Diffusion, sorption and stability of radionuclide-organic complexes in clays and clay-organic complexes
The dependence on various parameters of the diffusion coefficient of neptunium(V) in clay systems is studied. The effect of the clay mineralogy, the charge compensating cation in the clay, the ionic strength of the background perchlorate solution and the presence of three organic ligands are investigated. The diffusion coefficients are compared to those predicted when diffusion occurs only in the liquid phase and adsorption is reversible. Agreement is fairly good. An approximation to the diffusion coefficient can thus be obtained from readily measured experimental parameters. There is no evidence of surface phase diffusion. The most significant factor in determining the diffusion coefficient is the magnitude of the distribution ratio which is highly dependent on the nature of the clay. Neither EDTA nor citrate modified the diffusion coefficient. Although the presence of 1 or 100 mg/dm3 of Aldrich humic acid had little effect on the distribution ratio of neptunium, it caused a lowering of the measured diffusion coefficient. This is interpreted in terms of the limiting liquid phase diffusion coefficient and the true liquid phase impedance factor of neptunium-humic acid complexes.
Bibliographic Reference: EUR 13432 EN (1991) 54 pp., FS, ECU 6.25
ISBN: ISBN 92-826-2662-8
Record Number: 199110986 / Last updated on: 1994-12-02
Original language: en
Available languages: en