Study on a recovery of rare earth oxides from a LiCl-KCl-RECl3 system

Radioactive rare earth chlorides in waste LiCl-KCl molten salts have to be separated as a stable form to minimize waste volume and to achieve stable solidification. In this work, thermal behavior of rare earth chlorides (CeCl₃, GdCl₃, NdCl₃, PrCl₃) was investigated in an oxygen condition to recover rare earth oxides from a LiCl-KCl-RECl₃ system. The rare earth chlorides in the LiCl-KCl molten salts were smoothly converted to an oxychloride form at a higher temperature than 650 °C, except for CeCl₃. CeCl₃ was totally converted to an oxide from at a higher temperature than 450 °C. The rare earth oxychlorides (GdOCl, NdOCl, PrOCl) were effectively converted to oxide forms at a higher temperature than 1100 °C. It was confirmed that rare earth oxides can be recovered from a LiCl-KCl-RECl₃ system without impurity generation.     

Extraction mechanisms of uranyl ions by 1-butyl-3-methylimidazolium nonafluorobutanesulfonate containing N-dodecyl-2-pyrrolidone

Extraction of U(VI) in HNO₃ to 1-butyl-3-methylimidazolium nonafluorobutanesulfonate (BMINfO) by using N-dodecyl-2-pyrrolidone as an extractant has been investigated. With increasing the concentration of HNO₃ from 0.01 to 3.0 mol/dm³ (M), distribution ratio decreased. This suggests that uranyl ions are extracted by ion exchange with a cation component of BMINfO, i.e. BMI⁺. The amount of BMI⁺ transferred to aqueous phase accompanied by extraction of U(VI) was evaluated with ¹H NMR measurement. Plots of the amount of U(VI) extracted versus the amount of BMI⁺ transferred from BMINfO phase to the aqueous phase indicated linear relationship. The slope of the line was about 1.0 and 0.63 in the extraction system of U(VI) performed in 0.1 and 1.0 M HNO₃, respectively. This result means that two types of extraction mechanisms exist depending on the concentration of HNO₃. One is the ion exchange mechanism. Another is the ion-pair extraction mechanism.     

Rapid Separation of Fission-Product Rare Earths and Yttrium by Electromigration

The separation of fission-product La, Ce, Pr, Nd and Y was performed in 4 min by electro-migration. As complexing agent, nitrilotriacetic acid was used at two concentrations of the NTA ion selected so as to optimize mutual separation of the elements. Rapid location of the zone on the paper strip reached after migration was obtained by color reaction of the carrier added to the irradiated sample. The purity of the elements thus separated was checked by γ-ray spectrometry. At the higher concentration of NTA ([[NTA]=1.0×10^?2M, pH=4.1) under which all of rare earths and Y migrate toward the anode, the elements were well separated from each other, although appreciable amounts of other F.P. were also found in each fraction. On the other hand, at the lower NTA concentration ([NTA]=4.0 × 10^?3M, pH=2.0) where the F.P. all migrate toward the cathode, each zone contained the isotopes of the respective element almost exclusively, except for a few small photo-peaks attributable to other elements. In each fraction, the 92.5 min ¹⁴²La and 14 min ¹⁴³La, the 14 min ¹⁴⁶Ce (24 min ¹⁴⁶Pr), the 24 min ¹⁴⁶Pr and 12 min ¹⁴⁷Pr, the 1.8 hr ¹⁴⁹Nd, the 20.3 min ⁹⁴Y and 10.9 min ⁹⁵Y were identified from the energies of photo-peaks and their decay rates.     

Solvent Extraction of Pentavalent Neptunium with n-Octyl(phenyl)-N,N-Diisobutyl- carbamoylmethylphosphine Oxide

Solvent extraction of Np(V) from HNO₃ solution was experimentally studied with n-octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) as an extractant mixed with TBP and n-dodecane. In the low HNO₃ concentration, the Np(V) is weakly extractable, but effectively extracted in the high HNO₃ concentration (>4M) due to the disproportionation of Np(V) to Np(IV)and Np(VI). The distribution ratio of Np was increased by use of H₂O₂as a reductant of Np(V). More than 95% of Np was extracted with 0.8 M H₂O² in 2.2 M HNO₃ solution. It was shown that most of the Np extracted is in tetravalent state as expected from redox mechanism. The Np(IV) extracted in the organic phase was effectively stripped to the aqueous phase with H₂C₂O₄.     

