The influence of smectite content on microstructure and geotechnical properties of calcium and sodium bentonites

Ca-bentonite with 68% and 92% of smectite, and Na-bentonite with 68% and 92% of smectite were studied by XRD, chemical analysis and scanning electron microscopy (SEM) to evaluate differences in microstructure formation and geotechnical properties. Plasticity and liquid limit, water adsorption by Enslin test, free swell test and standard swell test were performed, as well as the determination of ignition loss and permeability test. fferences in bentonite quality and quantity of smectite critically influence permeability, which is confirmed by the decrease in permeability in the direction Ca (68%)→Ca (92%)→Na (68%)→Na (92%). Ca-bentonite with 92% smectite content showed similar permeability as the 68% Na-bentonite, but it retained lower water sorption characteristics. Na-bentonite is used as a sealing component in geosynthetic clay liners (GCL) and may undergo an ion exchange by calcium ions, converting it to Ca-bentonite because the calcium content of most soils is sufficient to induce such a process. All significant Na-bentonite properties are being changed when converted back to Ca form. Our study has made an attempt to uncover differences in various bentonite-type behaviors and suggests one way to improve sealing properties of Ca-bentonite with lower smectite content upgrading it by flotation to smectite-rich Ca equivalent instead of natrification.