The formation of manganese (Mn) oxides is influenced by environmental conditions and, in some red soils, Mn oxides occur as coatings on the surface of kaolinite particles in the form of colloidal films or fine particles. The present study aimed to explore the types of formation mechanisms of Mn oxide minerals on the surface of kaolinite. Mn oxide minerals synthesized by reducing the Mn in KMnO₄ with a divalent Mn salt (MnSO₄) were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of various initial molar ratios of Mn²⁺/Mn⁷⁺ (R = 1:0.67, 1:1, 1:2, and 1:4), cationic species (Na⁺ or Mg²⁺), synthesis temperatures (30, 60, and 110°C), and amount of added kaolinite (0.25, 0.5, 1.0, 2.0, and 5.0 g) on the formation of Mn oxides were studied. The results showed that Mn oxide mineral types were affected by the initial R value and the background cation. With decreases in the initial R value, the synthesized minerals transformed from cryptomelane to birnessite. The relative mass ratios of kaolinite to Mn oxide were calculated as 1:0.92, 1:0.63, 1:1.15, and 1:1.63. The sodium cation (Na⁺) had a greater role than Mg²⁺ in promoting the dissolution–recrystallization of birnessite to cryptomelane. The synthesis temperature had no effect on mineral types, but Mn content increased as temperature increased. When the amount of added kaolinite was increased from 0.25 to 5.0 g, Mn oxide minerals formed gradually and transformed from birnessite to cryptomelane. This work revealed a possible formation process and reaction mechanism on the surface of kaolinite particles in some red soils.

锰 (Mn) 氧化物的形成受环境条件的影响，在一些红壤中，锰氧化物以胶体膜或细颗粒的形式出现在高岭石颗粒表面的涂层中。本研究旨在探讨高岭石表面氧化锰矿物的形成机制类型。使用 X 射线衍射 (XRD) 和扫描电子显微镜 (SEM) 检查通过用二价 Mn 盐 (MnSO _{4 ) 还原 KMnO 4}中的 Mn 合成的 Mn 氧化物矿物。^{Mn 2+} /Mn ⁷⁺的各种初始摩尔比（R = 1:0.67、1:1、1:2 和 1:4）、阳离子物质（Na ⁺或 Mg ²⁺）的影响)、合成温度（30、60 和 110°C）和添加的高岭土量（0.25、0.5、1.0、2.0 和 5.0 g）对 Mn 氧化物形成的影响进行了研究。结果表明，氧化锰矿物类型受初始R值和本底阳离子的影响。随着初始 R 值的降低，合成矿物从钾锰矿转变为水钠锰矿。经计算，高岭石与氧化锰的相对质量比为1:0.92、1:0.63、1:1.15、1:1.63。钠阳离子 (Na ⁺ ) 的作用大于 Mg ²⁺促进水钠锰矿溶解再结晶为钾锰矿。合成温度对矿物种类无影响，但Mn含量随温度升高而增加。当高岭石的添加量从0.25 g增加到5.0 g时，氧化锰矿物逐渐形成，并由水钠锰矿转变为钾锰矿。这项工作揭示了某些红壤中高岭石颗粒表面可能的形成过程和反应机制。