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Rates of abiotic Mn^(II) oxidation by O₂: Influence of various multidentate ligands at high pH

Morgan, James J. and Schlautman, Mark A. and Bilinski, Halka (2020) Rates of abiotic Mn^(II) oxidation by O₂: Influence of various multidentate ligands at high pH. In: 260th ACS National Meeting & Exposition, 23-27 August 2020, San Francisco, CA.

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Oxidn. of manganous manganese (Mn^(II)) is an important process driving manganese cycles in natural aquatic systems and leading to the formation of solid-phase Mn^(III,IV) (hydr)oxide products. Previous research has shown that some simple ligands (e.g., phosphate, sulfate, chloride, fluoride) can bind with Mn^(II) to make it unreactive to oxidn. by dissolved oxygen. However, there is little to no understanding of the role played by strong, complex-forming ligands in Mn^(II) oxidn. reactions. The objective of this study was to evaluate the rates of abiotic Mn^(II) oxidn. by O₂ in the presence of several strong complex-forming ligands (pyrophosphate, tripolyphosphate, EDTA, oxalate) in bicarbonate-carbonate buffered lab. solns. of pH 9.42, 9.65 and 10.19. The influence of increasing ligand concns. on obsd. autocatalytic patterns of Mn^(II) oxidn. was investigated, and initial oxidn. rates have been tentatively linked to the initial Mn^(II) speciation in exptl. solns. Obsd. rates of Mn^(II) oxidn. decreased with increasing ligand concn. for all four ligands tested. However, the profiles obsd. and the magnitudes of decrease in initial oxidn. rates were different for the different ligands. Likely explanations for these observations include the denticity of the tested ligands, the relative strength of the ligands to complex Mn^(II) vs. Mn^(III), and the ability of some ligands to act as an electron donor and thereby enhance the back reaction.

Item Type:Conference or Workshop Item (Paper)
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Schlautman, Mark A.0000-0001-6522-4345
Additional Information:© 2020 American Chemical Society.
Record Number:CaltechAUTHORS:20201221-093509174
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107232
Deposited By: Tony Diaz
Deposited On:21 Dec 2020 17:50
Last Modified:21 Dec 2020 17:50

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