150 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



10-5 



10-8 



10-8 



5 10-7 2 



FREE METAL (M) 



10"6 



Fig. 2 Comparison of the relative complexing of Zn, Cd, Np(V), Ca, and Sr by soil 

 humic acids (pH 7.0). 



5 X 10~^yif; if no sodium nitrate were added, strontium adsorption increased to a 

 maximum around pH 7 and then decreased. When 1% NaNOa was added, no decrease was 

 observed with increasing pH. Cesium showed the same effect: tracer Cs (5 x \Q~^M) 

 displayed maximum adsorption around pH 7.7, but increasing the Cs concentration to 

 5 X lO'^^M removed this effect. These resuUs suggest that the decrease above pH 7 to 8 

 observed with ~10~^MPu was due to dispersion of clay-size particles containing sorbed 

 ions. As the ionic strength was increased in the Sr and Cs studies, the clay remained 

 flocculated and the observed K^ increased. 



Plutonium represents an element in which the simultaneous presence of more than 

 one oxidation-state species in solution can influence the observed adsorption behavior. 

 Determination of the extent of this problem has unfortunately been ignored in most Pu 

 adsorption experiments reported in the literature. Bondietti and Reynolds (1976), 



