Transport of dimethyl phthalate on loess with modified bentonite: A batch and column test investigation

Abstract

Phthalic acid ester (PAE) is a toxic pollutant commonly found in high concentrations in municipal solid waste landfills. Soil–bentonite is widely used as a barrier material to control groundwater contaminants from landfill leachates. Traditional soil–bentonite materials always have a limited capacity for organic pollutant adsorption. To address this issue, the adsorption and transport behavior of dimethyl phthalate (DMP) on loess amended with two kinds of modified bentonite (HTMAC-B, modified with hexadecyltrimethylammonium chloride; CMC-B, modified with hydrophobic cationic surfactant, and carboxymethyl cellulose) were investigated. The kinetics of DMP adsorption indicates that film diffusion contributes significantly to the kinetic adsorption of DMP on HTMAC-B. The adsorption isotherm results showed that partitioning dominated DMP adsorption on loess with both modified bentonites. Owing to the in-ionic sites in HTMAC-B, which attracted hydrophobic compounds such as DMP, the adsorption capacity of 5 % HTMAC-B-amended loess (LH) was increased by a factor of 3.2. However, because CMC-B provided mostly ionic sites, 5 % CMC-B-amended loess (LC) had a little effect on DMP adsorption. The hydraulic conductivity values of LH and LC were 5.95 × 10−10 and 1.65 × 10−11 m/s, respectively. The X-CT result showed that there is a significant porosity change for both LH and LC. Dual-porosity model reveals that the leaching process primarily affects micro-pores, rather than larger pores in the soil matrix. The predicted retardation factors for LH and LC were 38.89 and 9.67, respectively. When using loess-bentonite as barrier material, the amendment of HTMAC-B and CMC-B can help to increase the retardation ability and reduce the permeability, respectively.