The Effect of Cu (II) on Swelling and Shrinkage Characteristics of Sodium Bentonite in Landfills

Wastes in municipal landfills will release heavy metal cations over a long period of time. Therefore, the objective of this paper was to investigate the effect of copper (Cu) in the leachate from landfill on the swell-shrinking potential of bentonite liner. Copper sulfate solution with 4 different groups of concentrations (0 g/L, 2.5 g/L, 5 g/L, 10 g/L) were added to bentonite for conducting a series of swelling and shrinkage experiments. Then the Does Response model was used to describe the swelling and shrinkage process of bentonite in different copper sulfate solutions and the applicability of the model was evaluated. At the same time, clay mineral analysis experiments (XRD and XRF) were carried out to analyze the variation of interlayer space and element content of montmorillonite. The results show that the swell volume of bentonite decreases with the increase of the concentration of Cu (II). The rate of swelling was high and inversely proportional to the concentration of Cu (II). The shrinkage curve of bentonite could be divided into uniform velocity stage, variable velocity stage, and stable stage. The shrinkage rate at the uniform velocity stage and shrinkage at the stable stage decreased with the increase of the concentration of Cu (II). The model was suitable for describing swelling (or shrinkage) curves with smaller expansibility (or shrinkage). Results of XRD and XRF show that the erosion of Cu (II) led to the decrease of Na+ content in sodium bentonite, and then narrowed interlayer space of montmorillonite. When the solution concentration increases, both values of interlayer space of montmorillonite and Na+ content in sodium bentonite become lower, and that led to swelling and shrinkage of bentonite liner was getting smaller and smaller.