Adsorption of Microplastics on Aquifer Media: The Effect of Action Time, Initial Concentration,Ionic Strength, Ionic Types and Dissolved Organic Matter

The adsorption of microplastic MPs (1μm) on aquifer media is affected by its own properties and environmental factors. The research results showed that the order of the adsorption capacity of the three media for MPs is: fine sand>medium sand>coarse sand, and the adsorption equilibrium time is 8h, 12h and 24h, respectively. The adsorption process goes through three stages of fast linear distribution, slow adsorption and equilibrium stability, and the action law is compounded by the pseudo-second-order kinetic equation. After adsorption, MPs were observed on the three media, and there were single existence and aggregation phenomena. From the results of the energy spectrum analysis, it can be seen that elemental carbon (C) appears on the surface of the medium after the action, and the surface of the media adsorbed MPs to varying degrees. According to the results of infrared spectroscopy, after the action, the peak areas of the absorption peaks at 680-880cm-1 and 1450-1620cm-1 increase. The absorption peaks are mainly C-H out-of-plane bending vibrations of aromatic hydrocarbons and C-H stretching vibrations on the benzene ring skeleton. As the initial concentration increases, the equilibrium adsorption capacity increases linearly. The isothermal adsorption of MPs in porous media conforms to the Freundlich model. The adsorption process is also affected by different anions and cations. The higher the ionic strength of NH4+, the weaker the electrostatic effect of negatively charged MPs, thereby increasing the adsorption capacity of microplastics on porous media. Ca2+ can promote the adsorption of MPs by the media through the formation of ternary complexes between cations, MPs and surface functional groups. The increase of SO4 2- and HCO3- concentration gradually inhibits the adsorption of MPs. Dissolved organic matter may affect the adsorption process of MPs through complex interactions between the aromatic structure and the π-π conjugation.