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

The adsorption/desorption of contaminant ions on soil constituents such as metal oxides occurs within milliseconds. The rapid kinetics of Cu2+ and arsenate adsorption/desorption on goethite (alpha-FeOOH) were investigated using the pressure-jump (p-jump) relaxation technique, which provides rate constants and mechanistic information for fast reactions. 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 goethite. In both cases, the rate constants for the adsorption reactions exceeded those for desorption, indicating that the desorption of Cu2+ and arsenate from the goethite surface was the rate-limiting process. Pressure-jump relaxation techniques can be used to predict the adsorption behavior of heavy metals in soil environments.