Exploring the mechanisms of enhanced activated carbon's toluene adsorption and regeneration by utilizing inherent pyrite in coal

The inherent minerals in coal play a significant role in the adsorption and regeneration performance of activated carbon (AC). This study investigates the mechanisms and impacts of inherent pyrite on the toluene adsorption and regeneration capabilities of AC. The results demonstrate that adding 0.5% pyrite significantly enhances both adsorption capacity and regeneration stability. Specifically, 0.5% pyrite-modified AC exhibits a 17.64% increase in toluene adsorption capacity compared to unmodified AC, while retaining over 77.59% of its initial adsorption capacity after five regeneration cycles. Pyrite enhances micropore formation, leading to a 39.11% increase in micropore surface area and a 39.28% increase in micropore volume, both of which are essential for efficient toluene adsorption. Furthermore, pyrite reduces surface oxygen-containing functional groups, resulting in a more hydrophobic AC surface, which enhances π-π interactions between AC and toluene, thereby improving adsorption efficiency. Adsorption kinetics analysis indicates that pyrite enhances the process by increasing active sites and promoting intraparticle diffusion. In terms of regeneration, activated carbon modified with pyrite maintains a higher adsorption capacity for toluene after multiple cycles, which is superior to unmodified activated carbon and samples with higher pyrite concentration. Fe₃O₄, transformed from pyrite during activation, plays a catalytic role in restoring active sites and maintaining micropore structure during thermal regeneration, ensuring consistent performance. The presence of inherent pyrite provides a cost-effective means to improve the adsorption and regeneration capacities of AC, offering practical implications for the development of high-performance, reusable toluene adsorbents.