| The currently available surface complexation models, such as the Two-Plane Model and Triple Layer Model, are based on experiments at equilibrium status, and thus, need to be validated by the experiments of kinetics. A set of novel column experiments were designed and carried out based on the system identification approach. The input signals, the sinusoidal change of concentrations of solute in the influent solutions, were designed to excite the adsorption/desorption at the mineral systems at both pH 4 and pH 10, and the corresponding output signals, the dynamic concentrations of solute in effluent solution, were obtained. Mathematical models in the frequency domain, transfer functions, were derived according to the various surface complexation models. Complex curve fitting of transfer functions was used to identify the proper model.; The columns were separately packed with variable charge minerals including bauxite, goethite, hematite, and kaolinite. The tracers, acetone, nitrate and phosphate, were sequentially used to study their adsorption/desorption at the mineral/water interfaces.; When acetone was used as inert tracer, the transfer function of Convection-Dispersion Equation (CDE) was simplified into two linear equations. The dispersion coefficients and water velocities were estimated by least squares methods.; The algorithm of complex curve fitting adjusted the weights of the real and imaginary parts of the logarithmic transfer function, and estimated the model parameters with Gauss-Newton nonlinear procedure. The adsorption/desorption of nitrate and H+ or OH- for the mineral systems at both pH 4 and pH 10 were linear or approximately linear. The relationships of the concentrations of H+ or OH- and nitrate in the effluent solutions were linear. Similar results were obtained for the study of P adsorption/desorption at the mineral/water interface. The proper mechanisms for nitrate adsorption/desorption at mineral/water interfaces were Triple-Layer Model at pH 4 and Two-Plane Model at pH 10. The proper mechanisms for phosphate adsorption/desorption at mineral/water interfaces were Triple-Layer Model at pH 4 for all four minerals and gibbsite and goethite at pH 10, and Two-Plane Model for hematite and kaolinite at pH 10. |
