The Formation and Transformation of Manganese Oxide Minerals on the Surface of Kaolinite

文献类型： 外文期刊

第一作者： Zhao, Fan

作者： Zhao, Fan;Zhang, Guangyao;Jiang, Yong;Cao, Chi;Qi, Yongbo;Wang, Qingyun;Zhao, Huaiyan;Wang, Hui

作者机构：

关键词： Birnessite; Cationic species; Cryptomelane; Kaolinite; Mn2+; Mn7+ molar ratios; Synthesis temperature

期刊名称：CLAYS AND CLAY MINERALS （ 影响因子：2.2； 五年影响因子：2.1 ）

ISSN： 0009-8604

年卷期： 2023 年 71 卷 1 期

页码：

收录情况： SCI

摘要： 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 degrees 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.

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