Calculation of Distribution Ratios of Rare Earth Elements in Multistage Counter Current Extraction with HDEHP

Extraction of rare earth elements with di (2-ethylhexyl) phosphoric acid (HDEHP) - tributyl-phosphate (TBP)-n-paraffin system was studied as functions of concentrations of the quantity of H⁺ released into aqueous phase. The ratio of rare earth elements extracted into organic phase was found to depend on the initial composition of the aqueous solution. The ratios determined for various concentrations of rare earth elements and acid were shown as a linear function of the concentrations of acid in aqueous phase and that of rare earth elements in organic phase after extraction. The acid concentration in aqueous phase after extraction can be estimated from any initial concentrations of acid and rare earth elements in aqueous solution by this equation. Also a graphic process of experimental results could give approximate values of distribution ratio for various initial concentrations of rare earth elements and nitric acid. For calculation of the distribution ratio of each stage in multi-stage counter current extraction, a computation code was programmed on the basis of the graphical process. The calculated values agreed well with those obtained experimentally in multistage extraction.     

Simultaneous separation and recovery of Cs(I) and Sr(II) using a hybrid macrocyclic compounds loaded adsorbent. Kinetic,equilibrium and dynamic adsorption studies

In this study, simultaneous separation and recovery of Cs(I) and Sr(II) from nitric acid solution was investigated using a silica-based hybrid adsorbent. The adsorbent was prepared by successive impregnation and fixing of two supramolecular recognition agents namely, 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-Calix[4]-arene(Calix[4]arene-R14) and 4',4' (5")-di(tert-butylcyclohexano)-18-crown-6, onto a silica-based polymer support(SiO₂-P). Uptake properties, characterization, equilibrium kinetics, and dynamic adsorption properties of Cs(I) and Sr(II) were then assessed. Distribution coefficients (K_d) higher than 10² cm³/g for Cs(I) and Sr(II) were obtained using 3 M HNO₃ at 298 K, and the K_d values decreased with increasing temperature. Adsorption kinetics and equilibrium studies fitted well with pseudo-second-order model and Redlich–Peterson isotherm model, respectively. The constant total organic carbon values in the aqueous phase were obtained after adding 10^?3 ～ 4 M HNO₃. Results of the dynamic adsorption/elution test indicated that Cs(I) and Sr(II) were efficiently and simultaneously captured and eluted even under a flow rate of 1.5 cm³/min.     

Characteristics of Oxidation Reaction of Rare-earth Chlorides for Precipitation in LiCl-KCl Molten Salt by Oxygen Sparging

The precipitation reaction of some rare earth chlorides (La/Ce/Nd/GdCl3) in a LiCl-KCl molten salt has been carried out by using the oxygen sparging method. In this study, regardless of the oxygen sparging time and the molten salt temperature, oxychlorides (REOCl) for LaCl₃, NdCl₃ and GdCl₃, and an oxide (REO₂) for CeCl₃ are formed as a precipitate. The conversion of rare-earth chlorides into insoluble precipitates was described by using a conversion ratio. The conversion ratio increased exponentially with the oxygen sparging time and finally showed asymptotic value at 1,023 K of the molten salt temperature condition. The conversion ratios of LaCl₃, NdCl₃ and GdCl₃ were increased with the molten salt temperature, however, even though the conversion ratio was increased from 0.660 to 0.995 with increasing molten salt temperature from 823 to 923 K at 60 min of a sparging time, the values of the conversion ratio of CeCl₃ were nearly constant (over 0.999) with the molten salt temperature. As a result of the thermogravimetric analysis of the precipitates (oxychlorides), about 11–13% of a weight loss happened in the case of LaOCl, NdOCl and GdOCl, and all the oxychlorides were converted to their oxides i.e. La₂O₃, Nd₂O₃ and Gd₂O₃ at a high temperature and oxygen atmosphere.     

