RELA TI ON SHIP OF MICR OBI A L PR OCESSES 307 



6200 - 



g 4960 



D 



Z 



O 3720 



I- 

 D 



a. 



m 



_i 



CQ 



D 

 _l 

 O 



00 



2480 



1240 



20 40 



TIME OF CONTACT, hr 



60 



Fig. 3 Quantity of soluble plutonium removed from three soils by 0.0171/ CaCK . Soil : 



solution = 1 : 100. o o, distilled water. • •, O.OlAf, CaCl.. [From Garland, 



Wildung, and Routson (1976).] 



and 0.0 IM CaCl2 differed with soil type. In the CaCli solution, solubility was lowest in 

 the Muscatine soil, which exhibited higher silt and clay content than the other soils. 

 Importantly, at equilibrium there was more plutonium extracted by water than by O.OIM 

 CaClo in the Muscatine soil. The Hesson and Ritzville soils did not exhibit this property. 

 This may be related to a difference in the dispersibility of fine colloids in this soil and/or 

 the presence of higher concentrations of stabilizing ligands. However, the lack of a 

 proportional dilution effect (not shown in Fig. 3) in the water extractability of 

 plutonium at lower solution-to-soil ratios in this soil, as compared with that in the 

 Ritzville and Hesson soils, provided presumptive evidence for the presence of a dispersible 

 ligand in higher concentration in the Muscatine soil. 



Applying diffusion principles to characterization of mobile plutonium species in soils. 

 Garland and Wildung (1977) estimated the concentrations and molecular weights of 

 mobile plutonium in five surface soils representing a range in particle size distributions. 

 pH (4.4 to 6.2), organic C (0.7 to 12.5%), and cation-exchange capacities (14 to 

 45 meq/100 g). Diffusion coefficients were calculated from measurements of the rate and 

 extent of plutonium migration from soil through an agar matrix. The diffusion 

 coefficients calculated for the most mobile species in the five soils varied from 1.5 to 

 3.0 X 10"^ cm^/sec (Table 2). Estimated concentrations and molecular weights of the 

 most mobile plutonium components in the five soils ranged from 9 to 55 pg/g and from 

 5000 to 21,000 g/mole, respectively. Thus estimated concentrations of the most mobile 

 plutonium species were of the same order of magnitude as those observed by water 

 extraction and subsequent ultrafiltration through the 0.001 0-)Um membrane (Table I). 

 This membrane retained Pu-DTPA (molecular weight. 1700). Hypothetical globular 

 peptides of molecular weights of less than 500 would pass through this membrane. 

 However, if the molecule were a hydrated PuO^ sphere of similar dimensions, it would 



