Structural response of phyllomanganates to wet aging and aqueous Mn(II)
Structural response of phyllomanganates to wet aging and aqueous Mn(II)
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DOI：
10.1016/j.gca.2016.07.035
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发表时间：
2016-11-01
影响因子：
5
通讯作者：
Catalano, Jeffrey G.
中科院分区：
文献类型：
--
作者：
Hinkle, Margaret A. G.;Flynn, Elaine D.;Catalano, Jeffrey G.
天然存在的Mn（IV/III）氧化物通常通过微生物Mn（II）氧化形成，从而产生具有不同Mn(IV), Mn（III）和空位含量的活性层状锰酸盐。残余的Mn（II）可以吸附在八面体薄片空位上方的叶状锰酸酯夹层中。层间Mn（II）与层间Mn（IV）的比例反应以及随后形成结构Mn（III）的可能性表明，水溶Mn（II）可能导致层锰酸盐结构改变，从而改变矿物反应性或微量金属清除能力。本文研究了在pH值为4和7的条件下，在存在和不存在溶解的Mn（II）的情况下，不同初始空位和Mn（III）含量对叶甘酸盐老化的影响。研究了三种层状锰酸盐：两种为涡层堆积（高空位含量的δ - mno2和既有空位又有Mn（III）取代的六方birnite），另一种为旋转有序堆积（主要含有Mn（III）取代的三斜birnite）。结构分析表明，在pH值为4的老化过程中，Mn（II）吸附在上面的空位上，促进形成具有旋转有序片状和混合对称排列成超级细胞的叶门酸盐，而结构Mn（III）则发生歧化。相对于48小时的反应，pH 4下的这些结构变化与25天后三斜和六方birnite上Mn（II）的吸收减少有关，这表明随着Mn（II）的老化，叶状锰酸盐的反应性降低，或者涉及Mn（II）吸收的再结晶过程发生在25天以上。在pH为7时，Mn（II）吸附并产生有限的结构效应，主要是增加delta-MnO2中的片状堆积。这些结果表明，老化引起的叶甘酸盐结构变化受水相Mn（II）、pH和初始固相Mn（III）含量的影响。这种重组可能会改变锰氧化物与环境和地质系统中其他成分的反应，特别是微量金属和氧化还原活性化合物。(C) 2016 Elsevier Ltd.版权所有。
Naturally occurring Mn(IV/III) oxides are often formed through microbial Mn(II) oxidation, resulting in reactive phyllo-manganates with varying Mn(IV), Mn(III), and vacancy contents. Residual aqueous Mn(II) may adsorb in the interlayer of phyllomanganates above vacancies in their octahedral sheets. The potential for interlayer Mn(II)-layer Mn(IV) comproportionation reactions and subsequent formation of structural Mn(III) suggests that aqueous Mn(II) may cause phyllomanganate structural changes that alters mineral reactivity or trace metal scavenging. Here we examine the effects of aging phyllomanganates with varying initial vacancy and Mn(III) content in the presence and absence of dissolved Mn(II) at pH 4 and 7. Three phyllomanganates were studied: two exhibiting turbostratic layer stacking (delta-MnO2 with high vacancy content and hexagonal birnessite with both vacancies and Mn(III) substitutions) and one with rotationally ordered layer stacking (triclinic birnessite containing predominantly Mn(III) substitutions). Structural analyses suggest that during aging at pH 4, Mn(II) adsorbs above vacancies and promotes the formation of phyllomanganates with rotationally ordered sheets and mixed symmetries arranged into supercells, while structural Mn(III) undergoes disproportionation. These structural changes at pH 4 correlate with reduced Mn(II) uptake onto triclinic and hexagonal birnessite after 25 days relative to 48 h of reaction, indicating that phyllomanganate reactivity decreases upon aging with Mn(II), or that recrystallization processes involving Mn(II) uptake occur over 25 days. At pH 7, Mn(II) adsorbs and causes limited structural effects, primarily increasing sheet stacking in delta-MnO2. These results show that aging-induced structural changes in phyllomanganates are affected by aqueous Mn(II), pH, and initial solid-phase Mn(III) content. Such restructuring likely alters manganese oxide reactions with other constituents in environmental and geologic systems, particularly trace metals and redox-active compounds. (C) 2016 Elsevier Ltd. All rights reserved.