An Investigation into the Clay Adsorption Behavior of Polycyclic Aromatic Hydrocarbons

Abstract

The rise of hydraulic fracturing in the United States has caused the release of hundreds of contaminants into natural systems. Understanding how these contaminants interact with the clay minerals that make up soils is critical for being able to predict their behavior in the environment and engineer proper remediation technologies. However, clear trends describing the interactions between clays and nonpolar organics do not exist within the literature. In an effort to amend this issue, this research set out to explore how polycyclic aromatic hydrocarbons (PAHs), a class of nonpolar organics known for their carcinogenicity and environmental persistence, interacted with purified montmorillonite clay. To do this, two methods were used. Batch adsorption experiments were completed with fluorene, a model PAH, to evaluate the effect of the exchangeable cation present within the clay interlayer space on fluorene adsorption. Simultaneously, molecular dynamics (MD) simulations were run with fluorene, fluoranthene, and chrysene to measure how compound solubility affected adsorption. After both tests were completed, the results of the batch adsorption experiments were compared to those found from the simulations in order to evaluate the accuracy of the MD model. Unfortunately, due to a host of experimental setbacks no conclusions were able to be drawn regarding the effect of the exchangeable cation on organic clay adsorption, or the validity of the MD model. However, MD simulations were successful in showing that all three nonpolar contaminants adsorbed to clay. Further, the logarithm of a compound’s calculated partition coefficient was shown to be strongly inversely proportional to the logarithm of its solubility. From this, it was concluded that clay adsorption had the potential to play a significant role in organic soil partitioning, especially for highly insoluble compounds like PAHs.