BACKGROUND Todorokite, a 3 × 3 tectomanganate, is one of three main manganese oxide minerals in marine nodules and can be used as an active MnO6 octahedral molecular sieve. The formation of todorokite is closely associated with the poorly crystalline phyllomanganates in nature. However, the effect of the preparative parameters on the transformation of "c-disordered" H(+)-birnessites, analogue to natural phyllomanganates, into todorokite has not yet been explored. RESULTS Synthesis of "c-disordered" H(+)-birnessites with different average manganese oxidation states (AOS) was performed by controlling the MnO4 (-)/Mn(2+) ratio in low-concentrated NaOH or KOH media. Further transformation to todorokite, using "c-disordered" H(+)-birnessites pre-exchanged with Na(+) or K(+) or not before exchange with Mg(2+), was conducted under reflux conditions to investigate the effects of Mn AOS and interlayer cations. The results show that all of these "c-disordered" H(+)-birnessites exhibit hexagonal layer symmetry and can be transformed into todorokite to different extents. "c-disordered" H(+)-birnessite without pre-exchange treatment contains lower levels of Na/K and is preferably transformed into ramsdellite with a smaller 1 × 2 tunnel structure rather than todorokite. Na(+) pre-exchange, i.e. to form Na-H-birnessite, greatly enhances transformation into todorokite, whereas K(+) pre-exchange, i.e. to form K-H-birnessite, inhibits the transformation. This is because the interlayer K(+) of birnessite cannot be completely exchanged with Mg(2+), which restrains the formation of tunnel "walls" with 1 nm in length. When the Mn AOS values of Na-H-birnessite increase from 3.58 to 3.74, the rate and extent of the transformation sharply decrease, indicating that a key process is Mn(III) species migration from layer into interlayer to form the tunnel structure during todorokite formation. CONCLUSIONS Structural Mn(III), together with the content and type of interlayer metal ions, plays a crucial role in the transformation of "c-disordered" H(+)-birnessites with hexagonal symmetry into todorokite. This provides further explanation for the common occurrence of todorokite in the hydrothermal ocean environment, where is usually enriched in large metal ions such as Mg, Ca, Ni, Co and etc. These results have significant implications for exploring the origin and formation process of todorokite in various geochemical settings and promoting the practical application of todorokite in many fields.Graphical abstractXRD patterns of Mg(2+)-exchanged and reflux treatment products for the synthetic "c-disordered" H(+)-birnessites.

中文翻译：

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从“ c-无序” H（+）-水钠锰矿形成钙锰矿：平均锰的氧化态和层间阳离子的作用。

背景技术3×3的锰锰矿Todorokite是海洋结核中三种主要的锰氧化物矿物之一，可用作活性MnO6八面体分子筛。钙锰矿的形成与自然界中结晶性较差的层锰酸盐密切相关。但是，尚未研究制备参数对“ c-无序” H（+）-水钠锰矿（类似于天然叶锰酸锰）转化为钙锰矿的影响。结果通过控制低浓度NaOH或KOH介质中的MnO4（-）/ Mn（2+）比，可以合成具有不同平均锰氧化态（AOS）的“ c无序” H（+）水钠锰矿。使用预先与Na（+）或K（+）预先交换或不交换与Mg（2+）的“ c-无序” H（+）-水钠锰矿，进一步转化为todorokite，在回流条件下进行了研究，以研究Mn AOS和层间阳离子的影响。结果表明，所有这些“ c-无序” H（+）-水钠锰矿均表现出六边形的层对称性，并且可以在不同程度上转化为钙锰矿。未经预交换处理的“ c紊乱” H（+）水钠锰矿含有较低水平的Na / K，最好是转变为具有较小1×2隧道结构的斜方锰矿，而不是斜方锰矿。Na（+）预交换（即形成Na-H-水钠锰矿）极大地增强了向斜辉石的转化，而K（+）预交换（即形成KH-水钠锰矿）则抑制了转化。这是因为水钠锰矿的中间层K（+）不能与Mg（2+）完全交换，这限制了长度为1 nm的隧道“壁”的形成。当钠-水钠锰矿的Mn AOS值从3.58增加到3.74时，转变的速率和程度急剧下降，这表明关键的过程是在锰锌矿期间Mn（III）物种从层间迁移到层间以形成隧道结构。编队。结论结构Mn（III）以及层间金属离子的含量和类型在将具有六边形对称性的“ c无序” H（+）水钠锰矿转变为钙锰矿中起着至关重要的作用。这进一步说明了在热液海洋环境中常出现的todorokite，那里通常富含大型金属离子，例如Mg，Ca，Ni，Co等。