Change of microstructure of clays due to the presence of heavy metal ions in pore water
Institut de Recherche en Génie Civil et Mécanique-GeM, UMR CNRS
6183, Ecole Centrale de Nantes, 1 Rue de la Noë
Nantes cedex 3,
The compressibility of engineered barrier clays is, to a large extent, controlled by microstructure change due to the presence of chemical ions in clay-water system. This paper aims to investigate the change of microstructure of clays due to the presence of heavy metal ions in pore water. We use two pure clays (kaolinite and bentonite) in the study. One-dimensional consolidation tests were performed on reconstituted samples, which are prepared with distilled water and three types of heavy metal solutions (Pb(NO3)2, Cu(NO3)2, Zn(NO3)2,). In order to better understand the impact of chemical pore fluid on microstructure of the two clays, following the consolidation test, scanning electron microscope (SEM) observations and mercury intrusion pore size distribution measurements (MIP) were conducted. Due to the measurement range of MIP, which is only allowed to measure the minimal pore size 20 Å, BET method by gas sorption, whose measurement pore size range is from 3.5 Å to 500 Å, is used to measure the micropore size distribution. By this method, specific surface area of the soils can be also determined. It can be employed to demonstrate the difference of creep performance between the soils. Furthermore, a series of batch equilibrium tests were conducted to better understand the physical-chemical interactions between the particles of soils and the heavy metal ions. With the further consideration of the interparticle electrical attractive and repulsive force, an attempt has been made to predict the creep behaviour by using the modified Gouy-Chapman double layer theory. The results of calculation were compared with that of tests. The comparison shows that the prediction of compressibility of the clays according to the modified double diffuse layer theory can be reasonably agreement with the experimental data.
Key words: microstructure / BET method / clay / heavy metal contaminant / consolidation
© Owned by the authors, published by EDP Sciences, 2010