Effect of Phosphate Anion on the Formation of Imogolite
T. Henmi, P. M. Huang, 1985. "Effect of Phosphate Anion on the Formation of Imogolite", Proceedings of the International Clay Conference Denver, 1985, Leonard G. Schultz, H. van Olphen, Frederick A. Mumpton
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The influence of phosphate anion on the interaction of hydroxy-Al ions and monomelic silicic acid was studied in systems having an initial Si concentration of 1.54 × 10−3 M, a Si/Al molar ratio of 0.5, an OH/Al molar ratio of 2.0, and P/Al molar ratios of 0–0.04. Parent solutions were heated to 95°-100°C for 110 hr (1 atm), and the precipitation (>0.01 Mm) and soluble products (<0.01 μm) formed were examined by X-ray powder diffraction, infrared spectroscopic, electron optical, and chemical analyses. The amount of imogolite in the precipitates decreased with increasing the P/Al molar ratio of the parent solution from 0 to 0.005. The tube length and the degree of order of imogolite formed decreased as the P/Al molar ratio of the parent solution increased. Imogolite was not found in the precipitates formed in the solution at a P/Al molar ratio of 0.01. As the P/Al molar ratio of the solution rose, the amount of “proto-imogolite” (soluble complexes of hydroxy-Al ions and orthosilicic acid) in freeze-dried soluble products increased; bayerite and/or boehmite also were present in the precipitates. No material precipitated from the solution having a P/Al molar ratio of 0.04. The phosphate anion apparently strongly inhibits the growth of “proto-imogolite” nuclei and the subsequent formation of imogolite tube structure. The present study indicates that phosphate anion, common in soil solutions and natural waters, affects the genesis of imogolite in nature.
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Proceedings of the International Clay Conference Denver, 1985
The papers included in this proceedings volume are representative of the research on clays being conducted in all parts of the world at the time of publication. Many of the subjects treated are controversial, and although some ideas expressed may not necessarily represent the views of the editors, the referees, or the publisher, they deserve to be brought to the attention of the international clay community.