps. Solvent conditioning with glycine buffer solutions is shown to be effective for the removal of entrained HNO3 while also managing Pd concentration prior to actinide stripping. The efficacy of the DPA derivative during the actinide-selective strip was assessed, focusing explicitly on the effects of pH and ligand concentration and evaluating the stripping kinetics. These ligands were shown to be highly selective for americium, producing in the TALSPEAK-MME platform separation factors comparable to commonly used actinide selective stripping agents for radiotracer Eu, Am, a trans-lanthanide series and selected transition metals. The stripping kinetics study revealed very rapid phase-transfer reactions, reaching equilibrium in less than 10 s on vigorous agitation. Further work will be required to address the possible contamination of the product by selected transition metals (such as Zr) during the stripping step.

Solvent Extraction Studies for the Separation of Trivalent Actinides from Lanthanides with a Triazole-functionalized 1,10-phenanthroline Extractant

ABSTRACT A new N-atom donor extractant 2,9-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)-1,10-phenanthroline (EH-BTzPhen) was synthesized and used in solvent extraction studies to separate the trivalent minor actinide americium(III) and curium(III) from europium(III), representing fission product lanthanides. The extractant was found to be soluble in 1-octanol and in the Aliquat-336 nitrate ([A336][NO3]) ionic liquid diluent, but insoluble in n-dodecane. The [A336][NO3] is a fully incinerable room temperature ionic liquid, and has a higher flash point than aliphatic diluents such as 1-octanol. The EH-BTzPhen proved to be effective for selective minor actinide extraction only in combination with 2-bromohexanoic acid synergist when 1-octanol was used as a diluent (SF Am/Eu > 200). The change of the diluent from 1-octanol to Aliquat-336 nitrate allowed selective An(III) extraction from low acidity feed solutions without the need of a synergist (SF Am/Eu ~ 70 and SF Am/Cm ~ 1.9–2.2). The phase transfer kinetics of the ligand-metal complexes is however very slow at 22 °C in the case of both solvents. With this newly synthesized extractant, the achieved SF Am/Cm was comparable to the values achieved with the established CyMe4BTBP and CyMe4BTPhen extractants.

Preparation of nanoscale organosols and hydrosols via the phase transfer route

Aqueous reactions support the preparation of a wide variety of inorganic nanoparticles (NPs), starting from relatively inexpensive precursors. However, the long-term stability of hydrosols is sensitive to changes in water chemistry, especially at high NP concentrations. On the other hand, by using an appropriate stabilizer, NPs prepared in organic phases more commonly display smaller sizes, higher stability, and monodispersity. Subsequently, phase transfer of freshly prepared NPs from an aqueous medium into an organic carrier constitutes a reliable and inexpensive route for preparing highly concentrated and stable organosols. The reverse transfer serves the preparation of small-sized and highly monodispersed hydrosols. The kinetics of phase transfer and the stability of the resultant sols are key considerations and are reliant on mixing and on the hydrophilic/lipophilic balance (HLB) of the particles. This balance is in turn dependent on the surface interaction between the phase transfer agent and the particles, as well as the interactions between the phase transfer agent, the continuous phase, and other additives, whenever applicable. This article reviews different studies that examined the phase transfer of NPs between organosols and hydrosols and elucidates the governing interactions. Scale-up of this preparation route lies in readily dispersible dried coated particles, or stable highly concentrated sols. Particle-independent multi-cycle phase transfer, with a minimum effect on NP size, monodispersity, and functionality is an attractive frontier.

Gastric and Postgastric Processing of 13C Markers Renders the 13C Breath Test an Inappropriate Measurement Method for the Gastric Emptying of Lipid Emulsions in Healthy Adults

