ASSOCIATIONS OF Pu AND OTHER ACTINIDES IN SOILS 131 



9 10 



Fig. 3 Estimated concentrations of hydrolyzed Pu(lV) species in solutions saturated 

 with crystalline PuO^. (Adapted from C. F. Baes and R. E. Mesmer, The Hydrolysis of 

 Cations, John Wiley & Sons, Inc., New York, 1976.) 



however, reported the presence (and problem) of multiple oxidation states in Pu— clay 

 equilibrations. These data are summarized in Table 2. 



When ^^^Pu(IV) (as the nitrate) was added to treated clays, the organic-matter 

 removal treatment showed the least Pu sorption at 3 weeks (61.5%). With time, sorption 

 values approached the other two treatments (i.e., 99+%). The reduced adsorption was not 

 directly caused by the removal of organic matter but was influenced by disproportiona- 

 tion of Pu(IV), yielding Pu(III) and Pu(V) and/or Pu(VI) during the tracer addition. The 

 low initial adsorption in the organic-matter removal treatment was apparently due to the 

 fact that the clays were "oxidized" from the NaOCl treatment used to remove organic 

 matter and the PuOt and/or PuOj , resulting from disproportionation, became 

 stabilized. For the Fe removal treatment, the clays were in a reduced state, which 

 minimized the presence of Pu(V + VI). The memory of these treatments is observable 

 2 yr after treatment (Table 2). For the intact clay, 79% of the soluble Pu was present as 

 Pu(III + IV) (Bondietti and Reynolds, 1976). The largest amount of oxidized Pu 

 [Pu(V) + Pu(VI)] was found in the organic removal treatment (35%o). Very little oxidized 

 Pu was found in the iron treatment (7%). The presence of more than one oxidation state 

 in the control solutions provides support for an initial disproportionation reaction since 

 oxidized or reduced clay surfaces were not present. 



