Types of Acidic Organophosphorus Extractants and Their Applications to Transuranic Separations

Certain applications of acidic organophosphorus extractants to transuranic separations devised in the authors' laboratory are described. In a system employing mono-2-ethyl hexyl phosphoric acid, (2-EtHexO)PO(OH)₂, symbolized as H₂MEHP, in toluene vs. a concentrated aqueous NH₄CNS solution, the ratio K_Pm/K_Am is approximately 50, while in the corresponding TBP system it is considerably less than unity. The H₂MEHP (in toluene) vs. HCl system has been used in effecting mutual M(III), M(IV), and M(VI) separations. Throughout the 1–12 M HCl range the extractant dependency (0.05-0.3 F H₂MEHP) approximates first power for lanthanides(III), Pu(III), Am (III), Np(IV) and U(VI). Comparable studies of other H₂MGP and H₂[GP] compounds, i.e., (GO)PO(OH)₂ and GPO(OH)₂, are reported. A system employing HDΦP, i.e. (C₆H₅0)₂PO(OH), in toluene vs. a concentrated aqueous chloride phase serves to effect the difficult Cf-Y separation, the ratio K_Cf/K_Y being approximately 400. Systems involving a mono acidic phosphate, HDGP, or phosphonate, HG[G'P], in a diluent vs. an aqueous mineral acid solution have proved valuable in effecting the Cf-Cm separation, Cf extracting the better. The fact that actinides(IV) are much more extractable than actinides(III) in HDGP vs. mineral acid systems is utilized in the purification of Bk(IV) by extraction from a nitrate solution into a n-heptane solution of di 2-ethyl hexyl phosphoric acid, HDEHP.