Adsorption Kinetics of Pb2+ and Cu2+ on Variable Charge Soils and Minerals: Ⅱ. Equations for Describing Experimental Data

Different mathematical methods,including linearization,differential,integration and nonlinear least squares approximation (Newton-Marquardt method),were used to fit different kinetic equations,such as zero-order,first-order (i.e.membrane diffusion),second-order,parabolic-diffusion,Elovich,two-constant equations,to the experimental data of Pb^2 and Cu^2 adsorption on variable charge soils and kaolinite.Assuming each M^2 occupied two adsorption sites,two more equations,the so-caled surface second-order equation and third-order equation were derived and compared with the above equations according to the fitting results,which showed that the second-order equation and surface second-order equation,being one equation in different expressions under some conditions,were better than the other equations in describing the Pb^2 and Cu^2 adsorption kinetics,and the latter was the best.