Effect of Nd and Pr addition on the thermal and mechanical properties of (U, Ce)O2

The thermal conductivity, Young’s modulus, and hardness of (U_0.65−xCe_0.3Pr_0.05Nd_x)O₂ (x = 0.01, 0.08, 0.12) were evaluated and the effect of Pr and Nd addition on the properties of (U, Ce)O₂ were studied. The polycrystalline high-density pellets were prepared with solid state reactions of UO₂, CeO₂, Pr₂O₃, and Nd₂O₃. We confirmed that all Ce, Pr, and Nd dissolved in UO₂ and formed solid solutions of (U, Ce, Pr, Nd)O₂. We revealed that the thermal conductivity of (U_0.65−xCe_0.3Pr_0.05Nd_x)O₂ (x = 0.12) was up to 25% lower than that of x = 0.01 at room temperature. The Young’s modulus of (U_0.65−xCe_0.3Pr_0.05Nd_x)O₂ decreased with x, whereas the hardness values were constant in the investigated x range.     

Prediction of corrosion product stability in high-temperature aqueous systems

Calculated thermodynamic data for metal oxidation/oxide reduction reactions of Fe, Ni, Co and Cu, and for formation, oxidation and reduction of NiFe₂O₄, CoFe₂O₄, CuFeO₂ and CuFe₂O₄, are examined for aqueous systems containing dissolved hydrogen and oxygen at temperatures up to 300°C. The data are presented as equilibrium partial pressures of oxygen and hydrogen for specific reactions. This information is used to predict which solids are stable in an equilibrium system containing known concentrations of oxygen and hydrogen, and in a non-equilibrium system in which γ and neutron radiation fields cause the concentrations of oxygen and hydrogen to be much greater than the equilibrium values. Results of X-ray diffraction studies of corrosion products filtered from the heat-transport system of the Douglas Point Generating Station are compared with phase stability predictions.     

辛醇溶液、水溶液、固态及液-液萃取体系中TRDGA与Pr(Ⅲ)的配位研究

为加深对四烷基-3-氧杂-戊二酰胺（TRDGA）类配体与三价锕/镧离子配位的认识,利用光谱及单晶X射线衍射分析技术,分别在含水辛醇溶液、水溶液、晶体及液-液萃取体系中对比研究了脂溶性N,N′-二甲基-N,N′-二辛基-3-氧杂-戊二酰胺（DMDODGA,L）以及水溶性四甲基-3-氧杂-戊二酰胺（TMDGA,L′）与Pr(Ⅲ)的配位。光谱滴定实验结果表明,两配体在溶液中均可与Pr(Ⅲ)形成金属离子与配体比值为1∶1、1∶2及1∶3的配合物,并获得了配合物稳定常数及标准吸收光谱。配合物中金属离子与配体比值相同时,L和L′与Pr(Ⅲ)形成的每对配合物中Pr(Ⅲ)特征吸收峰的位置及形状均几乎完全相同,说明每对配合物的内配位层结构相同或相近。PrL′3(ClO4)3晶体漫反射光谱与PrL3+3及PrL′3+3标准吸收光谱的特征也相同,说明1∶3配合物均为三帽三棱柱配位构型。与加入硝酸根的光谱滴定实验相结合,通过有机相吸收光谱与已知固体/溶液配合物的漫反射/吸收光谱对比,确定了液-液萃取萃合物中,Pr(Ⅲ)至少有PrL2(NO3)(H2O)2+和PrL3+3 2种化学形态。     

