Diamylamylphosphonate Solvent Extraction of Am(VI) from Nuclear Fuel Raffinate Simulant Solution

The separation of hexavalent americium from the lanthanides in simulated PUREX raffinate solution using 1 M diamylamylphosphonate in dodecane extraction was investigated. Hexavalent americium was prepared using room-temperature sodium bismuthate oxidation. Under these conditions the majority of the lanthanides were not oxidized and remained inextractable. A separation factor of ～50 was provided for americium from europium over the nitric acid concentration range 6–7 M. Cerium was the exception with oxidation to Ce^IV resulting in its co-extraction with Am^VI. However, since americium is readily reduced to Am^III it was easily stripped with a dilute acidic solution of hydrogen peroxide. Although hydrogen peroxide also reduces cerium, it does so slowly, and a selective americium strip was achieved, with a separation factor of as high as 35. Alternatively, since americium spontaneously reduced in the loaded organic phase, samples allowed to stand for 2 hours could be selectively stripped of americium by contact with 1 M HNO₃ containing no additional reagents. Further, the separation was demonstrated using solutions containing macro-amounts of cerium and americium. The implications for use in fuel cycle separations are discussed.     

Partitioning of neodymium and americium in the liquid radioactive waste by oxalate precipitation

The partitioning of americium and neodymium by precipitation with oxalic acid was investigated in the simulated radwaste, which was composed of 10 elements of alkali, akaline earth, and transition metals in nitric acid solution. The effect of concentrations of oxalic acid and nitric acid in the simulated waste on the precipitation yield and purity of Nd and Am was examined in this study. As a result, the precipitated fraction of each element was increased with increasing concentration of oxalic acid and decreasing concentration of nitric acid. At an initial concentration of 0.5 M nitric acid and 0.5 M oxalic acid, both Am³ and Nd³⁺ were precipitated over 99% and other elements almost remained in the simulated solution. It was also found that Am was completely coprecipitated with Nd-oxalate precipitates, and Zr^4- caused the coprecipitation of Cs₂, Sr₂₊, and Pd₂₊.     

Feasibility of Using Di-Dodecyl-Di-Octyl Diglycolamide for Partitioning of Minor Actinides from Fast Reactor High-Level Liquid Waste

The unsymmetrical diglycolamide, di-dodecyl-di-octyl diglycolamide (D³DODGA) is a modifier-free extractant proposed for partitioning of trivalent actinides from nitric acid medium. D³DODGA has been evaluated for the feasibility of using it in the absence of a phase modifier, for the partitioning of minor actinides from fast reactor high-level liquid waste (FR-HLLW). The extraction behavior of various metal ions present in the simulated FR-HLLW was studied in a solution of 0.1 M D³DODGA/n-dodecane from nitric acid medium. The distribution ratio of about 20 metal ions was measured as a function of concentration of nitric acid and other interfering ion. The extraction was found to be strongly dependent on the oxidation state of the metal ion. The extraction of Am(III) from 3–4 M nitric acid medium was quantitative in a single contact. However, it was accompanied by the quantitative extraction of fission products such as trivalent lanthanides (Ln(III)), Y(III), and Zr(IV). The extraction of Sr(II), Pd(II), and Ru(III) in 0.1 M D³DODGA/n-dodecane was not insignificant, but quite low. The extraction of Ba(II), Ni(II), Mo(VI), and Fe(III) was marginal and the extraction of Co(II), Sb(III), Mn(II), and Cs(I) in 0.1 M D³DODGA/n-dodecane was negligible. Our results indicated that 0.1 M D³DODGA/n-dodecane is a promising candidate for the separation of trivalent actinides from fast reactor high-level liquid waste containing significant quantities of trivalent lanthanides and actinides.     

A Novel Solvent System Involving Terpyridine and Cyanex-301 for Am(III) and Eu(III) Separation from Weakly Acidic Feeds

Separation of trivalent actinides and lanthanides is a challenging task and has a great relevance in the nuclear fuel cycle. Bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex-301) show high selectivity for the trivalent actinides over the lanthanides at pH 3 or higher and N-donor ligands were reported to enhance the selectivity. 2,2?:6?,6”-Terpyridine (terpy), on the other hand, has shown to be quite effective at lower pH values and the combination of Cyanex 301 and terpy was evaluated in the present study, for the first time, for the separation of Am(III) from Eu(III), representative actinide and lanthanide elements, respectively at pH 2.0.

