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.     

Low‐Temperature Molten‐Salt Production of Silicon Nanowires by the Electrochemical Reduction of CaSiO3

Silicon is an extremely important technological material, but its current industrial production by the carbothermic reduction of SiO₂ is energy intensive and generates CO₂ emissions. Herein, we developed a more sustainable method to produce silicon nanowires (Si NWs) in bulk quantities through the direct electrochemical reduction of CaSiO₃, an abundant and inexpensive Si source soluble in molten salts, at a low temperature of 650 °C by using low‐melting‐point ternary molten salts CaCl₂–MgCl₂–NaCl, which still retains high CaSiO₃ solubility, and a supporting electrolyte of CaO, which facilitates the transport of O²⁻ anions, drastically improves the reaction kinetics, and enables the electrolysis at low temperatures. The Si nanowire product can be used as high‐capacity Li‐ion battery anode materials with excellent cycling performance. This environmentally friendly strategy for the practical production of Si at lower temperatures can be applied to other molten salt systems and is also promising for waste glass and coal ash recycling.     

Inorganic Molten Salts as Solvents for Cellulose

Inorganic molten salts can be used as efficient solvents for cellulose in a wide range of degrees of polymerization. Furthermore, molten salts can be applied as reaction medium for the derivatization of cellulose. For both dissolution and derivatization of cellulose, knowledge of the solution state as well as information about chemical interactions with the solvent system is essential. Using the melts of LiClO₄·3H₂O, NaSCN/KSCN/LiSCN·2H₂O and LiCl/ZnCl₂/H₂O as cellulose solvents, factors which determine the dissolving ability will be discussed. Besides the specific structure of the molten salt hydrate, the cation and the water content of the melt are the most important factors for the dissolving capability of a molten salt hydrate system. FT-Raman spectroscopy, ⁷Li and ¹³C NMR spectroscopy were applied to describe solvent–cellulose interactions and the state of cellulose dissolved in the molten salts. Using Raman and solid state NMR spectroscopy it was proved that cellulose is amorphous in the frozen solvent system. The application of inorganic molten salts as a medium for cellulose functionalization is demonstrated for cellulose carboxymethylation and acetylation.     

锕系元素在熔盐体系中的电化学及萃取特性研究进展

熔融盐是一类非水溶剂,分为高温熔盐、室温熔盐和低温熔盐。 作为反应介质和电解介质,因其优良性能,可以溶解很多难溶于水的活泼金属。 近年来,该领域的研究热点是将熔盐作为干法后处理的电解质分离和回收锕系元素。 本文综述了锕系元素在高温熔盐中的电化学行为、热力学等物理特性,介绍了近几年室温离子液体(RTILs)的研究进展及锕系元素在RTILs中萃取特性的最新研究成果,展望了熔盐体系未来的研究方向。     

Synthesis of Al Nanopowders in an Anodic Arc

Nanopowders of metals and metal oxides have been produced using an arc operated between a refractory rod anode and a hollow cathode (J. Haidar in A method and apparatus for production of material vapour, Australian Patent No. 756273, 1999). the arc attachment to the anode is through a small region of molten metal located at the tip of the rod anode. Heat from the arc evaporates the molten metal and the vapour is passed through the arc plasma before condensing into sub-micron particles downstream of the cathode. A precursor metal is continuously fed onto the tip of the anode to maintain the molten metal region and compensate for losses of materials due to evaporation. The particle size of the produced powder depends on the pressure in the arc chamber and for production of nanoparticles in the range below 100 nm we use a pressure of 100 torr. Aluminium has been used as a precursor material, leading to production of aluminium metal nanopowders when the arc is operated in argon and to aluminium oxide nanopowders for operation in air. For operation in air, the products are made of γ-Al₂O₃.     