N,N'-二(2-乙基己基)二甘酰胺酸对Dy(Ⅲ)的萃取

以正十二烷作为稀释剂,研究了N,N'-二(2-乙基己基)二甘酰胺酸(HDEHDGA,简称HL)萃取剂对硝酸介质中Dy(Ⅲ)离子的萃取性能。结果表明:该萃取剂对Dy(Ⅲ)有良好的萃取性能,在硝酸浓度为0.3~4.0mol/L时,Dy(Ⅲ)的分配比(D(Dy))随水溶液中平衡酸度的增加先减小后增大,在HNO_3浓度大约为1.0mol/L时,分配比最小。萃取分配比随水相硝酸浓度变化的关系表明,HDEHDGA萃取Dy(Ⅲ)的机理随硝酸浓度变化而不同。从3.0mol/L HNO_3中萃取Dy(Ⅲ)的分配比与萃取剂浓度及硝酸根浓度的关系表明,萃取过程中HDEHDGA主要以中性萃取剂形式与Dy(Ⅲ)配位,萃取反应方程式可能为:Dy(Ⅲ)+2HL+3NO_3~-=Dy(Ⅲ))(HL)_2(NO_3)_3该反应为放热反应,反应的热焓为-63.38kJ/mol,降低萃取温度有利于HDEHDGA对Dy(Ⅲ)的萃取。     

The heats of formation of UAl2, UAl3, and UAl4

Preparations of the intermetallic compounds UAl₂, UAl₃ and UAl₄ were obtained by high-temperature interdiffusion of aluminum and dispersed uranium, prepared by decomposing its hydride then grinding the product and heating the powder obtained. Debye x-radiographic investigation showed that the preparations obtained consisted of one phase and the parameters of their structures were close to those published earlier. The amount of hydrogen evolved during separate solution of the preparations and the starting components in a specially selected solvent (mixture of HCl, H₃PO₄, Na₂SiF₆, H₂PtCl₅ and CuSO₄· 5H₂O) Indicated that the preparations had the compositions; UAl_1.997, UAl_2.994 and UAl_3.997.The differences in the heats of solution of these preparations and appropriate mixtures of their components gave die heats of formation (–H°₂₉₃)UAl₂, UAl₃ and UAl₄, which were 22.3±2.4, 25.2±2.2 and 31.2±3.1 kcal/mole, respectively.The authors would like to thank N. T. Chebotarev and P. N. Petrov for the x-radiographic analyses of the preparations, T. S. Men'shikova for the metallographic investigation and L. M. Kopytin for his valuable advice and interest in the work.     

Stability constants of nitrate complexes of trivalent plutonium in aqueous and tributyl phosphate solutions

The extractability of nitrate complexes of trivalent plutonium from an aqueous phase at various concentrations was investigated. It was shown that tributyl phosphate (TBP) will extract trivalent plutonium from nitric acid solutions in the form of Pu(NO₃)₃. TBP at nitrate ion concentrations up to 1.2 M. Under the conditions studied, the distribution coefficient of trivalent plutonium depended very little on the concentration of hydrogen ions. The stability constants of the complexes Pu(NO₃)₃ · 3TBP, Pu(NO₃)₃, Pu(NO₃) ₂ ⁺ and Pu(NO₃)²⁺ were determined and equaled 0.75 ± 0.1; 14.4 ± 0.8; 14.3 ± 0.8 and 5.9 ± 0.5.     

Synthesis of rare earth phosphates in molten LiCl-KCl eutectic: Application to preliminary treatment of chlorinated waste streams containing fission products

The precipitation of rare earth phosphates (RE = La, Ce, Pr, Nd, and Lu), from RECl₃ was investigated in molten LiCl-KCl eutectic at 500 °C in air. Ammonium dihydrogenphosphate (NH₄H₂PO₄) was used as the phosphorus precursor. X-ray diffraction analysis indicated the formation of compounds with monazite (La, Ce, Pr, and Nd) or xenotime (Lu) structures. ³¹P NMR spectroscopy measurements confirmed that lanthanum formed pure monazite, which indicates a LaCl₃ → LaPO₄ conversion factor near 100%. These results demonstrate that the stoichiometric addition of NH₄H₂PO₄ is sufficient to obtain quantitative precipitation at 500 °C of anhydrous rare earth phosphates in molten LiCl-KCl. The use of this type of precursor, which has the advantage of not modifying the chemical composition of the medium after recovery of the rare earth phosphates, could be considered during the first step of purification of chlorinated baths containing fission products arising from spent fuel reprocessing by a pyrochemical process.     

