Engineering investigation of zeolite-bentonite mixtures for landfill liner applications

Industrial, municipal as well as nuclear wastes should be capped into impervious liners in order to protect the environment from the chemical attack and to prevent subsurface contamination. In general, clay liners are used for this purpose for their low hydraulic conductivity and relatively high mechanical and chemical stability during the entire period of their life. Recently, zeolite-bentonite mixtures (BEZ) are proposed as an alternative to clay liners. However, the study on the use of zeolitebentonite mixtures as landfill liners is very limited. In this dissertation, a study on determining the engineering properties of BEZ is presented. The adsorption, compaction, volumetric shrinkage characteristics as well as hydraulic conductivity behavior of BEZ were investigated in this study. The obtained results were compared with the same characteristics of sand-bentonite mixtures (BES). The experimental data obtained are analyzed herein. Factors affecting the adsorption characteristics of zeolite and bentonite are discussed. Compaction characteristics of either of BEZ or BES are determined and volumetric shrinkage behavior is investigated by means of compaction energy, bentonite content, dry unit weight and compaction water content. Detailed hydraulic conductivity tests are conducted for BEZ in order to determine the effects of smearing, aspect ratio, hydraulic gradient, permeameter type and grain size of zeolite on the permeability. The role of bentonite in the binary mixtures is evaluated by modeling the water contents of bentonite based on the experimental data. At the end, conclusions and recommendations are presented regarding the engineering properties of the mixtures. Keywords: zeolite-bentonite mixture, sand-bentonite mixture, heavy metal removal, compaction, volumetric shrinkage, hydraulic conductivity, bentonite water content