Thermodynamic parameters (enthalpy, entropy, and free energy) for the two phase extraction were also determined from the distribution studies at variable temperatures. Extraction of both Am³⁺ and Eu³⁺ was favored by negative enthalpy of extraction. More negative ΔG value indicated that Am³⁺ extraction was more favoured as compared to Eu³⁺ extraction using this solvent system. Effect of diluent composition on the extraction of Am³⁺ and Eu³⁺ was also studied in the present work.     

Solvent Extraction and Fluorescence Spectroscopic Investigation of the Selective Am(III) Complexation with TS-BTPhen

An americium(III) selective separation procedure was developed based on the coextraction of trivalent actinides (An(III)) and lanthanides (Ln(III)) by TODGA (N,N,N′,N′-tetraoctyl-diglycolamide), followed by Am(III) selective stripping using the hydrophilic complexing agent TS-BTPhen (3,3′,3?,3?′-[3-(1,10-phenanthroline-2,9-diyl)-1,2,4-triazine-5,5,6,6-tetrayl]tetrabenzenesulfonic acid). Distribution ratios were found at an acidity of 0.65 mol L^?1 nitric acid that allowed for the separation of Am(III) from Cm(III) (D_Cm > 1; D_Am < 1), giving a separation factor between curium and americium of SF_Cm/Am = 3.6 within the stripping step. Furthermore, Am(III) was readily separated from the lanthanides with the lowest selectivity for the Ln(III)/Am(III) separation being lanthanum with a separation factor of SF_La/Am = 20. The influence of the TS-BTPhen concentration on Am(III) distribution ratios was studied, giving a slope (logD vs. log[TS-BTPhen]) of approximately ?1 for the stripping of An(III) with TS-BTPhen from the TODGA-based organic phase. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements of curium(III) were used to analyze the speciation of Cm(III)-TS-BTPhen complexes. Both 1:1 and 1:2 complexes were identified in single-phase experiments. The formation of the 1:1 complex was suppressed in 0.5 mol L^?1 nitric acid but it was significantly present in HClO₄ at pH 3. Conditional stability constants of the complex species were calculated from the TRLFS experiments.     

Extraction of Lanthanides(III) and Am(III) by Mixtures of Malonamide and Dialkylphosphoric Acid

Abstract

N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide, DMDOHEMA, and di‐n‐hexylphosphoric acid, HDHP, are the extractants of reference for the French DIAMEX–SANEX process for the separation of trivalent actinide ions from the lanthanide ions. In this work, the extraction of Eu³⁺ and Am³⁺ by the two extractants, alone or in mixtures, has been investigated under a variety of experimental conditions. The two cations are extracted by HDHP as the M(DHP · HDHP)₃ complexes with an Eu/Am separation factor of ～10. With DMDOHEMA, Eu³⁺ and Am³⁺ are extracted as the M(NO₃)₃(DMDOHEMA)₂ disolvate species with an Am/Eu separation factor of ～2. The metal distribution ratios measured with a mixture of the two reagents indicated that almost all lanthanides are extracted equally well. The extraction of Eu³⁺ and Am³⁺ by HDHP‐DMDOHEMA mixtures exhibits a change of extraction mechanism and a reversal of selectivity taking place at ～1 M HNO₃ in the aqueous phase. Below this aqueous acidity, HDHP dominates the metal extraction by the mixture, whereas DMDOHEMA is the predominant extractant at higher aqueous acidities. Some measurements indicated apparent modest antagonism between the two extractants in the extraction of Eu³⁺ and synergism in the extraction of Am³⁺. These data were interpreted as resulting from the formation in the organic phase of mixed HDHP‐DMDOHEMA species containing two HDHP and five DMDOHEMA molecules.     