Background: Breath tests (BTs) present an alternative gastric-emptying (GE) measure. However, their efficacy in the measurement of the GE rate of lipid emulsions (LEs) is unknown.Objective: The objective of this work was to investigate the validity of 13C BTs as a measure of fat GE rate in LEs.Methods: The lipophilic 13C octanoate (OCC) BT marker was investigated for fat GE with the hydrophilic 13C sodium acetate (ACC) and the triglyceride 13C trioctanoin (TCC) markers as comparators. Data from 2 randomized studies were combined [50 healthy participants; 25 men, mean ± SD age: 23 ± 2.8 y; mean ± SD body mass index (in kg/m2): 22.4 ± 1.7]. Each participant was given either an acid-stable LE (LE1) or an acid-unstable LE (LE4) at each visit. Twenty-three participants underwent simultaneous MRI. The effect of LEs on 13CO2 excretion profiles was determined. The BT half-emptying times (BT T50) were validated with the MRI half-emptying time of the ingested fat volume (MRI T50).Results: The effect of LEs on 13CO2 excretion depended on the properties of the 13C marker. T50 for OCC was shorter by 98 min for LE1 than for LE4 (P < 0.001). Other markers showed either no LE dependency or a longer T50 for LE1 than for LE4. No difference in T50 between OCC and ACC was detected in LE1. In LE4, the T50 was longer by 154 min (P < 0.0001). There was some concordance between MRI T50 and OCC BT T50 for LE1 (rc = 0.7). No other marker showed any concordance with fat GE. 13C-Nuclear magnetic resonance in vitro findings were compatible with changes in the kinetics of phase transfer of OCC dependent on its protonation state.Conclusions: The structure of fat present in the stomach affects 13CO2 excretion. The chemical properties of the 13C marker and their gastric and postgastric interaction with fat renders 13CO2 excretion an inappropriate measure of LE emptying in healthy adults. This trial was registered at clinicaltrials.gov as NCT02226029 and NCT02602158.

Direct valorisation of waste cocoa butter triglycerides via catalytic epoxidation, ring-opening and polymerisation.

BACKGROUNDDevelopment of circular economy requires significant advances in the technologies for valorisation of waste, as waste becomes new feedstock. Food waste is a particularly important feedstock, containing large variation of complex chemical functionality. Although most food waste sources are complex mixtures, waste from food processing, no longer suitable for the human food chain, may also represent relatively clean materials. One such material requiring valorisation is cocoa butter.RESULTSEpoxidation of a triglyceride from a food waste source, processing waste cocoa butter, into the corresponding triglyceride epoxide was carried out using a modified Ishii‐Venturello catalyst in batch and continuous flow reactors. The batch reactor achieved higher yields due to the significant decomposition of hydrogen peroxide in the laminar flow tubular reactor. Integral and differential models describing the reaction and the phase transfer kinetics were developed for the epoxidation of cocoa butter and the model parameters were estimated. Ring‐opening of the epoxidised cocoa butter was undertaken to provide polyols of varying molecular weight (Mw = 2000–84 000 Da), hydroxyl value (27–60 mg KOH g−1) and acid value (1–173 mg KOH g−1), using either aqueous ortho‐phosphoric acid (H3PO4 ) or boron trifluoride diethyl etherate (BF3 ·OEt2)‐mediated oligomerisation in bulk, using hexane or tetrahydrofuran (THF) as solvents. The thermal and tensile properties of the polyurethanes obtained from the reaction of these polyols with 4,4′‐methylene diphenyl diisocyanate (MDI) are described.CONCLUSIONThe paper presents a complete valorisation scheme for a food manufacturing industry waste stream, starting from the initial chemical transformation, developing a process model for the design of a scaled‐up process, and leading to synthesis of the final product, in this case a polymer. This work describes aspects of optimisation of the conversion route, focusing on clean synthesis and also demonstrates the interdisciplinary nature of the development projects, requiring input from different areas of chemistry, process modelling and process design. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Coordination Chemistry and f-Element Complexation by Diethylenetriamine-N,N″-bis(acetylglycine)-N,N',N″-triacetic Acid.

