Rare Earth Element Complexation by PO43− Ions in Aqueous Solution
Digital Object Identifier (DOI)
Complexation of trivalent rare earths by PO43− ions has been assessed at t = 25°C by examining the influence of aqueous phosphate concentrations on the distributions of 144Ce and 153Gd between 0.68 molar NaClO4 and tributyl phosphate (TBP). Estimated Ce3+ and Gd3+ phosphate complexation constants appropriate to zero ionic strength are Ce3+ + PO43− ↔ CePO40; logLβ10 ≤ 11.7Gd3+ + PO43− ↔ GdPO40; logLβ1o = 12.2. Our estimates of these formation constants at zero ionic strength are approximately seven to eight orders of magnitude lower than previously reported estimates for lanthanide and actinide PO43− complexation. Linear free energy relationships relating the complexation of Ca2+ and lanthanides (Ln3+) by a variety of organic ligands, in conjunction with previous direct observations of CaPO4− formation, are consistent with the experimentally derived CePO40 and GdPO40 formation constants reported in this work.
Gadolinium speciation calculations indicate that the PO43− ion can effectively compete with the CO32− ion for free Gd3+ in model groundwater at pH 7–9. Rare earth element phosphate complexation is a significant process in natural freshwater systems which are neutral to mildly basic when the concentration ratio [HPO42−][HCO3−]">[HPO42−][HCO3−] is greater than approximately 1 × 10−3.
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Citation / Publisher Attribution
Geochimica et Cosmochimica Acta, v. 55, issue 10, p. 2729-2735
Scholar Commons Citation
Byrne, Robert H.; Lee, Jong Hyeon; and Bingler, Linda S., "Rare Earth Element Complexation by PO43− Ions in Aqueous Solution" (1991). Marine Science Faculty Publications. 1691.