156 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



Chemical Characterization 



Plutonium Behavior in ORNL Soil 



We have conducted a partial characterization of Pu behavior in an alluvial soil 

 contaminated in 1944 at ORNL. The nature of the Pu source material appears to have 

 been low-level waste solutions in which the Pu was probably present in monomeric forms. 

 This soil probably represents the oldest contamination event since the tlrst milligram and 

 gram amounts of Pu were extracted from the Oak Ridge graphite reactor in January and 

 February 1944. The study area was used for low-level radioactive-waste retention from 

 March 1944 to September 1944 and was subsequently abandoned. 



Because the mode of release was soluble Pu rather than calcined Pu02, the site is 

 proving invaluable for developing concepts on the biogeochemistry of Pu. Plutonium 

 distributions in the contaminated floodplain soil and biota are available (Dahlman, 

 Gartin, and Hakonson, this volume). Total soil Pu has been determined by hot 8M HNO3 

 leaching. These values are the same as those for HF— HNO3 leaches. 



Comparative Behavior of Pu, Tli, and U. Comparative extractions have been conducted 

 to compare the extractabilities of Pu, U, and Th. Two extractants are used, \M HNO3 

 and 10% sodium carbonate and 5% sodium bicarbonate. The former represents a weak 

 acid extraction, and the latter is used for U extraction in ore processing. Table 3 



Table 3 Extraction of U, Th, and Pu from 

 Floodplain Soil Using Mild Extractants 



♦Based on Ul UNO, extractable LI (8.18 Mg/g). 

 Th (16.8 /jg/g), and Pu (135 dpm/g). 



illustrates that Pu and Th are extracted similarly, whereas U is much more readily 

 extracted. Althougli U extraction changes little between the acid and basic systems, Th 

 and Pu are extracted more readily with carbonate. In the case of carbonate extraction, 

 considerable organic matter (humic material) was solubilized; dialysis studies in carbonate 

 indicate that the carbonate-extracted Pu was not bound to the solubilized organic matter 

 but was present as a diffusible carbonate complex. As is discussed later, however, some of 

 the Pu was associated with humic acids in the soil. 



Thorium-234 and plutonium-236 were added to replicate 10-g samples containing 

 20 ml of 0.5M nitric acid to further characterize the relative behavior of Pu and Th in the 

 floodplain soil. The samples were equilibrated for 0.5. 1, 4, and 24 hr. The amount of 

 indigenous 239,240pjj ^^^ ^^^Th in solution and the amount of added isotopes in 

 solution were assayed. The results are plotted in Fig. 6. The hot 8M nitric acid extractable 

 ^^ Th and '''''Pu were used as tlie basis for inventorying the total indigenous elements; 

 thus, witliin 0.5 hr for Th and 1 hr tor Pu. both indigenous isotopes achieved the same 

 soil-to-solution distribution as the added isotopes. The sluggishness of the ^'''"Pu toward 



