Removal behavior of Cs from molten salt by using zeolitic materials

Radioactive molten salt generated from a pyrochemical process to separate reusable U and TRU elements is one of problematic wastes to manage for a final disposal. For the minimization of final waste, it is desirable to selectively remove radionuclides from the waste salts. In this paper, structural change of some zeolites in a series of molten salt systems and its removal behavior of CsCl was investigated. Zeolite-4A(LTA) was transformed into LiAlSiO₄ and Li-sodalite with the mol-fraction of LiCl in LiCl–KCl system at 650 °C while it was not changed in NaCl–KCl at 750 °C, regardless of mol-fraction of metal chloride. Other commercial zeolite with specific structure (FAU) had the same trends on the structural stability in molten salt system. From the Cs removal experiments, the decomposed zeolitic materials in molten salt lost their removal ability of Cs. In conclusion, a new selective material or method should be investigated or developed for obtaining the validity on the separation of group I and II radionuclides from a molten waste salt because the zeolite 4A is unstable in the LiCl system and it also showed a low capacity in the LiCl–KCl phase. This paper gives basic information on the removal of radionuclides from molten systems by using zeolitic materials.     

Selective adsorption and separation of Cs(I) from salt lake brine by a novel surface magnetic ion-imprinted polymer

A new Cs(I) magnetic ion-imprinted polymer (Cs(I)-MIIP) aimed at the selective adsorption and separation of Cs(I) from salt lake brine was prepared. The Fe₃O₄@SiO₂ was used as supporter, Cs(I) as template ion, and carboxymethyl chitosan as functional monomer. The product was characterized by Fourier transform infrared spectra, XRD, energy-dispersive spectrometry, scanning electron microcopy, thermogravimetric analysis, and vibrating sample magnetometer. The adsorption of the Cs(I)-MIIP in solution was investigated, which indicated the maximum adsorption capacity was 36.15?mg·g^?1 under the optimum conditions. The pseudo-first-order kinetic model and the Freundlich isotherm model were applied to predict the adsorption process of Cs(I) onto Cs(I)-MIIP. Selectivity experiments showed that the relative selectivity coefficient (k′) were 24.995, 1.73, 1.43, 4.83, and 1.63 to Cs(I)/Li(I), Cs(I)/Na(I), Cs(I)/K(I), Cs(I)/Rb(I), and Cs(I)/Sr(II) binary solutions, higher than those of NIP, respectively. Furthermore, the Cs(I)-MIIP was successfully applied to the enrichment and separation of Cs(I) from the salt lake brine of Qinghai, with satisfactory Cs(I) recovery rates.     

On the existence of phases with a structure of NaZr2(PO4)3 in series of binary orthophosphates with different alkaline element to zirconium ratios

Complex phosphates M_xZr_2.25–0.25x(PO₄)₃, where M=Li, Na,K, Rb or Cs and x may be an integer or fraction from 0 to 9, have been synthesized, and their structure has been investigated. The concentration and temperature ranges of stability of the phosphate phases NaZr₂(PO₄)₃ have been found. The influence of the method for the synthesis of these phases and of the annealing temperature on their crystal properties is studied. It was found that the structure of NaZr₂(PO₄)₃ [NZP] exists in the above phosphate series when 0≤x≤5 for Na and K, 0≤x≤3 for Rb, and 0≤x≤1 for Cs. N. I. Lobachevskii Nizhnii Novgorod State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 6, pp. 1104–1113, November–December, 1996. Translated by L. Smolina     

Computer-assisted structure simulation, synthesis, and phase formation of molybdophosphates A1−x Zr2(PO4 3−x (MoO4)x (A is an alkali metal)

Structure simulation is performed for molybdophates of variable composition A_1?x Zr₂(PO₄)_3?x (MoO₄)_x, where A is Na (0≤x≤0.6), K (0≤x≤0.6), K (0≤x≤0.3), Rb (0≤x≤0.2), or Cs (0≤x≤0.1), using the minimization of the interatomic interaction energy; these molybdophosphates crystallize in the NaZr₂(PO₄)₃ (NZP) structure type. The results of the computer-assisted structure simulation are verified by the synthesis of the molybdophosphates and their characterization by X-ray powder diffraction and IR spectroscopy. The crystallization field of the NZP molybdophosphate shrinks as the alkali cation size increases. The key factors that govern the stability of the NZP structure in alkali zirconium molybdophosphates are determined.     

