A Study on Hydraulic Properties of Compacted Fe(III)-montmorillonite

Abstract

Hydraulic conductivities were determined for compacted Fe(III)-montmorillonite sample. The Fe(III)-montmorillonite sample used in this study, which was prepared by the ion-exchange treatment of Namontmorillonite in FeCl 3 solution, contains less than 20% of Na þ ions as exchangeable cations and negligibly small amounts of iron precipitates. The measured hydraulic conductivities of compacted Fe(III)-montmorillonite were determined to be the order of 10 À9 , 10 À11 , and 10 À13 m s À1 at dry densities of 0.80, 1.01, and 1.20 Mg m À3 , respectively. These values were found to be kept constant during the experimental period, suggesting no significant change in the physicochemical properties of Fe(III)-montmorillonite during the experiment. When compared with Na-montmorillonite, remarkably high values of hydraulic conductivities were found for Fe(III)-montmorillonite at the dry densities of 0.8 and 1.0 Mg m À3 . On the other hand, almost the same value of hydraulic conductivity was obtained at the dry density around 1.2 Mg m À3 . This different effect of exchangeable cations on the hydraulic conductivity of montmorillonite could be attributed to the different sizes of macropores in compacted montmorillonite and/or the different thicknesses of electrical double layers formed over montmorillonite sheets.

A model for estimating the hydraulic conductivity of bentonite under various density conditions

“…Figure 6 shows the relation of the effective montmorillonite density and hydraulic conductivity, which is the comparison of this study with experimental data of previous studies (Suzuki et al 1992;Matsumoto et al 1997;Maeda et al 1998;Hasegawa 2004;Butsuda et al 2006;Ito et al 2010aIto et al , 2010b. For Na-montmorillonite, the M&Q model of n ¼ 3 is in good agreement with the experimental data of previous studies.…”