119th General Meeting of the KCS

Type Oral Presentation
Area Current Trends in Environmental and Energy Chemistry
Room No. 407호
Time THU 09:15-:
Code ENVR.O-2
Subject Formation of diverse Mn oxides by various geochemical reactions
Authors 남궁선이, 이기현*
연세대학교 지구시스템과학과, Korea
Abstract Mn (oxyhydr)oxides (collectively referred to as oxides) are widely distributed in the environment (e.g., soil, groundwater, ocean, and hydrothermal vent) and playing an essential role together with Fe oxides by controlling the fate and transport of various chemical species (e.g., nutrients, contaminants). A variety of Mn oxides have their unique physico-chemical properties and reactivity, which are correlated to the different atomic arrangement, wide ranging of crystallinity, and mixed valence of structural Mn. Previous studies have mostly focused on the mobility of various contaminants by the sorption and redox reactions with specific Mn oxides. However, the geochemical processes of diverse Mn oxides formation under varying environmental conditions have not been fully understood yet. Hence, this study aimed at investigation of the geochemical factors controlling the formation and phase transformation of diverse Mn oxides through various redox reactions.
Batch experiments were conducted through homogeneous or surface catalyzed Mn(II) oxidation, and during the redox reactions of Mn oxides (i.e., birnessite) with aqueous Mn(II) or common redox sensitive materials (i.e., Cr(OH)3(s)). The results of homogeneous Mn(II) oxidation ([Mn(II)]0 = 0.05 or 1.0 mM) at pH 9.0 open to the atmosphere showed the production of pure hausmannite (Mn3O4), whereas surface catalyzed Mn(II) oxidation on the surface of Cr(OH)3(s) otherwise under the same conditions produced mixed phase of Mn oxides, consisting of dominantly feitknechtite (β-MnOOH) with minor of groutite (α-MnOOH) and hausmannite. During the redox reactions between birnessite and aqueous Mn(II) under both oxic and anoxic conditions, groutite, feitknechtite, and manganite (α-, β-, and γ-MnOOH, respectively) were produced at pH 7.0, while hausmannite was produced at pH 8.0 and 9.0. Feitknechtite was recognized as the secondary Mn oxide phase during the redox reactions between birnessite and Cr(OH)3(s) at pH 7.0 – 9.0 open to the atmosphere. Overall, the results of this study suggested the potential geochemical factors controlling the formation and the phase transformation of diverse Mn oxides at different conditions.
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