Solubility and redox equilibria of plutonium

In this comprehensive plenary presentation, Thomas Fanghänel of the Joint Research Center of the European Commission at the Institute for Transuranium Elements, Karlsruhe, Germany, offered a plethora of information on the redox behavior of aqueous systems containing plutonium solids at the element’s four environmentally common oxidation states (III, IV, V, and VI).

Before plunging into the rather extensive substance of his presentation, Fanghänel reviewed the impressive plutonium chemistry initiative at Karlsruhe, where analytical methods for determining speciation of plutonium solids, aqueous species, and colloids encompass quite a large array of techniques. Presenting an equally large array of experimental findings, Fanghänel offered an updated view of plutonium’s aqueous equilibria, one including a more-current view of this chemistry, with the inclusion of both superstoichiometric oxyhydroxides and of Pu(IV)-containing colloids.

His assertion was essentially that in this more-complete system, total plutonium solubility and distribution of oxidation states, can be explained solely in terms of equilibrium thermodynamics, somewhat downplaying processes such as radiolysis. Establishing the parameters for this system required, of course, accurate experimental determination of concentrations of the various species, using techniques such as laser-induced breakdown detection (LIBD) for colloid quantification (see ARQ, 3rd/4th Quarters 2003).

Continued...