INTERNATIONAL SYMPOSIUM ON MOLTEN SALTS AND IONIC LIQUIDS 2011

Bronsted acids are formed in ionic liquids by the introduction of a protic molecule to a liquid salt or by reaction of it with an appropriate neutral base (e.g. HCl + pyridinium chloride, H2SO4 + 1-methylimidazole).The mixture of the pure protic acid HA, with pure base B, is often gauged for its ability to react to completion, thus forming the pure liquid salt [BH]+[A]-, from the behaviour of HA and B in water. While aqueous acid-base solutions are often the starting point of any discourse regarding acidity in general, we must realise that water is an atypical solvent. In this way, water is unsuitable as the universal acid-base reference system, since the varieties of acidities possible in non-aqueous media, either cannot form, or, are unstable, in water, due to the levelling effects of [H3O]+ or [HO]-.Indeed, acid speciation outside the realm of aqueous solution chemistry is rather varied and much more complex than that available in water, where homo- and hetero-conjugate ion speciation (e.g.[HCl2]-, [H2F3]+ and [HCl (AlCl4)]- ) can occur. Furthermopre, these species can form on either side of full 1:1 (or 1:2 etc) equivalence, where quantities of unreacted HA can be consumed by [A]- formed post proton-transfer, prior to consumption by unreacted base B.The current situation for acid/base chemistry in ionic liquids needs much more attention, with actual acidities determined on a per system basis: This can be done using available spectrophotometric and electrochemical methods. We present the wide world of acidity beyond that available in water, from the gas phase to the solvated proton under various constraints, and emphasize the differences in solvent levelling, ionisation, dissociation, ion speciation and the stabilisation of proton transfer products, for various acids in various media ( proton affinities and pK values are included for protic molecules in various solvents).

Pyrochemical separations technology using high-temperature molten salt and metal media shows potential as a component of an overall separation and transmutation strategy for long-lived radionuclides. It could also be used for advanced fuel cycles associated with new types of reactors (Gas Cooled Reactor, Molten Salt Reactor, Fast reactor with metallic fuels, Accelerator Driven Systems).A pyrochemical process has been developed at the laboratory scale. The separation between the actinides and the fission products is operated by liquid-liquid extraction between a molten fluoride salt and a liquid metallic aluminum phase. Actinides are then back-extracted from the aluminum phase in a molten LiCl-CaCl2 salt at 700°C. Among the different steps of the process that still need to be studied is the head-end step with the recovery of the actinides from the molten chloride salt under an oxide form.The use of carbonate salts that deliver O2- ions and induce the actinides precipitation under oxide and oxychloride forms is known. However this method is increasing the solvent volume and therefore the waste production.Another method consists in precipitating the actinides with a carrier gas that brings O2- ions. This paper presents the results of our back-extraction and precipitation studies from the molten LiCl-CaCl2 salt at 700°C with lanthanides and actinides. We first describe our methodology used to monitor both reactions and to determine the reaction yield. The characterization of the different phases obtained after the precipitation and the calcination is then presented. As a conclusion, the viability of this process is discussed.

High temperature alkali metal chloride-based melts are prospective media for non-aqueous pyrochemical processing of fresh and reprocessing of spent nuclear fuels. Knowing and understanding the behaviour and properties of the spent fuel constituent elements is important for developing feasible technological process. Of all the elements of interest radioactive ones, for obvious reasons, are the least studied. Spectroscopic techniques, especially applied in situ, offer a valuable tool for determining speciation and studying the reactions taking place in molten salt media. Combining spectroscopy with electrochemistry provides even deeper inside into the properties of studied systems. In the present work electronic absorption spectroscopy was applied for studying the behaviour of uranium species containing the metal in the oxidation states +3, +4, +5 and +6 that were formed in a variety of reactions including anodic dissolution of uranium, chlorination of the metal and its oxides, chemical and electrochemical oxidation and reduction of uranium ions. Experimental conditions, such as temperature or even cationic composition of the solvent melt, often influence the outcome of the reactions taking place. An example of this is the reaction of uranium dioxide with hydrogen chloride that depending on temperature and chosen solvent can lead to the formation of U(IV) or U(V) species.Technetium is one of the least studied d-metals. The reactions of technetium metal and its dioxide were studied in fused alkali chlorides by spectroscopic and spectroelectrochemical techniques. The behaviour of technetium is compared with that of rhenium, the element often employed in experimental studies as a stable substitute for technetium.For uranium and technetium the information obtained from the EAS measurements is compared with the results of X-ray absorption spectroscopy experiments performed with molten and quenched chloride salts.

Among industrial processes, extraction and separation of actinides and lanthanides from nuclear waste is one of the most challenging fields. For this purpose, liquid–liquid extraction procedures using neutral organophosphorus compounds, such as carbamoylmethylphosphine oxides (CMPO), are used in current practice in the TRUEX process. Ionic-liquid phases are suitable extraction solvents for metallic radioactive species in liquid/liquid extraction processes as they show high stability under a and γ irradiations and enhanced safety towards criticality.Several groups reported that replacing dodecane in the TRUEX process by a ‘‘hydrophobic’’ IL significantly enhances the extraction of the metal cation by CMPO.Another very promising approach for metal extraction (and many others applications) lies in the concept of task-specific ionic liquids (TSILs). These compounds, consisting of extracting entities grafted onto the cation of the IL, combine the properties of ILs (e.g., nonvolatility, nonflammability) with those of conventional extracting compounds. Upon grafting complexing substructures onto the organic cation of RTILs, the resulting TSILs behave both as the organic phase and the extracting agent, suppressing the problems encountered through extractant/solvent miscibility and facilitating species extraction and solvent recovery.We report the synthesis of a functionalized ionic liquid based on quaternary ammonium cations bearing a CMPO substructure (N,N-dibutylcarbamoylmethyldiphenylphosphine oxide). TSIL In order to evaluate the extracting properties of the newly synthesized TSIL, the extraction of a number of radioactive elements was investigated. Experimental tests with Am(III), Eu(III) and U(VI) were performed at different acid conditions and different TSIL concentrations.Preliminary studies show that high extraction values can be obtained for U(VI) and Am(III) with the new TSIL. The americium loaded in the RTIL phase could be back extracted by contacting the organic phase with a 6M nitric acid solution.

