Comparative carbonate complexation of yttrium and gadolinium at 25 °C and 0.7 mol dm−3 ionic strength

Stability constants for yttrium and gadolinium complexation by carbonate ions have been measured by solvent extraction procedures at 25 °C and 0.7 mol dm−3 ionic strength. The results of six experiments indicate that logCO3β1′(Y) = 5.71, logCO3β2′(Y) = 10.34, logCO3β1′(Gd) = 5.65 and logCO3β2′(Gd) = 10.12 whereCO3βn′(M) = [M(CO3)n3 − 2n][M3+]−1[CO32−]T−n, [ ] represents concentrations and [CO32−]T = [CO32−] + [NaCO3−]. When compared with previous complexation results for Eu3+, Gd3+ and Tb3+ obtained using identical procedures, excellent agreement is observed for Gd3+ complexation, and the solution complexation of Y3+ in seawater is seen to closely resemble that of Tb3+. In spite of closely linked solution chemistries of Y3+ and Tb3+, the shale normalized concentrations of these elements in seawater should be distinct due to their differing reactivities with organic ligands on particle surfaces. Model calculations indicate that while shale normalized Y3+ concentrations in seawater may exceed the shale normalized concentrations of all rare earths, similarities in Y3+ and Tb3+ solution chemistries may produce substantial coherence in the oceanic distributions of these elements.