The redox chemistry of Pu(V)O 2+ interaction with common mineral surfaces in dilute solutions and seawater
It has long been recognized that the Pu 4+ ion can be readily adsorbed on solid surfaces, but it has been assumed that the generally more abundant Pu(V)O 2+ ion should have little affinity for surfaces. Our results indicate that Pu(V)O 2+ can be adsorbed from dilute solutions and seawater on goethite, aragonite, calcite, and δ-MnO 2. Adsorption on δ-MnO 2 is severely depressed in seawater, probably as a result of site competition with seawater cations. The sorption behavior of PuO 2+ is influenced by oxidation-reduction reactions occurring on the mineral surfaces. Adsorption on δ-MnO 2 results in oxidation of adsorbed Pu(IV) and Pu(V) to Pu(VI). However, adsorption on goethite results in a reaction in which Pu(IV) and Pu(VI) are formed on the mineral surface. The Pu(VI) is slowly reduced to Pu(IV), leaving Pu(IV) as the dominant surface Pu species. This reaction can be photochemically catalyzed. PuO 2+ adsorbed on carbonate minerals behaves similarly to Np(V)O 2+ and undergoes little change in oxidation state after adsorption.