Evaluating physical properties of molten salt reactor fluoride mixtures

In the last years, interest in the use of high-temperature molten fluoride salts as fluid fuels and coolants in nuclear power systems has been increasing. The comprehensive information on the properties of molten fuel and coolant salts is necessary for development of new designs. Experimental data on physical properties of some prospective molten salt mixtures of Li, Na, Be, Zr fluorides containing fertile and fissile materials as well as soluble fission products are unknown. At the first stage of the conceptual development estimation of the required properties from the known experimental data can be useful for selection of suitable molten salt compositions. In this paper the approaches for estimation of the physicochemical properties such as density (ρ), dynamic viscosity (η), isobaric heat capacity (c_p), and thermal conductivity (λ) for molten salt fluoride mixtures are proposed. The calculation algorithm was based on the additivity principle for the properties (P_x) of multi-component molten salt mixtures, which can be found from the relationship P_x = ΣN_iP_i. Here N_i and P_i denote mole fraction and corresponding property of individual molten salts or their binary mixtures as constituents of the more complex systems. The empirical expressions connecting the property with molar volume and molecular mass of selected fluoride compositions are also derived and tested. Estimated values are compared with each other and available experimental data.     

Thermodynamic evaluation of the intermolecular interactions of potassium fluoride crystal dihydrate in gas chromatography

Summary Potassium fluoride crystal dihydrate is used as the stationary phase for the rapid analysis of polar compounds in aqueous solutions. KF·2H₂O is compared with some conventional stationary phases, organic salts and molten crystal hydrates of inorganic salts.     

Short range order in molten Al–Si alloys

We have studied the microscopic structure such as, concentration fluctuation in long wavelength limit (S_CC(0)), Warren–Cowely short range order parameter (α ₁), ratio of mutual and intrinsic diffusion coefficients (D _M/D _id) of molten Al–Si alloy at 1700?K using a statistical model of complex formation on the basis of quasi-lattice theory for weakly interacting systems. The approach used in this article reveals that molten Al–Si alloy at 1700?K is a weakly interacting heterocoordinating system and the alloy is more ordered in the Al-rich end.     

Electrochemical synthesis of coatings in the system Ti-Si-B from molten salts

Powder and coatings of metal-like refractory compounds (MLRC) can be produced by electrochemical synthesis from molten salts. The stoichiometry of the deposited MLRC was found to correlate with the molar ratio of MLRC component ions in the melts. The system Ti-Si-B is of particular interest in terms of electrochemical synthesis since the titanium, silicon and boron potentials in the melt are close together. The electrochemical synthesis has been investigated in the system NaCl-KCl-NaF-K₂TiF₆-K₂SiF₆-KBF₄ at 700°C. The opportunity of deposition of new ternary compound in the system Ti-Si-B is shown by the electrochemical synthesis from molten salts.     

The cohesive energy of molten salts and its density

The cohesive energies ces of uni-univalent molten salts and the corresponding cohesive energy densities ceds and solubility parameters δ were calculated from literature data. The ceds are much larger than the internal pressures, P_i, as expected for highly structured liquids. The solubility parameters δ are too large to be significant for the solubility of the solutes, except gases, in these molten salts.     

熔盐体系及有关应用的新进展

介绍近年来熔盐体系的概况,着重室温熔盐的发展.熔盐在电化学制备合金和功能材料、能源、分析和分离、用作反应介质和催化剂、环境保护等方面应用前景良好.     

Vibrational spectra of molten and aqueous NaClO3 and KClO3

Raman spectra of molten NaClO₃ and KClO₃ and of aqueous solutions of these salts were measured over the frequency interval from 50 to 1200 cm⁻¹|. Infrared emission spectra of the molten chlorates and of chlorate-nitrate mixtures were recorded, and absorption spectra of aqueous sodium and potassium chlorate also were determined. The ν₃(e) and ν₄(e) modes of ClO⁻₃ were split in the molten salt and aqueous solution spectra, and a single, weak band was observed between ca. 80 and 200 cm⁻ in the Raman spectra of molten NaClO₃ and KClO₃.     

