ELECTRON-PARAMAGNETIC RESONANCE STOPPED-FLOW KINETIC-STUDY OF MANGANESE(II) SORPTION DESORPTION ON BIRNESSITE

Many important reactions involving colloidal suspensions are rapid. Here, we introduce the application of a technique capable of rapidly measuring a reactant species (within 20 ms after the reaction initiation) in situ: an electron paramagnetic resonance spectroscopically monitored stopped-flow method (EPR-SF). The utility of this technique is demonstrated by investigating the sorption of Mn2+ on delta-MnO2. The sorption reaction was complete in <1 s, with >80% of the Mn2+ being sorbed within 200 ms. A first-order rate dependence on Mn2+ was observed. Measurement of the initial reaction rate allowed the forward (sorption) rate constant to be determined (k(f) = 3.74 x 10(-3) s-1), and the reverse (desorption) rate constant was determined using an integrated reversible first-order rate expression (k(r) = 3.08 x 10(-4) s-1). Using these rate constants, the predicted time dependence of Mn2+ sorption was in good agreement with the measured sorption rate. The results indicate that chemical kinetics are being measured that allow determination of precise reaction rates and mechanisms.