A Quantitative Model for the Coupled Kinetics of Arsenic Adsorption/Desorption and Oxidation on Manganese Oxides

The ability to predict coupled kinetic reactions of arsenic (As) that occur at the manganese oxide aqueous solution interface is crucial for management and remediation of As-contaminated sites worldwide. A quantitative understanding of the coupling between As oxidation and adsorption/desorption kinetics will enable us to more accurately predict the kinetic behavior of As. In this study, we developed a novel quantitative model for the coupled kinetics of As adsorption/desorption/oxidation on delta-MnO2. The kinetics of As(III) adsorption and oxidation on delta-MnO2 was studied using a stirred-flow method under varying influent As(III) concentrations. The model was able to account for the variations in As concentration, different binding behavior of As(III) and As(V), and flow rates. Our model quantitatively shows that the coupled As adsorption/desorption/oxidation processes are highly dependent on As mass loading rates on delta-MnO2. Our model suggests that the As(III) adsorption rate is much higher than its oxidation rate. Both As(III) oxidation and subsequent As(V) desorption may proceed with similar reaction rates and control the overall reaction rates, although As(V) desorption rates may be affected by As(V) re-adsorption. Our kinetic model contributes to prediction of the dynamic behavior of As when manganese oxides are present.