Phosphate Complexation of Gadolinium(III) in Aqueous Solution

Examination of the distribution of high specific activity Gd153 between tributyl phosphate and a 0.68 M aqueous phase at 25.0°C permits investigation of lanthanide phosphate complexation within rigorous solubility constraints. Our experiments provide the following formation constants with estimated standard errors: β′= [GdHPO4+] [Gd3+−1I[HPO42−]−1 = (8.05±0.7) x 103; β′2 = [Gd(HPO4)2−][Gd3+]−1 [HPO42−]− = (8.1± 1.9) x 106; β′H = [GdH2PO42+][Gd3+]−1[H2PO4−]−1 = 50.4 ± 6.8. Our results indicate that phosphate complexation of lanthanide ions and trivalent actinides is significant in natural systems, and that the use of phosphate salts as pH buffers in laboratory examinations of metal hydrolysis is generally inadvisable