Abstract
Comparison of di(2-ethylhexyl)phosphoric acid (HDEHP), 2-ethylhexyl phenylphosphonic acid (HEH[ΦP], and 1-methylheptyl phenylphosphonic acid (HMeH[ΦP] in an aliphatic and an aromatic diluent as intragroup separating agents for trivalent lanthanides and actinides shows some important advantages of HMeH[ΦP]. In extractive power, HMeH[ΦP] is intermediate to the other compounds. In several separations systems HMeH[ΦP] is at least twice as effective as HDEHP and significantly better than HEH[ΦP] for separation of tracer-level Eu from Ce, and its advantage for separating Cf from Cm is nearly as great. Neither of the phosphonic acids is suitable for separating natural lanthanides at the usual high concentrations because of solubility limitations. Extractions of these elements frequently deviate from the theoretical third-power dependence on extractant concentration and inverse third-power dependence on acid concentration. Extractant concentration dependence varies with extractant and diluent. Acid concentration dependence varies somewhat with extractant and diluent, and much more with element and aqueous acid. A process which has been used successfully for separating Cf from Cm is based on extraction by an aliphatic solution of HDEHP from HCl. More effective separation can be obtained with HMeH[ΦP]. With HEH[ΦP] oor HMeH[ΦP], HNO 3 can be substituted for HCl, giving a separation superior to that with the HDEHP-HCl system, provided that solubility limitations are not exceeded.
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