The extraction of selected M(III) metals by bis 2-ethylhexyl phosphoric acid in n-heptane

The extraction of Y3+, Pm3+, Eu3+, Tm3+, Lu3+, Am3+ and Cm3+ from an aqueous chloride phase into a solution of (2-C2H5.C6H120)2P0(0H),HDEHP, in n-heptane has been studied as a function of the concentration of extractant in the organic phase and of hydrogen ion in the aqueous phase. From these data the stoichiometries of extraction have been deduced as: Msub(A)3+ + 2.5 (HY)20 = MY(HY2)20 + 3Hsub(A)+ where the subscripts A and 0 refer, respectively to mutually equilibrated aqueous and organic phases. (The formulation of extracted entities is based solely upon established ratios and is in no sense to be interpreted in terms of established structure.) Corresponding to the stoichiometries, values of K, F and [H+] obtained from the hydrogen ion dependency plots were inserted in the equation: K = Ksub(s)Fsup(a)/[H+]sup(b) to obtain values of Ksub(s), (K is the observed distribution ratio, F the equilibrium concentration of HDEHP in the organic phase, [H+] the equilibrium concentration of hydrogen ion in the aqueous phase, and a and b the respective extractant and hydrogen ion dependencies.) The equation is applied specifically to a system embodying 1.0F(NaCl + HCl) at 22 +- 20C. The Ksub(s) (n-heptane) value is higher than the Ksub(s) (benzene) value for each of the cations studied. Comparisons with extraction systems employing (n-C8H170)2P0(0H) and [C4H9C(CH3)2CH20]2 P0(0H), respectively symbolized as HDOP and HDNOP, are made. (author)