HYDRAULIC PERFORMANCE OF A NATURAL BENTONJTE GCL IN INORGANIC SOLUTIONS AND POLYMER TREATMENT PROPOSAL TO PREVENT DEGRADATION IN LONG TERM LANDFILL CONDITIONS

摘要

Geosynthetic clay liners (GCLs) are the most popular manufactured barriers used in landfill applications. GCLs generally contain a thin layer of sodium bentonite (dry thickness between 5 and 10 mm), sandwiched between two geotextiles or glued to a geomembrane. The excellent hydraulic performances of GCLs, have to be attributed, in absence of a glued geomembrane, to bentonite characteristics (Shackelford et al., 2000). The main problem concerning the use of bentonite as a sealing material is represented by the cation exchange of sodium with multivalent cations, such as calcium, dominant in the pore water of many soils, which causes the degradation of sodium bentonite into calcium bentonite and consequently a compression of the DDL that will turn in (1) a reduction of swelling ability, (2) expulsion of adsorbed water and (3) worsening of containment performances. To improve chemical resistance of bentonite to the cation exchange phenomenon, several innovative materials have been recently developed (Schroeder, 2001; Kolstad et al., 2004, Katsumi et at., 2008; Di Emidio, 2010; Scalia et al. 2011). The present trend, as reported in literature, is to prevent DDL compression and, accordingly, bentonite lamellae collapse, by adding large organic molecules, such polymers, that link to the montmorillonite surface and tend to maintain a wide interparticle distance even in the presence of strong electrolyte pore solutions.