COMPARATIVE CARBONATE COMPLEXATION OF YTTRIUM AND GADOLINIUM AT 25-DEGREES-C AND 0.7 MOL DM(-3) IONIC-STRENGTH

Stability constants for yttrium and gadolinium complexation by carbona te ions have been measured by solvent extraction procedures at 25 degr ees C and 0.7 mol dm(-3) ionic strength. The results of six experiment s indicate that log(CO3) beta(1)'(Y)= 5.71, log(CO3) beta(2)'(Y) = 10. 34, log(CO3) beta(1)'(Gd) = 5.65 and log(CO3) beta(2)'(Gd) = 10.12 whe re (CO3) beta(n)'(M) = [M(CO3)(3-2n)][M(3+)](-1)[CO32-](-n)(T), [] rep resents concentrations and [CO32-](T) = [CO32-] + [NaCO3-]. When compa red with previous complexation results for Eu3+, Gd3+ and Tb3+ obtaine d using identical procedures, excellent agreement is observed for Gd3 complexation, and the solution complexation of Y3+ in seawater is see n to closely resemble that of Tb3+. In spite of closely linked solutio n chemistries of Y3+ and Tb3+, the shale normalized concentrations of these elements in seawater should be distinct due to their differing r eactivities with organic ligands on particle surfaces. Model calculati ons indicate that while shale normalized Y3+ concentrations in seawate r may exceed the shale normalized concentrations of all rare earths, s imilarities in Y3+ and Tb3+ solution chemistries may produce substanti al coherence in the oceanic distributions of these elements.