Birnessite controls the fate and transport of metals and affect the cycling of carbon and nitrogen due to its ubiquity in natural environments and extraordinary adsorption and oxidation properties. Structure and composition of birnessite govern its adsorption and oxidation properties. Recent laboratory studies show that reactions between birnessite and Mn(II) strongly affect birnessite structure and Mn oxidation state composition. Natural waters contain abundant oxyanions, such as phosphate and silicate, and they can complex with Mn(II) or adsorb on birnessite edge sites, thus potentially affecting the reactions between birnessite and Mn(II). In this study, δ-MnO2 was reacted with Mn(II) at pH 6, 7 or 8 in the presence of phosphate or silicate under anoxic conditions, and the solids collected at different time intervals were characterized using X-ray diffraction, atomic pair distribution function analysis and X-ray absorption spectroscopy. Our ongoing experiments indicate that the oxyanions affect the reactions of δ-MnO2 with Mn(II) and the structure and composition of δ-MnO2. The results provide insights into how solution chemistry affects birnessite-Mn(II) reactions in natural environment.

Effects of ligands on structural transformation of birnessite during the reaction with Mn(II)

255th National Meeting (2018)

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