ASSOCIATIONS OF Pu AND OTHER ACT IN IDES IN SOILS 157 



o 



Z) 



o 





< 



Q 



LU 



Q 

 Q 

 < 



_l 

 < 



o 



LU 



o 

 cc 



2 5 



EQUILIBRATION TIME, hr 



Fig. 6 Comparative behavior of added ^^*'Pu, ^^^Th, and indigenous 2 3 9.24opu ^j^j 

 ^ ^ ^ Th during equilibration with O.SM HNO3 . Soil was contaminated with ^ ^ ' "^ "" Pu in 

 1944. 



50 



equilibration during the first 0.5 hr is not yet understood. It may have been due to the 

 presence of a small amount of Pu(V and VI) at the start of the equilibration. It is 

 apparent, however, that the SM nitric acid soluble isotopes rapidly redistribute in the 

 same manner as the added isotopes and that the solution-phase indigenous isotopes are in 

 equilibrium with soil-bound elements. This behavior strongly suggests that both Pu and 

 &M nitric acid soluble Th are surface sorbed rather than occluded or trapped in mineral 

 matrices. The strong carbonate-extraction results further support this concept since only 

 a few elements are soluble in this extractant. Iron, for example, is not solubilized. 



Other Observations on Physicochemical Associations. Bondietti, Reynolds, and Shanks 

 (1976) discussed the probable association of part of the Pu with soil organic matter. This 

 conclusion was based on the solubilization of part of the soil humic acids using chelating 

 resin (Na form). The resin was prebuffered to the soil pH (6.5); the subsequent 

 decalcification of soil solubilized 15% of the soil organic C. These soluble humates 

 contained 5% of the soil Pu. In addition to the humic-associated Pu, 13% of the Pu was 

 associated with the resin itself. Assuming equal distribution of Pu with soil organic C 

 (which is not likely) and assuming that the resin-associated Pu was organically bound 

 initially, 55% of the Pu at most was associated with organic matter. In reality, the 

 fraction was probably substantially less. Repeated treatments of the soil with NaOCl to 

 destroy organic matter did, however, remove 82% of the soil Pu. The bleach treatment, 

 which was conducted at pH 9.5, minimized inorganic mineral destruction. Removal of 

 most of the Pu with bleach also suggests that the Pu was surface sorbed. 



