Iron (Fe) and manganese (Mn) are the two most common redox-active elements in the Earth's crust and are well known to influence mineral formation and dissolution, trace metal sequestration, and contaminant transformations in soils and sediments. Here, we characterized the reaction of aqueous Fe(II) with pyrolusite (β-MnO2) using electron microscopy, X-ray diffraction, aqueous Fe and Mn analyses, and 57Fe Mössbauer spectroscopy. We reacted pyrolusite solids repeatedly with 3 mM Fe(II) at pH 7.5 to evaluate whether electron transfer occurs and to track the evolving reactivity of the Mn/Fe solids. We used Fe isotopes (56 and 57) in conjunction with 57Fe Mössbauer spectroscopy to isolate oxidation of Fe(II) by Fe(III) precipitates or pyrolusite. Using these complementary techniques, we determined that Fe(II) is initially oxidized by pyrolusite and that lepidocrocite is the dominant Fe oxidation product. Additional Fe(II) exposures result in an increasing proportion of magnetite on the pyrolusite surface. Over a series of nine 3 mM Fe(II) additions, Fe(II) continued to be oxidized by the Mn/Fe particles suggesting that Mn/Fe phases are not fully passivated and remain redox active even after extensive surface coverage by Fe(III) oxides. Interestingly, the initial Fe(III) oxide precipitates became further reduced as Fe(II) was added and additional Mn was released into solution suggesting that both the Fe oxide coating and underlying Mn phase continue to participate in redox reactions when freshly exposed to Fe(II). Our findings indicate that Fe and Mn chemistry is influenced by sustained reactions of Fe(II) with Mn/Fe oxides.

中文翻译：

---

Fe（II）还原软锰矿（β-MnO2）和二次矿物逸出。

铁（Fe）和锰（Mn）是地壳中最常见的两种氧化还原活性元素，众所周知，它们会影响矿物的形成和溶解，痕量的金属螯合以及土壤和沉积物中污染物的转化。在这里，我们使用电子显微镜，X射线衍射，Fe和Mn水溶液分析以及57FeMössbauer光谱表征了Fe（II）水溶液与软锰矿（β-MnO2）的反应。我们将软锰矿固体与3 mM Fe（II）在pH 7.5下反复反应，以评估是否发生电子转移并跟踪Mn / Fe固体的反应性。我们将Fe同位素（56和57）与57FeMössbauer光谱结合使用，以分离Fe（III）沉淀物或软锰矿对Fe（II）的氧化。利用这些补充技术，我们确定Fe（II）最初会被软锰矿氧化，而纤铁矿是主要的Fe氧化产物。额外的Fe（II）暴露会导致软锰矿表面磁铁矿的比例增加。在一系列添加的9个3 mM Fe（II）中，Fe（II）继续被Mn / Fe颗粒氧化，这表明Mn / Fe相并未被完全钝化，甚至在被Fe（III）广泛覆盖后仍具有氧化还原活性。 ）氧化物。有趣的是，最初的Fe（III）氧化物沉淀随着Fe（II）的添加而进一步减少，并且另外的Mn释放到溶液中，这表明当刚暴露于Fe（III）时，Fe氧化物涂层和下面的Mn相都继续参与氧化还原反应。 II）。我们的发现表明，Fe和Mn的化学性质受Fe（II）与Mn / Fe氧化物的持续反应的影响。