STUDY ON ADSORPTION OF ~(237)Np(Ⅴ) ON BENTONITE

The adsorption of 237Np(Ⅴ) for bentonite as buffer/backfill material is investigated.The adsorption coefficients of 237Np are determined for three kinds of bentonite under atmosphere and anoxic atmosphere. Furthermore, it is studied that how Kd values are affected by pH and CO2-3. The results shows as follows: (1)Adsorption coefficients Kd under atmosphere: mixed bentonite, 47.3 mL/g; Mgbentonite, 52.0 mL/g and Cabentonite, 42.4 mL/g.The corresponding Kd under anoxic atmosphere:89.3 mL/g,38.8 mL/g and 29.0 mL/g, respectively. (2)Under anoxic atmosphere,when pH is lower than 9.2, Kd of the mixed bentonite increases with the increase of pH and the biggest Kd value appears at pH=9.2. (3) Kd of the mixed bentonite gets lower in high carbonate concentration when the total neptunium concentration is smaller than the solubility of NaNpO2CO3.