Influence mechanism of organic matter and low-molecular-weight organic acids on the interaction between minerals and PAHs

Abstract

Investigate the effect of soil organic matter (SOM) and low molecular weight organic acids (LMWOAs) on minerals adsorption of PAHs. Batch adsorption experiments have been carried out to study the adsorption of PAHs (Naphthalene (NaP), Phenanthrene (Phe) and Pyrene (Pyr)) by minerals (Montmorillonite (Mnt), kaolinite (Kln) and calcite (Cal)). This research found that compared with Kln and Cal, Mnt showed the maximum adsorption capability for PAHs. And the order of PAHs adsorption by Mnt was: Pyr > Phe > Nap, which corresponds to the octanol-water partition coefficient (K_ow) of different PAHs. The adsorption kinetic and isotherm were well fitted by Pseudo-second-order kinetic model, Freundlich and Linear isotherm model. Furthermore, inorganic ions (Ca²⁺) impacted PAHs adsorption by competitive adsorption and cation-π interactive. Cal has the maximum desorption of PAHs among three minerals, and there was desorption hysteresis phenomenon. Field emission-scanning electron microscope (Fe-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) analysis indicated that SOM enhanced the sorption of PAHs by van der Waals, hydrogen bonding, π-π interactions, and chemical bonding. LMWOAs significantly inhibited PAHs adsorption and promote PAHs desorption from the minerals. As a result, LMWOAs increased of PAHs bioavailability, which provide a new strategy to improve PAHs cleanup efficiency.

Keywords: Adsorption; Low molecular weight organic acids; Mineral; Polycyclic aromatic hydrocarbons; Soil organic matter.