Study on the Competitive Adsorption of Pb (II) and Ni (II) in Aqueous Solution Onto B-nZVI and Its Stability After Adsorption

In this study, the bentonite-supported nanoscale zero-valent iron (B-nZVI) for simultaneous adsorption of Pb (II) and Ni (II) is described and compared to single adsorbate situation. Adsorbents are characterized by Transmission Electron Microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), and Brunner - Emmet - Teller (BET) measurements. The effect of reaction conditions on adsorption efficiency and the stability of the B-nZVI after adsorbing heavy metals is also investigated. In binary mixtures, competition for the binding sites and interactions between B-nZVI and metal ions are identified. The adsorption efficiency of Ni (II) decreases with the increase of Pb (II) concentration, whereas the existence of Ni (II) in the solution has little effect on Pb (II) removal. In single-component system, the removal kinetics of Pb (II) and Ni (II) follow a pseudo-second-order kinetics. The linear fitting of experimental data for the theoretical isotherms indicates that the adsorption of Pb (II) and Ni (II) by the B-nZVI follows the Langmuir model and the maximum adsorptions are 312.5 mg g(-1) and 84 mg g(-1). Webber-Morris adsorption model and Dubinin-RadushKevich model are used to describe the adsorption mechanism. The adsorption potential of Pb (II) and Ni (II) on B-nZVI is calculated to be 93 and 35 kJ mol-1 through D-R model fitting, which means that the removal of heavy metal ions includes chemical adsorption.