Chemical Compatibility of a Fly ash-bentonite based Hydraulic Barrier

To assess the durability of the liner material,it is important to study its chemical compatibility. In an attempt to define the hydraulic conductivity characteristics of clay liners, use of normal water is far from being representative of the in-situ conditions. Therefore, influence of chemical solutions (inorganic) of different concentrations on hydraulic conductivity of fly ash-bentonite mixtures used as hydraulic barriers was examined. Hydraulic Conductivity of the liner material proved to be more sensitive to the permeant solution. The bentonite content in the fly ash-bentonite mixture is taken up to 15% @ 5% increment starting from 5%. The permeant solutions used include NaCl, NaOH, HCl, CaCl2, H2SO4, and FeCl3 which are chosen to best represent the acidic, basic, neutral nature of the landfill leachate as well as to better portray the effect of monovalent, divalent, trivalent cations present in the in-situ landfill leachate. Initially for a lower bentonite content, NaCl solution prove to be more prominent and to have more influence on the hydraulic conductivity than at higher bentonite content. The effect of the valence of cation is more at higher concentrations than at lower concentrations (0.01M). An overall percentage decrease in the permeability for fly ash-bentonite mixture with 5% bentonite content from 0.01M to 1M NaCl solution is reduced from 343% to 85% for fly ash-bentonite mixture with 15% entonite content. Highest increase in the permeability of order 103times is observed when FeCl3 is used as a permeant solution,which ensured higher valence ations has significant effect on the hydraulic conductivity characteristics and are to be considered the most important while designing a landfill liner