Effect of Zn(II) coprecipitation on Mn(II)-induced reductive transformation of birnessite
Effect of Zn(II) coprecipitation on Mn(II)-induced reductive transformation of birnessite
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DOI：
10.1016/j.chemgeo.2018.05.031
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发表时间：
2018-08
期刊：
影响因子：
3.9
通讯作者：
Shiliang Zhao;Yaneira A. González-Valle;E. Elzinga;E. M. Saad;Yuanzhi Tang
中科院分区：
文献类型：
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作者：
Shiliang Zhao;Yaneira A. González-Valle;E. Elzinga;E. M. Saad;Yuanzhi Tang
锰氧化物 (MnOx) 是几乎所有环境中普遍存在的金属氧化物矿物。它们在金属、有机物和营养物质等许多环境成分的运输和归宿中发挥着重要作用。在溶解的 Mn(II) 存在下，MnOx 相会发生成熟和转变，从而形成具有更高结构有序度的相，从而在较长时间内强烈影响 MnOx 的反应活性。在自然环境中，金属阳离子可以通过吸附、掺入和/或共沉淀等机制与 MnOx 发生强烈相互作用，但关于金属共沉淀对 MnOx 转化的影响仍然未知。本研究研究了 Zn 共沉淀对 Mn(II) 诱导的水钠锰矿（一种常见的 MnOx 矿物相）还原转变的影响。合成了纯水钠锰矿相和锌共沉淀酸性水钠锰矿相，并在有氧或缺氧条件下研究了它们在 Mn(II) 存在下的转化动力学和途径。在转变过程中，锌共沉淀水钠锰矿表现出较高的吸收 Mn(II) 的能力，这可能是由于其粒径较小、Mn(II) 消耗速度快以及新相锌锰矿的沉淀。 Zn-共沉淀水钠锰矿的中间相——水钠锰矿的形成比纯水钠锰矿更快，这与吸附Zn的水钠锰矿体系相反。对于 Zn 共沉淀水钠锰矿，从中间相铁锰矿到最终稳定相锰锰矿的转变较慢，因为催化转变的 Mn(II) 浓度较低。这项研究揭示了了解金属阳离子杂质对氧化锰矿物的结构稳定性和长期反应性影响的重要性。
Mn oxides (MnOx) are ubiquitous metal oxide minerals in nearly all environmental settings. They play important roles in the transport and fate of many environmental components such as metals, organics, and nutrients. In the presence of dissolved Mn(II), MnOx phases can undergo ripening and transformation, resulting in the formation of phases with higher structural order, thus strongly affect the reactivity of MnOx over extended time scale. In natural environments, metal cations can strongly interact with MnOx through mechanisms such as sorption, incorporation, and/or coprecipitation, yet much still remain unknown about the effect of metal coprecipitation on the transformation of MnOx. This study investigates the effects of Zn coprecipitation on Mn(II)-induced reductive transformation of birnessite, a common MnOx mineral phase. Pure and Zn-coprecipitated acid birnessite phases were synthesized and their transformation kinetics and pathways in the presence of Mn(II) was investigated under oxic or anoxic conditions. During the transformation process, Zn-coprecipitated birnessite showed higher capability toward Mn(II) uptake, likely due to smaller particle size and the fast consumption of Mn(II) and precipitation of a new phase hetaerolite. The formation of an intermediate phase, feitknechtite, was faster for Zn-coprecipitated birnessite than pure birnessite, which is the opposite of Zn-sorbed birnessite system. Transformation from the intermediate phase feitknechtite to the final stable phase manganite was slower for Zn-coprecipitated birnessite, due to the lower Mn(II) concentration which catalyzed the transformation. This study revealed the importance of understanding the influence of metal cation impurities on the structural stability and long term reactivity of Mn oxide minerals.