Investigation on the Diluent Effect on Solvent Extraction Processes of Trivalent f-Elements by Acidic Di-Alkyl Organophosphorus Extractants
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Solvent extraction is the most common chemical technique used in hydrometallurgical separations and purification of transition metals and f-elements. Solvent extraction of metallic cations, such as the f-elements, needs the use of organic ligands (extractants) to coordinate the targeted cation, to make it soluble in an organic phase and then allow the phase transfer from the aqueous phase to the organic one. The family of acidic di-alkyl organophosphorus extractants are the extractants of choice for trivalent metals. Furthermore, the large catalogue of diluents available for experimentation is one of the delightful aspects of solvent extraction chemistry (and probably to other chemistry domains). There are so many to choose from, and each has its special applications where it outshines the rest. This dissertation is focusing on the influence of the choice of the diluent on the solvent extraction process of selected trivalent f-elements (Nd3+, Eu3+, Tm3+ and Am3+) by HEH[EHP]. The results show that the diluent influences the efficiency of the extraction (characterized by the Kex), but also the stoichiometry of the metal chelate. Spectrophotometry shows that the coordination of the metal chelate is invariant from one diluent to another. The results of the extraction of Eu3+ by HEH[EHP] are then compared to the diluent properties that are relevant for the solvation process (cavitation, dispersion and association). Finally, van’t Hoff analysis is applied to the extraction of Am3+ and Nd3+ by HDEHP in various diluents, reveling an entropy and enthalpy compensation effect.