Effects of compression on porous texture of clay powder: Application to uranium diffusion

• Published in: Chemical engineering research & design Vol. 92; no. 7; pp. 1267 - 1278
• Main Authors: Korichi, S., Keddam, M., Bensmaili, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2014
• Subjects: Adsorption; Clay (material); Clay minerals; Diffusion; Diffusion effects; Mathematical models; Porous media; Radioactive waste; Simulation; Surface layer; Texture; Uranium; Porous media; Radioactive waste; Adsorption; Simulation; Diffusion
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2013.11.003

•We characterize the porous texture of compacted bulk and Na-saturated clay.•We perform in-diffusion tests to investigate the effect of density on Uranium diffusion.•The apparent diffusion coefficients values of Uranium are determined.•Uranium diffusion depends on surface and pore diffusion models.•Results obtained will be used as basic data for the safety assessment of a repository. This paper presents the results of tests conducted on the compaction properties of clay. Swelling clays of Algeria are being examined as components of the buffer material. Knowledge of the porous texture in clay samples is a useful element in the microstructural characterization of such materials. The prepared materials were characterized by X-ray diffraction, Differential Thermal and Thermo Gravimetric Analysis, Laser Granulometry, Scanning Electron Microscopy, mercury porosimetry and nitrogen adsorption/desorption to obtain information about their structure and surface texture. The cationic exchange of clay minerals, in particular smectites, influences the cation retention and diffusion processes. These processes influence the migration of contaminants from waste disposal sites through clay barrier. In the present work we studied the effect of cation exchange and compaction on the textural properties of clay. Pellets of the Na-saturated and bulk clay samples were prepared by compression of the powder samples using uniaxial stress at different pressures in order to obtain different densities. The pressures of 31–127MPa are applied for the production of cylindrical samples with diameter of 20mm and heights of 15–30mm. The effect of compaction of clay on the diffusion behavior of uranium was studied for the safety assessment of the radioactive waste. The diffusion process of uranium in compacted clay has been modeled by second Fick's law taking into account the effect of sorption and considering the non-steady state. The diffusion coefficients and profiles concentration values of uranium were calculated by computational method using numerical program based on Newton–Raphson algorithm.