Actinide oxidation state

Figure 5.9. Lanthanide and actinide chemical properties. A scheme is shown of the oxidation states they present in their various classes of compounds. A rough indication of a greater frequency and a higher relative stability of each state is given by the darker blackening of each box. Notice the overwhelming presence of oxidation state 3, in the lanthanides and heavy actinides, oxidation state 2 in Eu andYb and of several higher oxidation states in U and nearby elements.

Figure 15.18 Comparison of complexation stability constants for the interaction of various ligands with different actinide oxidation states (Kim, 1986).

Because the preparative conditions of complex actinide oxides indicate that they favor higher actinide oxidation states, we have selected a model system in which both +4 and +6 actinides are easily prepared in similar oxide coordination. 

With the findings of Sects. 5.1 and 5.2 in mind, we began a series of experiments to investigate the control of actinide oxidation states by photocatalysis. In order to avoid complications associated with the photolysis of... 

Table 4 Important actinide oxidation states in the environment.

Given the variety of important actinide oxidation states, what naturally occurring anion would best effect actinide mineralization The lanthanides, chemically analogous to the trivalent actinides, occur naturally in three commercially important forms monazite and xenotime, which are orthophosphate minerals, and bastnasite, which has the approximate composition LnFCOs. Uranium ores may be divided into... 

In the present chapter, the focus will be primarily on those techniques which have proven useful, or which have some potential to develop into useful methods. The coverage of the literature will therefore be somewhat selective, although developments of the last 10-15 years will be given particular attention. The use of the multiple actinide oxidation states in lanthanide/actinide and actinide/actinide separations are... 

Fig. 9. Comparison of stabilities of 3 + /2 + lanthanide and actinide oxidation states (stable 3 + ions at left, stable 2 + ions at right).

Tables 14.4 and 14.5 list the oxidation states of the actinide elements and the color of the actinide ions, respectively. It is clear that the actinide oxidation states are far more variable than the lanthanides. The close proximity of the energy levels of the 7s, 6d, and 5f electrons almost guarantees multiple oxidation states for the actinide ions, at least in the first half of the actinide series. The multiplicity of oxidation states, coupled with the hydrolytic behavior of the ions, make the chemical behavior of the elements from protactinium to americium among the most complex of the elements in the periodic table.

Electrochemical measurements have been made of actinide ions in complexed aqueous media, especially carbonate-bicarbonate systems [66-68]. Such measurements are particularly useful in establishing the actinide oxidation states and species present in natural water and biological systems. Complexes such as fluoride, chloride, carbonate, and phosphotungstate are stronger with tetravalent than with trivalent cations, so they significantly stabilize the higher oxidation state. 

There are many oxyhalides of actinide oxidation states 34- through 6-t-. In general these are more stable than a mixture of oxide and halide, e.g. 

---