Comparison of Pb(II) and Cd(II) micro-interfacial adsorption on fine sediment in the Pearl River Basin, China

Abstract

The complex micro-interfacial interaction theories of heavy metal ions such as Pb(II) and Cd(II) adsorption on fine sediment in aqueous solution were not systematically investigated. The aim of this work was to reflect the micro-interfacial adsorption characteristics. Sediment samples were collected from an estuary. The Isothermal and kinetics adsorption experiment were done to acquire the data. Isothermal, kinetics, film diffusion and intraparticle diffusion models were adopted to fit the adsorption experimental data. The results indicated that the Langmuir, Freundlich and Temkin models were suitable for analyzing the isothermal experimental data. The maximum adsorption capacities of Pb(II) and Cd(II) on the sediment were 1.1377 and 0.9821 mg·g−1, respectively. The qm and KL of the Langmuir model, Kf and nF of the Freundlich model, and b and A of the Temkin model all exhibited a power function relationship with the initial adsorbate concentration. The pseudo-second-order model provided a better fit for the experimental kinetics data compared with the fit of the pseudo-first-order and Elovich models. The pseudo-second-order parameters k2 and qe of Pb(II) and qe of Cd(II) both had a power function relationship with adsorption time, additionally, the k2 of Cd(II) had an exponential function relationship with adsorption time. The liquid-film diffusion parameters kfd of Pb(II) and Cd(II) were 0.0569 and 0.1806 min−1, respectively. The intraparticle diffusion parameter kid values of Pb(II) and Cd(II) were 0.0055 mg·g−1·min1/2 and 0.0049 mg·g−1·min1/2, respectively. The physical significance of the model parameters showed that Pb(II) adsorption on sediment was stronger than Cd(II). The results of this study provided a theoretical reference for the micro-interfacial mechanism of heavy metal ion adsorption on sediment.