Utilization of bentonite-embedded zeolite as clay liner

Abstract

Bentonite-embedded zeolites (BEZ) with different bentonite content were developed for possible use as barrier material, as an alternative to bentonite-embedded sand (BES). Adsorption characteristics of Na-bentonite, Ca-bentonite and natural zeolite; cation exchange capacity (CEC) of Na-bentonite and natural zeolite; volumetric shrinkage, compaction characteristics; and hydraulic conductivity of the mixtures were investigated. Adsorption isotherm and CEC results indicate that the lead (Pb) adsorption capacity of natural zeolite is almost one-third of Na-bentonite. Considering the zero adsorption capacity of sand, the practical implication of high CEC is the remarkable savings in terms of both materials used and space where the waste is disposed. Furthermore, volumetric shrinkage and compaction results reveal that the optimum moisture content of BEZ is far less than the moisture content that can create 4% volumetric shrinkage, which is the upper limit for liner materials. Hydraulic conductivity tests on BEZ with 10% and 20% bentonite content show that the hydraulic conductivity of both mixtures are less than 1×10 −9 m s −1, which meets the common regulatory requirements. Moreover, the test results reveal that variations in hydraulic conductivity of the mixtures with different stress conditions are negligible for practical purposes.