Competitive adsorption and transport of phthalate esters in the clay layer of JiangHan plain, China

This study aimed to investigate the adsorption behavior of phthalate esters (PAEs) in the clay layer of JiangHan Plain, China, so as to make better understanding about the source and control of PAEs in groundwater. Adsorption kinetics, isotherms, and miscible displacement experiments were conducted, and different models were used to simulate the experiment data. Results showed that the adsorption kinetics followed pseudo-second-order model. The kinetic parameters showed quantitative relationships with straight and branched chain carbon numbers of PAEs. These relationships were simulated and carefully discussed. The adsorption isotherms followed linear model better. And partition coefficient (Kd) increased with the carbon chain length of PAEs. Miscible displacement experiments showed that DEHP could not flow out of the column in 100 d. HYDRUS-1D and two-site sorption model (linear, first order nonequilibrium adsorption) were used for the simulation of the breakthrough and transport curves of DMP, DEP, DBP, and DiBP. Results showed that the dispersion coefficients (D) and partition coefficient (Kd′) increased with the carbon chain length. About 10% DBP and DiBP and 1% DMP and DEP were absorbed on the type-1 sites. DMP and DEP were much easier to transfer into the type-2 sites than DBP and DiBP. DBP and DiBP might aggregate in micro-pores of the sorbent. Retardation coefficient and Damkohler number were also calculated and discussed. It was proved that clay layer is an important retarder for PAEs downward transport. However, it can be passed through if the time is sufficient.