Determination of subSO/subsubsub4/sub/subβsub1/sub for Yttrium and the Rare Earth Elements at I = 0.66 M and T = 25°C—implications for YREE Solution Speciation in Sulfate-rich Waters

Johan Schijf, Robert H. Byrne

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Abstract

We present a complete set of stability constants ( SO 4 β 1 ) for the monosulfato-complexes of yttrium and the rare earth elements (YREE), except Pm, at I = 0.66 m and t = 25°C, where SO 4 β 1 = [MSO 4 + ] × [M 3+ ] −1 [SO 4 2− ] −1 (M ≡ YREE and brackets indicate free ion concentrations on the molal scale). Stability constants were determined by investigating the solubility of BaSO 4 in concentrated aqueous solutions of MCl 3 . This is the first complete set to be published in more than 30 years.

The resulting SO 4 β 1 pattern is very similar in shape to one reported by de Carvalho and Choppin (1967a) ( I = 2 mol/L; t = 25°C) that has been largely ignored. Stability constants vary little between La and Sm, but display a weak maximum at Eu. Between Eu and Lu, SO 4 β 1 decreases by 0.2 log units, substantially exceeding the ±0.02 log unit average analytical precision. The stability constant for Y is approximately equal to that for Er. Our SO 4 β 1 pattern is consequently distinctly different from the consensus pattern, based on a single data set from 1954, which is essentially flat, with a range of only 0.07 log units between the lowest and highest SO 4 β 1 values within the lanthanide series (excluding Y).

Values of SO 4 β 1 obtained in this work, in conjunction with the ion-pairing model of Millero and Schreiber (1982), allow prediction of SO 4 β 1 between 0 and 1 m ionic strength. These results are used to assess both the absolute and relative extent of YREE sulfate complexation in acidic, sulfate-rich waters.

Original languageAmerican English
JournalGeochimica et Cosmochimica Acta
Volume68
DOIs
StatePublished - Jan 1 2004

Disciplines

  • Life Sciences

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