Abstract:Pore structure, surface property and chemical constitution of plant ash were determined. Two pesticides-sevin and diuron whose physicochemical properties were close, but steric configurations were different, were chosen as sorbates. Their sorption isotherms and kinetics on plant ash were examined, respectively. Their sorption models were significantly varied. Linear model and pseudo one-stape dynamics equation could fit the sorption of planar sevin on plant ash, implying that its sorption possibly was simple linear partition process. Freundlich model and two-stape dynamics equation fitted best the sorption of non-planar diuron on plant ash, implying that its sorption was complex multi-process. The sorption isotherm and kinetic fitting parameters indicated that the sorption capacity of planar sevin was larger than that of non-planar diuron, suggesting that the steric effect of sorbate molecule played important role on sorption.