The mutual effects of metal cations （Cu2＋, Pb2＋, Zn2＋, and Cd2＋） and p-nitrophenol （NP） on their adsorption desorption behavior onto wheat ash were studied. Results suggested that Cu2＋, Pb2＋, and Zn2＋ diminished the adsorption and increased the desorption of NP remarkably, while Cd2＋ had no such effect. In contrast, NP diminished the adsorption of Cu2＋, Pb2＋, and Zn2＋ onto ash, however, this suppression effect depended on the initial concentrations of metal cations. NP had no effect on Cd〉 adsorption on ash. Fourier transform infrared （FT-IR） and X-ray absorption spectroscopic （XAS） studies suggested the following mechanisms responsible for the metal suppression effect on NP adsorption： （1） large hydrated Cu2＋, Pb2＋, and Zn〉 shells occupied the surface of ash and prevent nonspecific adsorption of NP onto ash surface; （2） Cu2＋, Pb2＋, and Zn2＋ may block the micropores of ash, resulting in decreased adsorption of NP; （3） cornplexation of Cu2＋, Pb2＋, and Zn2＋ was likely via carboxyl, hydroxylic and phenolic groups of wheat ash and these same groups may also react with NP during adsorption. As a ＂soft acid＂, Cd2＋ is less efficient in the complexation of oxygencontaining acid groups than Cu2＋, Pb2＋, and Zn2＋. Thus, Cd2＋ had no effect on the adsorption of NP on wheat ash.
