Adsorption Kinetics and Isotherms of Ag(I) and Hg(II) onto Silica Gel with Functional Groups of Hydroxyl- or Amino-Terminated Polyamines

Five kinds of silica-gel adsorbents with functional groups of hydroxyl- or amino-terminated polyamines (SiO2-EA, SiO2-DEA, SiO2-EDA, SiO2-DETA, and SiO2-TETA), whose structures of functional groups were characterized according to the results of elemental analysis, were chosen to investigate the adsorption kinetics and isotherms toward Ag(I) and Hg(II). The results of the kinetics adsorption showed that all of the adsorption processes followed a pseudo-second-order model, suggesting that the five adsorbents can be applied in Ag(I) and Hg(II) removal from lower concentration solutions. Film diffusion might dominate in the adsorption process of Ag(I) and Hg(II) onto the five adsorbents. The linear and nonlinear Langmuir, Freundlich, and Redlich-Peterson models were employed to fit the isothermal adsorptions. The results revealed that all the above-mentioned isotherm models can be used to predict the experimental data. The relationship between the structure of functional groups and the adsorption mechanism is also discussed.