Impact of acid leachates on microtexture of bentonites used in geosynthetic clay liners

Abstract

This study reports supportive evidence, from scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM) of bentonite cakes, of the textural effects caused by reaction of concentrated sulfuric acid on the bentonite component of geosynthetic clay liners (GCLs) and how these effects may influence observed bentonite hydraulic performance. SEM images revealed that changes to the natural micro-textures of bentonite were due to interaction with acidic leachate, the effects being greater with increased concentration. It was observed from high resolution TEM images that most of the effects detrimental to hydraulic performance were related to re-arrangement of smectite quasi-crystals, as expected for textural responses to increased ionic strength. Significant bentonite dissolution was also observed in both SEM and TEM images after reaction at room temperature for as much as 48 h with sulfuric acid. The observed changes in the microtexture of the bentonite component by both SEM and TEM provide a physical explanation to the bulk experimental results as well as a benchmark for the application of GCLs under acidic conditions.