RAPID KINETICS OF CU(II) ADSORPTION-DESORPTION ON GOETHITE

The kinetics of Cu2+ adsorption/desorption on goethite (alpha-FeOOH) w as evaluated using the pressure-jump (p-jump) relaxation technique. Th is technique provides kinetic and mechanistic information for reaction s occurring on millisecond time scales. A double relaxation event was observed for Cu2+ adsorption/desorption on goethite. The rate of these relaxations (r) decreased with an increase in pH, along the adsorptio n edge. The mechanism ascribed to the relaxations is the formation of a monodentate inner-sphere Cu2+/goethite surface complex. The calculat ed intrinsic rate constant for adsorption (k1'int) was 10(6.81) L mol- 1 s-1 and was about 2 orders of magnitude larger than the intrinsic ra te constant for desorption (k-1'int = 10(4.88) L mol-1 s-1). Using res ults from this study and others, it was established that the rate of a dsorption of divalent metal cations on goethite was directly related t o the rate of removal of a water molecule from the primary hydration s phere of a particular divalent metal cation.