Hydraulic conductivity of zeolite–bentonite mixtures in comparison with sand–bentonite mixtures

Hydraulic conductivity tests were conducted using tap water on zeolite–bentonite mixtures (ZBMs), sand–bentonite mixtures (SBMs), and a zeolite–sand–bentonite mixture (ZSBM) at various bentonite contents (BCs). The hydraulic conductivities of ZBMs were at least one order of magnitude higher than those of SBMs at the same BCs. It was also determined that the hydraulic conductivity of 30% ZBM (i.e., 30% bentonite and 70% zeolite) was still higher than that of 10% SBM (i.e., 10% bentonite and 90% sand). The higher hydraulic conductivity of ZBMs with respect to SBMs is attributed to the porous structure of zeolite. Zeolite grains form a network in ZBMs that helps transmit water throughout this network. Moreover, bentonite water contents were calculated using a model proposed previously. Through the modified model, it is shown that not only the zeolite network, but also larger pores between bentonite particles may cause higher hydraulic conductivities for ZBMs. Finally, the influence of zeolite particle size on the hydraulic conductivity was tested. It was observed that the hydraulic conductivities of ZBMs were more or less the same, indicating that the hydraulic conductivity of ZBM is independent of zeolite particle size within the considered BC range.