Electrolysis of Burnup-Simulated Uranium Nitride Fuels in LiCl-KCl Eutectic Melts

The electrochemical behavior of burnup-simulated uranium nitride fuels containing representative solid fission product elements, UN+Mo (Mo = 2.84 wt%), UN+Pd (Pd = 4.6 wt%) and (U, Nd)N (NdN = 8.0 wt%), was investigated in the molten LiCl-KCl eutectic salt with 0.54 wt% UCl₃ in order to clarify the effects of fission products on the dissolution of actinide nitrides and the behavior of FPs in the electrorefining of spent nitride fuel. The rest potentials of burnup-simulated UN pellets were similar to that of pure UN. The electrochemical dissolution of UN began at about _0:75V vs Ag/AgCl reference electrode in all samples as well as that of pure UN. After the electrolyses at the constant anodic potential of ?0:65––0:60V vs Ag/AgCl, most of UN was dissolved into LiCl-KCl as UCl₃ at the anode, and U was recovered in the liquid Cd cathode in all samples. Furthermore, Nd was dissolved at the anode and accumulated into LiCl-KCl as NdCl₃, while Mo and Pd were not dissolved but remained at the anode.     

New Phase Transitions in Non-Stoichiometric U3O8-x at High Temperatures, (I)

The phase equilibrium of non-stoichiometric U₃O_8-x has been studied by thermogravimetry in the range 765°≦T≦995°C and 10^?4≦Po₂≦1 atm. The results suggest the presence of six phases within U₃O_8-x the phase, separated by second (or higher) order transitions. The relative partial molar free energies, enthalpies and entropies within an each of the six phases, as well as the standard free energies, enthalpies and entropies for the phase changes are calculated and compared with previous works.     

(DdO)2DGA萃取Nd(Ⅲ)形成三相的研究

N,N′-二辛基-N,N′-二(十二烷基)-3-氧戊二酰胺（(DdO)₂DGA）是一种用于提取高放废液中三价锕系、镧系元素的不对称酰胺荚醚萃取剂，为确定其在萃取时的三相行为，本文以镧系元素中的代表性元素Nd为研究对象，考察酸度、温度、共存离子浓度对(DdO)₂DGA-正十二烷体系萃取Nd(Ⅲ)的极限有机相浓度（LOC）的影响，并采用红外光谱、紫外-可见吸收光谱、荧光光谱研究了三相出现前后(DdO)₂DGA-Nd(Ⅲ)萃合物结构的变化。结果表明，降低酸度、升高温度、降低共存离子浓度，Nd(Ⅲ)的LOC增加，但三相出现前后，萃合物结构没有改变，三相的形成是由于萃合物聚集形态改变所致。     

Third Phase Formation in Extraction of Nd(Ⅲ) by (DdO)2DGA

N,N′-di-octyl-N,N′-di-dodecyl-3-oxapentane-1,5-diamide ((DdO)₂DGA) is a new unsymmetrical diglycolamide extractant for the separation of trivalent actinides and lanthanides from high level liquid waste. In this paper, the representative element Nd in lanthanides was taken as the research object to study the third phase formation behavior of Nd(Ⅲ) in (DdO)₂DGA, the influence of aqueous phase acidity, temperature and co-existing metal ion concentration on the limiting organic concentration (LOC) of Nd(Ⅲ) in (DdO)₂DGA/n-dodecane solution was investigated. The structural variation of (DdO)₂DGA-Nd(Ⅲ) complex formed in the organic phase before and after third phase formation was also studied by infrared spectra, UV-vis spectra and fluorescence spectra. The results show that LOC of Nd(Ⅲ) increases with temperature, and decreases with increase of aqueous acidity and co-existing metal ion concentration. However, the structure of (DdO)₂DGA-Nd(Ⅲ) complex is not varied before and after third phase formation, and the reason for third phase formation is the variation of aggregation behavior of extracted complexes.     

冠醚-1,2-二氯乙烷在苦味酸体系中对轻希土元素的萃取

本文在文献[1]的基础上,研究了二环己基-18-冠-6(DC18C6)和二环己基-15-冠-5(DC15C5)在苦味酸体系中对La~(3+),Ce~(3+),Pr~(3+),Nd~(3+),Sm~(3+),Eu~(3+),Gd~(3+)七个轻希土元素的萃取,求得了萃合常数和萃合物在有机相中的离解常数,并测定了苦味酸在水相对七个希土元素的一级络合常数。