异辛酸铬中铬的测定

比较分析了异辛酸铬的2种消解方法即湿法消解和干法消解。实验结果表明,湿法消解是通过将样品溶剂蒸干、硫酸炭化、硝酸消化等方法,使样品变成三价铬溶液;干法消解是用合适的有机溶剂稀释样品,精确吸取适量的样品稀释溶液,通过干燥、炭化和干法灰化,再选择适当浓度的硫酸溶解样品等合适的化学处理方法来制备样品试验溶液。在酸性溶液中,以硝酸银作催化剂,用过硫酸铵将三价铬氧化成六价铬,用硫酸亚铁铵滴定法测定六价铬含量。2种方法所得结果误差0.2%。     

Novel Diglycolamic Acid Functionalized Iron Oxide Particles for the Mutual Separation of Eu(III) and Am(III)

Iron oxide (Fe₃O₄) particles functionalized with diglycolamic acid (Fe-DGAH) were synthesized and characterized by TG-DTA, X-Ray diffraction,¹H NMR, and scanning electron microscopy (SEM). The extraction behavior of Am(III) and Eu(III) in Fe-DGAH was studied from dilute nitric acid medium to examine the feasibility for the mutual separation of trivalent actinides and lanthanides using Fe-DGAH. For this purpose, the effect of various parameters such as the duration of equilibration and concentrations of europium, nitric acid, and diethylenetriaminepentaacetic acid (DTPA) in the aqueous phase on the distribution ratio (K_d) of Am(III) and Eu(III) was studied. The conditions needed for the efficient separation of Am(III) from Eu(III) were optimized using DTPA. The distribution ratio of ?10⁴ mL/g was obtained for both Am(III) and Eu(III) at pH 3, and it decreased with an increase in the concentration of nitric acid. However, a separation factor of Eu(III) over Am(III) of ?150 was achieved in the presence of DTPA. Rapid sorption of metal ions in the initial stages of equilibration followed by the establishment of equilibrium occurred within 2 h. The sorption data were fitted to the Langmuir adsorption model, and the apparent europium sorption capacity was determined to be ?50 mg/g. The study indicated the feasibility of using Fe-DGAH particles for magnetic separation of Eu(III) from Am(III) with high separation factors.     

Electrochemical behaviour of Mn3+/Mn2+, Co3+/Co2+ and Ce4+/Ce4+ redox mediators in methanesulfonic acid

The redox behaviour of Mn³⁺/Mn²⁺, Co³⁺/Co²⁺ and Ce⁴⁺/Ce³⁺ mediators commonly used in indirect oxidation of organic compounds were evaluated in methane sulfonic acid on a glassy carbon working electrode employing cyclic voltammetry. Manganic methanesulfonate exhibits higher instability in dilute methanesulfonic acid. The solid MnO₂ formed during disproportionation on the glassy carbon electrode further affects the reproducibility. Cobaltic methanesulfonate formation occurs only at oxygen evolution region rendering the overall oxidation process less efficient. Ceric methane sulfonate formation is highly efficient over a wide acid concentration range. Ceric methanesulfonate can also be employed over a wide temperature range to oxidize different aromatic compounds.     

Re‐use of Exhausted Ground Coffee Waste for Cr(VI) Sorption

Abstract

Exhausted ground coffee waste has been investigated as metal biosorbent for Cr(VI) from aqueous solution. Maximum metal sorption was found to occur at initial pH 3.0. Kinetic studies revealed that the initial uptake was quite rapid; nevertheless, it took five days to reach equilibrium. The value of the Langmuir maximum uptake was found to be 10.2 mg Cr(VI)/g waste. The sorbent is able to reduce hexavalent chromium to its trivalent form. A solution of 1 M NaOH was the most effective desorption agent and after 24 hours contact 42% of total chromium was desorbed in both hexavalent and trivalent oxidation states.     