Potentiometric and spectroscopic techniques were used to evaluate the coordination behavior and thermodynamic features of trivalent f-element complexation by diethylenetriamine-N,N″-bis(acetylglycine)-N,N',N″-triacetic acid (DTTA-DAG) and its di(acetylglycine ethyl ester) analogue [diethylenetriamine-N,N″-bis(acetylglycine ethyl ester)-N,N',N″-triacetic acid (DTTA-DAGEE)]. Protonation constants and stability constants of trivalent lanthanide complexes (except Pm3+) were determined by potentiometry. Six protonation sites and three metal-ligand complexes [ML2-, MHL-, and MH2L(aq)] were quantified for DTTA-DAG. Four protonation sites and one metal-ligand complex [ML(aq)] were observed for DTTA-DAGEE, consistent with the presence of two ester groups. Absorption spectroscopy was utilized to measure the stability constants for complexation of trivalent neodymium and americium by DTTA-DAG and trivalent neodymium by DTTA-DAGEE. The coordination environment of trivalent europium in the presence of DTTA-DAG was investigated at various acidities by luminescence lifetime measurements. Decay constants indicate one water molecule in the inner coordination sphere across the 1.0 < pH < 5.5 range, presumably due to octadentate coordination by DTTA-DAG. A trans-lanthanide pattern of complex stabilities for DTTA-DAG was found to be analogous to that observed for DTPA, with a ∼106 reduction of the complex stability. The lessened strength of complexation, relative to DTPA, was attributed to significant reduction of the total ligand basicity for DTTA-DAG due to the electronic influence of amide functionalization. When DTTA-DAG is used as an aqueous holdback complexant in liquid-liquid distribution experiments, the preferential coordination of Am3+ in the aqueous environment offers efficient An/Ln differentiation. The separation extends to pH 2 conditions, where the kinetics of phase transfer in such liquid-liquid systems are aided by the acid-catalyzed dissociation of a metal/aminopolycarboxylate complex.

Synthesis and Characterization of 6,6ˊ-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)-2,2ˊ-bipyridine (EH–BTzBP) for Actinide/Lanthanide Extraction and Separation

ABSTRACTA new N-donor extractant, 6,6ˊ-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)-2,2ˊ-bipyridine (EH-BTzBP), was synthesized and tested for Am(III)/Ln(III) extraction and separation. EH-BTzBP in combination with 2-bromohexanoic acid (as lipophilic anion source) selectively extracts Am(III) from acidic solutions (HNO3 ≤ 0.1M) with Am(III)/Eu(III) separation factors of about 70. Phase transfer kinetics is rapid, back-extraction of metal ions posed no issues, and there is no evidence of ligand degradation by acid hydrolysis or contact with hydrogen peroxide (which simulates some effects of radiolysis).

Radon, CO2 and CH4 as environmental tracers in groundwater/surface water interaction studies − comparative theoretical evaluation of the gas specific water/air phase transfer kinetics

The applicability of radon as environmental tracer in groundwater/surface water interaction studies has been documented in a considerable number of publications. In some of these reports it has also been suggested to validate the radon based results by using CO2 and CH4 as supplementary tracers. The on-site measurement of the three gaseous parameters relies on their extraction from the water followed by the measurement of their concentration by means of mobile gas-in-air detectors. Since most related practical applications require the recording of time series, a continuous extraction of the gases from (e.g.) a permanently pumped water stream is necessary. A precondition for the sound combined interpretation of the resulting time series is that the individual temporal responses of the extracted gas-in-air concentrations to instantaneously changing gas-in-water concentrations are either identical or in reproducible relation to each other. The aim of our theoretical study was the comparison of the extraction behavior of the three gaseous solutes with focus on the individual temporal responses to changing gas-in-water concentrations considering in particular the gas specific water/air phase transfer kinetics. We could show that the overall mass transfer coefficients of radon, CO2 and CH4 result in a virtually similar temporal response to aqueous concentration changes, thus confirming the straightforward combined measurement/utilization of the dissolved gases as environmental tracers in groundwater/surface water interaction studies.

Effect of temperature on the protonation of N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid in aqueous solutions: Potentiometric and calorimetric studies

