Effects of copper and lead on the sorption and desorption behaviors of benzene onto humic acids and black carbons

Due to rapid urbanization and industrialization, combined pollution caused by BTEX (benzene, toluene, ethylbenzene, and xylene) and heavy metals has become ubiquitous in soils, which would pose serious health risks to humans. However, the effects of heavy metals on the sorption and desorption behaviors of BTEX have not been fully elucidated. In this study, the effects of Cu²⁺ and Pb²⁺ ions on the sorption and desorption of benzene onto humic acids and black carbons were investigated. The results showed that Cu²⁺ and Pb²⁺ ions significantly reduced the sorption capacity, slowed down the sorption rate, and made the desorption less hysteretic of benzene on both humic acids and black carbons. Furthermore, the inhibitory effects by Pb²⁺ were significantly stronger than those of Cu²⁺. By combining the results of Fourier transform infrared spectroscopy and the site energy distribution model, it can be speculated that the hydration shells of Cu²⁺ and Pb²⁺ ions partially cover the surface of humic acids and black carbons, blocking their micropores and shielding sorption sites, consequently inhibiting the sorption of benzene. This study highlights that coexisting metal cations can significantly influence the fate of BTEX in soils.