ION EXCHANGE BEHAVIOUR OF CHELATING RESIN DOWEX A-1WITH ACTINIDES AND LANTHANIDES

Adsorption studies of several actinides and lanthanides have been carried out by chelating ion exchange resin Dowex A-1. The metal ions studied were Pu⁴⁺, Zr⁴⁺, UO₂ ⁺⁺, Am³⁺, Cm³⁺, Bk³⁺, Cf³⁺, Eu³⁺, and Tm³⁺. The separation factors between consecutive trivalent actinides and between Am(III) and Eu(III) have been evaluated. Mechanism of adsorption of actinides and lanthanides from different aqueous media has been discussed. An ion exchange procedure for the separation of Pu⁴⁺ and UO₂ ⁺⁺ has been developed using this resin.     

An Advanced TALSPEAK Concept for Separating Minor Actinides. Part 2. Flowsheet Test with Actinide-spiked Simulant

An Advanced TALSPEAK (trivalent actinide–lanthanide separations by phosphorus-reagent extraction from aqueous complexes) counter-current flowsheet test was demonstrated using a simulated feed spiked with radionuclides in annular centrifugal contactors. A solvent comprising 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP] or PC88A) in n-dodecane was used to extract trivalent lanthanides away from the trivalent actinides Am³⁺ and Cm³⁺, which were preferentially complexed in a citrate-buffered aqueous phase with N-(2-hydroxyethyl)ethylenediamine-N,N´,N´-triacetic acid (HEDTA). In a 24-stage demonstration test, the trivalent actinides were efficiently separated from the trivalent lanthanides with decontamination factors >1000, demonstrating the excellent performance of the chemical system. Clean actinide and lanthanide product fractions and spent solvent with very low contaminations were obtained. The results of the process test are presented and discussed.     

Electrochemical behaviour of americium ions in LiCl-KCl eutectic melt

This work presents a study on the electrochemical properties of AmCl₃ in a molten LiCl-KCl eutectic, at a temperature range of 733-833 K. Transient electrochemical techniques, such as cyclic voltammetry and chronopotentiometry, on inert metallic tungsten working electrode have been used to investigate the reduction mechanism of Am³⁺ ions. The results show that Am³⁺ is reduced to Am metal by a two-step mechanism corresponding to the Am³⁺/Am²⁺ and Am²⁺/Am⁰ transitions. Formal standard potentials of Am³⁺/Am²⁺ ( versus Cl₂/Cl⁻ at 733 K) and Am²⁺/Am⁰ ( versus Cl₂/Cl⁻ at 733 K) redox couples as well as diffusion coefficients of Am³⁺ and Am²⁺ (2.4 × 10⁻⁵ and 1.15 × 10⁻⁵ cm² s⁻¹ at 733 K, respectively) have been calculated at three different temperatures. In the studied range of temperature, the DAm3+/DAm2+ ratio was found to be around 2. In addition, thermodynamic properties have been calculated for Am³⁺ () and Am²⁺ () and compared to thermodynamic reference data in order to estimate activity coefficients (Am³⁺ = 4.7 × 10⁻³ and Am²⁺ = 2.7 × 10⁻² at 733 K) in the molten LiCl-KCl eutectic.     

Preparation of a chelating poly(β-diketone) resin from poly(vinyl alcohol) and its use in the reversible complexing of metal ions

Summary A water-insoluble poly (-diketone) chelating resin has been prepared by the controlled oxidation of poly(vinyl alcohol) with chromic acid. The polymer forms stable complexes with divalent and trivalent cations, such as Co⁺², Cu⁺², Mn⁺², Ni⁺², Fe⁺³, Au⁺³, and UO₂ ⁺², and removes them completely from dilute aqueous solution. The ions may be recovered quantitatively from the resin complex by elution with dilute aqueous acid and the resin is reusable     

Recovery of chromium from tannery effluents using a redox–adsorption approach

Adsorption isotherms for sodium and trivalent chromium uptake from aqueous solutions onto Amberlite resin were prepared at 18°C. Adsorption of each cation followed the Langmuir model. The rate of uptake of each cation was found to be film diffusion controlled with sodium showing the most rapid uptake. In aqueous solutions containing both chromium and sodium as the only cationic species, it was found that with increasing initial concentration of sodium, the trivalent chromium uptake on the resin decreased substantially. To overcome this difficulty a four step redox–adsorption system has been developed for the removal of Cr³⁺ from tannery effluents. The first step comprises the oxidation of trivalent chromium to the hexavalent form using selected common oxidising agents. The liquid effluent is then passed through an Amberlite cation-exchange resin in step 2 where the sodium in the waste stream is completely removed. The anionic hexavalent form of chromium (Cr₂O) passes unaltered through the resin along with the waste stream. In the third stage the dichromate is reduced back to the trivalent cationic form which is subsequently removed from the waste stream by a second Amberlite ion-exchange bed in stage 4. Each step in this process is assessed in batch and flow mode using simulated and real tannery effluents.     

