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Sorption Behavior of Neptunium on Bentonite-Effect of Calcium Ion on the Sorption -

Published online by Cambridge University Press:  15 February 2011

Naofumi Kozai ,
Toshihiko Ohnuki  and
Susumu Muraoka
Naofumi Kozai
Affiliation:
Department of Environmental Safety Research, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, 319–11, Japan
Toshihiko Ohnuki
Affiliation:
Department of Environmental Safety Research, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, 319–11, Japan
Susumu Muraoka
Affiliation:
Department of Environmental Safety Research, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, 319–11, Japan
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Abstract

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 Ca2+ (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 (Kd) of neptunium for bentonite was constant from pH 2 to 7, while for pure Na-smectite Kd 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 Ca2+ in solution, an effect most pronounced at pH <5. These results show that Ca2+ limits the specific sorption capacity of Na-smectite for neptunium. Similarly, in the mixture of Na-smectite and calcite, sufficient Ca2+ was solubilized to depress neptunium sorption. This investigation demonstrates that Ca2+ contained in bentonite as exchangeable cation and released from calcite reduces the specific sorption of neptunium.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 353: Symposium – Scientific Basis for Nuclear Waste Management XVIII , 1994 , 1021
Copyright
Copyright © Materials Research Society 1995

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References

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