COMPARATIVE YTTRIUM AND RARE-EARTH ELEMENT CHEMISTRIES IN SEAWATER

Comparisons of yttrium and rare earth stability constants for organic ligands indicate that Y(III)-organic complexation behavior most closely resembles, on average, the complexation characteristics of Sm(III). Yttrium organic complexation behavior distinctly differs from the behavior of Ho(III), whose ionic radius is most similar to that of yttrium. However, our stability constant comparisons demonstrate that the most reliable basis for predicting Y(III) organic stability constants are predictions based on the complexation behavior of Ho(III). Linear free energy relationships between Ho(III) and Y(III) exhibit better fits than those obtained for other rare earth elements, and much better fits than those obtained between Sm(III) and Y(III). The comparative abundances and distributions of yttrium and the rare earths in seawater are controlled by competitive equilibria between inorganic solution ligands and organic surface ligands. Due to yttrium solution complexation with hard inorganic ligands resembling that of Ho(III) and, yttrium surface complexation with soft organic ligands resembling that of light rare earth elements, the input normalized abundances of yttrium and the rare earths should be decoupled in seawater. In its seawater scavenging behavior, yttrium should act as a pseudolanthanide even heavier than the heaviest rare earth element, lutetium.