Reactions of 144Ce in Solution and Suspensions of Soil Humie Acid and Bentonite

Abstract

AbstractA study was made of the formation of radiocolloids by 144Ce and the adsorption of Ce by equilibrated suspensions of humic acid, bentonite clay, and a mixture of these two colloids saturated with either Ca or K and H. The availability of Ce in these suspensions was measured using excised roots. Ionic strength, Ce concentration, and pH were critical factors affecting the equilibrium between radiocolloidal and monomeric Ce. As ionic strength and Ce concentration decrease and as pH increases the equilibrium is shifted towards the radiocolloidal form of Ce. At pH 6.5 and ionic strength 10‐3 about 90% of the Ce in a solution is in the radiocolloidal form. A multiple regression equation was presented which showed the effects of pH, ionic strength, and Ce concentration on the formation of radiocolloidal Ce in salt solutions. Humic acid adsorbed much greater amounts of 144Ce and restricted uptake by barley and soybean roots more than did bentonite in the Ca‐H saturated system. However, humic acid and bentonite adsorbed similar amounts of 144Ce in the K‐H saturated systems. Mixing bentonite and humic acid produced a synergistic‐type effect in regard to Ce adsorption. It was proposed that the strong bonding of Ce by Ca‐humic acid and humic acid‐bentonite mixtures resulted from a more favorable orientation of the humic acid molecule for chelation of Ce.