Mould powders with a C/S-ratio between 0.61 and 1.34 were investigated with respect to their melting and crystallisation behaviour. Therefore the Hot Stage Microscope (HSM), Simultaneous Thermal Analysis (STA) and Single Hot Thermocouple Technique (SHTT) were used. With the STA differences in enthalpy according to the reactions taking place during heating and cooling are detected. Contrary the HSM enables the in-situ observation of a polished sample during heating. Crystallisation of transparent slags can be investigated with the HSM and the SHTT. For the SHTT the slag is stretched to a thin layer. Therefore the evaporation of alkalis and fluorine has to be taken into account.Some differences between the results of the methods applied are caused by the following circumstances: Thermocouple measures rather the furnace temperature in case of STA and the specimen temperature in case of HSM and SHTT. Furthermore for detection of effects in the DTA-curve more intense reactions have to take place. Also the higher magnification factor of the HSM compared to the SHTT for continuous cooling measurements has impact on the deviation of especially the crystallisation temperature.Using the HSM for some mould powders the formation of intermediate liquid with following crystallisation is observed during heating. This leads to the assumption of disequilibrium due to a too high heating rate. In contrast to this detection of intermediate phases by STA is hindered by overlap of peaks.Using the HSM during cooling diverse crystal shapes are observed. On the contrary the results of the SHTT show the crystallisation of denrites for continuous cooling and isothermal measurements at high temperatures. But for lower temperatures small crystals precipitate in the whole sample.Comparing results of these methods with mineralogical investigations of samples taken from service analogies are observed.

The phase diagrams of trivalent lanthanide–alkali metal halide systems range from simple eutectic systems to systems with one (several) congruently or incongruenly melting compounds. Using both literature information and our extensive experimental results, the LnX3-MX binary mixtures phase diagrams were screened in terms of the IPM+/IPLn3+ ratio (IPi= zi/ri ; Zi: Ionic charge; Ri: Ionic radius; Ln: Lanthanide, X: Halide and M: Alkali metal). A similar approach was conducted on the divalent LnX2-MX lanthanide-alkali halides phase diagrams ranging from simple eutectic to one or more congruently melting compounds. Lanthanides being widely used as simulants of actinides, this classification can constitute a useful predictive tool for those still unexplored systems.

Specimens of Ni were conditioned in the test piece with a work area of 0.07917 cm2, each one of them was polished. The electrochemical information was obtain by mean of anodic potentiodinamic polarization and polarization resistance. The anodic polarization indicates that the critical current has a linear relationship with the NaOH concentration. The diffusion coefficient was determinated by the Randles- Sevcik.

The world faces some considerable challenges over the next 50 years and these include the use of renewable energy, its generation and storage, green processing of materials (including recycling), feeding an ever growing population and, finally, care of an ageing population.The skills of the Chemical Metallurgy community include thermodynamics, phase diagrams, kinetics and mass transfer and electrochemistry of aqueous solutions, solid electrolytes and molten salts. However, it is not just sufficient to have these skills – it is equally important to be aware of the problems that need solving. The combination of these two factors can lead to innovation but this can only be successful when the ideas are put into practice and this requires a partner with the financial and technical resources to make the projects a successful reality.Several examples will be given and these may include: (1) novel anodes for lithium ion batteries deriving insight from phase diagrams and intercalation to produce tin filled carbon nanotubes, (energy generation and storage), (2) production of metal and oxygen directly from metal oxides (green processing), (3) treatment of waste electronic scrap(recycling), (4) widening the supply of fertiliser (feeding a growing population), (5) healing of long term wounds (caring for an ageing population)This paper will illustrate how knowledge of a problem coupled with an understanding of the requisite science can lead to innovative solutions that can attract venture capital leading to their successful industrial development.

Partial or full solidification of metallurgical slags occurs in many industrial pyrometallurgical processes. To enhance the fundamental knowledge of this phenomon, this research focuses on the simulation and in-situ observation of crystallizing minerals in oxide melts. The isothermal crystallization of Wollastonite (CaO.SiO2) in a ternary CaO-Al2O3-SiO2 melt is investigated. We used a confocal laser microscope (CLSM) to observe the dendritic crystallization and measured the dendrite tip radius and its velocity as a function of undercooling. The phase field method is chosen to model and simulate the crystallization, because it has proven its power for phase transformations in metals. The phase field model uses a vast number of physical input data, such as Gibbs energies of the phases, diffusion coefficients of the components and the interfacial energy of the solid-liquid interface. The thermodynamic data is retrieved from the FACTSage database for oxide systems. Diffusion coefficients are taken from literature, while surface energies are estimated from both Molecular Dynamics data and wetting experiments. By comparing experimental values for the dendrite tip velocity with values obtained with simulations, the influence of surface energy and diffusion coefficients on the crystallization behavior can be assessed.