Selective removal of cesium and strontium by crystalline silicotitanates

Crystalline silicotitanate ion exchanger (58.5 mmol Ti, and 620 mmol Na) with 6 mmol of SiO₂ after 10 days of hydrothermal synthesis was optimized for selective removal of ⁹⁰Sr. Studies on X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy revealed that the silicotitanate is highly crystalline with bright cubic and rod like morphology with varying amounts of Ti, Si, Na, and O. The decontamination factor and distribution coefficient values for uptake of ¹³⁷Cs and ⁹⁰Sr from actual radioactive waste solutions by the ion exchanger after 24 h of equilibration was found to be 40 and 176 and 4025 ml g^?1 and 7525 ml g^?1, respectively. The exchange capacity for ⁹⁰Sr and ¹³⁷Cs was estimated to be 14.6 and 4.4 meq g^?1, respectively.     

Thermodynamic exploitation of the liquidus curves in the MIPO3–Pb(PO3)2, MIPO3–Cu(PO3)2 and MIPO3–Ce(PO3)3 systems (M I=Li, Na, K, Rb, Cs, Ag, Tl)

The thermodynamic exploitation of the solid–liquid equilibria in the M^IPO₃–Pb(PO₃)₂, M^IPO₃–Cu(PO₃)₂ and M^IPO₃–Ce(PO₃)₃ systems (with M ^I=Li, Na, K, Rb, Cs, Ag, Tl) is carried out using a semi-empirical equation of the liquidus curves already used with success for similar binary systems. The enthalpy of fusion is calculated for each pure polyphosphate on the assumption that the liquid solution is ideal and only formed by M^IPO₃ and M(PO₃)_q entities (q=2 for Pb and Cu, q=3 for M=Ce). In the most binary systems, a wide difference between the calculated values of the melting enthalpies of these polyphosphates and the measured ones determined from the DTA curves, was observed. This difference is probably due to the existence of some molecular associations in the liquid phase.     

IR study of the structure of rhombohedral zirconium and alkali metal orthophosphates

Zirconium orthophosphates with different alkali cations MZr₂(PO_{4 3}, M₂Zr(PO₄)₂, and M₅Zr(PO₄4)₃, where M is Na, K, Rb, Cs, were synthesized and studied by IR spectroscopy. X-ray diffraction, and ⁴⁰K radiometric analysis. It is confirmed that MZr₂(PO_{4 3} (M = Na, K, Rb, Cs) exist as rhombohedral phases crystallizing as NaZr₂(PO_{4 3}) (NZP) structures. For Na₅Zr(PO_{4 3} it is shown that an NZP phase with a monoclinic superstructure is formed as a result of statistical distribution of Na and Zr in the ZrO₆ octahedm and ordered distribution of sodium atoms in the interstices of the channels. Formation of K₂Zr(PO₄)₂ and K₅Zr(PO₄)₃ phases with NZP structures is shown to be possible. Translated from Zhumal Struktumoi Khimii, Vol. 41, No. 1, pp. 74-79, January-February, 2000.     