Solvation and microdynamics of La(III) in molten 80LiF-20CaF2 at 1100 K according to molecular dynamics and Monte Carlo calculations

The structural features of solvation and diffusion of La(III) ion in model molten 80LiF-20CaF₂ salts at 1100 K were studied by molecular dynamics and Monte Carlo simulations.     

Viscosity of molten NaCI,NaBF4 and KBF4

Abstract

The viscosities of molten NaBF₄ and KBF₄ were determined over a 120°C interval and the viscosity of molten NaCl was redetermined over a 200°C interval by use of an oscillating cup viscometer. The viscosities of all three samples followed an Arrhenius type temperature dependence. The measured viscosity for NaCl agreed better with predicted values and the trend established by the other sodium and potassium halides than did previous determinations. The Batchinskii free volume concept of viscosity held for the sodium and potassium halides and the two MBF₄ salts. An equation based upon a hard-sphere model predicted viscosity values in agreement with experimental values for the alkali metal halides and KBF₄ but was not suitable for NaBF₄.     

Catalase activity of coarse-grained and nanosized oxide tungsten bronzes obtained by electrolysis of molten salts

Nanocrystalline samples of K _x Li _y WO₃ with hexagonal structure obtained by electrodeposition of molten salts were several times more active in catalytic decomposition than the coarse-grained materials.     

Effective Charges and Ionicity in Molten Salts

Abstract

We have used experimental values of the entropies, near melting, of molten salts to calculate their effective charges by using a charge a spheres model in the Mean Spherical Approximation (MSA).

We compare the values of the effective charges with the electronegativity differences for a number of 1:1 molten salts. We find a reasonable good correlation for the alkali halides, but no for the copper, silver and thallium halides, and we offer an explanation for these results.     

Charging and discharging rate studies of polypyrrole films in AlCl3: 1-methyl-(3-ethyl)-imidazolium chloride molten salts and in CH3CN

The chronocoulometric charging and discharging of polypyrrole films in basic AlCl₃/1-methyl-(3-ethyl)-imidazolium chloride molten salts and CH₃CN have been investigated. Both processes follow a t^{$\text{1}\text{2}$} time dependence and are significantly faster in the molten salts. Comparison with redox polymer and porous electrode models shows that neither model is satisfactorily applicable over the entire potential region studied. The charging and discharging rates are limited by ion migration in the polymer and for potential steps in the “double layer charging” region polypyrrole behaves as a porous electrode material. In this region there is a good correlation between the charging/discharging rates and the solvent conductivity.     

Radiochemical separations in molten salts. Determination of carbon in metals by photon activation

A systematic study of radiochemical separations of carbon in molten salts was achieved. It combined forecasting of salt mixtures from literature data and experimental work The basic three mixtures of molten salts which were studied, are the following: Pb₃O₄−B₂O₃, NaOH−NaNO₃ and H₂SO₄−KIO₄ with some additions of complexing agents Selected procedures for the determination of carbon by photon activation were issued for the following samples: Ag, Al, Cr, Fe, Mg, Mo, Ni, Si, Ti, W, Zn, Zr, AlMg, AgZn and ZnMgTe. The detection limit for carbon was 10⁻⁸ g and the accuracy from 5 to 10%. Applications to solid state science are given.     

Foreword

Electrochemical behaviors of U⁴⁺ in LiCl–KCl–UF₄ eutectic and deposition of U metal were investigated. It was found that the presence of F^? has influence on the diffusion of U³⁺ and U⁴⁺ as comparing to data obtained in pure chloride molten salts. Electrochemical deposition of U was carried out by using pulse current electrolysis. Characterization results indicate that U metal was obtained at the cathode, implying U metal can be directly deposited from LiCl–KCl–UF₄ eutectic in this case and the extractive ratio is calculated to be 98%. Our results demonstrate feasible separation of U from LiCl–KCl–UF₄ molten salt by electrochemical method.