New lanthanide oxalato-nitrates crystallized from acidic solutions
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1265-AA04-05
New lanthanide oxalato-nitrates crystallized from acidic solutions C. Tamain1, M. Rivenet2, B. Arab-Chapelet1, S. Grandjean1, F. Abraham2 1
CEA MARCOULE, DEN/DRCP/SCPS, Laboratoire de Conversion et Chimie des Actinides BP17171, 30207 Bagnols sur Cèze cedex, FRANCE 2 Unité de Catalyse et Chimie du Solide (UCCS UMR CNRS 8181) - Groupe Chimie du Solide ENSCL- USTL, BP 90108, 59652 Villeneuve d’Ascq cedex, FRANCE ABSTRACT To identify the various oxalates and oxalato-nitrates likely to form during the nuclear fuel reprocessing we study crystallization of such compounds by various methods (slow diffusion, hydrothermal syntheses, in situ oxalate syntheses ...), in different conditions and in presence of monovalent ions. In a first stage, lanthanides are used as surrogates of the actinides (III) radioactive elements. This communication reviews various lanthanides (III) compounds obtained by crystallization from nitric acid solution containing hydrazinium ions. Diethyl oxalate was used as a precursor for oxalate ions. A careful adjustment of the experimental conditions allowed us to synthesize single crystals of nitrates, oxalato-nitrates and oxalates with various ligand/Ln(III) ratio and containing nitrates as ligands or as counter ions. In all the compounds hydrazinium ions are present as counter ions. The crystal growth method is described and the crystal structures, determined by X-ray diffraction from single crystals, are discussed in terms of metal-oxalate frameworks. INTRODUCTION Due to the very low solubility of An(IV) or An(III) oxalate compounds in acidic solutions, oxalic acid is a very common reagent to recover actinides from radioactive liquid waste using precipitation methods. For example, the oxalic precipitation of plutonium is widely used at an industrial scale during the reprocessing of the nuclear fuel, e.g. in the current PUREX process where this energetically valuable actinide is converted in this way into oxide. Recently our group of research showed that the flexibility of the oxalate ligand allows the formation of mixed An(IV)–An(III) actinides oxalate solid compounds based on two or three-dimensional actinide-oxalate frameworks [1-3]. As these materials are particularly suitable precursors of actinides oxide solid solutions, the actinides co-precipitation is one option for the comanagement of actinides in an integrated closed fuel cycle currently under evaluation for Generation III/IV systems. In these oxalates, An(III) and An(IV) occupy the same crystallographic site, the charge compensation being insured by monovalent ions such as hydrazinium ions which are present in the acidic solutions to prevent the oxidation of U(IV) in presence of nitrate ions. Owing to the acidic conditions, the incorporation of nitrate species in the solids can also occur. However, investigation of the nitrate-oxalate-rare-earth elements systems remains rather rare to date [4-12]. Most of the rare-earth oxalato-nitrates were found unexpectedly without introducing oxalate in the starting reaction mixture [7-10]
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