General Chemical Properties of the Actinides

Many of the elements of importance in fuel reprocessing are found within the sixth and seventh periods of the periodic system. In the sixth period the rare-earth fission products, lanthanum to dysprosium, are difficult to separate from each other by chemical means. Their close similarity in chemical properties is explained on the basis of their electronic configurations [SI ] as shown in Table 9.1. 

The series of 15 elements, lanthanium to lutetium, is known as the lanthanide series. These elements all form trivalent ions in solution quadrivalent oxidation states of cerium, praseodymium, and terbium, and bivalent states of samarium and europium are also obtained. 

The seventh period of the periodic table is occupied by a similar series called the actinide series. Beginning with actinium the 5/ electron shell is populated in a matmer analogous to filling the 4/ electron shell in the lanthanide series. A suggested electronic configuration [K2, M6], is shown in Table 9.2. After the alkaline earth radium, additional electrons are added to the 6d and 5/ shells, beginning the actinide series. At the beginning of the actinide series electrons are added 

The chemical properties of the actinides are much less similar to each other than those of the lanthanides, because the additional electrons added to the 5/ and 6d are bound less t tly than those of the 4/and 5d shells of the lanthanides. As shown in Table 9.4, the lanthanides in aqueous solutions exist principally in a single, tiivalent oxidation state, whereas four or more oxidation states are observed in the aqueous chemistry of uranium, neptunium, and plutonium. The actinide ions normally formed in solution by the oxidation states II through VI are M, M, M, MO2, MOj , respectively. 

The oxidation states of the lanthanide and actinide elements are summarized [K2] in Table 

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