Investigation of the structure of neodymium-di-(2-ethylhexyl) phosphoric acid combinations using electrospray ionization
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NTRODUCTION
DURING solvent extraction of rare-earth (RE) elements (e.g., scandium, yttrium, and neodymium) with di-(2-ethylhexyl) phosphoric acid (DEHPA), the organic phase is gelatinous at high metal concentrations. The phenomenon starts with the organic layer becoming turbid. When the molar ratio of RE:DEHPA is increased, turbidity and viscosity increase, and, finally, at complete loading, the upper layer obtains the typical consistency of a gel. A photo of samples with the different loading stages is shown in the Appendix. The DEHPA is present in the solutions with kerosene, octane, and other aliphatic diluents, mainly as dimer (DEHPA)2. It is usually assumed that, in the completely liquid range, three dimers react with one RE atom, forming the molecule RE(DEHPDEHPA)3, and that at high loading, the molecule RE(DEHP)3, containing three monomers, is increasingly formed. Then, at complete loading, RE(DEHP)3 is believed to be the sole species. Many articles have been published on the distribution equilibria in solvent extraction involving DEHPA and related agents. But, there are only a few in which gel formation in systems with RE metals has been mentioned.[1–6] Peppard and Ferraro[2] examined the material formed at complete CHRISTIANE SCHARF and ANDRÉ DITZE, Scientists, and KLAUS SCHWERDTFEGER, University Professor Emeritus, Institut für Metallurgie, and DIETER E. KAUFMANN, University Professor, and JAN C. NAMYSLO, Scientist, Institut für Organische Chemie, are with the Technische Universität Clausthal, 38678 Clausthal-Zellerfeld, Germany. Contact e-mail: schwerdtf@ t-online.de. SVEN FÜRMEIER and TORSTEN BRUHN, Scientists, are with Institut für Reine und Angewandte Chemie–Organische Chemie, Carl von Ossietzky Universität Oldenburg, 26111 Oldenburg, Germany. Manuscript submitted January 14, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS B
loading of DEHPA with scandium. After evaporating the diluent toluene, an infrared spectroscopic analysis of the obtained solid matter yielded an Sc:DEHPA molar ratio of 1:2.8, which is close to the theoretical ratio of 1:3. Lenz and Smutz,[3] as well as Owens and Smutz,[4] stated that the transition to the gel occurs in a more complicated manner than usually assumed. That is, the gelatinous material may form at a RE:DEHPA ratio much less than 1:6. Anticó et al.[5] investigated the gel formed in the extraction of yttrium with the scanning electron microscopy–energy-dispersive X-ray technique and determined a Y:P ratio of 1:3. These authors deduced from their measurements of distribution equilibria that at low and medium concentrations (clear liquid), the yttrium is associated with four and five DEHPA (or DEHP) groups rather than with six, and they concluded that gel formation at a high yttrium concentration could be conceptually realized by chain formation of the species with five DEHPA (or DEHP) molecules. The present study was carried out as part of a research program on magnesium. Magnesium alloys are increasingly used in the automotive industry because of their light weight. T
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