SEM Study of Mineralogical Changes to GCLs Following Permeation by Strongly Alkaline Leachates

Geosynthetic clay liners (GCLs) are important components of hydraulic barriers in waste containment systems, but leachate from the mining industry can alter their hydraulic performance. Usually increases in saturated hydraulic conductivity result, but sometimes decreases occur; the latter believed to be associated with pore-filling reactions. We report here the results of a scanning electron microscopy (SEM) study to determine whether pore-filling reactions occurred in GCLs permeated with solutions of 1.3 mM CsCl (GCLA) or 1M NaOH +1.3 mM CsCl (GCLB). SEM images reveal that in GCLA hydration induced swelling in resulted in an open fabric but ∼5 μ thick, dense and low porosity interfaces of smectite particles having a highly orientated pore structure was observed between clay domains. X-ray mapping conducted across a compression join (and into the domains on either side) indicated that Cs was largely concentrated near the compression zones, indicating that advective transport of CsCl may be along preferential flow paths between domains. Where compression joins existed in GCLB, individual domains were <30 μm in extent and direct evidence of precipitation of pore-filling phases was observed. Analysis indicates that average pore diameters were reduced by up to 30 times and flow path tortuosity would increase significantly.