It is well known in f-element science that the cationic radii of trivalent lanthanide cations decrease steadily across the series from La3+ to Lu3+, that the metal-ligand bonding interactions are generally explained using electrostatic models, and that the cations are strongly hydrated, with the primary hydration sphere shrinking from nine to eight somewhere in the vicinity of europium. All other things being equal, one might predict that separations of lanthanide ions in aqueous systems (including ion exchange and solvent extraction methods) would in general exhibit some variety of a linear trend as one proceeds across the series. There are certainly examples in which exactly such behavior is observed, simple cation exchange on H+-form cation exchange resin or solvent extraction systems based on liquid cation exchangers like di-2-ethyl(hexyl) phosphoric acid representing two examples. But as it turns out simple linear trends are more the exception than the rule. Trans-lanthanide patterns of thermodynamic stability in lanthanide extraction systems tend to exhibit an interesting variety. Some of these patterns are readily understood and predicted, others are not. In this presentation, selected features of the thermodynamics of lanthanide extraction reactions will be discussed in an effort to develop improved understanding of the basic chemistry that controls these separations.

Patterns of stability in f element separations: Trans-lanthanide trends in solvent extraction

248th National Meeting (2014)

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