Co-Transport of Aniline and TNT with Loess Colloid Particles in Saturated Loess Columns: Mechanism and Processes

Abstract

The transport of mobile colloidal particles with organic pollutants in porous media has attracted considerable attention. Aniline and 2,4,6-trinitrotoluene (TNT), as aromatic compounds and key components of energetic materials, are continuously released into the environment. This study compared the co-transport of loess colloidal particles with aniline and TNT, aiming to investigate the influence of structural and physicochemical properties of the pollutants. The colloids were prepared and characterized, and static adsorption and dynamic column experiments were conducted. The results indicate that the adsorption processes of aniline and TNT both conformed to the quasi-second-order kinetic and the intra-particle diffusion models, with aniline exhibiting higher rate constants than TNT. The main adsorption mechanism involved van der Waals force, hydrogen bonding, and electrostatic interaction. Response surface experiments indicated that the adsorption capacity increased with higher initial concentration of organic compound but decreased with larger particle size and higher Na+ concentration. In column experiments, the adsorption of loess colloid particles on aniline and TNT was strongly correlated with the concentration of loess colloid particles. Loess colloid particles could be used as carriers to enhance the co-transport, with aniline exhibiting a faster transport rate due to the differences in polarity and molecular structure compared to TNT. In summary, loess colloidal particles enhanced the transport behavior of aniline and TNT in saturated loess columns. The differences in polarity and molecular structure of aniline and TNT further affect their co-transport mechanism in loess.