Impact of Mn(II)-Manganese Oxide Reactions on Ni and Zn Speciation
Impact of Mn(II)-Manganese Oxide Reactions on Ni and Zn Speciation
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DOI：
10.1021/acs.est.6b04347
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发表时间：
2017-03-21
影响因子：
11.4
通讯作者：
Catalano, Jeffrey G.
中科院分区：
文献类型：
--
作者：
Hinkle, Margaret A. G.;Dye, Katherine G.;Catalano, Jeffrey G.
层状氧化锰矿物通常控制着自然系统中痕量金属的命运。金属如镍和锌的强烈吸收是通过吸附在空位上或结合到空位而产生的。Mn(II)也与空位结合，随后与结构的Mn(IV)的并列可能通过形成更大且扭曲的Mn(III)O6八面体来改变片状结构。因此，这种锰(II)-锰根酸盐反应可能会通过阻断关键的反应部位来改变金属的吸收。本文研究了在厌氧条件下，在pH为4和7的条件下，Mn(II)对不同初始空位含量的叶锰酸盐(？-MnO_2、六方水钠锰矿和三斜水钠锰矿)与镍和锌结合的影响。PH为4时，溶解的Mn(II)会降低镍、锌的宏观吸收，但在pH为7时不会。扩展X射线吸收精细结构谱表明，在pH为4时，吸收的减少与镍、锌吸附机制的改变相对应。这些金属从层间结合过渡到片状边缘，锌增加了它的四面体配位分数。这些对金属吸附和结合的影响与Mn(II)诱导的结构变化有关，在pH为4比7时更明显。通过这些结构效应和Mn(II)-金属竞争吸附的pH依赖性，体系pH在很大程度上控制了在溶解的Mn(II)存在的情况下金属与叶锰酸盐的结合。
Layered Mn oxide minerals (phyllomanganates) often control trace metal fate in natural systems. The strong uptake of metals such as Ni and Zn by phyllomanganates results from adsorption on or incorporation into vacancy sites. Mn(II) also binds to vacancies and subsequent comproportionation with structural Mn(IV) may alter sheet structures by forming larger and distorted Mn(III)O6 octahedra. Such Mn(II)-phyllomanganate reactions may thus alter metal uptake by blocking key reactive sites. Here we investigate the effect of Mn(II) on Ni and Zn binding to phyllomanganates of varying initial vacancy content (?-MnO2, hexagonal birnessite, and triclinic birnessite) at pH 4 and 7 under anaerobic conditions. Dissolved Mn(II) decreases macroscopic Ni and Zn uptake at pH 4 but not pH 7. Extended X-ray absorption fine structure spectroscopy demonstrates that decreased uptake at pH 4 corresponds with altered Ni and Zn adsorption mechanisms. These metals transition from binding in the interlayer to sheet edges, with Zn increasing its tetrahedrally coordinated fraction. These effects on metal uptake and binding correlate with Mn(II)-induced structural changes, which are more substantial at pH 4 than 7. Through these structural effects and the pH-dependence of Mn(II)-metal competitive adsorption, system pH largely controls metal binding to phyllomanganates in the presence of dissolved Mn(II).