Alkyl phosphoric acids, actinide

The alkyl phosphoric acids were first recognized as excellent actinide extractants because dibutyl phosphoric acid existed as an impurity in TBP (8). They extract well from unsalted solutions and from systems such as sulfate in which TBP is ineffective. Organo-phosphorus acids are thus suitable for uranium hydr metallurgical applications where ore is leached with sulfuric acid. The Dapex process is an example in which bis(2-ethylhexyl) phosphoric acid (HDEHP) is used alone or in synergistic combination with neutral organophosphorus compounds for uranium and vanadium recovery (9,10). 

Alkyl phosphoric acids. Perhaps the largest single group of extractants for actinides are the alkylphosphoric acids of three main types dialkylphosphoric acids, dialkylphosphonic acids, and... 

There are various types of organic proton exchangers (34, 35, 38). Diesters of phosphoric acid, (RO)2P = 0(0H), phosphonic acids, R(RO)P = 0(0H), and phos-phinic acids, R2P = 0(0H), where R represents linear or branched alkyl or phenyl substituents, are the most common cation exchangers developed in liquid-liquid extraction for the extraction of trivalent 4/and 5/elements. They were initially developed for the American TALSPEAK and the Japanese DIDPA processes and have recently been introduced in the French DIAMEX-SANEX process. As for previously described NOPCs, these organophosphorus acids present oxygen-donor atoms (hard bases) in their structures and therefore will easily coordinate trivalent lanthanide and actinide cations, but they will not allow complete discrimination of the two families of elements. However, contrary to previously described neutral organophosphorus... 

The degradation of several trialkylphosphates has been investigated, because lengthening the alkyl chain can enhance the actinide loading capacity in normal long-chain diluents. The main degradation products were the related dialkyl phosphoric acid HO(RO)2P = O and monoalkyl phosphoric acid (HO)2(RO)P = O (18, 84, 152). The yield of formation of the main compound HO(RO)2P = O varied from 2.83 for R = CH3 to 1.47 for R = C5Hn (18). 

Extraction processes (TRUEX, PUREX, Talspeak, DIAMEX, PARC, etc.) generally involve complexation of transplutonium elements by alkyl phosphines, phosphine oxides, phosphoric acids, carbamoyl phosphonates, diamides, and thiophosphinates in aqueous/organic extractions, within derivatized solid supports, or on coated particles. There are excellent reviews of the processes and significant complexes by Mathur et al. and selected chapters in The Chemistry of the Actinide and Transactinide Elements to be published in 2003. " Work on the separation for nuclear waste management in the United States, France, and Russia have been reviewed. " ... 

The addition of an ether linkage in the alkyl chains of dialkylphosphoric acids has been found to increase its extractive power for trivalent actinides, resulting in an extractant that is more effective from acid solutions than is HDEHP (69). Bis(hexoxy-ethyl)phosphoric acid (HDHqEP) is a compound of this type that has been studied extensively (70,71). The ether linkage may contribute to the coordination of the metal ion, resulting in the formation of a seven-membered ring. 

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