CATALYTIC SYNTHESIS OF HUMIC SUBSTANCES BY NATURAL CLAYS, SILTS, AND SOILS

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Abstract
Using Warburg respirometers, we studied the oxidative power of various soils, as well as the clays and silts isolated from them. We also examined the humic substances formed through the catalytic polymerization of phenolic compounds by a soil derived from loess deposits and the silt of a Mollisol. The catalytic oxidative power of the silt fraction (2 to 50 micrometers) of the soils ranges from 23 to 67 percent of that of the corresponding clays. The oxidative power of the oxides removed by the citrate-dithio-nite-bicarbonate treatment accounts for 1 to 45 percent and 7 to 25 percent of that of the nontreated clays and silts, respectively. The percentages of the conversion of the total phenolic acids and other compounds added to the loess-derived soil and Mollisol silt into phenolic polymers are 38.7 and 27.4 percent respectively, indicating that the formation of many other yet unidentified products as a result of side reactions during the polymerization of phenolic compounds is substantial. Furthermore, the rate of the polymerization varies with the nature of the phenolic compounds. The resultant humic acids formed outweigh the fulvic acids. The nature of the humic substances formed is characterized by elemental analysis, functional groups, and infrared and electron spin resonance spectra.

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