Effect of salinity on the microscopic interaction and sedimentation behavior of halloysite clay

Abstract Pore-fluid salinity has a predominant effect on the formation of soil suspensions, especially for clays adjacent to the ocean, including bays, lagoons, sounds, slough, and estuaries. However, the clay response to changes in pore fluid salinity (e.g., salt intrusion or extrusion) has yet to be investigated. Herein, the influence of salinity on the microscopic interaction and sedimentation behavior of halloysite clay was investigated in an aqueous condition. Macro-scale sedimentation experiments and in-situ microscopic observations showed that halloysite clays in pore fluids with high ionic strength tended to disperse because salt ions weaken the edge-to-face halloysite fabrics. In the ensuing drop of the salinity, salt ions adsorbed onto the double layer of the clay surface were not reversely released. Comparing to sediment with a similar initial salinity, desalination resulted in weakened edge-to-face structures (a lower initial settling rate) and loose final sediment (a higher final sediment void ratio). Our study provides a thorough understanding of the salt effect on sediment formation, including changes in the microscopic clay particle fabric as salinity changes.