EVALUATION FOR CONTAMINANT ION ADSORPTION-DESORPTION ON GOETHITE USING PRESSURE-JUMP RELAXATION KINETICS

The adsorption/desorption of contaminant ions on soil constituents suc h as metal oxides occurs within milliseconds. The rapid kinetics of Cu 2+ and arsenate adsorption/desorption on goethite (alpha-FeOOH) were i nvestigated using the pressure-jump (p-jump) relaxation technique, whi ch provides rate constants and mechanistic information for fast reacti ons. Results of p-jump experiments at 25-degrees-C revealed that both Cu2+ and arsenate were specifically adsorbed on goethite. The divalent copper ion formed an inner-sphere monodentate surface complex, while arsenate formed an inner-sphere bidentate surface complex with goethit e. In both cases, the rate constants for the adsorption reactions exce eded those for desorption, indicating that the desorption of Cu2+ and arsenate from the goethite surface was the rate-limiting process. Pres sure-jump relaxation techniques can be used to predict the adsorption behavior of heavy metals in soil environments.