Di n-octyl phosphinic acid as a selective extractant for metallic cations: Selected M(III) and M(VI) tracer studies

Abstract

Hydrogen ion dependencies and extractant dependencies of M(III) elements represented by Ce 3+, Eu 3+, Tm 3+, Yb 3+, Y 3+, Am 3+ and Cm 3+ and of an M(VI) element, UO 2 2+, into a benzene solution of di n-octyl phosphinic acid, ( n-C 8H 17) 2PO(OH), H[DOP], from an aqueous acidic chloride medium have been determined radiometrically. The observed stoichiometries are represented as: M A +3 + 2·5(HY) 2 0 ⇌ MY(HY 2) 2 0 + 3H A + UO 2 A +2 + 2(HY) 2 0 ⇌ UO 2 (HY 2) 2 0 + 2H A + where the subscripts A and O refer, respectively, to the mutually equilibrated aqueous and organic phases and (HY) 2 represents the dimeric form of H[DOP]. Values of K s , defined by the expressions: K s = K[H +] 3/ F 2.5, for M(III) K s = K[H +] 2/ F 2, for U (VI) where [H +] is the molar hydrogen ion concentration in the aqueous phase, F is the formal concentration of extractant in the organic phase and K is the observed distribution ratio of the metal are reported for the above elements from an aqueous phase 1·0 M in (NaCl + HCl). Comparison of the K s values of Pm(III), Cm(III) and U(VI) in systems involving di n-octyl phosphinic acid, (n-octyl) 2PO(OH), H[DOP]; 2-ethyl hexyl 2 ethyl hexyl hydrogen phosphonate, (2-ethyl hexyl 0) (2-ethyl hexyl)PO(OH), HEH[EHP]; and di 2-ethyl phosphoric acid, (20-ethyl hexyl 0) 2PO(OH), HDEHP, have been made. A plot of log K vs. Z, in a study involving all of the lanthanides (III) except Gd, shows a slight odd-even effect, the even Z elements lying above a straight line which acceptably represents the the odd- Z elements. It is tentatively concluded that in the series: (GO) 2PO(OH), (GO)(G)PO(OH) if G remains fixed the extraction of U(VI) increases slightly to the right while that of the M(III) elements considered decreased markedly.