t58 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



12 



4 8 12 



EXTRACTION TIME, weeks 



Fig. 7 Extraction of Pu from contaminated soil by chelating and cation-exchange resins. 



Mild Extractants. Bondietti, Reynolds, and Shanks (1976) reported on the transfer rates 

 of this soil-bound Pu to chelating resin. The objective was to evaluate what fraction of the 

 soil Pu would transfer from the soil sohd phase to a resin solid phase as an approximation 

 of soil— root interactions. For three soil samples, the transfer of Pu was characterized by 

 an initial period of rapid Pu transfer followed by much slower rates (Fig. 7). Between 9 

 and 1 1% of the Pu desorbed from the soil in 14 weeks. The soil-bound Pu did not transfer 

 to a cation-exchange resin (Dowex-50) (Fig. 7). These observations indicate that there is a 

 form of Pu present that will transfer from the soil to resin, but it is not bound by cation 

 exchange. Also, the mobile species are exhausted rather quickly, which suggests that only 

 Pu on the surface of soil peds is involved in the redistribution. 



Tamura (1976) reported that 7% of the Pu desorbed when equilibrated with sodium 

 citrate (pH 7.3), which suggests a fraction similar to the resin-extractable Pu. Extraction 

 of the soil with citric acid (pH 3) removed 23% of the Pu in that study. Bondietti, 

 Reynolds, and Shanks (1976), using DTPA (pH 6.5) to extract Pu from this soil, found 

 that 28% was removed with no difference between 4 and 20 hr of equilibration. In 

 addition to the extractions using organic chelating agents, the soil was equOibrated for 

 18 hr with 10 ^M sodium bicarbonate. At a 4/1 solution/ soil ratio, 0.08% of the Pu was 



