Reductive Transformation of Birnessite by Aqueous Mn(II)
Reductive Transformation of Birnessite by Aqueous Mn(II)
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DOI：
10.1021/es2013038
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发表时间：
2011-08-01
影响因子：
11.4
通讯作者：
Elzinga, Evert J.
中科院分区：
文献类型：
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作者：
Elzinga, Evert J.
水性 Mn(II) 与六方水钠锰矿在 pH 7.5 下反应，通过从吸附的 Mn(II) 到结构 Mn(IV) 原子的界面电子转移以及产物 Mn(III) 排列成 MnOOH，导致水钠锰矿还原转变为铁水锰矿 (β-Mn(III)OOH) 和亚锰矿 (γ-Mn(III)OOH)，总结 由 Mn(II) + Mn(IV)O(2) + 2 H(2)O → 2 Mn(III)OOH + 2 H(+)。铁锰矿是最初的转化产物，随后在与 Mn(II) 持续反应过程中转化为更稳定的亚锰矿多晶型物。在比热力学阈值低 2 个数量级的 Mn(II) 浓度下观察到镁铁锰矿的产生，反映了锰氧化物矿物热力学数据的不确定性和/或 Mn(II) 与水钠锰矿表面位点之间促进电子交换的特定相互作用。在有氧条件下，相对于缺氧系统，通过 O(2) 表面催化氧化 Mn(H) 形成铁辉石，导致从溶液中额外去除 Mn(II)。这些结果表明 Mn(II) 可能是 Mn 氧化物氧化还原循环还原臂的重要调节剂。表明 Mn (II) 在调节地球化学环境中与页锰酸盐反应的金属污染物（包括 Co、Ni、As 和 Cr）的溶解度和形态方面具有控制作用。
Reaction of aqueous Mn(II) with hexagonal birnessite at pH 7.5 causes reductive transformation of birnessite into feitknechtite (beta-Mn(III)OOH) and manganite (gamma-Mn(III)OOH) through interfacial electron transfer from adsorbed Mn(II) to structural Mn(IV) atoms and arrangement of product Mn(III) into MnOOH, summarized by Mn (II) + Mn(IV)O(2) + 2 H(2)O -> 2 Mn(III)OOH + 2 H(+). Feitknechtite is the initial transformation product, and subsequently converted into the more stable manganite polymorph during ongoing reaction with Mn(II). Feitknechtite production is observed at Mn(II) concentrations 2 orders of magnitude below thermodynamic thresholds, reflecting uncertainty in thermodynamic data of Mn-oxide minerals and/or specific interactions between Mn(II) and birnessite surface sites facilitating electron exchange. Under oxic conditions, feitknechtite formation through surface-catalyzed oxidation of Mn(H) by O(2) leads to additional Mn(II) removal from solution relative to anoxic systems. These results indicate that Mn(II) may be an important moderator of the reductive arm of Mn-oxide redox cycling, and. suggest a controlling role of Mn (II) in regulating the solubility and speciation of phyllomanganate-reactive metal pollutants including Co, Ni, As, and Cr in geochemical environments.