The TALSPEAK process (Trivalent Actinide Lanthanide Separations by Phosphorus-reagent Extraction from Aqueous Komplexes) has been demonstrated in several pilot-scale operations to be effective at separating trivalent actinides (An3+) from trivalent lanthanides (Ln3+). However, fundamental studies have revealed undesired aspects of TALSPEAK, such as the significant partitioning of Na+, lactic acid, and water into the organic phase, thermodynamically unpredictable pH dependence, and the slow extraction kinetics. In the modified TALSPEAK process, the combination of the aqueous holdback complexant HEDTA (N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid) with the extractant HEH[EHP] (2-ethyl(hexyl) phosphonic acid mono-2-ethylhexyl ester) in the organic phase has been found to exhibit a nearly flat pH dependence between 2.5 and 4.5 and more rapid phase transfer kinetics for the heavier lanthanides. To help understand the speciation of Ln3+ and An3+ in the modified TALSPEAK, systematic studies are underway on the thermodynamics of major reactions in the HEDTA system under conditions relevant to the process (e.g., higher temperatures). Thermodynamics of the protonation and complexation of HEDTA with Ln3+ were studied at variable temperatures. Equilibrium constants and enthalpies were determined by a combination of techniques including potentiometry and calorimetry. This paper presents the protonation constants of HEDTA at T=(25 to 70)°C. The potentiometric titrations have demonstrated that, stepwise, the first two protonation constants decrease and the third one slightly increases with the increase of temperature. This trend is in good agreement with the enthalpy of protonation directly determined by calorimetry. The results of NMR analysis further confirm that the first two protonation reactions occur on the diamine nitrogen atoms, while the third protonation reaction occurs on the oxygen of a carboxylate group. These data, in conjunction with the thermodynamic parameters of Ln3+/An3+ complexes with HEDTA at different temperatures, will help to predict the speciation and temperature-dependent behavior of Ln3+/An3+ in the modified TALSPEAK process.

The Chemistry of TALSPEAK: A Review of the Science

The TALSPEAK Process (Trivalent Actinide Lanthanide Separation with Phosphorus-Reagent Extraction from Aqueous Komplexes) was originally developed at Oak Ridge National Laboratory by B. Weaver and F.A. Kappelmann in the 1960s. It was envisioned initially as an alternative to the TRAMEX process (selective extraction of trivalent actinides by tertiary or quaternary amines over fission product lanthanides from concentrated LiCl solutions). TALSPEAK proposed the selective extraction of trivalent lanthanides away from the actinides, which are retained in the aqueous phase as aminopolycarboxylate complexes. After several decades of research and development, the conventional TALSPEAK process (based on di-(2-ethylhexyl) phosphoric acid (extractant) in 1,4-di-isopropylbenzene (diluent) and a concentrated lactate buffer containing diethylenetriamine-N,N,N’,N”,N”-pentaacetic acid (actinide-selective holdback reagent)) has become a widely recognized benchmark for advanced aqueous partitioning of the trivalent 4f/5f elements. TALSPEAK aqueous chemistry has also been utilized to selectively strip actinides (Reverse TALSPEAK) with some notable success. Under ideal conditions, conventional TALSPEAK separates Am3+ from Nd3+ (the usual limiting pair) with a single-stage separation factor of about 100; both lighter and heavier lanthanides are more completely separated from Am3+. Despite this apparent efficiency, TALSPEAK has not seen enthusiastic adoption for advanced partitioning of nuclear fuels at process scale for two principle reasons: first, all adaptations of TALSPEAK chemistry to process scale applications require rigid pH control within a narrow range of pH, and second, phase-transfer kinetics are often slower than ideal. To compensate for these effects, high concentrations of the buffer (0.5–2 M H/Na lactate) are required. Acknowledgement of these complications in TALSPEAK process development has inspired significant research activities dedicated to improving understanding of the basic chemistry that controls TALSPEAK (and related processes based on the application of actinide-selective holdback reagents). In the following report, advances in understanding of the fundamental chemistry of TALSPEAK that have been reported during the past decade will be reviewed and discussed.

Trivalent Lanthanide/Actinide Separation Using Aqueous-Modified TALSPEAK Chemistry

TALSPEAK is a liquid/liquid extraction process designed to separate trivalent lanthanides (Ln3+) from the minor actinides (MAs) Am3+ and Cm3+. Traditional TALSPEAK organic phase is comprised of the monoacidic dialkyl bis(2-ethylhexyl)phosphoric acid extractant (HDEHP) in diisopropyl benzene (DIPB). The aqueous phase contains a soluble aminopolycarboxylate diethylenetriamine-N,N,N’,N”,N”-pentaacetic acid (DTPA) in a concentrated (1.0–2.0 M) lactic acid (HL) buffer with the aqueous acidity typically adjusted to pH 3.0. This process balances the selective complexation of the actinides by DTPA against the electrostatic attraction of the lanthanides by the HDEHP extractant to achieve the desired trivalent lanthanide/actinide group separation. In this study, the aqueous phase has been modified by replacing the lactic acid buffer with a variety of simple and longer-chain amino acid buffers. The results show successful trivalent lanthanide/actinide group separation with the aqueous-modified TALSPEAK process at pH 2. The amino acid buffer concentrations were reduced to 0.5 M (at pH 2), and separations were performed without any effect on phase-transfer kinetics. Successful modeling of the aqueous-modified TALSPEAK process (p[H+] 1.6–3.1) using a simplified thermodynamic model and an internally consistent set of thermodynamic data is presented.

