Physicochemical analysis of permeability changes in the presence of zinc

Permeability measurements were carried out on specimens of a compacted natural montmorillonite polluted by zinc. The permeability of the polluted clay is higher than that of the clay saturated with water and increases with the zinc concentration between 0.01 and 1 M. The permeability of the sample saturated with water is 2.9 · 10− 12 ms− 1; its value is multiplied by 1.3 when the sample is saturated by a 0.01 M zinc solution and 1.6 for a 1 M solution. The aim of this paper is to study the changes in the particle organisation and porosity of the samples due to the presence of the metals by using several physicochemical methods and to correlate the permeability changes to fabric changes. Both X-ray diffraction and BET measurements indicate an increase in the particle size when the zinc concentration increases from 0 to 1 M. X-ray diffraction results suggest that, for the sample saturated with the 0.01 M solution, the fabric is flocculated (isotropic) whereas, when the zinc concentration increases to 1 M, the fabric becomes more anisotropic. Mercury intrusion porosimetry shows that the increase in the zinc concentration results in an increase in the inter-aggregate pore spaces that become progressively larger, whereas the interparticular pore volume decreases. All these results are supported by SEM observations and highlight the fact that the permeability changes are due to a reorganisation of the particles leading to fabric changes.