With high surface reactivity and weak crystallinity, ferrihydrite (Fh) tends to be transformed to other thermodynamically stable iron (hydr)oxides, and its transformation is strongly influenced by the coexisting substances. Clay minerals widely coexist with Fh in the near-surface areas, but there is limited information about their effects on the transformation of Fh. In this work, the effect of montmorillonite (Mt) on the formation of hematite (Hem) nanoparticles from Fh under heat treatment was studied. Fh, Mt, and their mixed samples (Fh-Mt) were heated at different temperatures (350, 450, 600, 700, and 800 °C) for various times (3, 5, and 10 h), and the samples before and after heating were well characterized. X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy results revealed that Fh was transformed to Hem after heat treatment in both the presence and absence of Mt. Scanning electron microscopy and transmission electron microscopy images indicated that Mt could well disperse Fh and distinctly decrease the particle sizes of the formed Hem after heating. In particular, the particle size of Hem reached ~1000 nm in the pure Fh system, while it was only 15–75 nm in the systems containing Mt. Fourier transform infrared spectroscopy patterns displayed the strong interactions between Mt and Fh (through the formation of Si−O−Fe and Al−O−Fe bonds), which may also reduce the aggregation of Fh and inhibit the phase transformation of Fh particles into large Hem particles. This work verifies the important protective effect of clay minerals on coexisting iron oxide under high-temperature conditions, which would contribute to better understanding the formation and preservation of natural nano-sized minerals (particles) in nature.

具有高的表面反应性和弱的结晶度，铁水合物（Fh）倾向于转化为其他热力学稳定的氧化铁（氢）氧化物，并且其转化受到共存物质的强烈影响。粘土矿物与Fh在近地表广泛共存，但是关于它们对Fh转化的影响的信息有限。在这项工作中，研究了蒙脱石（Mt）对热处理后Fh形成赤铁矿（Hem）纳米粒子的影响。将Fh，Mt及其混合样品（Fh-Mt）在不同温度（350、450、600、700和800°C）加热不同的时间（3、5和10 h），然后将样品加热至加热后得到很好的表征。X射线衍射和⁵⁷FeMössbauer光谱结果表明，在存在和不存在Mt的情况下，热处理后Fh都会转化为Hem。扫描电子显微镜和透射电子显微镜图像表明，Mt可以很好地分散Fh，并显着降低加热后形成的Hem的粒径。特别是，在纯Fh系统中，Hem的粒径达到〜1000 nm，而在含有Mt的系统中，Hem的粒径仅为15-75 nm。傅里叶变换红外光谱图显示了Mt和Fh之间的强相互作用（通过形成Si-O-Fe和Al-O-Fe键），这也可能减少Fh的聚集并抑制Fh颗粒相变成大颗粒。下摆颗粒。