Sorption behavior of neptunium on bentonite -- Effect of calcium ion on the sorption
- Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Dept. of Environmental Safety Research
The sorption behavior of neptunium on bentonite was studied with batch type sorption and desorption experiments over a pH range of 2 to 8. A series of parallel studies using Na-smectite, Ca-smectite and admixtures of Na-smectite and calcite quantified the capacity of Ca{sup 2+} (which occurs in bentonite as an exchangeable cation of smectite and as a component of calcite) to inhibit the sorption of neptunium. The distribution coefficient (K{sub d}) of neptunium for bentonite was constant from pH 2 to 7, while for pure Na-smectite K{sub d} increased below pH 5 due to specific sorption of neptunium on Na-smectite. Specific sorption was defined as occurring when neptunium could be desorbed by a strong acid (1 M HCl) but was stable in the presence of 1 M KCl. It was found that the quantity of neptunium sorbed on Na-smectite was inversely proportional to the concentration of Ca{sup 2+} in solution, an effect most pronounced at pH < 5. These results show that Ca{sup 2+} limits the specific sorption capacity of Na-smectite for neptunium. Similarly, in the mixture of Na-smectite and calcite, sufficient Ca{sup 2+} was solubilized to depress neptunium sorption. This investigation demonstrates that Ca{sup 2+} contained in bentonite as exchangeable cation and released from calcite reduces the specific sorption of neptunium.
- OSTI ID:
- 382880
- Report Number(s):
- CONF-941075--; ISBN 1-55899-253-7
- Country of Publication:
- United States
- Language:
- English
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