Study on a separation method of radionuclides (Ba, Sr) from LiCl salt wastes generated from the electroreduction process of spent nuclear fuel

In this paper, a separation method of radionuclides (Ba, Sr) from LiCl salt wastes generated from the electroreduction process of spent nuclear fuel was studied to recover pure LiCl salts and reduce radioactive wastes. The method consisted of chemical conversion process of BaCl₂ and SrCl₂ in LiCl molten salts by using lithium compounds and vacuum distillation process of LiCl salts. In the chemical conversion, BaCl₂ and SrCl₂ in LiCl molten salts were mainly converted into (Ba,Sr)CO₃ or (Ba,Sr)SO₄. Contents of Ba and Sr in LiCl salts recovered from the vacuum distillation process were equal to about 0.01 of initial concentrations of Ba and Sr in LiCl molten salts. These results will be utilized to recycle the LiCl salt wastes.     

Thermal Expansion in the Zr and 1-, 2-valent Complex Phosphates of NaZr2(PO4)3 (NZP) Structure

A_5–4xZr_xZr(PO₄)₃ (A=Na, K;0≤x≤1.25), Na_1-xCd_0.5xZr₂(PO₄)₃ (0≤x≤1), Na_5–xCd_0.5xZr(PO₄)₃ (0≤x≤4) compositions which belong to the NZP structural family were synthesized using the sol-gel method. The lattice thermal expansion of members of these rows were determined up to 600°C by high-temperature X-ray diffractometry. The axial thermal expansion coefficients change from -5.8·10^-6to 7.5·10^-6 °C^-1 (α_a) and from 2.6·10^–6 to 22·10^–6 °C^-1 (α_c). These results, in addition to those for other NZP compounds allow us to explain their low thermal expansion. The mechanism can be attributed to strongly bonded three-dimensional network structure, the existence of structural holes capable to damp some of the thermal vibrations and anisotropyin the thermal expansion of the lattice. This revised version was published online in August 2006 with corrections to the Cover Date.     

A new type of orthoborates: ASr4La3(BO3)6 (A = Li,Na)

Two new rare earth containing orthoborate crystals ASr₄La₃(BO₃)₆ (A = Li, Na) have been obtained by spontaneous nucleation from high-temperature melts of A₂O–SrO–La₂O₃–B₂O₃–AF. X-ray diffraction analyses show that they both crystallize in the rhombohedral space group R-3 with cell parameters of a = 12.309(7) Å, c = 9.316(7) Å and a = 12.4049(13) Å, c = 9.348(2) Å for the Li and Na compounds respectively. Similar to the large A′₆MM′(BO₃)₆ family, these compounds are all related to the structure of Sr₃Y(BO₃)₃ with La and Sr statistically occupy the Sr site, and the alkaline elements and remaining Sr enter the ordered Y1 and Y2 sites, which can be approximately represented as (La_2.91Sr_3.09)(La_0.09Sr_0.91)Li[B₆O₁₈] and (La_2.85Sr_3.15)(La_0.15Sr_0.85)Na[B₆O₁₈]. The characteristic of the structure is that the La/Sr and isolated BO₃ groups form a network with tunnels along the c-axis where the alkaline A and Sr ions alternatively reside. The optical transmission spectrum shows that the ultraviolet absorption edge of NaSr₄La₃(BO₃)₆ crystal is about 193 nm and Raman spectra reveal that both crystals possess sharp peaks at 930 cm⁻¹.     

Electronegativity force of cations and thermal decomposition of complex fluorides

The thermal decomposition of anhydrous fluoroborates MBF₄ (M=Li, Na, K, Rb, Cs) and M(BF₄)₂ (M=Ca, Sr, Ba) was investigated. The decomposition proceeds according to a simple acid-base mechanism with evolution of BF₃. The influence of the acidity of cationic counterions, expressed by the electronegativity force on the course of thermal decomposition was estimated quantitatively.     

