Response of fly ash-bentonite based landfill liner to chemical solutions

Abstract

Hydraulic barriers are a part of lining systems which are responsible for preventing a potential pollutant present in the waste containment from migrating to surface water, groundwater and thus polluting them. Natural clays, calcium or sodium-based bentonite mixed with specific geo-materials are widely used in the construction of hydraulic barriers such as liners and covers due to their low hydraulic conductivity (i.e. k ≤ 10-7 cm/sec). However, the long term interaction of landfill liner with leachate leads to the change in its permeability. Thus, addressing the need to study the interaction of leachate with liner material. In the present study, Sodium bentonite (low sodium content) instead of calcium bentonite was used as the hydraulic conductivity of Na-bentonite is approximately five times lower than that of the Ca-bentonite at similar void ratios (Mesri and Olson 1971). Chlorides and Sulphates are widely distributed in nature and are common constituents in the leachate (Arasan and Yetimoglu 2006; Yilmaz et al. 2008), the chemical properties of the landfill leachate listed by Kayabali et al. 1998, also showed larger amounts of Cl-, Na+, K+ ions which are exchangeable. Therefore, chlorides and sulphates of different cations such as Sodium, Calcium, and Iron etc. are chosen for the permeation process, which best represents the in-situ conditions in the laboratory. The preference for replacement is the lyotropic series, which is Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Ba2+, Cu2+, Al3+, Fe3+ (Sposito 1981; McBride 1994). Because Na+ is at the lower end of the lyotropic series, Na-bentonites are more prone to cation exchange when permeated with solutions containing divalent or trivalent ions (Sposito 1981). Therefore, in the present study, bentonite mixed with fly ash (FA-B) was permeated with different chemical solutions and their chemical compatibility as a liner material was assessed.