The chemistry of Fe and Mn in natural geochemical systems are closely coupled, as Fe and Mn always co-exist in various forms (e.g., hydrated ions, soluble complexes, and particles) in a variety of surface and near-surface environments (e.g., waters, soils, and sediments) and show strong mutual interactions. The redox cycling of Fe and Mn functions as a “pump” for element cycling and energy flow, assuring the significant roles of Fe and Mn species in environmental system dynamics. Specifically, an increasing number of studies have found that the coupled redox between Fe and Mn can bilaterally affect the crystallization and transformation of the (oxyhydr)oxides of Fe and Mn (i.e., FeO_x and MnO_x), which are among the most consequential nanominerals and mineral nanoparticles in these environments. In this review, we map the complex reaction networks between Fe and Mn by discussing the reaction characteristics and mechanisms of each coupled system with various co-existing Fe and Mn species (i.e., FeO_x-Mn(II), MnO_x-Fe(II), and Fe(II)-Mn(II) systems). Due to the higher redox potentials of MnO_x/Mn(II) compared to those of FeO_x/Fe(II), MnO_x can trigger the oxidation of Fe(II) through direct electron transfer, with MnO_x undergoing reductive dissolution; while in the FeO_x-Mn(II) system, where direct redox reaction between FeO_x and Mn(II) is thermodynamically unfavorable, surface-catalyzed oxidation of Mn(II) can be induced by FeO_x. In the Fe(II)-Mn(II) system, these species can experience complex homo-and heterogeneous oxidation and crystallization in aerobic environments. The coupled redox cycling of Fe and Mn, which involves crystallization of FeO_x and MnO_x, dissolution of MnO_x substrates, production of reactive oxidants, and the blockage of reactive surfaces of substrates, etc., can exert more complex and significant influences on the biogeochemical processes as compared to individual Fe or Mn.

天然地球化学系统中 Fe 和 Mn 的化学性质密切相关，因为 Fe 和 Mn 在各种地表和近地表环境（例如，水、土壤和沉积物）并显示出强烈的相互作用。Fe 和 Mn 的氧化还原循环作为元素循环和能量流动的“泵”，确保了 Fe 和 Mn 物种在环境系统动力学中的重要作用。具体而言，越来越多的研究发现，Fe和Mn之间的耦合氧化还原可以双向影响Fe和Mn的（羟基）氧化物（即FeO _x和MnO _{x ）的结晶和转化。})，它们是这些环境中最重要的纳米矿物和矿物纳米粒子之一。在这篇综述中，我们通过讨论每个耦合系统与各种共存的 Fe 和 Mn 物种（即 FeO _x -Mn(II)、MnO _x -Fe( II) 和 Fe(II)-Mn(II) 体系）。由于MnO _x /Mn(II)的氧化还原电位高于FeO _x /Fe(II)，MnO _x可通过直接电子转移触发Fe(II)的氧化，MnO _x发生还原溶解；而在 FeO _x -Mn(II) 体系中，FeO _{x之间的直接氧化还原反应}并且Mn(II)在热力学上是不利的，Mn(II)的表面催化氧化可以由FeO _x诱导。在 Fe(II)-Mn(II) 体系中，这些物种可以在有氧环境中经历复杂的均相和异相氧化和结晶。Fe 和 Mn 的耦合氧化还原循环，包括 FeO _x和 MnO _{x的结晶、MnO x}底物的溶解、活性氧化剂的产生以及底物反应表面的阻塞等，对与单个 Fe 或 Mn 相比的生物地球化学过程。