Redox chemistry isolating elements

A second reason for the wealth of chemical investigations of the early actinide elements is the relative diversity of their chemistry. While the chemistry of the later actinides is most often restricted to that of the tri- and tetravalent oxidation states, compounds of the early actinides can be isolated in all oxidation states from +3 to +7. The accessibility of a range of oxidation states is the impetus for signficant chemical interest in the early actinides, but also vastly complicates investigation of these elements under some circumstances, such as aqueous redox behavior. In the case of plutonium, ions in four different oxidation states (+3, +4, +5, and - -6) can exist simultaneously in comparable concentrations in the same solution. 

Many of the actinoids are also separated by exploiting their redox behavior. Thorium is exclusively tetravalent and berkelium is chemically similar to cerium, so iodate precipitation of Th and extraction of Bk(IV) with bis(2-ethylhexyl)orthophos-phoric acid (HDEHP) are used to isolated these elements. The differing stabilities of the (III), (IV), (V), and (VI) states of U, Np, and Pu have be exploited in precipitation and solvent extraction separations of these elements from each other and from fission product and other impurities with which they are found. Because of its technical importance, the process chemistry to separate U and Pu in nuclear materials has been highly developed. Extraction of Bk(IV) with HDEHP is used to separate Bk from neighbouring elements. 

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