Effects of citrate on the dissolution and transformation of biotite,analyzed by chemical and atomic force microscopy |
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| Institution: | 1. Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, Japan;2. National Institute for Agro-Environmental Sciences, 3-1-3 Kan-nondai, Tsukuba, Ibaraki 305-8604, Japan;3. Fukushima Agricultural Technology Center, 116 Shimonakamichi, Takakura, Hiwada-Machi, Koriyama, Fukushima 963-0531, Japan;4. Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto 606-8522, Japan;1. Key Laboratory for High Temperature and High Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. State Key Laboratory of Ore Deposit Geochemistry Chinese Academy of Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;1. Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Ave, Ann Arbor, MI 48109-1005, USA;2. Institut für Mineralogie, Leibniz Universität Hannover, Callinstraße 3, 30167 Hannover, Germany;3. Department of Petrology and Economic Geology, Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark;4. Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street N., London, Ontario N6A 5B7, Canada |
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| Abstract: | The aim of this study was to investigate the dissolution and transformation characteristics of phyllosilicate under low molecular weight organic acids in the farmland environment (pH 4.0–8.0). Changes of dissolution and morphology of biotite were evaluated using chemical extraction experiments and in situ/ex situ atomic force microscopy (AFM) with fluids of citric acid (CA) solution at pH 4.0, 6.0, and 8.0. Results of extracting experiments show that CA solutions contributed to the release rate of potassium (K), silicon (Si), and aluminum (Al) from biotite relative to a control aqueous solution. In situ AFM observations indicate that the dissolution of biotite from the biotite (0 0 1) surface occurred on the terrace, segment, and fringe of pits, while new etch pits did not readily form on biotite (0 0 1) surfaces in aqueous solutions. However, dissolution rates of terraces can be greatly accelerated with the help of citrate. In pH 4.0 CA solution, 70 min dissolution reactions of biotite (0 0 1) surfaces result in more etch pits than in pH 6.0 and 8.0 solutions. In addition, the transformation of biotite occurred simultaneously with the dissolution process. Secondary coating was observed on the biotite (0 0 1) surface after 140 h of immersion in a weak acid environment. Thus, the protons have a dominant role in the dissolution process of biotite with organic (carboxyl) acting as a catalyst under acidic condition. Based on the theory of interactions on a water–mineral interface in a weak acid environment, dissolution of biotite starts from defect/kink sites on the surface, one layer by one layer, and develops along the h k 0] direction. A secondary coating that forms on the biotite (0 0 1) surface may restrain the formation and growth of etch pits, whereas this process may have a positive role on the stability of soil structure during long-term soil management. |
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