Mössbauer study of photolysis and γ-radiolysis of alkali bis(citrato) ferrates(III)

The photolysis of alkali bis(citrato) ferrates(III) M₃Fe(cit)₂·xH₂O (M = Li, Na, K, Cs, NH₄) in solid and solution phases and γ-radiolysis in solid state has been investigated using Mössbauer and IR spectroscopic techniques. The formation of iron(II) species as the ultimate product in all these complexes has been observed except the solid state photolysis of potassium bis(citrato) ferrate(III) in which the intermediate iron(II) moiety is oxidized to an octahedral iron(III) species.     

A New Carrier for Direct Spectrographic Determination of Trace Alkalies and Alkaline Earths in High Purity Thorium Oxide

Abstract

A d.c. arc emission spectrographic method is described for the determination of sub ppm levels of Ba, Li and Sr and ppm levels of Cs, K and Na in high purity thorium oxide. The method which employs RbCl as carrier is simple and rapid and does not involve the use of any special atmosphere for exciting the sample. It was observed that RbCl shows definite improvement over AgCl in carrier action. The carrier distillation technique reported makes possible the following range of estimations: Li: 0.02 – 5.0 ppm, Ba, Sr: 0.5 – 20 ppm, Cs: 2–50 ppm, K,Na: 5–100 ppm. The detection limit obtained by this method for Li and Sr is lower than that obtained by the earlier carrier-distillation methods reported as well as other direct sensitive techniques of Zeidel and Avni for the analysis of Tho₂. The precision of the method ranges from 8% for Cs to 17% for Ba. Volatilization studies on the choice of carrier material are presented.     

Ammonium-Alkali-Hexafluorometallate(lll) vom Elpasolith-Typ

Inhaltsübersicht. Durch Festkörperreaktion in Gold- oder Platinampullen unter Druck wurde die Darstellung von Ammonium-Alkali-Hexafluorometallaten(III) vom Typ (NH₄)₂AMF₆ (A = Li, Na, K, Rb) und A₂NH₄MF₆ (A = Eb, Cs) mit M = Al, Ga, Cr, Fe und V versucht. Die Verbindungen (NH₄)₂NaMF₆, (NH₄)₂KMF₆ und Cs₂NH₄MF₆ kristallisieren kubisch flächenzentriert im Elpasolith-Typ, wie aus Röntgenpulveraufnahmen, z. T. auch durch Intensitätsrechnung, belegt wird. Die Ammoniumionen liegen hier entweder in reiner 12facher (Na- und K-Verbindung) oder in reiner 6facher Koordination (Cs-Verbindung) vor. Ammonium Alkali Hexafluorometallates(III) of Elpasolite Type The preparation of ammonium alkali hexafluorometallates(III) of type (NH₄)₂AMF₆ (A = Li, Na, K, Rb) and A₂NH₄MF₆ (A = Rb, Cs), where M means Al, Ga, Cr, Fe and V, was attempted (by solid state reaction in sealed gold or platinum tubes under pressure. The compounds (NH₄)₂NaMF₆, (NH₄)₂KMF₆ and Cs₂NH₄MF₆ crystallize cubic face centered in the elpasolite structure as could be showed by X-ray powder patterns, in part by calculations of intensities. The ammonium ion have the coordination number 12 (Na and K compounds) or 6 respectively (Cs compounds).     

Role of interlayer M k atoms and H2O molecules in the structure formation of M k (VUO6) k · nH2O uranovanadates

M ^k (VUO₆) _k · nH₂O uranovanadates of alkali (Li, Na, K, Rb, Cs), alkaline-earth (Mg, Ca, Sr, Ba), 3d transition (Mn, Fe, Co, Ni, Cu, Zn), and rare-earth (Y, La, Ln) elements were prepared by precipitation from solutions under hydrothermal conditions and in solid-phase reactions. The composition and structure of these compounds and the role of M ^k atoms and H₂O molecules in the formation of their structure were studied by X-ray diffraction, IR-spectroscopy, thermal analysis, and chemical analysis.     

