The diffusion of sodium and iodide ions and of urea in clay pastes

• Published in: Journal of colloid science 1957-02, Vol.12 (1), p.40-52
• Main Author: Bloksma, A.H
• Format: Article
• Language: English
• ISSN: 0095-8522
• DOI: 10.1016/0095-8522(57)90027-2

By means of layer analysis and the use of radioactive isotopes the author measured the rates of self-diffusion of sodium and iodide ions in clay-water pastes. In the same pastes the diffusion rates of sodium iodide and of urea were measured. The clays used were montmorillonite and kaolinite having sodium ions as adsorbed ions. By comparison of the diffusion rate of iodide ions with that of urea it could be made plausible that the retardation of the iodide ions in these pastes is due to steric hindrance; the mobilities of the iodide ions, as calculated from these data, were approximately 0.4 to 0.5 times as large as the mobilities in aqueous solutions. Assuming that the dissolved sodium ions in the pastes are retarded in the same degree as the iodide ions one obtains for the mobility of the adsorbed sodium ions in the montmorillonite pastes 0.37 and in the kaolinite pastes 0.28 of their mobility in aqueous solutions. On the basis of these experiments the retardation of the adsorbed ions cannot be divided into a part caused by the geometry of their diffusion path and a part caused by forces exerted upon them by the wall charges.