A novel and thorough research into desorption behavior of PAHs from sediments to seawater: Aging process, thermodynamics, kinetics, influencing factors

Abstract

Understanding the desorption process of polycyclic aromatic hydrocarbons (PAHs) from sediments is crucial for evaluating pollutant transport and transformation rule. However, there have been limited studies on the desorption behavior of PAHs from sediments, particularly in relation to the aging process. Herein, batch desorption experiments were conducted to investigate the effects of the aging process, desorption mechanism, and influencing factors on the desorption behavior of PAHs from sediments. The results showed that the aging process significantly inhibited the desorption of PAHs. Specifically, the desorption rates of phenanthrene (Phe), pyrene (Pyr), and benzo(a)pyrene (BaP) were reduced by 38.60%, 23.27%, and 17.64%, respectively. The aging processes of sediments involved molecular penetration, bond breaking, and cross-linking, which resulted in tighter agglomeration of the sediment particles. A thermodynamic analysis of the desorption process revealed that it was a spontaneous and feasible heat-absorbing reaction. The desorption process could be divided into three stages: fast desorption, slow desorption and smooth desorption. Kinetic analyses revealed that the limiting factor for PAHs desorption was the chemisorption via hydrogen bonding, ligand bonding, and chemical bonding, between the sediment and the PAHs. Strongly acidic or basic conditions inhibited PAHs desorption, while low salt and dissolved oxygen concentrations promoted desorption. Additionally, smaller sediment particle sizes with larger specific surface areas resulted in higher adsorption capacities, decreasing the likelihood of PAHs desorption. The findings of this study provide important insights into the desorption mechanism and influencing factors of PAHs.