Extraction of U(VI), Th(IV), Am(III) and Eu(III) by bis para-octylphenyl phosphoric acid in benzene diluent

Abstract

The extraction of U(VI) from both chloride and nitrate aqueous phases and of Th(IV), Am(III) and Eu(III) from a chloride aqueous phase by bis para-octylphenyl phosphoric acid, [ p-(1,1,3,3-tetramethylbutyl) phenyl O] 2PO(OH), HDOøP, in benzene as carrier diluent has been studied as a function of the concentration of HDOøP in the organic phase and of the concentration of H + in the aqueous phase. The distribution ratios, K, of the tracer-level metallic ions were determined by radiometric techniques. From 1.00 F (NaCl + HCl) and from 1.00 F (NaNO 3 + HNO 3), the extraction of U(VI) is represented as: UO 2A 2++2( HY) 2o⇄ UO 2(H 2Y 4) O+2H A + where (HY) 2 represents the dimer of HDOøP, the subscripts A and O refer, respectively, to mutually equilibrated aqueous and organic phases, and the formulation of the extracted species is empirical—not intended to imply any specific structure. Similarly, from 1.00 F (NaCl + HCl) the extraction of Th(IV) and of Am(III) and Eu(III) is represented respectively as: TH A 4++3( HY) 2O⇄Th(H 2Y 6) O+4H A + M A 3++3( HY) 2O⇄M(H 3Y 6) O+3H A + the formulation of the extracted species, again, being empirical. It is suggested that logical formulations of the U(VI), Th(IV) and M(III) extracted species are: UO 2(HY 2) 2, Th(Y) 2(HY 2) 2 and M(HY 2) 3. Th3 expressions for the extraction of UO 2 2+, of Th 4+ and of Am 3+ and Eu 3+, in terms of extraction parameters, from an aqueous phase of constant ionic strength, 1.00 μ, are: UO 2 2+:K=K sF 2/[H +] 2 Th 4+:K=K sF 3/[H -] 4 Am 3+, Eu 3+:K=K sF 3/[H +] 3 where K S is a constant characteristic of the system, F the concentration in formality units of HDOøP in the equilibrated organic phase, and [H +] the concentration of hydrogen ion in the equilibrated aqueous phase. A comparison of the K S values calculated for the system currently reported with those of selected previously reported examples of the same generic LLE (liquid-liquid extraction) system shows a wide variation in K S values for Th(IV), the overall range exceeding 10 14, and a relatively small variation in K S values for U(VI) the overall range being only 2.5 × 10 2. In the specific example of the generic LLE system generalized as: ( X 1)( X 2) PO(OH) in carrier diluent versus aqueous mineral acid currently reported, the ratio of K S values favors Th(IV) over U(VI) by a factor of 2 × 10 5, whereas in an example of this generic system previously reported by us the ratio of K S values favors U(VI) over Th(IV) by a factor approximating 5 × 10 6. Consequently, regardless of which of the two, U(VI) and Th(IV), is the minor component, a system may be employed in which the minor component is preferentially extracted and the major component reports to the aqueous phase.