Retention of redox sensitive waste elements in compacted bentonite

The diffusion of technetium, iodine, uranium and neptunium in compacted bentonite has been studied. The possible reduction of the transport rate of these elements (i.e. redoxsensitive elements) by mixing the clay with metallic iron (for technetium, uranium and neptunium) or by adding a chemisorbent (for iodine) to the clay is reported. Technetium has an apparent diffusivity about 5 times higher in the heptavalent state (TcO4-) than in the tetravalent state (TcO(OH)2 or TcO2), uranium and neptunium in their higher oxidation state (VI and V) have apparent diffusivities about 6 and 50 times higher, respectively, than in the tetravalent state. Iodine, as I- (or IO3-), has a transport rate more than one order of magnitude lower than TcO4-. 10 references, 5 figures, 3 tables