Effect of Humic and Fulvic Acids on the Formation of Allophane
K. Inoue, P. M. Huang, 1985. "Effect of Humic and Fulvic Acids on the Formation of Allophane", Proceedings of the International Clay Conference Denver, 1985, Leonard G. Schultz, H. van Olphen, Frederick A. Mumpton
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The effects of humic substances on the interaction of hydroxy-Al ions and orthosilicic acid at a Si concentration of 1.6 x 10−3 M, a Si/Al molar ratio of 1.0, an OH/Al molar ratio of 3.0, and humic or fulvic acid concentrations of 1 to 1000 mg/liter were studied. Humic substances at concentrations > 100–300 mg/liter significantly perturbed this interaction and thus inhibited the formation of allophane. The Na-pyrophosphate- and Na2CO3-soluble fractions of the precipitates (>0.01 μm), formed in the presence of the humic substances at a concentration of 300 mg/liter, were, respectively, 71% and 22% in the humic acid system and 17–24% and 36–40% in the fulvic acid systems. Selective dissolution data and differential infrared spectroscopy showed that “proto-imogolite” allophane was a major component in the pyrophosphate- and Na2CO3-insoluble fraction of the precipitates formed in the presence of fulvic acid. The pyrophosphate- and Na2CO3-insoluble fraction of the precipitates formed in the presence of humic acid showed a very weak infrared spectrum. The present results show that humic substances are pedogenically significant in impeding the formation of allophane.
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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.