Rare earth element complexation by PO 4 3- ions in aqueous solution

Details Rare earth element complexation by PO 4 3- ions in aqueous solution Rare earth element complexation by PO 4 3- ions in aqueous solution

Oct 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55.2729b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 55, Issue 10, pp.2729-2735

Computer Science

5

Scientific paper

Complexation of trivalent rare earths by PO 4 3- ions has been assessed at t = 25° C by examining the influence of aqueous phosphate concentrations on the distributions of 144 Ce and 153 Gd between 0.68 molar NaClO 4 and tributyl phosphate (TBP). Estimated Ce 3+ and Gd 3+ phosphate complexation constants appropriate to zero ionic strength are Ce 3+ + PO 4 3- CePO 4 0 ; log L 1 0 11.7 Gd 3+ + PO 4 3- GdPO 4 0 ; log L 1 o = 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 PO 4 3- complexation. Linear free energy relationships relating the complexation of Ca 2+ and lanthanides (Ln 3+ ) by a variety of organic ligands, in conjunction with previous direct observations of CaPO 4 - formation, are consistent with the experimentally derived CePO 4 0 and GdPO 4 0 formation constants reported in this work. Gadolinium speciation calculations indicate that the PO 4 3- ion can effectively compete with the CO 3 2- ion for free Gd 3+ 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 [ HPO 4 2- ]/[ HCO 3 - ] is greater than approximately 1 × 10 -3 .

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