The Ionic Strength Dependence of Rare Earth and Yttrium Fluoride Complexation at 25°C

Yu-Ran Luo, Robert H. Byrne

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Abstract

Formation constants for the complexation of yttrium and rare earth elements(YREE) by fluoride ions have been measured at 25°C. The ionic strength (μ)dependence of YREE formation constants in perchlorate solution for ionicstrengths between 0 and 6 molar can be expressed aslog F β 1 (M, μ) =log F β 1 o (M) −3.066 μ 0.5 /(1 + 1.769 μ 0.5 )+ 0.1645 μwhere log F β 1 o (M) represents MF 2+ formation constants at zero ionic strength.The log F β 1 o (M) results obtained inthis work are: Y(4.46), La(3.62), Ce(3.86),Pr(3.84), Nd(3.82), Sm(4.15), Eu(4.27), Gd(4.24), Tb(4.37), Dy(4.39), Ho(4.28),Er(4.27), Tm(4.29), Yb(4.39), and Lu(4.25). The relative magnitudes of YREEformation constants are independent of ionic strength. The pattern oflog F β 1 (M,μ),formation constants obtained in this work [relative magnitudes oflog F β 1 o (M)],exhibits a shallow minimum between Dy and Yb. In contrast to the smoothpattern of stability constants expected if fluoride were to interact with bare ions(with monotonically decreasing crystal radii between La and Lu), theinteractionof F with YREEs, which have extensive hydration spheres[M(H 2 O) 8–9 3+ ] resultsin a relatively complex pattern of lanthanide stability constants. The fluoridecomplexation behavior of yttrium differs distinctly from the behavior of any rareearth. Although the crystal radius of Y3;pl is approximately equalto that of Ho 3+ ,differences in the covalence/ionicity of Y 3+ relative to therare earths leads to aYF 2+ stability constant that exceeds that of any rare earthelement (REE).

Original languageAmerican English
JournalJournal of Solution Chemistry
Volume29
DOIs
StatePublished - Jan 1 2000

Keywords

  • Rare earth elements
  • fluoride complexation
  • stability constants
  • sodium perchlorate
  • ionic strength
  • lanthanide
  • yttrium

Disciplines

  • Life Sciences

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