An x-ray diffraction study of humic acids

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Abstract
A, Rp and P type humic acids and certain related materials were subjected to X-ray diffraction analysis. In general, the soil humic acids exhibited y- and (002)-bands. A and Rp type humic acids showed (002)- and y-bands, respectively. P type humic acid exhibited y- and (002)-bands, with the former predominating with regard to the latter. The (002)-band of A type humic acids was further analyzed using the Fourier transformation method. The number of layers stacked parallel to each other was 9 on the average. The most commonly found stacking units consisted of 2 and 3 layers. The average maximum number of layers per stack was 2.66. The weight percent of stack per humic acid was up to 32. In the case of Sochicken-1 humic acid (A type) extracted from Kuroboku soil, the presence of layer stacking was confirmed by transmission electron microscopy. Based on these results, the structure of humic acids is discussed.

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