Elucidation of aniline adsorption–desorption mechanism on various organo–mineral complexes

Complexes formed by organic matter and clay minerals, which are active components of soil systems, play an important role in the migration and transformation of pollutants in nature. In this study, humic-acid–montmorillonite (HA–MT) and humic-acid–kaolin (HA–KL) complexes were prepared, and their structures before and after the adsorption of aniline were analyzed. The aniline adsorption–desorption characteristics of complexes with different clay minerals and varying HA contents were explored using the static adsorption–desorption equilibrium method. Compared with the pristine clay minerals, the flaky and porous structure of the complexes and the aromaticity were enhanced. The adsorption of aniline on the different clay mineral complexes was nonlinear, and the adsorption capacity increased with increasing HA content. Additionally, the adsorption capacity of HA–MT was higher than that of HA–KL. After adsorption, the specific surface area of the complexes decreased, the surfaces became more complicated, and the aromaticity decreased because aniline is primarily adsorption onto the complexes via aromatic rings. Aniline was adsorbed onto the complexes via spontaneous exothermic physical adsorption. The amount of aniline desorbed from the complexes increased with increasing HA content, and a lag in desorption was observed, with a greater lag for HA–KL than for HA–MT.