Solvent extraction behavior of rare earth ions with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone-II : an examination of gadolinium break, tetrad effect, double-double effect and the relevance of -inclined-W- plot

Abstract

Solvent extraction behavior of all rare earth ions (excepting promethium) and yttrium have been investigated using 1-phenyl-3-methyl-4-benzoly-5-pyrazolone (HPMBP) as the extractant in aqueous-chloroform medium at 25 ± 1°C. The initial concentration of HPMBP was 5 × 10^-2M, and the aqueous phase was maintained at constant ionic strength 0.1 M (Na, H)⁺ClO₄^-. From distribution coefficients (D), extraction equilibrium constants (K_3,0), for the formation of Ln (PMBP)₃, two-phase stability constants (logβ₃·P_Ln(PMBP)3), pH for 50% extraction of metal chelates (pH₅₀) and separation factors (S) between the adjacent elements have been evaluated. These values have been examined in the light of double-double effect and tetrad effect. A plot of log K_3,0 values against atomic number, Z show tetrad grouping. A similar plot of log K_3,0 values against L (total angular momentum of rare earth ions) forms an -inclined W-, agreeing with a recent suggestion of Sinha. On the other hand, logβ₃·P_Ln(PMBP)3 values versus r^-1 (r, ionic radii of rare earth ions) may be fitted into two straight lines for the lower and higher members of the series with a break at gadolinium.