Adsorption Mechanism of Humic Acid on Cu/Fe Bimetallic Particles and Its Influence on the Reduction of Nitrobenzene in Groundwater
2014
Kong, Shuqiong | Wang, Yanxin | Zhan, Hongbin | Yuan, Songhu | Hu, Qinhong
Humic acid (HA) is ubiquitous in groundwater, and poses great influence on the biogeochemical controls on, as well as treatment of, contaminants. This study deals with the adsorption of HA on a bimetallic iron system, Cu/Fe, and its influence on the reduction of nitrobenzene in synthetic groundwater. The adsorption kinetics, isotherms, and enthalpy of HA on bimetallic Cu/Fe particles are investigated. Compared with the adsorption of HA on Fe⁰particles, the adsorption on Cu/Fe is faster than that on Fe⁰. The adsorption isotherms of HA at different pH values and temperatures show that the adsorption is always greater on Cu/Fe than on Fe⁰, and increases when the pH decreases and temperature increases. Moreover, the influences of pH and temperature on adsorption by Cu/Fe are less than those observed in adsorption on Fe⁰. The adsorption enthalpy on Cu/Fe is lower than that on Fe⁰, and both adsorptions are spontaneous and endothermic. Characterization of the corrosion products by SEM-EDX, XRD, and XPS reveals the appearance of maghemite (γ-Fe₂O₃) and magnetite (Fe₃O₄) on Cu/Fe with HA adsorption, which were more crystalline than those of Fe⁰, indicating that bimetallic Cu/Fe facilitated the formation of crystalline corrosion products. The adsorption of HA accelerates the release of iron ions but suppresses the reduction of nitrobenzene. Compared with Fe⁰, Cu/Fe accelerates the adsorption of HA and Cu/Fe increases the reduction of nitrobenzene. The suppression on nitrobenzene reduction increased with the increase in HA concentration.
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