喹啉氧基乙酰胺的Li(I)/Na(I)配合物及其高氯酸盐的结构和荧光性质

合成并通过X射线单晶衍射表征了配合物[Li（L）₂]ClO₄（1）和[Na（L）₂]ClO₄（2）的结构（L为2-（5-氯-喹啉-8-基氧基）1-吡咯烷酮）。单晶衍射结果表明,配合物1与2同构,金属离子与来自2个酰胺配体L的N₂O₄电子供体配位,形成扭曲的八面体配位构型。此外,还测定了配体高氯酸盐（HL） ClO₄·H₂O的结构,并详细研究了3个化合物的荧光性质。     

Thermal Study of A2O–(MoO3)2–P2O5 (A=Li, Na) Glasses

Alkali phosphomolybdate glasses have been prepared by quenching melted mixtures of P₂O₅, MoO₃ and A₂O(A=Li, Na). The composition dependence of the transition temperature of glasses belonging to ternary A₂O–(MoO₃)₂–P₂O₅ (A=Li, Na) systems is studied for several series of glasses corresponding to either a fixed A₂O rate or a constant Mo/P ratio. The interpretation of the results is based on the presence of different types of molybdenum and phosphorous structural groups and P–O–M (M=P, Mo) linkages in glasses. This revised version was published online in August 2006 with corrections to the Cover Date.     

EMK-Messungen in binären ladungsunsymmetrischen Salzschmelzen aus Bariumchlorid und Alkalimetallchloriden

EMF Measurements in Binary Chargeunsymmetrical Salt Melts of Barium- and Alkali Chlorides The EMF is measured of cells with transference of the type Cl₂[C]/MCl//MCl? BaCl₂(x)/[C]Cl₂ in the molten mixtures BaCl₂? MCl (M ? Li, Na, K, Rb, Cs). From the EMF values and values of activities from another independent methods the transference numbers of the cations Ba²⁺ and M⁺ relative to the chloride ion in the molten mixtures BaCl₂? (Li, Na, K) Cl are calculated. The values of activities for the system BaCl₂? LiCl are calculated from cryoscopic analysis of the phase diagram.     

Syntheses and Crystal Structures of Novel Ternary Alkali Metal Gold Acetylides MIAuC2 (MI = Li,Na, K,Rb, Cs)

By the reaction of AuI with alkali metal hydrogen acetylides M^IC₂H (M^I = Li–Cs) in liquid ammonia and subsequent heating of the remaining residue in refluxing pyridine (M^I = Li, Na, K) or as a solid phase at about 110 °C in vacuum (M^I = Rb, Cs) ternary alkali metal gold acetylides M^IAuC₂ were obtained. Their crystal structures were investigated by the means of X‐ray powder diffraction. [Au(C₂)_2/2^–] chains are the characteristic structural motif which are packed in a hexagonal (LiAgC₂) and tetragonal arrangement (NaAuC₂–CsAuC₂), respectively. Simple calculations based on the close packing of rods and spheres can explain these different arrangements. The existence of C–C triple bonds in the title compounds is confirmed by Raman spectroscopic investigations.     

Effect of cationic composition of melts M2WO4-M2W2O7-UO2WO4 (M = Li, Na, K, Cs) and parameters of electrolysis to uranium dioxide electrodeposition characteristics

The effect of solvent salt cation, temperature of electrolysis, and cathodic deposition potential to basic characteristics of uranium dioxide potentiostatic electrodeposition (cathodic current efficiency, current density, and product deposition rate) in electrolyte system M₂WO₄-M₂W₂O₇-UO₂WO₄ (M = Li, Na, K, Cs) was studied in air. A conclusion was made that optimum electrodeposition and production of deposits not contaminated with supporting electrolyte decomposition products need higher cathodic polarization close to the solvent decomposition potentials and higher temperatures (up to 900°C). A melt based on K₂WO₄ was selected as the electrolyte providing satisfactory electrodeposition parameters of uranium dioxide with the composition close to stoichiometric.