Glycolamide-functionalized ionic liquid: Synthesis and actinide ion extraction studies

A glycolamide-functionalized ionic liquid (G-FIL) was synthesized for the first time and was evaluated for the extraction of actinide ions such as Am³⁺, Pu⁴⁺ and UO₂²⁺ and fission product element ions such as Eu³⁺, Sr²⁺ and Cs⁺. The extraction of the trivalent metal ions was found to be exceptionally high at low acid concentrations, which rapidly decreased with increasing acidity. In view of the high viscosity of the G-FIL, the studies were carried out using its diluted solution in a commercial ionic liquid, viz. 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₄mim][Tf₂N]).     

Demonstration of a TODGA‐Based Continuous Counter‐Current Extraction Process for the Partitioning of Actinides from a Simulated PUREX Raffinate,Part II: Centrifugal Contactor Runs

Abstract

The efficiency of the partitioning of trivalent actinides from a PUREX raffinate is demonstrated with a TODGA+TBP extractant mixture dissolved in an industrial aliphatic solvent TPH. Based on the results of cold and hot batch extraction studies and with the aid of computer code calculations, a continuous counter‐current process is developed and two flowsheets are tested using miniature centrifugal contactors. The feed solution used is a synthetic PUREX raffinate, spiked with ²⁴¹Am, ²⁴⁴Cm, ²⁵²Cf, ¹⁵²Eu, and ¹³⁴Cs. More than 99.9% of the trivalent actinides and lanthanides are extracted and back‐extracted and very high decontamination factors are obtained for most fission products. The co‐extraction of zirconium, molybdenum, and palladium is prevented using oxalic acid and HEDTA. However, 10% of ruthenium is extracted and only 3% is back‐extracted using diluted nitric acid. The experimental steady‐state concentration profiles of important solutes are determined and compared with model calculations and good agreement is generally obtained.     

Kinetics of oxidation of butadiene to crotonaldehyde

The oxidation of butadiene to crotonaldehyde has been investigated using an aqueous catalyst solution containing palladium chloride–cupric chloride in dilute hydrochloric acid. Unlike the oxidation of ethylene, propylene, etc., this oxidation was found to be a zero-order reaction with respect to butadiene. The effects of temperature and the concentration of Pd²⁺, Cu²⁺, Cl^? and H⁺ ions on the reaction rate were studied. The order of reaction with respect to Cl^? and H⁺ ions in this case (approximately 1.5 and ?0.25, respectively) is different from that observed in the case of lower alkenes.     

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.     

AISI 304 L stainless steel decontamination by a corrosion process using cerium IV regenerated by ozone Part I: Study of the accelerated corrosion process

This paper describes the study of a new decontamination process of AISI 304L stainless steel from dismantled nuclear power plants. A very thin active contaminated surface layer was stripped from the underlying metal by corrosion in a solution of nitric acid with the addition of cerium nitrate. The Ce⁴⁺/Ce³⁺ concentration ratio was initially equal to unity and ozone/oxygen bubbles were used to regenerate Ce³⁺ ions into Ce⁴⁺ ions. The study was performed in a laboratory cell prior to preliminary optimization in a three-litre reactor. The objective was to obtain a corrosion rate of about 10 micrometers per day. This target was reached in 10^–2 mol l^–1 of cerium nitrate with bubbling of a 1.56 g h^–1 ozone flow in a 60 l h^–1 total gas flow. The corrosion rate depended essentially on the Ce⁴⁺ concentration. The stainless steel exhibited intergranular corrosion. The corrosion rate was monitored by measuring the solution oxidizing potential using a precious metal electrode.