152 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



Fig. 4 Literature observations on the effect of pH on Pu sorption to soils. A, 

 soil/solution ratio. 1/12.5 (Nishita, 1976». •.soil/solution ratio. 1/10 (Proiil. 1958). □, 

 soil/solution ratio. l/10(Prout. 1958). .soil/solution ratio. 1/20 (Rhodes, 1957). 



It is significant to note that, in the results described above, the initial ^^^Pu 

 concentration was about 3 ng/ml (1.3 x lO^^M). Experiments described by Jacobson 

 and Overstreet (1948) and Prout (1958) indicated that Pudll) was adsorbed more readily 

 than Pu(IV), which was itself adsorbed more readily than Pu(VI). However, the molar 

 concentrations of Pu used by these investigators [Jacobson and Overstreet (1948), 

 7 X 10" "^M; Prout (1958), 10~^M] were greater than those used here. Consequently the 

 reason the Pu(IV) sorption was interrnediate between Pu(III) and Pu(VI) was probably 

 due to an initial disproportionation of the added Pu(IV). The true order is probably 

 IV > III > VI, as shown in Tables 1 and 2 (intact clay). Additional support for this 

 concept is provided in data by Bondietti, Reynolds, and Shanks ( 1976), where the Kj for 



