Adsorption Behavior of PAEs on Loess-HTMAC Bentonite and Its Effects on the Performance of Cut-Off Walls

Phthalic acid estes (PAEs) are typical organic contaminants in landfill leachate. Loess-bentonite cut-off walls were widely used to control the transport of organic contaminants. Bentonite modified by hexadecyltrimethylammonium chloride (HTMAC-B) mixed with loess material may play a good role in enhancing the adsorption of organic pollutants. The adsorption batch tests were used to analyze the adsorption characteristics and mechanisms of loess-HTMAC-B for single and mixed solutions of dimethyl phthalate (DMP) and diethyl phthalate (DEP). Contaminant transport simulations were then performed to investigate the performance of the modified bentonite-loess cut-off wall. The results show that the adsorption capacity of loess-bentonite for single DMP can be 1.7 times lower than that for mixed DMP. Results of numerical transport simulations based on the adsorption results show that the Toth model performs better than the Langmuir model as it can well capture adsorption behavior induced by the heterogeneous surface morphology due to the presence of an HTMAC cation in the bentonite interlayer. We show that HTMAC amended loess-bentonite can effectively increase the breakthrough time of PAEs. In order to meet the designed service time of 50 years, P-L should be controlled below 0.9 for DMP and 10.1 for DEP in the case of 1.2 m cut-off walls.