Toward a robust analytical method for separating trace levels of nano-materials in natural waters: cloud point extraction of nano-copper(II) oxide

Cloud point extraction (CPE) factors, namely Triton X-114 (TX-114) concentration, pH, ionic strength, incubation time, and temperature, were optimized for the separation of nano-sized copper(II) oxide (nCuO) in aqueous matrices. The kinetics of phase transfer was studied using UV-visible spectroscopy. From the highest separation rate, the most favorable conditions were observed with 0.2 % w/v of TX-114, pH = 9.0, ionic strength of 10 mM NaCl, and incubation at 40 °C for 60 min, yielding an extraction efficiency of 89.2 ± 3.9 % and a preconcentration factor of 86. The aggregate size distribution confirmed the formation of very large nCuO-micelle assemblies (11.9 μm) under these conditions. The surface charge of nCuO was also diminished effectively. An extraction efficiency of 91 % was achieved with a mixture of TX-100 and TX-114 containing 30 wt.% of TX-100. Natural organic and particulate matters, represented by humic acid (30 mg/L) and micron-sized silica particles (50 mg/L), respectively, did not significantly reduce the CPE efficiency (<10 %). The recovery of copper(II) ions (20 mg/L) in the presence of humic acid was low (3-10 %). The spiked natural water samples were analyzed either directly or after CPE by inductively coupled plasma mass spectrometry following acid digestion/microwave irradiation. The results indicated the influence of matrix effects and their reduction by CPE. A delay between spiking nCuO and CPE may also influence the recovery of nCuO due to aggregation and dissolution. A detection limit of 0.04 μg Cu/L was achieved for nCuO.

The role of carboxylic acids in TALSQuEAK separations

Recent reports have indicated that Trivalent Actinide–Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes (TALSPEAK)-type separations chemistry can be improved through the replacement of bis-2-ethyl(hexyl) phosphoric acid (HDEHP) and diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) with the weaker reagents 2-ethyl(hexyl) phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA), respectively. This modified TALSPEAK has been provided with an adjusted acronym of TALSQuEAK (Trivalent Actinide–Lanthanide Separation using Quicker Extractants and Aqueous Komplexes). Among several benefits, TALSQuEAK chemistry provides more rapid phase transfer kinetics, is less reliant on carboxylic acids to mediate lanthanide extraction, and allows a simplified thermodynamic description of the separations process that generally requires only parameters available in the literature to describe metal transfer. This article focuses on the role of carboxylic acids in aqueous ternary (M-HEDTA-carboxylate) complexes, americium/lanthanide separations, and extraction kinetics. Spectrophotometry (UV-Vis) of the Nd3+ hypersensitive band indicates the presence of aqueous ternary Nd–Lac–HEDTA species (Lac = lactate, K 111 = 1.83 ± 0.01 at 1.0 mol L−1 ionic strength, Nd(HEDTA) + Lac− ⇄ Nd(HEDTA)Lac−). While lower levels (0.1 mol L−1 vs. 1.0 mol L−1) of carboxylic acid will still be necessary to control pH and encourage phase transfer of the heavier lanthanides, application of different carboxylic acids does not have an overwhelming impact on Ln/Am separations or extraction kinetics relative to conventional TALSPEAK separations. TALSQuEAK separations come to equilibrium in two to five minutes depending on the system pH using only 0.1 mol L−1 total lactate or citrate.

Alternatives to HDEHP and DTPA for Simplified TALSPEAK Separations

The TALSPEAK process is an established option for lanthanide/minor actinide separations using solvent extraction. In this process, selective extraction of lanthanides is achieved by contacting a water-soluble aminopolycarboxylate complexant in a concentrated carboxylic acid buffer with a liquid cation exchanging extractant in an immiscible organic diluent. Although TALSPEAK process development has been successful on several levels, studies of the detailed fundamental chemistry have revealed undesirable complex interactions between aqueous and organic solute species. These complications threaten to impair process modeling and could impact engineered operations. In the present work, results are reported describing equilibrium partitioning and phase transfer kinetics trends for trivalent lanthanide ions and americium into bis-2-ethyl(hexyl) phosphoric acid (HDEHP) or structural analog 2-ethyl(hexyl) phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) organic phases from aqueous lactate solutions containing di...

