Modified bentonite and fly ash bentonite landfill liners

Use of bentonite clay for landfill liners has certain disadvantages such as low workability, low shear strength, high swell potential, low adsorptive capacity for hydrophobic substances and increased hydraulic conductivity due to cracking. Two modifications of the bentonite were considered; one involved replacement of the exchangeable cation by a hydroxy-A1 cation and the other involved addition of fly ash to the bentonite. The hydroxy-A1 cation changes the nature of the clay from hydrophillic to hydrophobic, such that the hydrophobic material can partition onto these clays. Thus, hydroxy-A1 pillared clays and regular bentonite can be used to adsorb the entire range of pollutant species. Alberta fly ash is a non plastic silt like material with self-hardening properties. Further, fly ash is a waste by-product, and its usage should assist in mitigating the environmental problems associated with its disposal.; An experimental program was designed to study the feasibility of preparing hydroxy-A1 pillared clays and its usage in landfills. A number of parameters of fly ash bentonite mixtures were studied to test the feasibility of using such mixtures for landfill liners. Besides, a model for the hydraulic flow through compacted bentonitic clays was developed. The concepts of porous media, the electric double layer and aggregation of clays were considered to develop the model. The model was also extended for sand clay mixtures.; The test results indicate that hydroxy-A1 clays are stable and have a hydraulic conductivity of about 1 {dollar}times{dollar} 10{dollar}sp{lcub}-7{rcub}{dollar} cm/s (minimum required for a liner material). Fly ash bentonite mixtures have higher strength, lesser cracking potential and improved workability compared to bentonite alone. The leaching from the fly ash is low, and the adsorption potential of fly ash is significantly higher than its leaching potential.; The model predictions for pure bentonitic clays and for Na-bentonite fly ash mixtures match with those obtained in laboratory tests. However, further research may be required to adequately model the hydraulic flaw through Ca-bentonite fly ash mixtures.