Effect of temperature and hydroxy aluminum interlayers on the adsorption of trace radioactive cesium by sediments near water‐cooled nuclear reactors

Abstract

The adsorption of 137Cs by sediments from the Savannah River Plant follows a theoretically expected linear relationship between ln Kd* and l/T where Kd* and T are the equilibrium distribution coefficient (Cs adsorbed, meg g−1/Cs+ in solution, meq ml−1) and the temperature in kelvins, respectively. The slope of these plots decreases after removal of hydroxy Al interlayers with citrate pretreatment. Hydroxy Al interlayers thus make Cs+ adsorption more temperature dependent. This thermal effect of hydroxy Al interlayers becomes more significant in sediments containing a nonswelling 2:1–2:2 intergrade clay mineral than in those containing a swelling 2:1–2:2 intergrade clay mineral. The phenomenon is explained by considering hydroxy Al interlayers as a source of hydronium ions H3O+ which compete with Cs+ for exchange positions in wedge zones. An increase in temperature favors an increase in H3O+ ions, which in turn favors less adsorption of Cs+. Aside from their thermal effect the positively charged hydroxy aluminum polymeric groups drastically decrease the cation exchange capacity and consequently the adsorption of cesium.