Lactic Acid Partitioning in TALSPEAK Extraction Systems

The TALSPEAK process, developed in the 1960s at the Oak Ridge National Laboratory and demonstrated in various forms up to pilot scale elsewhere, has emerged as a primary method for partitioning of trivalent transplutonium actinides from fission product lanthanides in advanced nuclear fuel cycles. The baseline process relies on the monoacidic dialkyl phosphoric acid extractant bis-(2-ethylhexyl)phosphoric acid (HDEHP), the aqueous complexant diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA), and high concentrations of a pH 3.5 buffer, usually 1-2 M lactic acid (HL). Previous reports have established that HL not only buffers the pH, but also increases phase transfer kinetics, improves the radiation stability of DTPA, and has been implicated as a possible participant in the formation of ternary complexes in both the aqueous and organic phases. One feature central to the interpretation of these results is the extent of partitioning of HL between the phases. In this study, 14C-labeled HL has been used to examine the details of its partitioning between aqueous solutions and organic solutions relevant to the possible deployment of TALSPEAK. It is found that, contrary to previous reports, HL partitions into the organic phase independently of the amount and identity of the metal ions that are present.

PEG-400 Partitioning in the HCCD/PEG Process for Cs and Sr Recovery

The properties of the chloro-protected cobalt bis(dicarbollide) anion in the acidic form (HCCD), and in the presence of polyethylene glycol (PEG-400), are well known for the recovery of Cs and Sr from acidic radioactive streams. In the early development of HCCD/PEG extraction processes, questions were raised regarding the ability to control the concentration of PEG-400 in the organic phase due to its high solubility in the aqueous process solutions relative to HCCD or the diluent. The purpose of this study was to quantify the partitioning behavior of PEG-400 under a wide variety of relevant process conditions. PEG distribution ratios (D PEG ) were measured by equilibrium batch contacts between the organic and aqueous phases over a wide range of conditions using radiometric techniques with 14C labeled PEG-400 to monitor the behavior of the bulk material. The results vary dramatically from 0.1 < DPEG < 50, indicate that the PEG phase transfer kinetics are rapid, and that the aqueous phase nitric acid concentration has minimal impact on PEG solubility. The molar concentration ratio of [HCCD]:[PEG] in the organic phase has the greatest impact on PEG solubility. This ratio should be maintained at [HCCD]:[PEG] greater than or equal to approximately 6 to minimize PEG losses from the organic phase.

Surface modification of graphitized carbonaceous materials by electropolymerization of thiophene and their effects on electrochemical properties

Highly oriented pyrolytic graphite (HOPG) and graphitized carbonaceous thin films prepared by plasma-assisted chemical vapor deposition (PACVD) were surface-modified by electropolymerization of thiophene. The electrochemical properties of the carbonaceous materials were studied by cyclic voltammetry and ac impedance spectroscopy. Irreversible cathodic current of the carbonaceous materials above 0.5 V (vs. Li/Li +) in the cyclic voltammograms significantly decreased by electropolymerization of thiophene, indicating that electropolymerization of thiophene suppress the decomposition of electrolytes on the carbonaceous materials. On the Nyquist plots, a semi-circle due to surface film resistance was observed, and the value significantly decreased at around 1.5 V. At potentials below 0.9 V, another semi-circle appeared in the middle to lower frequency region, which was assigned to the charge transfer resistance due to lithium-ion transfer at the surface-modified carbon electrode/electrolyte interface. The charge-transfer resistances were dependent on electrode potentials. The activation energy for lithium-ion transfer through interface between the surface-modified HOPG electrode and electrolyte was evaluated, and the value was almost identical to that obtained for an untreated HOPG electrode. Based on these results, it is concluded that electropolymerization of thiophene played an important role not in the phase transfer kinetics of lithium-ion but in reduction of the electrolyte decomposition at a graphite electrode.