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Fractionation and Characterization of Naturally Occurring Organo-Clay Complexes¹

ABSTRACT

Clay separated from a Solonetz Bnt horizon was fractionated lnto coarse (2–0.2 µ), medium (0.2–0.14 µ), fine (0.14–0.08 µ) and very fine (<0.08 µ) size fractions. Organic matter from these fractions was obtained by extractions with 0.1M Na₄P₂O₇ (pH 11.0), followed by extractions with 0.1N NaOH. The residue was then repeatedly treated with an HF-HCl mixture and the remaining organic fraction was extracted with 0.1M Na₄P₂O₇ (pH 11.0). The organic and clay fractions were analyzed for C and N contents, and by X-ray diffraction, electron microscopy and infrared spectroscopy.

Experimental data indicated that the largest portion of the complexed organic matter was associated with the coarse clay fraction which contained relatively large amounts of kaolinite, whereas a small percentage was associated with the fine clay fraction where kaolinite occurred as traces. The percentage of extractable organic matter increased with decrease in clay particle size. No evidence was found for the adsorption of organic matter in the interlamellar spaces as reported by some previous workers.

Study of humic acids isolated from the clay fractions showed that aliphatic structures were more common in humic acids derived from fine clay than in those separated from the coarse clay fraction. Aromatic structures of the humic acids increased in the order of pyrophosphate humic acidalkali humic acidresidual humic acid. The humic acids unextractable by the solvents commonly employed appeared to be highly humified and aromatic in nature.

¹ Contribution No. 337, Research Council of Alberta, Edmonton, Canada.

² Post-doctoral Research Fellow and Research Officer, respectively, Soils Div., Res. Council of Alberta, Edmonton, Can. The authors wish to express their thanks to Dr. J. C. Wood for his helpful criticisms in reviewing the manuscript and to Mr. G. Menges for his assistance in operating the electron microscope.

Received for publication March 18, 1966. Accepted for publication August 31, 1966.