Comparative Hydrolysis Behavior of the Rare Earths and Yttrium: the Influence of Temperature and Ionic Strength

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Yttrium, Rare earth elements, Hydrolysis, Enthalpy, Ionic strength, Spectrophotometry

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In this work two techniques are used to determine hydrolysis constants (β1*(M)) of yttrium and the rare earths (YREEs), where β1*(M)=[MOH2+][H+][M3+]−1. Potentiometric experiments were conducted on time scales as long as 15 min and spectrophotometric experiments were complete on time scales much shorter than 500 ms. The stability constant patterns produced by both procedures are in excellent agreement. Potentiometric results obtained over a temperature range between 25 and 55°C indicate that enthalpies appropriate to YREE hydrolysis can be reasonably approximated as ΔH0(M)=11.3 kcal mol−1 for all YREEs. The dependence of YREE hydrolysis constants on temperature (T), ionic strength (I), and YREE identity (M) can be expressed as logβ1*M=log0β1*M−2.044I1/21+5.52I1/2+1.84×10−3I−2446KT+8.204">logβ1*M=log0β1*M−2.044I1/21+5.52I1/2+1.84×10−3I−2446KT+8.204 where the log 0β1*(M) values, appropriate at 25°C and zero ionic strength, are given as follows: log 0β1*(Y)=−7.80, log 0β1*(La)=−8.81, log 0β1*(Ce)=−8.34, log 0β1*(Pr)=−8.32, log 0β1*(Nd)=−8.18, log 0β1*(Sm)=−7.84, log 0β1*(Eu)=−7.76, log 0β1*(Gd)=−7.83, log 0β1*(Tb)=−7.64, log 0β1*(Dy)=−7.59, log 0β1*(Ho)=−7.56, log 0β1*(Er)=−7.52, log 0β1*(Tm)=−7.39, log 0β1*(Yb)=−7.24, log 0β1*(Lu)=−7.27.

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Polyhedron, v. 19, issue 1, p. 99-107