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The kinetics of iodide oxidation by the manganese oxide mineral birnessite

January 1, 2009

The kinetics of iodide (I) and molecular iodine (I2) oxidation by the manganese oxide mineral birnessite (δ-MnO2) was investigated over the pH range 4.5–6.25. I oxidation to iodate (IO3-)">(IO3-) proceeded as a two-step reaction through an I2 intermediate. The rate of the reaction varied with both pH and birnessite concentration, with faster oxidation occurring at lower pH and higher birnessite concentration. The disappearance of I from solution was first order with respect to I concentration, pH, and birnessite concentration, such that −d[I]/dt = k[I][H+][MnO2], where k, the third order rate constant, is equal to 1.08 ± 0.06 × 107 M−2 h−1. The data are consistent with the formation of an inner sphere I surface complex as the first step of the reaction, and the adsorption of I exhibited significant pH dependence. Both I2, and to a lesser extent, IO3-">IO3- sorbed to birnessite. The results indicate that iodine transport in mildly acidic groundwater systems may not be conservative. Because of the higher adsorption of the oxidized I species I2 and IO3-">IO3-, as well as the biophilic nature of I2, redox transformations of iodine must be taken into account when predicting I transport in aquifers and watersheds.

Publication Year 2009
Title The kinetics of iodide oxidation by the manganese oxide mineral birnessite
DOI 10.1016/j.gca.2009.02.016
Authors P.M. Fox, J.A. Davis, G. W. Luther
Publication Type Article
Publication Subtype Journal Article
Series Title Geochimica et Cosmochimica Acta
Index ID 70035105
Record Source USGS Publications Warehouse
USGS Organization Toxic Substances Hydrology Program