Adsorption Kinetics of Pb2+ and Cu2+ on Variable Charge Soils and Minerals: Ⅲ. Adsorption Kinetics of Pb2+ Within 30 Minutes

The adsorption kinetics of Pb2+ on different soils and minerals with variable charges was studied by the two ion-selective electrode technique at different pH and concentrations. The results showed that more than 95% of adsorption on all the samples occurred during the first 5 minutes. All adsorption time-dependent data could fit the surface second-order equation very well. The values of Xm were goethite > kaolinite, and latosol > red soil at the same initial reaction concentration. The values of k were kaolinite > > goethite, and latosol > red soil at the same reaction pH and initial concentration. The higher the suspension pH, the faster the adsorption occurred. The meaning of Xm got by the two ion-selective electrode technique (one kind of batch technique) was different from that by the miscible displacement technique in that the former was only the equilibrium adsorption amount at a definite concentration and pH, but the latter was almost equal to the adsorption capacity at a definite pH with much l