Abstract
The hydraulic conductivity of Na-montmorillonite in dual-cation solutions of Na+ and Mn+ (Mn+ = K+, Ca2+, Zn2+ and Al3+) with a constant ionic strength of 0.1mol/L was determined. The focus of this study was on the influence of Mn+ on the grain-size distribution of montmorillonite and hence its hydraulic conductivity. All the tested cations showed a high affinity towards montmorillonite, and the high valency favored the exchange between Mn+ and Na+. The hydraulic conductivity of montmorillonite increased to the maxima and then decreased in a left-skewed log-normal shape as the cation exchange progressed. The grain size of montmorillonite concurrently decreased monotonically with the cation exchange. The XRD patterns of montmorillonite confirmed the occurrence of demixing of Na+ and K+ in the interlayers. It is proposed that the rearrangement and reaggregation of grains during cation exchange occurred, leading to variations in the hydraulic conductivity of montmorillonite.
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